整理一些多线程相关的知识。
并行 & 并发
1、并行：并行是相对于多核而言的，几个任务同时执行。
2、并发：并发是相对于单核而言的，几个任务之间快速切换运行，看起来像是“同时”发生的一样
NSThread
优点：轻量级
缺点：需要手动管理线程活动，如生命周期、线程同步、睡眠等。
搭配runloop实现常驻线程
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NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(threadRun) object:nil];
[thread start];
- (void)threadRun {
@autoreleasepool {
NSLog(@"threadRun");
// NSTimer *timer = [NSTimer timerWithTimeInterval:2 target:self selector:@selector(timeTask) userInfo:nil repeats:YES];
// [[NSRunLoop currentRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
[NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(timeTask) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] run];
}
}
- (void)timeTask {
NSLog(@"timeTask:%@",[NSThread currentThread]);
}
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NSOperation & NSOperationQueue
NSOperation
NSOperation 是一个抽象类，只能使用它的自类来进行操作。系统为我们创建了两个子类NSInvocationOperation & NSBlockOperation。
直接使用这两个类执行任务，系统不会创建子线程，而是在当前线程执行任务。NSBlockOperation 使用 addExecutionBlock方法的任务是在多线程执行的
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//NSInvocationOperation
NSInvocationOperation *invocationOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationOperation) object:nil];
[invocationOperation start];
//NSBlockOperation
NSBlockOperation * blockOperation = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"blockOperation:%@",[NSThread currentThread]);
}];
//这里面的任务是多线程执行的
[blockOperation addExecutionBlock:^{
NSLog(@"addExecutionBlock:%@",[NSThread currentThread]);
}];
[blockOperation start];
- (void)invocationOperation {
NSLog(@"invocationOperation:%@",[NSThread currentThread]);
}
//invocationOperation:<NSThread: 0x60800007e1c0>{number = 1, name = main}
//blockOperation:<NSThread: 0x60800007e1c0>{number = 1, name = main}
//addExecutionBlock:<NSThread: 0x608000078800>{number = 3, name = (null)}
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NSOperationQueue
//主队列，任务在主线程执行，一般用于更新UI的时候使用。
NSOperationQueue queue = [NSOperationQueue mainQueue];
//子队列，任务在子线程执行，用于处理耗时任务。
NSOperationQueue queue = [[NSOperationQueue alloc] init];
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NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
//NSInvocationOperation
NSInvocationOperation *invocationOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(invocationOperation) object:nil];
//NSBlockOperation
NSBlockOperation * blockOperation = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"blockOperation:%@",[NSThread currentThread]);
}];
[operationQueue addOperation:invocationOperation];
[operationQueue addOperation:blockOperation];
- (void)invocationOperation {
NSLog(@"invocationOperation:%@",[NSThread currentThread]);
}
// invocationOperation:<NSThread: 0x60c00046b940>{number = 4, name = (null)}
// blockOperation:<NSThread: 0x60800026b580>{number = 3, name = (null)}
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也可以直接添加block
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NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue addOperationWithBlock:^{
NSLog(@"%@",[NSThread currentThread]);
}];
[operationQueue addOperationWithBlock:^{
NSLog(@"%@",[NSThread currentThread]);
}];
[operationQueue addOperationWithBlock:^{
NSLog(@"%@",[NSThread currentThread]);
}];
// <NSThread: 0x6080002637c0>{number = 4, name = (null)}
// <NSThread: 0x60c0002667c0>{number = 5, name = (null)}
// <NSThread: 0x60000047b2c0>{number = 3, name = (null)}
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可以通过 maxConcurrentOperationCount 来控制最大并发数，当最大并发数为1时，就相当于串行队列
NSOperation添加依赖关系
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NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
//NSBlockOperation
NSBlockOperation * blockOperation0 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"blockOperation0:%@",[NSThread currentThread]);
}];
NSBlockOperation * blockOperation1 = [NSBlockOperation blockOperationWithBlock:^{
sleep(1);
NSLog(@"blockOperation1:%@",[NSThread currentThread]);
}];
//blockOperation0 依赖 blockOperation1，只有在 blockOperation1 执行完成才能执行 blockOperation0
[blockOperation0 addDependency:blockOperation1];
[operationQueue addOperation:blockOperation0];
[operationQueue addOperation:blockOperation1];
//blockOperation1:<NSThread: 0x600000269c80>{number = 3, name = (null)}
//blockOperation0:<NSThread: 0x60c000479040>{number = 4, name = (null)}
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注意：NSOperationQueue 是非线程安全的，多个线程访问统一资源时，需要加锁。
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self.lock = [[NSLock alloc] init];
[self.lock lock];
//不能同时访问的资源
[self.lock unlock];
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GCD
创建队列，然后再往队列添加任务。也可以直接使用系统创建的队列。
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//创建串行队列
dispatch_queue_t queue = dispatch_queue_create("com.vhuichen.queue", DISPATCH_QUEUE_SERIAL);
//创建并发队列
dispatch_queue_t queue = dispatch_queue_create("com.vhuichen.queue", DISPATCH_QUEUE_CONCURRENT);
//获取主队列
dispatch_queue_t queue = dispatch_get_main_queue();
//获取全局并发队列
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
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创建同步、异步任务
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dispatch_sync(queue, ^{
//同步执行
});
// 异步执行任务创建方法
dispatch_async(queue, ^{
//异步执行
});
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GCD常用方法
dispatch_barrier
只有当添加在dispatch_barrier前面的任务完成了，才开始执行dispatch_barrier任务。
有两种方式：dispatch_barrier_sync 和 dispat 大专栏 iOS开发之多线程（NSThread、NSOperation、GCD）ch_barrier_async
dispatch_barrier_sync
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dispatch_queue_t queue = dispatch_queue_create("com.vhuichen.queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
NSLog(@"task0.....");
sleep(1);
});
dispatch_async(queue, ^{
NSLog(@"task1.....");
sleep(1);
});
dispatch_barrier_sync(queue, ^{
NSLog(@"task2.....");
sleep(5);
});
NSLog(@"test");
dispatch_async(queue, ^{
NSLog(@"task3.....");
sleep(2);
});
dispatch_async(queue, ^{
NSLog(@"task4.....");
sleep(1);
});
//task0.....
