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iOS多线程之NSOperationQueue-依赖、并发数、优先级、自定义Operation等最全的使用总结

2023-09-03 223
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简介： iOS多线程之NSOperationQueue-依赖、并发数、优先级、自定义Operation等最全的使用总结

1. 简介

NSOperation（任务）: 通过start方法开始执行任务、默认是同步执行的

NSOperationQueue（队列）: 将NSOperation添加到队列中执行（主队列除外），是异步执行的


2. NSOperation创建

1） NSOperation一般不直接使用，而是使用它的子类NSInvocationOperation和NSBlockOperation

2） 可以看到在没有添加到对列的时候都是在当前线程执行的

文末附工程源码



- (void)createOperation {
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    [op start];
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    [blockOp start];
}
- (void)createOperation {
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    [op start];
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    [blockOp start];
}

运行结果：



2021-04-11 11:12:24.522251+0800 OperationQueue[1485:43624] obj - <NSThread: 0x600003a0c900>{number = 1, name = main}
2021-04-11 11:12:24.522431+0800 OperationQueue[1485:43624] block - <NSThread: 0x600003a0c900>{number = 1, name = main}


3. 将NSOperation添加到Queue中

1）可以利用[queue addOperation:op]将NSOperation添加到NSOperationQueue中

2）也可以利用[queue addOperations:@[op, blockOp] waitUntilFinished:NO]将NSOperation添加到NSOperationQueue中

3）注意一不可用重复添加同一个NSOperation到NSOperationQueue中，否则会报如下错误

- (void)addToQueue {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
//    [op start];//调用start之后就不可以再入队
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    //添加单个
    [queue addOperation:op];
    [queue addOperation:blockOp];
    //添加一组
    [queue addOperations:@[op, blockOp] waitUntilFinished:NO];
//    [op start];
//    [op cancel];
}
- (void)addToQueue {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
//    [op start];//调用start之后就不可以再入队
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    //添加单个
    [queue addOperation:op];
    [queue addOperation:blockOp];
    //添加一组
    [queue addOperations:@[op, blockOp] waitUntilFinished:NO];
//    [op start];
//    [op cancel];
}

运行结果：



*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSOperationQueue addOperations:waitUntilFinished:]: 2 (of 2) operations are finished, executing, or already in a queue, and cannot be enqueued'
terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSOperationQueue addOperations:waitUntilFinished:]: 2 (of 2) operations are finished, executing, or already in a queue, and cannot be enqueued'
terminating with uncaught exception of type NSException

4）注意二不可将NSOperation调用start或者cancel之后再添加到NSOperationQueue中，否则会报如下错误

- (void)addToQueue {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    [op start];//调用start之后就不可以再入队
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    //添加单个
    [queue addOperation:op];
    [queue addOperation:blockOp];
    //添加一组
//    [queue addOperations:@[op, blockOp] waitUntilFinished:NO];
//    [op start];
//    [op cancel];
}

运行结果：



*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSOperationQueue addOperation:]: operation is finished and cannot be enqueued'
terminating with uncaught exception of type NSException
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSOperationQueue addOperation:]: operation is finished and cannot be enqueued'
terminating with uncaught exception of type NSException

5）注意三不可将NSOperation添加NSOperationQueue之后，再次调用star或者cancelt去修改状态，否则会报如下错误

- (void)addToQueue {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
//    [op start];//调用start之后就不可以再入队
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    //添加单个
    [queue addOperation:op];
    [queue addOperation:blockOp];
    //添加一组
//    [queue addOperations:@[op, blockOp] waitUntilFinished:NO];
    [op start];
//    [op cancel];
}
- (void)addToQueue {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
//    [op start];//调用start之后就不可以再入队
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    //添加单个
    [queue addOperation:op];
    [queue addOperation:blockOp];
    //添加一组
//    [queue addOperations:@[op, blockOp] waitUntilFinished:NO];
    [op start];
//    [op cancel];
}

运行结果：



*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSInvocationOperation start]: something is trying to start the receiver simultaneously from more than one thread'
terminating with uncaught exception of type NSException


4. 添加依赖关系

1）当需要某个NSOperation对象依赖于其它NSOperation对象时，可以通过addDependency方法添加一个或者多个依赖的对象，只有所有依赖的对象都已经完成操作的时候，当前NSOperation对象才会开始执行操作，也可以通过removeDependency方法来删除依赖对象

