【读书笔记】GCD-系统提供的dispatch方法

//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, ^{
//something
});

// 延迟2秒执行：
double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// 延迟2s在主线程中执行
});

//自定义queue
dispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL);
dispatch_async(urls_queue, ^{
//something
});

//让后台2个线程并行执行，然后等2个线程都结束后，再汇总执行结果
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{
// 并行执行的线程一
});
dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{
// 并行执行的线程二
});
dispatch_group_notify(group, dispatch_get_global_queue(0,0), ^{
// 汇总结果
});