iOS开发 多线程之”GCD“
2015-06-05 22:23
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GCD
GCD全称是GrandCentralDispatch,可译为“⽜逼的中枢调度器”纯C语⾔言,提供了⾮常多强⼤的函数
GCD的优势
GCD是苹果公司为多核的并⾏行运算提出的解决⽅方案
GCD会自动利用更多的CPU内核(比如双核、四核)
GCD会自动管理线程的生命周期(创建线程、调度任务、销毁线程)
程序员只需要告诉GCD想要执行什么任务（就是把任务放到队列里）不需要编写任何线程管理代码
两个核心概念
任务: 需要执行的对象队列：储存任务的框框
程序员需要做的两件事
定制任务添加任务到队列（队列的取出规则：先进先出，后进后出）
执⾏任务 ：
同步执行：一人任务结束，在执行下一个任务
dispatch_sync(dispatch_queue_t queue, dispatch_block_t block);
异步执行（多线程的代名词）：不需要前一个任务结束，就可以执行下一个任务
dispatch_async(dispatch_queue_t queue, dispatch_block_t block);
同步和异步的区别
同步执行:在当前线程中执⾏异步执行:在另一条线程中执⾏
任务队列
串⾏队列、并发队列、主队列、全局队列1、串⾏队列
GCD中获得串⾏行有2种途径
dispatch_queue_t queue = dispatch_queue_create("name", NULL); // 创建dispatch_release(queue);// 非ARC需要释放⼿手动创建的队列
2、使⽤主队列 (跟主线程相关联的队列)
主队列是GCD⾃自带的⼀种特殊的串⾏队列
放在主队列中的任务,都会放到主线程中执⾏行
3、并发队列
GCD默认已经提供了全局的并发队列,供整个应用使用,不需要⼿手动创建
使用dispatch_get_global_queue函数获得全局的并发队列
dispatch_queue_t dispatch_get_global_queue( dispatch_queue_priority_t priority, unsigned long flags);
dispatch_queue_t queue = dispatch_get_global_queue(0,0);
全局并发队列的优先级
为了适配IOS7 和 IOS8 最近一段时间，优先级都写 0● #define DISPATCH_QUEUE_PRIORITY_HIGH 2 // ⾼高
● #define DISPATCH_QUEUE_PRIORITY_DEFAULT 0 // 默认(中)
● #define DISPATCH_QUEUE_PRIORITY_LOW (-2) // 低
● #define DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN // 后 台
4、主队列
所有任务都在主线程执行
如果主线程当前有执行的任务，主队列中的任务不会调度
等待主线程空闲后，主队列才会调度任务
使⽤用
dispatch_get_main_queue()
获得主队列
dispatch_queue_t queue = dispatch_get_main_queue();
GCD演练
<code class="language-objc hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 实例</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo1 {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建一个串行队列</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, DISPATCH_QUEUE_SERIAL);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建一个block任务</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> (^task)() = ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
};
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 设置执行模式：异步执行 同时：添加任务</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, task);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 串行队列，同步执行</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo2 {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 创建一个串行队列</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 设置执行模式：同步执行 同时：添加任务</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%d---"</span>, i);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 上面的打印和第一句的添加任务到队列，都是在主线程上执行的</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(q, ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@ - %d"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread], i);
});
}
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 结果是 1 2 3 4 在线程1 一次出来 ，最后输出 come here</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 串行队列，异步执行</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo3 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%d---"</span>, i);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@ - %d"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread], i);
});
}
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come 123here"</span>);
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
首先是通过循环添加任务到串行队列中
0---
1---
2---
3---
4---
5---
6---
7---
8---
9---
因为是异步执行、然后就多线程执行（下面两个的输出顺序不确定）
主线程输出：come here
子线程输出：
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 0
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 1
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 2
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 3
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 4
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 5
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 6
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 7
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 8
<NSThread: 0x7fc3c8499e50>{number = 2, name = (null)} - 9
*/</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 并发队列，异步执行</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo4 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, DISPATCH_QUEUE_CONCURRENT); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// COUCURRENT 是表示并发队列</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@ - %d"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread], i);
});
}
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 输出结果是：多线程输出，无顺序输出</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 并发队列，同步执行</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo5 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, DISPATCH_QUEUE_CONCURRENT);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%d---"</span>, i);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 这里是上面输入下面输入交叉出现，说明同步执行的任务是添加一个，执行一个，只要有任务，就立即执行</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(q, ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@ - %d"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread], i);
});
}
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 输出结果是：都在主线程，顺序输出，最后come here</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 都是主线程--是因为同步执行就在当前线程实行</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 顺序输出-- 虽然并发队列能多出，但是队列的特性是 先进先出</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 主队列，异步执行</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo6 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_get_main_queue();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%d---"</span>, i);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@ - %d"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread], i);
});
}
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"睡会"</span>);
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
1---
2---
.
