iOS多线程

https://www.jianshu.com/p/0b0d9b1f1f19

Pthreads
NSThread
GCD
NSOperation & NSOperationQueue

线程同步、延时执行、单例模式

1、Pthreads：

POSIX线程

pthread_create(&thread, NULL, start, NULL);

2、NSThread

1—先创建线程类，再启动

// 创建

NSThread *thread = [[NSThread alloc] initWithTarget:self selector:@selector(run:) object:nil];

// 启动

[thread start];

2-创建并自动启动

[NSThread detachNewThreadSelector:@selector(run:) toTarget:self withObject:nil];

3-NSObject 的方法创建并自动启动

[self performSelectorInBackground:@selector(run:) withObject:nil];

3、GCD

任务和队列

同步（sync）和异步（async）

会不会阻塞当前线程，直到 Block 中的任务执行完毕！

串行队列和并行队列

异步：

串行队列：开多个线程，单个执行

并行队列：开很多线程，一起执行

主队列-串行

dispatch_queue_t queue = dispatch_get_main_queue();

自己创建的队列

DISPATCH_QUEUE_SERIAL 或 NULL 表示创建串行队列。传入 DISPATCH_QUEUE_CONCURRENT 表示创建并行队列。

全局并行队列

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

同步任务

dispatch_sync

异步任务

dispatch_async

队列组

dispatch_group_t group = dispatch_group_create();

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_group_async(group, queue, ^{

dispatch_group_async(group, dispatch_get_main_queue(), ^{

dispatch_group_async(group, queue, ^{

dispatch_group_notify(group, dispatch_get_main_queue(), ^{

？？阑珊用法：dispatch_barrier_async

4、NSOperation和NSOperationQueue

NSInvocationOperation 和 NSBlockOperation + start

addExecutionBlock

Operation 添加多个执行 Block，任务会并发执行，在主线程和其它的多个线程执行这些任务

自定义Operation

main()

NSOperationQueue

主队列

NSOperationQueue *queue = [NSOperationQueue mainQueue];

其他队列

NSOperationQueue *queue = [[NSOperationQueue alloc] init];

[operation addExecutionBlock:

[queue addOperation:operation];

maxConcurrentOperationCount = 1 串行队列

添加依赖

[operation2 addDependency:operation1]; //任务二依赖任务一

[operation3 addDependency:operation2]; //任务三依赖任务二

[queue addOperations:@[operation3, operation2, operation1] waitUntilFinished:NO];

removeDependency 来解除依赖关系。

线程同步

互斥锁：

@synchronized(self)

/需要执行的代码块

NSLock

NSRecursiveLock 嵌套锁

同步执行

1、dispatch_sync

2、

[queue addOperation:operation];

[operation waitUntilFinished];

延迟执行

[self performSelector:@selector(run:) withObject:@"abc" afterDelay:3];

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delay * NSEC_PER_SEC)), queue, ^{

[NSTimer scheduledTimerWithTimeInterval:3.0 target:self selector:@selector(run:) userInfo:@"abc" repeats:NO];

从其他线程回到主线程的方法

1、[self performSelectorOnMainThread:@selector(run) withObject:nil waitUntilDone:NO];

2、GCD

//Objective-C

dispatch_async(dispatch_get_main_queue(), ^{

});

3、NSOperationQueue

//Objective-C

[[NSOperationQueue mainQueue] addOperationWithBlock:^{

}];