iOS多线程编程——NSOperation的使用

NSOperation是苹果提供给我们的一套多线程解决方案。实际上NSOperation是基于GCD更高一层的封装，但是比GCD更简单易用、代码可读性也更高。NSOperation需要配合NSOperationQueue来实现多线程。因为默认情况下，NSOperation单独使用时系统同步执行操作，并没有开辟新线程的能力，只有配合NSOperationQueue才能实现异步执行。因为NSOperation是基于GCD的，那么使用起来也和GCD差不多，其中，NSOperation相当于GCD中的任务，而NSOperationQueue则相当于GCD中的队列。NSOperation实现多线程的使用步骤分为三步：（1）创建任务：先将需要执行的操作封装到一个NSOperation对象中。（2）创建队列：创建NSOperationQueue对象。（3）将任务加入到队列中：然后将NSOperation对象添加到NSOperationQueue中。之后系统就会自动将NSOperationQueue中的NSOperation取出来，在新线程中执行操作。
1、NSOperationQueue一共有两种队列：主队列、其他队列。其中其他队列同时包含了串行、并发功能。（1）凡是添加到主队列中的任务（NSOperation），都会放到主线程中执行。（2）添加到其他队列中的任务（NSOperation），就会自动放到子线程中执行，且 同时包含了：串行、并发功能。2、队列中的最大并发数maxConcurrentOperationCount（默认为-1）（1）当maxConcurrentOperationCount为-1，表示不进行限制，默认为并发执行。（2）当maxConcurrentOperationCount为1时，进行串行执行。（3）当maxConcurrentOperationCount大于1时，进行并发执行，当然这个值不应超过系统限制，即使自己设置一个很大的值，系统也会自动调整。3、队列中的任务间的依赖比如说有A、B两个操作，其中A执行完操作，B才能执行操作，那么就需要让B依赖于A。（1）不要建立循环依赖，会造成死锁，原因同循环引用（2）使用依赖建议只使用NSInvocationOperation，NSInvocationOperation和NSBlockOperation混用会导致依赖关系无法正常实现。（3）依赖关系不光在同队列中生效，不同队列的NSOperation对象之前设置的依赖关系一样会生效4、优先级，建议使用默认级别5、取消等操作- (void)cancel; NSOperation提供的方法，可取消单个操作- (void)cancelAllOperations; NSOperationQueue提供的方法，可以取消队列的所有操作，所有任务取消，包括正在执行的，还未执行的。- (void)setSuspended:(BOOL)b; 可设置任务的暂停和恢复，YES代表暂停队列，NO代表恢复队列- (BOOL)isSuspended; 判断暂停状态，暂停是指当前队列中正在执行，或还未执行的任务；恢复是指继续执行暂停后的任务。
注意：（1）单独使用任务NSOperation时，是在主线程中同步执行的。（2）NSInvocationOperation实例必须加到 NSOperationQueue 的方法" - (void)addOperation:(NSOperation *)op; "中才能开始执行.（3）NSInvocationOperation子线程的停止，可通过 NSOperationQueue 的方法" - (void)cancelAllOperations; "停止。
代码示例1、同步任务// 同步，在主线程中执行
- (void)runSynchronization
{
// 创建任务

// 方法1
// 使用子类 NSInvocationOperation 对象，在主线程中执行
NSInvocationOperation *operation1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@110];
[operation1 start];

NSInvocationOperation *operation2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@120];
[operation2 start];
}

- (void)showTime:(id)object
{
// 模拟操作时间耗时
double time = (arc4random() % 10 + 10 / 1000);
[NSThread sleepForTimeInterval:time];

NSLog(@"主线程：%d, 线程名称：%@, object = %@, time %f", [NSThread isMainThread], [NSThread currentThread], object, time);
}

2018-03-06 17:59:44.794 DemoThread[7885:1445277] 主线程：1, 线程名称：<NSThread: 0x6000000643c0>{number = 1, name = main}, object = 110, time 9.000000
2018-03-06 17:59:49.796 DemoThread[7885:1445277] 主线程：1, 线程名称：<NSThread: 0x6000000643c0>{number = 1, name = main}, object = 120, time 5.000000