.
9---
睡会
come here
主队列是负责主线程上调度任务的，必须等主线程的语句执行完毕以后，在执行异步执行的子线程任务
任务顺序输出
*/</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 主队列，同步任务</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo7 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_get_main_queue();
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"1---"</span>);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(q, ^{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"来啊"</span>);
});
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 这里会卡死</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 主队列要求：必须主线程执行完，才能执行调用任务</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 同步执行：不执行调用的任务，就不能往下走</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 主队列，同步任务，不死锁（不懂）</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo8 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> queue = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, DISPATCH_QUEUE_CONCURRENT);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(queue, ^{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_get_main_queue();
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"1--- %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(q, ^{
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6.0</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"来啊 %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// [NSThread sleepForTimeInterval:1.0];</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"到底来不来"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 到底来不来</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1--- <NSThread: 0x7fbf895c9220>{number = 2, name = (null)}</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 来啊 <NSThread: 0x7fbf8940fe50>{number = 1, name = main}</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// come here <NSThread: 0x7fbf895c9220>{number = 2, name = (null)}</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 整个是在 并发队列，异步执行 的大框架中</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 执行路径是 主队列任务--同步执行任务--主队列任务（确定的路径）</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 在这个框架里面，只要需要线程，系统就给提供，所以主队列和同步任务可以分别在两个不同的线程中执行</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - 同步任务的用处</span>
在网络开发中，通常会把很多任务放在后台异步执行，有的时候，有些任务会彼此有<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"依赖"</span>关系！
例子：小说的网站，用户登录，扣费，下载小说 A，扣费，下载小说 B...
利用同步任务，能够做到，任务依赖关系，前一个同步任务不执行完，队列就不会调度后面的任务！
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: - 同步任务的用处</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo9 {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, DISPATCH_QUEUE_CONCURRENT);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_sync</span>(dispatch_get_main_queue(), ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"用户登录 %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"下载 A %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^ {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"扣费 B %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
});
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"怎么能这样？"</span>);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果把同步的“用户登录”的位置放在下载和扣费后面，就可能会出现下载 扣费 再登录。如果在用户登录前睡三秒，则肯定会下载 扣费 用户登录 怎么能这样</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 猜测是，主线程只要有任务，就会执行任务，不调度其他线程的任务，所以如果放在下载和扣费后面，在主队类添加任务之前还睡了已汇入，主队列没有添加任务，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 睡觉的时候，下载和扣费就已经添加到并发队列并异步执行了，因为此时主队列中没有任务 ，就不会阻碍调度，这样就会先输出下载和扣费，</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//===============================================================</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - 全局队列</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// MARK: 全局队列（本质上就是并发队列）</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)gcdDemo9 {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
参数
第一个参数 1. 涉及到系统适配
iOS 8 服务质量（让线程响应的更快还是更慢）
- QOS_CLASS_USER_INTERACTIVE 用户交互(用户迫切希望线程快点被执行，不要用耗时的操作)
- QOS_CLASS_USER_INITIATED 用户需要的(同样不要使用耗时操作)
- QOS_CLASS_DEFAULT 默认的(给系统用来重置队列的)