2）不添加依赖关系应该先打印block再打印obj见上方日志，设置依赖后见下方代码说明

3）设置依赖关系，必须在addOperation之前设置，否则没有效果

4）不可以相互依赖，否则都不会执行


- (void)addDependency {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    [op addDependency:blockOp];//添加依赖
//    [blockOp addDependency:op];//相互依赖
//    [op removeDependency:blockOp];//移除依赖
    [queue addOperation:op];
    [queue addOperation:blockOp];
}
- (void)addDependency {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
    }];
    [op addDependency:blockOp];//添加依赖
//    [blockOp addDependency:op];//相互依赖
//    [op removeDependency:blockOp];//移除依赖
    [queue addOperation:op];
    [queue addOperation:blockOp];
}

运行结果：



2021-04-11 11:29:47.303916+0800 OperationQueue[1586:56394] block - <NSThread: 0x600003ead180>{number = 5, name = (null)}
2021-04-11 11:29:47.304047+0800 OperationQueue[1586:56394] obj - <NSThread: 0x600003ead180>{number = 5, name = (null)}
2021-04-11 11:29:47.303916+0800 OperationQueue[1586:56394] block - <NSThread: 0x600003ead180>{number = 5, name = (null)}
2021-04-11 11:29:47.304047+0800 OperationQueue[1586:56394] obj - <NSThread: 0x600003ead180>{number = 5, name = (null)}


5. 优先级

1）执行顺序规则

不设置依赖关系的前提下：（可通过调试下方代码看执行结果）

(1)如果都不设置优先级、并且内部没有耗时操作，则按照添加顺序执行；

(2)如果都不设置优先级、并且内部有耗时操作，则耗时操作的后执行，没有耗时操作的先执行；

(3)如果设置了优先级、并且内部没有耗时操作，则按照处于ready状态的operation优先级等级的高低执行；

(4)如果设置了优先级、并且内部有耗时操作，则耗时操作的后执行，没有耗时操作的按照处于ready状态的operation优先级等级的高低执行；

2）优先级不能替代依赖关系并且依赖关系高于优先级的设置，在保证依赖关系的情况下才能考虑优先级


- (void)setQueuePriority {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
        sleep(3);
    }];
    [op setQueuePriority:NSOperationQueuePriorityHigh];
    [blockOp setQueuePriority:NSOperationQueuePriorityLow];
    [op addDependency:blockOp];
    [queue addOperation:op];
    [queue addOperation:blockOp];
}
- (void)setQueuePriority {
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSInvocationOperation *op = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationSel:) object:@"obj"];
    NSBlockOperation *blockOp = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"block - %@", [NSThread currentThread]);
        sleep(3);
    }];
    [op setQueuePriority:NSOperationQueuePriorityHigh];
    [blockOp setQueuePriority:NSOperationQueuePriorityLow];
    [op addDependency:blockOp];
    [queue addOperation:op];
    [queue addOperation:blockOp];
}

运行结果：


2021-04-11 11:39:07.960943+0800 OperationQueue[1621:62599] block - <NSThread: 0x600000715640>{number = 3, name = (null)}
2021-04-11 11:39:10.964436+0800 OperationQueue[1621:62599] obj - <NSThread: 0x600000715640>{number = 3, name = (null)}
2021-04-11 11:39:07.960943+0800 OperationQueue[1621:62599] block - <NSThread: 0x600000715640>{number = 3, name = (null)}
2021-04-11 11:39:10.964436+0800 OperationQueue[1621:62599] obj - <NSThread: 0x600000715640>{number = 3, name = (null)}

6. NSOperationQueue的挂起和恢复

可以根据你实际的需求来确定是否要挂起和恢复，挂起或者恢复NSOperationQueue，并不会影响正在执行的NSOperation

    [queue setSuspended:YES];//挂起
    [queue setSuspended:NO];//恢复
    [queue setSuspended:YES];//挂起
    [queue setSuspended:NO];//恢复


7. 等待完成

1） [blockOp waitUntilFinished]等待当前的操作完成后，才会继续向下执行，注意：会阻塞线程

2） [queue waitUntilAllOperationsAreFinished]等待所有的操作完成后，才会继续向下执行，注意：会阻塞线程



[blockOp waitUntilFinished];
[queue waitUntilAllOperationsAreFinished];
[blockOp waitUntilFinished];
[queue waitUntilAllOperationsAreFinished];


8. 取消Operations

取消所有正在执行的操作


[queue cancelAllOperations];// 两个操作都不会执行

9. 并发数

设置单次最大的执行数量，如果多于1个，是完成一个向队列里面追加一个的执行，而不是等待同时执行的最大个数执行完之后再执行后面的操作


queue.maxConcurrentOperationCount = 1;

