IOS开发－多线程编程技术（Thread、Cocoa operations、GCD）

每个正在系统上运行的程序都是一个进程。每个进程包含一到多个线程。进程也可能是整个程序或者是部分程序的动态执行。线程是一组指令的集合，或者是程序的特殊段，它可以在程序里独立执行。也可以把它理解为代码运行的上下文。所以线程基本上是轻量级的进程，它负责在单个程序里执行多任务。通常由操作系统负责多个线程的调度和执行。

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

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

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

            //
             获取/设置线程的名字
            
@property (copy) NSString *name NS_AVAILABLE(10_5, 2_0);

/**
 *  获取当前线程的线程对象
 *
 *  通过这个属性可以查看当前线程是第几条线程，主线程为1。
 *  可以看到当前线程的序号及名字，主线程的序号为1，依次叠加。
 */
+ (NSThread *)currentThread;

// 线程休眠（秒）
+ (void)sleepForTimeInterval:(NSTimeInterval)ti;

// 线程休眠，指定具体什么时间休眠
+ (void)sleepUntilDate:(NSDate *)date;

// 退出线程 
// 注意：这里会把线程对象销毁！销毁后就不能再次启动线程，否则程序会崩溃。
+ (void)exit;

            //
             创建线程任务
NSOperationQueue *queue = [[NSOperationQueue alloc] init];

// 线程A
NSInvocationOperation *operation = [[NSInvocationOperation alloc]
                                    initWithTarget:self
                                    selector:@selector(operation1)
                                    object:nil];
// 线程B
NSInvocationOperation *operation2 = [[NSInvocationOperation alloc]
                                    initWithTarget:self
                                    selector:@selector(operation2)
                                    object:nil];

// 把线程A/B添加至队列
[queue addOperations:@[operation, operation2] waitUntilFinished:YES];

            //
             创建线程任务
NSBlockOperation *blockOperation = [NSBlockOperation
                           blockOperationWithBlock:^{
                               NSLog(@"one - %@", [NSThread currentThread]);
                           }];;
// 添加新的操作
[blockOperation addExecutionBlock:^{
    NSLog(@"two - %@", [NSThread currentThread]);
}];

// 添加新的操作
[blockOperation addExecutionBlock:^{
    NSLog(@"three - %@", [NSThread currentThread]);
}];

// 执行线程任务
[blockOperation start];

            //
             创建操作队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];

// 线程A
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"op1");
    [NSThread sleepForTimeInterval:2];
}];

// 线程B
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"op2");
}];

// 线程C
NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
    NSLog(@"op3");
    [NSThread sleepForTimeInterval:2];
}];

// 线程B依赖线程C，也就是等线程C执行完之后才会执行线程B[op2 addDependency:op3];
// 线程C依赖线程A，同上，只不过依赖对象改成了线程A[op3 addDependency:op1];

// 为队列添加线程[queue addOperation:op1];
[queue addOperation:op2];
[queue addOperation:op3];

            //
             设置线程的最大并发数
            @property NSInteger maxConcurrentOperationCount;


            //
             线程完成后调用的Block
@property (copy) void (^completionBlock)(void);

// 取消线程
- (void)cancel;

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSLog(@"线程 - %@", [NSThread currentThread]);
});

dispatch_apply(4, DISPATCH_QUEUE_PRIORITY_DEFAULT, ^(size_t index) {
    // index则为执行的次数 0开始递增
    NSLog(@"one - %ld", index);
});

            //
             创建队列

            //
             第一个参数是“字符串标识”，第二个参数是可选的，可以是NULL
dispatch_queue_t queue = dispatch_queue_create("com.garvey.post", NULL);

// 传入一个队列并执行队列（顺序执行）
dispatch_async(queue, ^{
    NSLog(@"aaa");
    [NSThread sleepForTimeInterval:2];
});
dispatch_async(queue, ^{
    NSLog(@"bbb");
    [NSThread sleepForTimeInterval:1];
});
dispatch_async(queue, ^{
    NSLog(@"ccc");
});

            //
             创建群组
dispatch_group_t group = dispatch_group_create();

// 线程A
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSLog(@"group1");
    [NSThread sleepForTimeInterval:2];
});

// 线程B
dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSLog(@"group2");
});

// 待群组里的线程都完成之后调用的通知
dispatch_group_notify(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSLog(@"group success");
});

__block int time = 30;
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC, 0);
dispatch_source_set_event_handler(timer, ^{
    time--;
    NSLog(@"%d", time);
    if (time == 0) {
        dispatch_source_cancel(timer);
    }
});
dispatch_resume(timer);

            //
             获取主线程
            
dispatch_get_main_queue()


            //
             创建队列：第一个参数是“字符串标识”，第二个参数是可选的，可以是NULL
            
dispatch_queue_t dispatch_queue_create(
            const
            char *label, dispatch_queue_attr_t attr);

// 创建异步调度队列void dispatch_async(dispatch_queue_t queue, dispatch_block_t block);

// 恢复队列void dispatch_resume(dispatch_object_t object);

// 暂停队列void dispatch_suspend(dispatch_object_t object);