示例如下:
- (void)viewDidLoad {
NSLog(@"开始====%@",@"A");
[self loadListMenuWithFinishMark:@"A"];
NSLog(@"开始====%@",@"B");
[self loadListMenuWithFinishMark:@"B"];
NSLog(@"开始====%@",@"C");
[self loadListMenuWithFinishMark:@"C"];
}
- (void)loadListMenuWithFinishMark:(NSString *)mark{
// 创建信号量
dispatch_semaphore_t sema = dispatch_semaphore_create(0);
NSString *urlString = @"http://www.qubaobei.com/ios/cf/dish_list.php?stage_id=1&limit=20&page=1";
[[AFHTTPSessionManager manager] GET:urlString parameters:nil headers:nil progress:^(NSProgress * _Nonnull downloadProgress) {
} success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
// 发送信号 (+ 1)
dispatch_semaphore_signal(sema);
NSLog(@"结束======%@",mark);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(sema);
NSLog(@"结束======%@", mark);
}];
// 等待signal执行+1后(>0),才执行wait后的业务
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
}
打印结果:
2022-05-12 10:35:50.871154+0800 SemaphoreDemo[12896:3290528] 开始====A
原因是:
如果在主线程运行以上代码,会发现没有结果输出;这是因为AFNetworking
回调默认是主线程,这样dispatch_semaphore_wait
和dispatch_semaphore_signal
在同一个线程,这样就死锁了。
所以以上代码需要放在异步线程执行如下:
- (void)viewDidLoad {
dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@"开始====%@",@"A");
[self loadListMenuWithFinishMark:@"A"];
NSLog(@"开始====%@",@"B");
[self loadListMenuWithFinishMark:@"B"];
NSLog(@"开始====%@",@"C");
[self loadListMenuWithFinishMark:@"C"];
});
}
- (void)loadListMenuWithFinishMark:(NSString *)mark{
// 创建信号量
dispatch_semaphore_t sema = dispatch_semaphore_create(0);
NSString *urlString = @"http://www.qubaobei.com/ios/cf/dish_list.php?stage_id=1&limit=20&page=1";
[[AFHTTPSessionManager manager] GET:urlString parameters:nil headers:nil progress:^(NSProgress * _Nonnull downloadProgress) {
} success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
// 发送信号 (+ 1)
dispatch_semaphore_signal(sema);
NSLog(@"结束======%@",mark);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(sema);
NSLog(@"结束======%@", mark);
}];
// 等待signal执行+1后(>0),才执行wait后的业务
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
}
打印结果:
2022-05-12 10:29:55.555207+0800 SemaphoreDemo[12269:3284921] 开始====A
2022-05-12 10:29:55.706748+0800 SemaphoreDemo[12269:3284782] 结束======A
2022-05-12 10:29:55.706758+0800 SemaphoreDemo[12269:3284921] 开始====B
2022-05-12 10:29:55.712722+0800 SemaphoreDemo[12269:3284782] 结束======B
2022-05-12 10:29:55.712728+0800 SemaphoreDemo[12269:3284921] 开始====C
2022-05-12 10:29:55.715101+0800 SemaphoreDemo[12269:3284782] 结束======C
走过路过,点个👍🏻在走哈!!~~
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