10. 自定义NSOperation

1）NSInvocationOperation和NSBlockOperation不能满足我们的需求时就需要我们自定义，自定义NSOperation的场景主要是为了我们能更好的控制一个任务，什么情况下开始、取消、完成, 并且可以分离代码的实现

2）实现步骤：（可参考下面代码）

（1）实现start方法

（2）重写isAsynchronous，是否为并发任务、根据自己的情况即可

（3）main方法可根据自己的实际需要决定是否实现、一般实现并在里面做自己的事

（4）finished、executing更新任务的状态，用于触发KVO

（5）自己的任务完成后，一定要把当前的任务状态改为完成，否则队列中后面的任务，将永远不会执行



@property(assign, nonatomic, getter=isFinished) BOOL finished;
@property(assign, nonatomic, getter=isExecuting) BOOL executing;
@property(assign, nonatomic, getter=isStart) BOOL start;
@property(assign, nonatomic, getter=isFinished) BOOL finished;
@property(assign, nonatomic, getter=isExecuting) BOOL executing;
@property(assign, nonatomic, getter=isStart) BOOL start;

@implementation CustomOperation
@synthesize finished = _finished, executing = _executing;
- (BOOL)isAsynchronous {
    return NO;
}
- (void)setFinished:(BOOL)finished {
    [self willChangeValueForKey:@"finished"];
    _finished = finished;
    [self didChangeValueForKey:@"finished"];
}
- (void)setExecuting:(BOOL)executing {
    [self willChangeValueForKey:@"executing"];
    _executing = executing;
    [self didChangeValueForKey:@"executing"];
}
- (void)start {
    @synchronized (self) {
        self.start = YES;
        if (self.isCancelled) {
            [self completed];
            return;
        }
        @autoreleasepool {
            [self main];
        }
        self.executing = YES;
    }
}
- (void)main {//在此处做一些更复杂的操作
    NSLog(@"准备开始执行任务啦～ %@", [NSThread currentThread]);
    //模拟3s后执行doSomething
    [self performSelector:@selector(doSomething:) withObject:nil afterDelay:3.0];
    [[NSRunLoop currentRunLoop] run];//此处需要添加到Runloop，子线程默认没有开启，后期文章会具体说明
}
- (void)doSomething:(id)obj {
    NSLog(@"完成了当前的任务！%@", [NSThread currentThread]);
    [self completed];
}
- (void)completed {
    @synchronized (self) {
        self.executing = NO;
        self.finished = YES;
    }
}
- (void)cancel {
    [super cancel];
    if (self.isStart) {
        [self completed];
    }
}
@end
@implementation CustomOperation
@synthesize finished = _finished, executing = _executing;
- (BOOL)isAsynchronous {
    return NO;
}
- (void)setFinished:(BOOL)finished {
    [self willChangeValueForKey:@"finished"];
    _finished = finished;
    [self didChangeValueForKey:@"finished"];
}
- (void)setExecuting:(BOOL)executing {
    [self willChangeValueForKey:@"executing"];
    _executing = executing;
    [self didChangeValueForKey:@"executing"];
}
- (void)start {
    @synchronized (self) {
        self.start = YES;
        if (self.isCancelled) {
            [self completed];
            return;
        }
        @autoreleasepool {
            [self main];
        }
        self.executing = YES;
    }
}
- (void)main {//在此处做一些更复杂的操作
    NSLog(@"准备开始执行任务啦～ %@", [NSThread currentThread]);
    //模拟3s后执行doSomething
    [self performSelector:@selector(doSomething:) withObject:nil afterDelay:3.0];
    [[NSRunLoop currentRunLoop] run];//此处需要添加到Runloop，子线程默认没有开启，后期文章会具体说明
}
- (void)doSomething:(id)obj {
    NSLog(@"完成了当前的任务！%@", [NSThread currentThread]);
    [self completed];
}
- (void)completed {
    @synchronized (self) {
        self.executing = NO;
        self.finished = YES;
    }
}
- (void)cancel {
    [super cancel];
    if (self.isStart) {
        [self completed];
    }
}
@end

运行结果：



2021-04-11 11:48:12.601640+0800 OperationQueue[1671:69134] 准备开始执行任务啦～ <NSThread: 0x600000b58380>{number = 8, name = (null)}2021-04-11 11:48:15.605299+0800 OperationQueue[1671:69134] 完成了当前的任务！<NSThread: 0x600000b58380>{number = 8, name = (null)}

源码：https://github.com/gltwy/public

文章标签：
iOS开发
关键词：
线程优先级
iOS自定义
iOS多线程
iOS nsoperationqueue
iOS多线程nsoperationqueue
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