GCD深入了解

一.GCD应用 单例模式

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

NSLog(@"执行一次%@",[NSThread currentThread]);

});

二延迟操作

//1、

NSLog(@"开始执行");

// [self performSelector:@selector(handleAction) withObject:nil afterDelay:0];

[self performSelector:@selector(handleAction) withObject:nil afterDelay:2];

//2、

//DISPATCH_TIME_NOW 从现在开始

//delayInSeconds 延迟几秒

dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC));

dispatch_after(time, dispatch_get_main_queue(), ^{

　　NSLog(@"%@",[NSThread currentThread]);

});

三队列调度

1.

//创建调度组

dispatch_group_t group = dispatch_group_create();

//获取全局队列

dispatch_queue_t queue = dispatch_get_global_queue(0, 0);

//调度组的异步请求

dispatch_group_async(group, queue, ^{

NSLog(@"1--%@",[NSThread currentThread]);

[NSThread sleepForTimeInterval:2];

NSLog(@"下载第一张图");

});

dispatch_group_async(group, queue, ^{

NSLog(@"2--%@",[NSThread currentThread]);

[NSThread sleepForTimeInterval:3];

NSLog(@"下载第二张图");

});

dispatch_group_async(group, queue, ^{

NSLog(@"3--%@",[NSThread currentThread]);

[NSThread sleepForTimeInterval:1];

NSLog(@"下载第三张图");

});

dispatch_group_async(group, queue, ^{

NSLog(@"4--%@",[NSThread currentThread]);

[NSThread sleepForTimeInterval:5];

NSLog(@"下载第四张图");

});

//notify通知，当所有异步请求完成时调用dispatch_group_notify

dispatch_group_notify(group, queue, ^{

NSLog(@"5--%@",[NSThread currentThread]);

NSLog(@"更新UI");

});

2

//创建调度组

dispatch_group_t group = dispatch_group_create();

//获取全局队列

dispatch_queue_t queue = dispatch_get_global_queue(0, 0);

//进入队列

dispatch_group_enter(group);

dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:2];

NSLog(@"下载第一张图");

//离开队列

dispatch_group_leave(group);

});

dispatch_group_enter(group);

dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:1];

NSLog(@"下载第er张图");

dispatch_group_leave(group);

});

dispatch_group_enter(group);

dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:3];

NSLog(@"下载第san张图");

dispatch_group_leave(group);

});

//等待调度队列wait相当于一个阻塞状态

dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

NSLog(@"更新UI");

四中断操作

//dispatch_barrier_async一定是自定义队列

//这里指定的并发队列应该是自己通过dispatch_queue_create函数创建的。如果你传的是一个串行队列或者全局并发队列，这个函数等同于dispatch_async函数。

dispatch_queue_t queue = dispatch_queue_create("com.bjsxt", DISPATCH_QUEUE_CONCURRENT); //dispatch_get_global_queue(0, 0);

dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:1];

NSLog(@"1");

}); dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:3];

NSLog(@"2");

});

dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:2];

NSLog(@"3");

});

//中断操作dispatch_barrier_async

dispatch_barrier_async(queue, ^{

NSLog(@"--------");

[NSThread sleepForTimeInterval:1];

});

dispatch_async(queue, ^{

[NSThread sleepForTimeInterval:1];

NSLog(@"4");

});

dispatch_async(queue, ^{

NSLog(@"5");

});

五 遍历操作

dispatch_queue_t queue = dispatch_get_global_queue(0, 0);

//iterations 遍历的次数

dispatch_apply(5, queue, ^(size_t i) {

NSLog(@"%@",@(i));

});