** QOS_CLASS_UTILITY 实用工具(用来做耗时操作)
- QOS_CLASS_BACKGROUND 后台
- QOS_CLASS_UNSPECIFIED 没有指定优先级
iOS 7 调度的优先级
－ DISPATCH_QUEUE_PRIORITY_HIGH 2 高优先级
－ DISPATCH_QUEUE_PRIORITY_DEFAULT 0 默认优先级
－ DISPATCH_QUEUE_PRIORITY_LOW (-2) 低优先级
－ DISPATCH_QUEUE_PRIORITY_BACKGROUND 后台优先级
提示：尤其不要选择 BACKGROUND 优先级和服务质量，用户不需要知道线程什么时候执行完成！线程的执行会慢的令人发指！
有关服务质量的介绍，用在与 XPC 框架结合使用的，XPC 用在 MAC 平台上做进程间通讯的框架！
因为大家工作后，暂时会考虑 iOS7 & iOS8 的适配，无法使用服务质量，直接指定 0，能够做到 iOS7 & 8 的适配
dispatch_get_global_queue(0, 0);
2. 为未来使用保留的，应该始终传入0
*/</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_get_global_queue(QOS_CLASS_DEFAULT, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@ %d"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread], i);
});
}
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"com here"</span>);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li><li style="box-sizing: border-box; padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li><li style="box-sizing: border-box; padding: 0px 5px;">98</li><li style="box-sizing: border-box; padding: 0px 5px;">99</li><li style="box-sizing: border-box; padding: 0px 5px;">100</li><li style="box-sizing: border-box; padding: 0px 5px;">101</li><li style="box-sizing: border-box; padding: 0px 5px;">102</li><li style="box-sizing: border-box; padding: 0px 5px;">103</li><li style="box-sizing: border-box; padding: 0px 5px;">104</li><li style="box-sizing: border-box; padding: 0px 5px;">105</li><li style="box-sizing: border-box; padding: 0px 5px;">106</li><li style="box-sizing: border-box; padding: 0px 5px;">107</li><li style="box-sizing: border-box; padding: 0px 5px;">108</li><li style="box-sizing: border-box; padding: 0px 5px;">109</li><li style="box-sizing: border-box; padding: 0px 5px;">110</li><li style="box-sizing: border-box; padding: 0px 5px;">111</li><li style="box-sizing: border-box; padding: 0px 5px;">112</li><li style="box-sizing: border-box; padding: 0px 5px;">113</li><li style="box-sizing: border-box; padding: 0px 5px;">114</li><li style="box-sizing: border-box; padding: 0px 5px;">115</li><li style="box-sizing: border-box; padding: 0px 5px;">116</li><li style="box-sizing: border-box; padding: 0px 5px;">117</li><li style="box-sizing: border-box; padding: 0px 5px;">118</li><li style="box-sizing: border-box; padding: 0px 5px;">119</li><li style="box-sizing: border-box; padding: 0px 5px;">120</li><li style="box-sizing: border-box; padding: 0px 5px;">121</li><li style="box-sizing: border-box; padding: 0px 5px;">122</li><li style="box-sizing: border-box; padding: 0px 5px;">123</li><li style="box-sizing: border-box; padding: 0px 5px;">124</li><li style="box-sizing: border-box; padding: 0px 5px;">125</li><li style="box-sizing: border-box; padding: 0px 5px;">126</li><li style="box-sizing: border-box; padding: 0px 5px;">127</li><li style="box-sizing: border-box; padding: 0px 5px;">128</li><li style="box-sizing: border-box; padding: 0px 5px;">129</li><li style="box-sizing: border-box; padding: 0px 5px;">130</li><li style="box-sizing: border-box; padding: 0px 5px;">131</li><li style="box-sizing: border-box; padding: 0px 5px;">132</li><li style="box-sizing: border-box; padding: 0px 5px;">133</li><li style="box-sizing: border-box; padding: 0px 5px;">134</li><li style="box-sizing: border-box; padding: 0px 5px;">135</li><li style="box-sizing: border-box; padding: 0px 5px;">136</li><li style="box-sizing: border-box; padding: 0px 5px;">137</li><li style="box-sizing: border-box; padding: 0px 5px;">138</li><li style="box-sizing: border-box; padding: 0px 5px;">139</li><li style="box-sizing: border-box; padding: 0px 5px;">140</li><li style="box-sizing: border-box; padding: 0px 5px;">141</li><li style="box-sizing: border-box; padding: 0px 5px;">142</li><li style="box-sizing: border-box; padding: 0px 5px;">143</li><li style="box-sizing: border-box; padding: 0px 5px;">144</li><li style="box-sizing: border-box; padding: 0px 5px;">145</li><li style="box-sizing: border-box; padding: 0px 5px;">146</li><li style="box-sizing: border-box; padding: 0px 5px;">147</li><li