GCD

dispatch 用得最多的是全局队列的异步任务（耗时操作）、主线程队列异步任务（更新UI）、串行队列异步任务（需要顺序执行的耗时操作）

注意事项：主线程队列里面不能有同步任务，会阻塞

ARC里面不需要手动release

代码如下：

//

// ViewController.m

// GCDLearn

//

// Created by wusiping on 15/11/29.

// Copyright (c) 2015年 wusiping. All rights reserved.

//

#import "ViewController.h"

@interface
ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {

[super
viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

[self
globalQueue];

}

- (void)serailQueue

{

dispatch_queue_t q =
dispatch_queue_create("cn.wsp.gcddemo",
DISPATCH_QUEUE_SERIAL);


//串行队列，先进先出，异步任务先进去，就先执行异步任务，完了再执行同步任务

for (int i =
0 ; i < 5 ; i ++) {

dispatch_async(q, ^{

NSLog(@"串行队列的异步任务是在第二个线程中顺序执行的----%@----%d",[NSThread
currentThread],i );

});

}



for (int i =
0 ; i < 5 ; i ++ ) {

dispatch_sync(q, ^{

NSLog(@"串行队列同步任务是在主线程中顺序执行的----%@---%d ",[NSThread
currentThread ],i);

});

}



}

- (void)concurrentQueue

{

dispatch_queue_t q =
dispatch_queue_create("cn.wsp.gcddemo",
DISPATCH_QUEUE_CONCURRENT);



for (int i =
0 ; i < 5 ; i ++) {

dispatch_async(q, ^{

NSLog(@"并行队列,异步任务在多个线程中并发执行---%@--%d",[NSThread
currentThread],i);

});

}



for (int i =
0 ; i < 5 ; i ++) {

dispatch_sync(q, ^{

NSLog(@"并行队列,同步任务仍然是在主线程中顺序执行---%@--%d",[NSThread
currentThread],i);

});

}

}

- (void)globalQueue

{

dispatch_queue_t q =
dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
0);

for (int i =
0 ; i < 5 ; i ++) {

dispatch_sync(q, ^{

NSLog(@"全局队列,同步任务在主线程中顺序执行---%@--%d",[NSThread
currentThread],i);

});

}



for (int i =
0 ; i < 5 ; i ++) {

dispatch_async(q, ^{

NSLog(@"全局队列,异步任务在多个线程中并发执行---%@--%d",[NSThread
currentThread],i);

});

}

}

- (void)mainQueue

{

dispatch_queue_t q =
dispatch_get_main_queue();

/*

for (int i = 0 ; i < 5 ; i ++) {

dispatch_sync(q, ^{

NSLog(@"主线程队列,同步任务会被阻塞---%@--%d",[NSThread currentThread],i);

});

}

*/

for (int i =
0 ; i < 5 ; i ++) {

dispatch_async(q, ^{

NSLog(@"主线程队列,异步任务会在主线程上顺序执行,通常用于更新UI---%@--%d",[NSThread
currentThread],i);

});

}

}

@end