GCD(多线程)

系统提供的dispatch方法

//后台执行:

dispatch_async(dispatch_get_global_queue(0,0), ^{

//something

});

//主线程执行

dispatch_async(dispatch_get_main_queue(),^{

//something

});

//一次性执行  

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

//code to be executed once

});

//延迟两秒执行

double delayInSecond = 2.0f;

dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSecond * NSEC_PER_SEC);

dispatch_after(popTime, dispatch_get_main_queue(), ^{

//code to executed on the main queue after delay

});

//如果要自定义queue, 可以用dispatch_queue_create方法

dispatch_queue_t myQueue = dispatch_queue_create("www.baidu.com", NULL);

dispatch_async(myQueue, ^{

//your code

});