// 同步，在主线程中执行
- (void)runSynchronization
{
// 创建任务
// 使用子类 NSBlockOperation 对象，在主线程中执行
NSBlockOperation *operation1 = [NSBlockOperation blockOperationWithBlock:^{
[self showTime:@210];
}];
[operation1 addExecutionBlock:^{
// 并行，开辟子线程，在子线程中执行
[self showTime:@2110];
}];
[operation1 addExecutionBlock:^{
// 并行，开辟子线程，在子线程中执行
[self showTime:@2120];
}];
[operation1 start];
NSBlockOperation *operation2 = [NSBlockOperation blockOperationWithBlock:^{
[self showTime:@220];
}];
[operation2 addExecutionBlock:^{
// 并行，开辟子线程，在子线程中执行
[self showTime:@2210];
}];
[operation2 addExecutionBlock:^{
// 并行，开辟子线程，在子线程中执行
[self showTime:@2220];
}];
[operation2 start];
}

- (void)showTime:(id)object
{
// 模拟操作时间耗时
double time = (arc4random() % 10 + 10 / 1000);
[NSThread sleepForTimeInterval:time];

NSLog(@"主线程：%d, 线程名称：%@, object = %@, time %f", [NSThread isMainThread], [NSThread currentThread], object, time);
}

2018-03-06 17:56:23.772 DemoThread[7847:1441955] 主线程：0, 线程名称：<NSThread: 0x60800007d480>{number = 3, name = (null)}, object = 2110, time 2.000000
2018-03-06 17:56:26.697 DemoThread[7847:1441684] 主线程：0, 线程名称：<NSThread: 0x600000270500>{number = 4, name = (null)}, object = 2120, time 5.000000
2018-03-06 17:56:29.699 DemoThread[7847:1441602] 主线程：1, 线程名称：<NSThread: 0x6080000794c0>{number = 1, name = main}, object = 210, time 8.000000
2018-03-06 17:56:29.699 DemoThread[7847:1441684] 主线程：0, 线程名称：<NSThread: 0x600000270500>{number = 4, name = (null)}, object = 2210, time 0.000000
2018-03-06 17:56:32.768 DemoThread[7847:1441955] 主线程：0, 线程名称：<NSThread: 0x60800007d480>{number = 3, name = (null)}, object = 2220, time 3.000000
2018-03-06 17:56:38.701 DemoThread[7847:1441602] 主线程：1, 线程名称：<NSThread: 0x6080000794c0>{number = 1, name = main}, object = 220, time 9.000000

2、主队列，在主线程中执行// 主队列，在主线程中执行
- (void)runMainQueue
{
// 1 创建队列
NSOperationQueue *queue = [NSOperationQueue mainQueue];
[queue addOperationWithBlock:^{
[self showTime:@210];
}];
[queue addOperationWithBlock:^{
[self showTime:@220];
}];
}

- (void)showTime:(id)object
{
// 模拟操作时间耗时
double time = (arc4random() % 10 + 10 / 1000);
[NSThread sleepForTimeInterval:time];

NSLog(@"主线程：%d, 线程名称：%@, object = %@, time %f", [NSThread isMainThread], [NSThread currentThread], object, time);
}

2018-03-06 18:01:30.895 DemoThread[7918:1447374] 主线程：1, 线程名称：<NSThread: 0x608000065080>{number = 1, name = main}, object = 210, time 2.000000
2018-03-06 18:01:35.897 DemoThread[7918:1447374] 主线程：1, 线程名称：<NSThread: 0x608000065080>{number = 1, name = main}, object = 220, time 5.000000

// 主队列，在主线程中执行
- (void)runMainQueue
{
// 1 创建队列
NSOperationQueue *queue = [NSOperationQueue mainQueue];

// 2 创建任务，不需要调用任务的开始命令start
NSInvocationOperation *operation1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@110];
NSInvocationOperation *operation2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@120];
NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
[self showTime:@220];
}];
[operation3 addExecutionBlock:^{
// 并行，开辟子线程，在子线程中执行
[self showTime:@2210];
}];

// 3 添加到队列中
[queue addOperation:operation1];
[queue addOperation:operation2];
[queue addOperation:operation3];
}