style="box-sizing: border-box; padding: 0px 5px;">148</li><li style="box-sizing: border-box; padding: 0px 5px;">149</li><li style="box-sizing: border-box; padding: 0px 5px;">150</li><li style="box-sizing: border-box; padding: 0px 5px;">151</li><li style="box-sizing: border-box; padding: 0px 5px;">152</li><li style="box-sizing: border-box; padding: 0px 5px;">153</li><li style="box-sizing: border-box; padding: 0px 5px;">154</li><li style="box-sizing: border-box; padding: 0px 5px;">155</li><li style="box-sizing: border-box; padding: 0px 5px;">156</li><li style="box-sizing: border-box; padding: 0px 5px;">157</li><li style="box-sizing: border-box; padding: 0px 5px;">158</li><li style="box-sizing: border-box; padding: 0px 5px;">159</li><li style="box-sizing: border-box; padding: 0px 5px;">160</li><li style="box-sizing: border-box; padding: 0px 5px;">161</li><li style="box-sizing: border-box; padding: 0px 5px;">162</li><li style="box-sizing: border-box; padding: 0px 5px;">163</li><li style="box-sizing: border-box; padding: 0px 5px;">164</li><li style="box-sizing: border-box; padding: 0px 5px;">165</li><li style="box-sizing: border-box; padding: 0px 5px;">166</li><li style="box-sizing: border-box; padding: 0px 5px;">167</li><li style="box-sizing: border-box; padding: 0px 5px;">168</li><li style="box-sizing: border-box; padding: 0px 5px;">169</li><li style="box-sizing: border-box; padding: 0px 5px;">170</li><li style="box-sizing: border-box; padding: 0px 5px;">171</li><li style="box-sizing: border-box; padding: 0px 5px;">172</li><li style="box-sizing: border-box; padding: 0px 5px;">173</li><li style="box-sizing: border-box; padding: 0px 5px;">174</li><li style="box-sizing: border-box; padding: 0px 5px;">175</li><li style="box-sizing: border-box; padding: 0px 5px;">176</li><li style="box-sizing: border-box; padding: 0px 5px;">177</li><li style="box-sizing: border-box; padding: 0px 5px;">178</li><li style="box-sizing: border-box; padding: 0px 5px;">179</li><li style="box-sizing: border-box; padding: 0px 5px;">180</li><li style="box-sizing: border-box; padding: 0px 5px;">181</li><li style="box-sizing: border-box; padding: 0px 5px;">182</li><li style="box-sizing: border-box; padding: 0px 5px;">183</li><li style="box-sizing: border-box; padding: 0px 5px;">184</li><li style="box-sizing: border-box; padding: 0px 5px;">185</li><li style="box-sizing: border-box; padding: 0px 5px;">186</li><li style="box-sizing: border-box; padding: 0px 5px;">187</li><li style="box-sizing: border-box; padding: 0px 5px;">188</li><li style="box-sizing: border-box; padding: 0px 5px;">189</li><li style="box-sizing: border-box; padding: 0px 5px;">190</li><li style="box-sizing: border-box; padding: 0px 5px;">191</li><li style="box-sizing: border-box; padding: 0px 5px;">192</li><li style="box-sizing: border-box; padding: 0px 5px;">193</li><li style="box-sizing: border-box; padding: 0px 5px;">194</li><li style="box-sizing: border-box; padding: 0px 5px;">195</li><li style="box-sizing: border-box; padding: 0px 5px;">196</li><li style="box-sizing: border-box; padding: 0px 5px;">197</li><li style="box-sizing: border-box; padding: 0px 5px;">198</li><li style="box-sizing: border-box; padding: 0px 5px;">199</li><li style="box-sizing: border-box; padding: 0px 5px;">200</li><li style="box-sizing: border-box; padding: 0px 5px;">201</li><li style="box-sizing: border-box; padding: 0px 5px;">202</li><li style="box-sizing: border-box; padding: 0px 5px;">203</li><li style="box-sizing: border-box; padding: 0px 5px;">204</li><li style="box-sizing: border-box; padding: 0px 5px;">205</li><li style="box-sizing: border-box; padding: 0px 5px;">206</li><li style="box-sizing: border-box; padding: 0px 5px;">207</li><li style="box-sizing: border-box; padding: 0px 5px;">208</li><li style="box-sizing: border-box; padding: 0px 5px;">209</li><li style="box-sizing: border-box; padding: 0px 5px;">210</li><li style="box-sizing: border-box; padding: 0px 5px;">211</li><li style="box-sizing: border-box; padding: 0px 