//task1.....
//task2.....
//test....
//task3.....
//task4.....
//只有当task0、task1 执行完才会执行tast2.
//task2 执行完才会往下执行。
//test 执行完后，才会把task3、task4 加进队列.
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dispatch_barrier_async
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dispatch_queue_t queue = dispatch_queue_create("com.vhuichen.queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
NSLog(@"task0.....");
sleep(1);
});
dispatch_async(queue, ^{
NSLog(@"task1.....");
sleep(1);
});
dispatch_barrier_async(queue, ^{
NSLog(@"task2.....");
sleep(5);
});
NSLog(@"test");
dispatch_async(queue, ^{
NSLog(@"task3.....");
sleep(2);
});
dispatch_async(queue, ^{
NSLog(@"task4.....");
sleep(1);
});
//test....
//task1.....
//task0.....
//task2.....
//task3.....
//task4.....
//test、task0、task1 并发执行。
//task0、task1 执行完才会执行tast2.
//tast2 执行完才会执行tast3、tast4.
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dispatch_after
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dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
NSLog(@"dispatch_after task...");
});
//dispatch_after 会在到了指定的时间之后，将才将任务加到相应的队列中。
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dispatch_once
一般会以这种形式出现
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static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSLog(@"dispatch_once task...");
});
//block里面的任务只会执行一次。
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dispatch_apply
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dispatch_queue_t queue = dispatch_queue_create("com.vhuichen.queue", DISPATCH_QUEUE_CONCURRENT);
dispatch_apply(10, queue, ^(size_t index) {
NSLog(@"%zu",index);
});
NSLog(@"end");
// 0
// 1
// 3
// 2
// 4
// 5
// 6
// 7
// 8
// 9
// end
// dispatch_apply 会等待所有的任务完成了，才会往下执行。
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dispatch_semaphore
可以用于线程同步、线程加锁、控制并发线程数量
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//实现同步请求
let semaphoreSignal = DispatchSemaphore(value: 0)
ZBDepthAPI.GET(market: market.name!, succeed: { (depthModel) in
//......
semaphoreSignal.signal()
}) { (error) in
//......
semaphoreSignal.signal()
}
semaphoreSignal.wait()
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dispatch_group
当需要同时执行多个耗时任务，并且当所有任务执行完后更新UI。那么这时可以使用 dispatch_group 来实现。
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dispatch_group_t group = dispatch_group_create();
dispatch_queue_t global = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_async(group, global, ^{
NSLog(@"tast0.......");
});
NSLog(@"0");
dispatch_group_async(group, global, ^{
NSLog(@"tast1.......");
});
NSLog(@"1");
dispatch_group_async(group, global, ^{
NSLog(@"tast2.......");
sleep(1);
});
NSLog(@"2");
dispatch_group_enter(group);
dispatch_async(global, ^{
NSLog(@"tast00.......");
dispatch_group_leave(group);
});
// 所有任务完成的时候调用
//dispatch_group_notify(group, global, ^{
// NSLog(@"tast complete...");
//});
//会阻塞当前线程，直到 group 里面的任务全部完成
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
NSLog(@"wait");
// 异步加入的任务会立即执行
// dispatch_group_wait会阻塞当前线程，直到 group 里面的任务全部完成
// dispatch_group_enter & dispatch_group_leave 必须成对出现，相当于 dispatch_group_async
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总结
当遇到相应场景的时候，知道使用哪种方法比较合理就行了。