- (void)showTime:(id)object
{
// 模拟操作时间耗时
double time = (arc4random() % 10 + 10 / 1000);
[NSThread sleepForTimeInterval:time];

NSLog(@"主线程：%d, 线程名称：%@, object = %@, time %f", [NSThread isMainThread], [NSThread currentThread], object, time);
}

2018-03-06 18:03:42.451 DemoThread[7949:1449547] 主线程：1, 线程名称：<NSThread: 0x600000071400>{number = 1, name = main}, object = 110, time 7.000000
2018-03-06 18:03:46.453 DemoThread[7949:1449547] 主线程：1, 线程名称：<NSThread: 0x600000071400>{number = 1, name = main}, object = 120, time 4.000000
2018-03-06 18:03:47.455 DemoThread[7949:1449547] 主线程：1, 线程名称：<NSThread: 0x600000071400>{number = 1, name = main}, object = 220, time 1.000000
2018-03-06 18:03:49.454 DemoThread[7949:1450059] 主线程：0, 线程名称：<NSThread: 0x6080002678c0>{number = 3, name = (null)}, object = 2210, time 3.000000

3、其他队列，开辟子线程执行

// 定义变量
NSOperationQueue *queueOther;

// 其他队列，开辟新的子线程
- (void)runOtherQueue
{
// 1 创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.name = @"queue other";
// 优先级
queue.qualityOfService = NSQualityOfServiceDefault;
// 最大并发数（-1表示不进行限制，默认为并发执行；1表示串行执行；大于1时，进行并发执行）
queue.maxConcurrentOperationCount = 5;

//    // 2 创建任务，不需要调用任务的开始命令start
//    NSInvocationOperation *operation1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@110];
//    operation1.name = @"operation1";
//    NSInvocationOperation *operation2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@120];
//    operation2.name = @"operation2";
//    NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
//        [self showTime:@220];
//    }];
//    operation3.name = @"operation3";
//    [operation3 addExecutionBlock:^{
//        // 并行，开辟子线程，在子线程中执行
//        [self showTime:@2210];
//    }];
//    // 依赖关系
//    [operation1 addDependency:operation2];
//    [operation3 addDependency:operation1];
//
//    // 3 添加到队列中
//    [queue addOperation:operation1];
//    [queue addOperation:operation2];
//    [queue addOperation:operation3];

// 或3（省略2）
//    [queue addOperationWithBlock:^{
//        [self showTime:@210];
//    }];
//    [queue addOperationWithBlock:^{
//        [self showTime:@220];
//    }];

// 多任务
for (int i = 0; i < 1000; i++)
{
//
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(showTime:) object:@(i + 1)];
[queue addOperation:operation];

// 或
//        [queue addOperationWithBlock:^{
//            [self showTime:@(i + 1)];
//        }];
}

//
NSLog(@"start: %ld, %ld", queue.operationCount, queue.operations.count);
queueOther = queue;
}

- (void)showTime:(id)object
{
if (((NSNumber *)object).integerValue == 10)
{
NSInvocationOperation *operation = [queueOther.operations objectAtIndex:9];
[operation cancel];
if ([operation isCancelled])
{
NSLog(@"已经退出执行");
return;
}
}

// 模拟操作时间耗时
double time = (arc4random() % 10 + 10 / 1000);
[NSThread sleepForTimeInterval:time];

NSLog(@"主线程：%d, 线程名称：%@, object = %@, time %f", [NSThread isMainThread], [NSThread currentThread], object, time);
}