5px;">212</li><li style="box-sizing: border-box; padding: 0px 5px;">213</li><li style="box-sizing: border-box; padding: 0px 5px;">214</li><li style="box-sizing: border-box; padding: 0px 5px;">215</li><li style="box-sizing: border-box; padding: 0px 5px;">216</li><li style="box-sizing: border-box; padding: 0px 5px;">217</li><li style="box-sizing: border-box; padding: 0px 5px;">218</li><li style="box-sizing: border-box; padding: 0px 5px;">219</li><li style="box-sizing: border-box; padding: 0px 5px;">220</li><li style="box-sizing: border-box; padding: 0px 5px;">221</li><li style="box-sizing: border-box; padding: 0px 5px;">222</li><li style="box-sizing: border-box; padding: 0px 5px;">223</li><li style="box-sizing: border-box; padding: 0px 5px;">224</li><li style="box-sizing: border-box; padding: 0px 5px;">225</li><li style="box-sizing: border-box; padding: 0px 5px;">226</li><li style="box-sizing: border-box; padding: 0px 5px;">227</li><li style="box-sizing: border-box; padding: 0px 5px;">228</li><li style="box-sizing: border-box; padding: 0px 5px;">229</li><li style="box-sizing: border-box; padding: 0px 5px;">230</li><li style="box-sizing: border-box; padding: 0px 5px;">231</li><li style="box-sizing: border-box; padding: 0px 5px;">232</li><li style="box-sizing: border-box; padding: 0px 5px;">233</li><li style="box-sizing: border-box; padding: 0px 5px;">234</li><li style="box-sizing: border-box; padding: 0px 5px;">235</li><li style="box-sizing: border-box; padding: 0px 5px;">236</li><li style="box-sizing: border-box; padding: 0px 5px;">237</li><li style="box-sizing: border-box; padding: 0px 5px;">238</li><li style="box-sizing: border-box; padding: 0px 5px;">239</li><li style="box-sizing: border-box; padding: 0px 5px;">240</li><li style="box-sizing: border-box; padding: 0px 5px;">241</li><li style="box-sizing: border-box; padding: 0px 5px;">242</li><li style="box-sizing: border-box; padding: 0px 5px;">243</li><li style="box-sizing: border-box; padding: 0px 5px;">244</li><li style="box-sizing: border-box; padding: 0px 5px;">245</li><li style="box-sizing: border-box; padding: 0px 5px;">246</li><li style="box-sizing: border-box; padding: 0px 5px;">247</li><li style="box-sizing: border-box; padding: 0px 5px;">248</li><li style="box-sizing: border-box; padding: 0px 5px;">249</li><li style="box-sizing: border-box; padding: 0px 5px;">250</li><li style="box-sizing: border-box; padding: 0px 5px;">251</li><li style="box-sizing: border-box; padding: 0px 5px;">252</li><li style="box-sizing: border-box; padding: 0px 5px;">253</li><li style="box-sizing: border-box; padding: 0px 5px;">254</li><li style="box-sizing: border-box; padding: 0px 5px;">255</li><li style="box-sizing: border-box; padding: 0px 5px;">256</li><li style="box-sizing: border-box; padding: 0px 5px;">257</li><li style="box-sizing: border-box; padding: 0px 5px;">258</li><li style="box-sizing: border-box; padding: 0px 5px;">259</li><li style="box-sizing: border-box; padding: 0px 5px;">260</li><li style="box-sizing: border-box; padding: 0px 5px;">261</li><li style="box-sizing: border-box; padding: 0px 5px;">262</li><li style="box-sizing: border-box; padding: 0px 5px;">263</li><li style="box-sizing: border-box; padding: 0px 5px;">264</li><li style="box-sizing: border-box; padding: 0px 5px;">265</li><li style="box-sizing: border-box; padding: 0px 5px;">266</li><li style="box-sizing: border-box; padding: 0px 5px;">267</li><li style="box-sizing: border-box; padding: 0px 5px;">268</li><li style="box-sizing: border-box; padding: 0px 5px;">269</li><li style="box-sizing: border-box; padding: 0px 5px;">270</li><li style="box-sizing: border-box; padding: 0px 5px;">271</li><li style="box-sizing: border-box; padding: 0px 5px;">272</li><li style="box-sizing: border-box; padding: 0px 5px;">273</li><li style="box-sizing: border-box; padding: 0px 5px;">274</li><li style="box-sizing: border-box; padding: 0px 5px;">275</li></ul>全局队列和并发队列的区别
全局队列 & 并发队列1> 名称，并发队列有名称，适合于商业级软件跟踪错误报告！
2> release， 在 MRC 开发时，并发队列需要使用
dispatch_release(q);
