GCD

最新推荐文章于 2025-08-26 18:27:24 发布

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本文详细介绍了Grand Central Dispatch (GCD) 在iOS开发中的使用方法，包括如何利用dispatch_once实现单例模式，使用dispatch_after进行延时执行，通过dispatch_apply执行循环任务，运用dispatch_group_async监听多个任务的完成状态，以及如何使用dispatch_barrier_async确保任务执行的顺序，并解释了dispatch_semaphore的工作原理。此外，还提供了一个使用GCD异步加载图片的具体实例。

看朋友的分享文档记录下。

GCD：Grand Central Dispatch

dispatch_once：执行一次，可用于单例。

+ (id)sharedInstance{

static SomeClass *sharedInstance = nil;

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

sharedInstance = [[self alloc] init];

});

return sharedInstance;

}

dispatch_after：延时执行，可用于。

dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, 3ull *

NSEC_PER_SEC);

dispatch_after(time, dispatch_get_main_queue(), ^{!

NSLog(@"waited at least three seconds.“);

});

dispatch_apply：执行多次。

dispatch_queue_t queue =

dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);!

dipatch_apply([array count], queue, ^(size_t index){!

NSLog(@“%zu”, [array objectAtIndex:index]);!

});!

NSLog(@“done”);

dispatch_group_async：监听多个任务是否完成，完成后可以得到通知执行其它操作。

dispatch_group_t group = dispatch_group_create();

dispatch_queue_t queue = dispatch_get_global_queue(0,0);

dispatch_group_async(group, queue, ^(){

//do something

dispatch_group_async(group, dispatch_get_main_queue(), ^(){

self.foo = 23;

});

dispatch_group_async(group, queue, ^(){

//do something

dispatch_group_async(group, dispatch_get_main_queue(), ^(){

self.bar = 11;

});

}); dispatch_group_notify(group, dispatch_get_main_queue(), ^(){

NSLog(@“foo is %d”, self.foo);

NSLog(@“bar is %d”, self.bar);

});

dispatch_barrier_async：是在前面的任务执行结束后它才执行，而且它后面的任务等它执行完成之后才会执行。

dispatch_queue_t queue = dispatch_queue_create(“com.example.gcd.barrier”,

DISPATCH_QUEUE_CONCURENT);

dispatch_async(queue, blk0_for_reading);

dispatch_async(queue, blk1_for_reading);

dispatch_async(queue, blk2_for_reading);

dispatch_async(queue, blk3_for_reading);

dispatch_barrier_async(queue, blk_for_writing);

dispatch_async(queue, blk4_for_reading);

dispatch_async(queue, blk5_for_reading);

dispatch_async(queue, blk6_for_reading);

dispatch_semaphore：信号量是一个整型值并且具有初始计数值，信号量通常支持两个操作：通知和等待。当信号被通知的时候计数值会增加，当信号量在线程上等待的时候，必要的情况下线程会被阻塞掉，直至信号被通知时计数值大于0，然后线程会减少这个计数继续工作。

dispatch_queue_t queue =

dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);

dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);

NSMutableArray *array = [[NSMutableArray alloc] init];

for (int i = 0; i < 100000; i++)

{

dispatch_async(queue, ^{!

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);!

[array addObject:[NSNumber numberWithInt:i]];!

dispatch_semaphore_signal(semaphore);!

});

}

dispatch_sync：

dispatch_queue_t queue = dispatch_get_main_queue();

dispatch_sync(queue, ^{NSLog(@“never run…”);});

dispatch_queue_t queue = dispatch_get_main_queue();

dispatch_sync(queue, ^{NSLog(@“never run…”);});

dispatch_async(queue, ^{

});

dispatch_sync(queue, ^{NSLog(@“never run…”);});

dispatch_async(queue, ^{

});

异步加载图片的示例：

for (int i = 0 ; i < 10; i++) {
dispatch_async(dispatch_get_global_queue(0, 0), ^{
// 处理耗时操作的代码块...
UIImage *img = [self getImgeWith:[urlArr objectForIndex:i]];
//通知主线程刷新
dispatch_async(dispatch_get_main_queue(), ^{
//回调或者说是通知主线程刷新，
[myImgV[i] setImage:img];
});
});

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 耗时的操作
dispatch_async(dispatch_get_main_queue(), ^{
// 更新界面
});
});

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL * url = [NSURL URLWithString:@"http://avatar.youkuaiyun.com/2/C/D/1_totogo2010.jpg"];
NSData * data = [[NSData alloc]initWithContentsOfURL:url];
UIImage *image = [[UIImage alloc]initWithData:data];
if (data != nil) {
dispatch_async(dispatch_get_main_queue(), ^{
self.imageView.image = image;
});
}
});