iOS GCD学习笔记

//  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 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){
    // code to be executed on the main queue after delay
});

//自定义queue
dispatch_queue_t urls_queue = dispatch_queue_create("myQueue", NULL);
dispatch_async(urls_queue, ^{
     // your code
});
dispatch_release(urls_queue);

//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
});

//让 app 最多有 10 分钟的时间在后台长久运行
// AppDelegate.h 文件
@property (assign, nonatomic) UIBackgroundTaskIdentifier backgroundUpdateTask;

// AppDelegate.m 文件
- (void)applicationDidEnterBackground:(UIApplication *)application
{
    [self beingBackgroundUpdateTask];
    // 在这里加上你需要长久运行的代码
    [self endBackgroundUpdateTask];
}

- (void)beingBackgroundUpdateTask
{
    self.backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
        [self endBackgroundUpdateTask];
    }];
}

- (void)endBackgroundUpdateTask
{
    [[UIApplication sharedApplication] endBackgroundTask: self.backgroundUpdateTask];
    self.backgroundUpdateTask = UIBackgroundTaskInvalid;
}