结论：目前绝大多数的软件都会使用全局队列。比较优秀的第三方框架会使用自定义的并发队列！
日常使用：用全局队列！
全局队列和串行队列的选择
全局队列：
- 并发，能够调多个线程，效率高
- 费电，费流量
串行队列
- 如果任务之间需要依赖（ex登陆，下载，扣费），使用串行队列或者主队列
- 省电，省钱，省流量
所以选择的依据是：
- WIFI的情况下，有电，有流量，可以多开线程 （6条）
- 3G/4G蜂窝网络情况下尽量少开，2-3条线程即可
- 时刻替用户省钱省电
延时执行
<code class="language-objc hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">#pragma mark - 延时执行
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)delay {
NSLog(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
<span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
参数：
从现在开始，经过多少纳秒之后，让 queue 队列，调度 block 任务，异步执行！
1. when
2. queue
3. block(dispatch_block 是 iOS 8.0推出的)
*/</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 从现在开始，经过多少纳秒之后</span>
dispatch_time_t when = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1.0</span> * NSEC_PER_SEC));
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 主队列</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// dispatch_after(when, dispatch_get_main_queue(), ^{</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// NSLog(@"%@", [NSThread currentThread]);</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// });</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 全局队列</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// dispatch_after(when, dispatch_get_global_queue(0, 0), ^{</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// NSLog(@"%@", [NSThread currentThread]);</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// });</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 串行队列</span>
dispatch_after(when, dispatch_queue_create(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"itcast"</span>, NULL), ^{
NSLog(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@"</span>, [NSThread currentThread]);
});
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>一次性执行
有的时候，我们在开发中，有些代码，从程序启动之后，就只希望执行一次！尤其在单例设计模式中使用非常普遍，在iOS 开发中，单例的使用，已经到了“滥用”程度！
一次性执行是在当前线程执行的。不会另外分出线程来执行
就算在多线程中测试一次性执行，仍然只是执行一次就不再执行了。
通过在互斥锁之前添加判断，也能达到一次性执行的目的，但是效率相比一次性执行要低很多很多。所以不推荐使用互斥锁
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - 一次性执行</span>
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)once {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"来了"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 苹果提供了一个一次行执行的机制，不仅能够保证只被执行一次，而且是"线程安全"的</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 苹果推荐使用 dispatch_once_t 来做一次性执行！因为效率高！</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 不要使用互斥锁，互斥锁效率低！</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%ld"</span>, onceToken);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 只会执行一次的代码</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"执行了！%@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
}
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ViewController</span></span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> largeNmuber = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>;
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)viewDidLoad {
[<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> viewDidLoad];
}
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.04f"</span>, [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> syncDemo1]);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.04f"</span>, [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> onceDemo1]);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.04f"</span>, [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> syncDemo2]);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%.04f"</span>, [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> onceDemo2]);
}
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//=================================================================</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - 单线程测试</span>
- (CFAbsoluteTime)syncDemo1 {
CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 单线程测试互斥锁</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < largeNmuber; ++i) {
[DemoObj syncDemoObj];
}
CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> end - start;
