GCD
主要学习的知识点有：串行列队，并行列队，死锁，group，栅栏
·串行列队：A执行完，执行B，B执行完再执行C 排队执行 SERIAL
·并行列队：无序执行 CONCURRENT
·死锁没事少用同步方法，很容易造成主线程死锁
·栅栏：AB可以无序执行，CD也可以无序执行，但是我们要AB执行完再执行CD，这样我们就不好设置依赖关系了
·栅栏就可以挡在AB和CD的中间，等AB执行完了再执行CD
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
#if 0
// 主线程
dispatch_queue_t mainQueue = dispatch_get_main_queue();
// 子线程 异步执行
dispatch_queue_t subQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(subQueue, ^{
NSLog(@"task");
});
NSLog(@"hello");
#endif
#if 0
//异步执行
dispatch_queue_t globalQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
for (NSInteger i = 0; i<100; i++) {
dispatch_async(globalQueue, ^{
NSLog(@"i = %ld",i);
});
}
#endif
//自己创建一个新的线程
dispatch_queue_t customQueue = dispatch_queue_create("apple.queue",DISPATCH_QUEUE_CONCURRENT);
#if 0
dispatch_sync(customQueue, ^{
NSLog(@"task");
});
NSLog(@"hello");
#endif
#if 0
// 串联列队 有序执行打印 i = 0, i = 1, i = 2.... DISPATCH_QUEUE_SERIAL
customQueue = dispatch_queue_create("apple.queue2", DISPATCH_QUEUE_SERIAL);
customQueue = dispatch_get_main_queue();
for (NSInteger i = 0; i<100; i++) {
dispatch_async(customQueue, ^{
NSLog(@"i = %ld",i);
});
}
NSLog(@"hello world");
#endif
#if 0
NSLog(@"hello world");
//典型的死锁 dispatch等待main打印"welcome"，而打印这个方法是在主线程，造成死锁
//主线程执行dispatch，dispatch又要用到主线程，进入一个死循环中，死锁
dispatch_sync(dispatch_get_main_queue(), ^{
NSLog(@"welcome");
});
NSLog(@"======");
#endif
#if 0
//并联列队 无序执行，我们并不知道哪个先执行完 DISPATCH_QUEUE_CONCURRENT
dispatch_queue_t queue = dispatch_queue_create("apple.queu3", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
NSLog(@"1");
});
dispatch_async(queue, ^{
NSLog(@"2");
});
dispatch_async(queue, ^{
NSLog(@"3");
});
NSLog(@"done");
#endif
#if 0
dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_queue_create("apple.queu3", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_async(group, queue, ^{
NSLog(@"1");
});
//group_notify不能放在最上面，group里为空时就会执行，放在group最上面的话就为空，其他group_async方法还没有调用它就会先执行
//所有异步方法执行完后，打印"done"
dispatch_group_notify(group, queue, ^{
NSLog(@"done");
});
//异步方法中又有异步方法，比如网络请求，group有可能不知道什么时候才执行notify
dispatch_group_async(group, queue, ^{
//所以我们设置一个标记，在开始这个异步方法前enter
dispatch_group_enter(group);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSLog(@"2");
//执行完后leave
dispatch_group_leave(group);
});
});
dispatch_group_async(group, queue, ^{
NSLog(@"3");
});
dispatch_group_async(group, queue, ^{
NSLog(@"4");
});
dispatch_group_async(group, queue, ^{
NSLog(@"5");
});
#endif
dispatch_queue_t queue = dispatch_queue_create("apple.queu3",DISPATCH_QUEUE_CONCURRENT);
#if 0
//一个异步方法，比如说网络下载
dispatch_async(queue, ^{
//下载data...
NSData *data;//....
//当我们要显示时一定要在主线程里面执行
dispatch_async(dispatch_get_main_queue(), ^{
//主线程中显示图片
UIImage *image = [UIImage imageWithData:data];
});
});
#endif
#if 0
//1、2可以无序执行，3、4也可以无序执行，但是我们要1、2执行完再执行3、4. 这样我们就不好设置依赖关系了
dispatch_async(queue, ^{
NSLog(@"1");
});
dispatch_async(queue, ^{
NSLog(@"2");
});
//栅栏就可以挡在1、2和3、4的中间，等1、2执行完了再执行3、4
dispatch_barrier_async(queue, ^{
NSLog(@"barrier");
});
dispatch_async(queue, ^{
NSLog(@"3");
});
dispatch_async(queue, ^{
NSLog(@"4");
});
#endif
}
@end
