【读书笔记】iOS-GCD-系统提供的dispatch方法

系统提供的dispatch方法如下：

 //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
 });

 

 参考资料：

http://www.devtang.com/blog/2012/02/22/use-gcd/

http://www.cnblogs.com/pure/archive/2013/03/31/2977420.html