}
- (CFAbsoluteTime)onceDemo1 {
CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 单线程测试一次性执行</span>
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < largeNmuber; ++i) {
[DemoObj onceDemoObj];
}
CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> end - start;
}
最后的输出结果是，可以对比出效率来
单线程互斥锁 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.6975</span>
单线程一次性 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.1761</span>
多线程互斥锁 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6.2929</span>
多线程一次性 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.2352</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//=================================================================</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - 多线程测试</span>
- (CFAbsoluteTime)syncDemo2 {
CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
dispatch_group_t group = dispatch_group_create();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
dispatch_group_enter(group);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 异步执行 测试互斥锁</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> j = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; j < largeNmuber / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; j++) {
[DemoObj syncDemoObj];
}
dispatch_group_leave(group);
});
}
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> end - start;
}
- (CFAbsoluteTime)onceDemo2 {
CFAbsoluteTime start = CFAbsoluteTimeGetCurrent();
dispatch_group_t group = dispatch_group_create();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
dispatch_group_enter(group);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 异步执行 测试 一次性执行</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>), ^{
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> j = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; j < largeNmuber / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; j++) {
[DemoObj onceDemoObj];
}
dispatch_group_leave(group);
});
}
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
CFAbsoluteTime end = CFAbsoluteTimeGetCurrent();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> end - start;
}
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li><li style="box-sizing: border-box; padding: 0px 5px;">87</li><li style="box-sizing: border-box; padding: 0px 5px;">88</li><li style="box-sizing: border-box; padding: 0px 5px;">89</li><li style="box-sizing: border-box; padding: 0px 5px;">90</li><li style="box-sizing: border-box; padding: 0px 5px;">91</li><li style="box-sizing: border-box; padding: 0px 5px;">92</li><li style="box-sizing: border-box; padding: 0px 5px;">93</li><li style="box-sizing: border-box; padding: 0px 5px;">94</li><li style="box-sizing: border-box; padding: 0px 5px;">95</li><li style="box-sizing: border-box; padding: 0px 5px;">96</li><li style="box-sizing: border-box; padding: 0px 5px;">97</li><li style="box-sizing: border-box; padding: 0px 5px;">98</li><li style="box-sizing: border-box; padding: 0px 5px;">99</li><li style="box-sizing: border-box; padding: 0px 5px;">100</li><li style="box-sizing: border-box; padding: 0px 5px;">101</li><li style="box-sizing: border-box; padding: 0px 5px;">102</li><li style="box-sizing: border-box; padding: 0px 5px;">103</li><li style="box-sizing: border-box; padding: 0px 5px;">104</li><li style="box-sizing: border-box; padding: 0px 5px;">105</li><li style="box-sizing: border-box; padding: 0px 5px;">106</li><li style="box-sizing: border-box; padding: 0px 5px;">107</li><li style="box-sizing: border-box; padding: 0px 5px;">108</li><li style="box-sizing: border-box; padding: 0px 5px;">109</li><li style="box-sizing: border-box; padding: 0px 5px;">110</li><li style="box-sizing: border-box; padding: 0px 5px;">111</li></ul>调度组
在实际开发中，有时候需要监听多个异步执行的任务的完成情况。等到所有的任务都完成之后再通知，可以用调度组实现Ex: 下载三个电影，等所有的电影都下载完以后，在通知用户
1、创建队列
2、创建调度组
3、给调度组添加任务
4、所有任务执行完毕通知
注意：一般下载任务都是放在后台线程进行的，但是要把调度组的通知动作放到主线程，因为下载完以后进行通知会有UI的更新
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">调度组形式一