2018-03-06 18:05:10.013 DemoThread[7971:1451469] 主线程：0, 线程名称：<NSThread: 0x60000026b040>{number = 3, name = (null)}, object = 1, time 0.000000
2018-03-06 18:05:10.013 DemoThread[7971:1451484] 主线程：0, 线程名称：<NSThread: 0x6080002713c0>{number = 4, name = (null)}, object = 4, time 0.000000
2018-03-06 18:05:10.023 DemoThread[7971:1451407] start: 998, 998
2018-03-06 18:05:16.018 DemoThread[7971:1451587] 主线程：0, 线程名称：<NSThread: 0x60000026b400>{number = 5, name = (null)}, object = 6, time 6.000000
2018-03-06 18:05:17.017 DemoThread[7971:1451484] 主线程：0, 线程名称：<NSThread: 0x6080002713c0>{number = 4, name = (null)}, object = 7, time 7.000000
2018-03-06 18:05:17.018 DemoThread[7971:1451484] 主线程：0, 线程名称：<NSThread: 0x6080002713c0>{number = 4, name = (null)}, object = 9, time 0.000000
2018-03-06 18:05:17.019 DemoThread[7971:1451484] 已经退出执行
2018-03-06 18:05:18.016 DemoThread[7971:1451466] 主线程：0, 线程名称：<NSThread: 0x6080002712c0>{number = 6, name = (null)}, object = 5, time 8.000000
2018-03-06 18:05:18.421 DemoThread[7971:1451407] pause: 993, 993
2018-03-06 18:05:19.016 DemoThread[7971:1451485] 主线程：0, 线程名称：<NSThread: 0x608000461080>{number = 7, name = (null)}, object = 2, time 9.000000
2018-03-06 18:05:19.016 DemoThread[7971:1451467] 主线程：0, 线程名称：<NSThread: 0x608000271080>{number = 8, name = (null)}, object = 3, time 9.000000
2018-03-06 18:05:21.022 DemoThread[7971:1451469] 主线程：0, 线程名称：<NSThread: 0x60000026b040>{number = 3, name = (null)}, object = 8, time 5.000000
2018-03-06 18:05:21.253 DemoThread[7971:1451407] pause: 990, 990
2018-03-06 18:05:22.019 DemoThread[7971:1451466] 主线程：0, 线程名称：<NSThread: 0x6080002712c0>{number = 6, name = (null)}, object = 12, time 4.000000
2018-03-06 18:05:22.917 DemoThread[7971:1451407] cancle: 988, 988

- (void)pauseClick
{
if (queueOther)
{
// 暂停或继续
NSLog(@"pause: %ld, %ld", queueOther.operationCount, queueOther.operations.count);
queueOther.suspended = !queueOther.isSuspended;
}
}

- (void)cancleClick
{
if (queueOther)
{
// 停止
NSLog(@"cancle: %ld, %ld", queueOther.operationCount, queueOther.operations.count);
[queueOther cancelAllOperations];
}
}

图片下载示例

bool isCancelOperation = NO;
- (void)stopClick
{
if (self.queue)
{
NSLog(@"1 停止");
isCancelOperation = YES;
[self.queue cancelAllOperations];
}
}

- (void)showCount:(NSNumber *)number
{
NSInteger count = arc4random() % 1000;
for (int i = 0; i < count; i++)
{
NSLog(@"第 %@ 个 i = %@", number, @(i));

// 休眠n秒再执行
[NSThread sleepForTimeInterval:0.2];

// 停止
if (isCancelOperation)
{
NSLog(@"2 停止");
break;
}
}
}

- (void)downloadImage:(NSString *)imageUrl
{
NSURL *url = [NSURL URLWithString:imageUrl];
NSData *data = [[NSData alloc] initWithContentsOfURL:url];
UIImage *image = [[UIImage alloc] initWithData:data];
if (image == nil)
{

}
else
{
//        [self performSelectorOnMainThread:@selector(updateImage:) withObject:image waitUntilDone:YES];
[self performSelectorInBackground:@selector(updateImage:) withObject:image];
}
}

- (void)updateImage:(UIImage *)image
{
self.imageview.image = image;
}

NSString *imageUrl = @"http://ww1.sinaimg.cn/crop.0.0.1242.1242.1024/763fb12bjw8empveq3eq8j20yi0yiwhw.jpg";
NSInvocationOperation *operation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(downloadImage:) object:imageUrl];
self.queue = [[NSOperationQueue alloc] init];
[self.queue addOperation:operation];

NSInvocationOperation *operationCount1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(showCount:) object:@(11)];
[self.queue addOperation:operationCount1];
NSInvocationOperation *operationCount2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(showCount:) object:@(12)];
[self.queue addOperation:operationCount2];