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)group1 {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1. 队列</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2. 调度组</span>
dispatch_group_t g = dispatch_group_create();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 3. 添加任务，让队列调度，指定任务执行函数，最终通知群组</span>
dispatch_group_async(g, q, ^{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"download A %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
dispatch_group_async(g, q, ^{
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1.0</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"download B %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
dispatch_group_async(g, q, ^{
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.8</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"download C %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 4. 所有任务执行完毕后，获得通知</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 用一个调度组，可以监听全局队列调度的任务，执行完毕后，在主队列执行最终处理！</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// dispatch_group_notify 本身是异步的</span>
dispatch_group_notify(g, dispatch_get_main_queue(), ^{
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 更新UI，通知用户！</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"OK %@"</span>, [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> currentThread]);
});
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"come here"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果下载完以后，还需要做其他的动作，就不要调用调度组自带的通知动作，课用下面代码实现</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 等待到永远，死等，阻塞住线程执行，一直到所有的任务执行完毕，才会执行后续的代码！</span>
dispatch_group_wait(g, DISPATCH_TIME_FOREVER);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"全都完毕"</span>);
}
调度组形式二
钓鱼度的任务添加更加灵活
- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)group2 {
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1. 队列</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_queue_t</span> q = dispatch_get_global_queue(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2. 调度组</span>
dispatch_group_t g = dispatch_group_create();
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 3. 进入群组，执行此函数后，再添加的异步执行的block，会被group监听</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// dispatch_group_enter & dispatch_group_leave一定要配对出现</span>
dispatch_group_enter(g);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 4. 添加任务</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^{
[<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSThread</span> sleepForTimeInterval:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1.0</span>];
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"download A"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 异步任务中，所有的代码执行完毕后，最后离开群组</span>
dispatch_group_leave(g);
});
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 再次添加任务</span>
dispatch_group_enter(g);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 5. 添加任务 B</span>
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_async</span>(q, ^{
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"download B"</span>);
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 异步任务中，所有的代码执行完毕后，最后离开群组</span>
dispatch_group_leave(g);
});
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 6. 拦截通知，调度组执行完以后，调用此通知</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// dispatch_group_notify(g, q, ^{</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// NSLog(@"Over");</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// });</span>
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 等待到永远，死等，阻塞住线程执行，一直到所有的任务执行完毕，才会执行后续的代码！</span>
dispatch_group_wait(g, DISPATCH_TIME_FOREVER);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"全都完毕"</span>);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li><li style="box-sizing: border-box; padding: 0px 5px;">84</li><li style="box-sizing: border-box; padding: 0px 5px;">85</li><li style="box-sizing: border-box; padding: 0px 5px;">86</li></ul>
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