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最近遇到一个☝️问题。一个页面有多个接口，需要请求完接口后，在把接口数据组装排序后再展示。于是我第一反应是使用GCD_group或者barrier.经过实践失败了。最后经过多方调研，使用dispatch_semaphore解决了这个问题，但是也有遇到坑。。。
首先贴出解决方案
#1
// /创建信号量为0
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/journalismApi" param:nil success:^(id data) {
// 信号量📶+1
dispatch_semaphore_signal(semaphore);
NSLog(@"1请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
// 信号量📶+1
dispatch_semaphore_signal(semaphore);
}];
});
dispatch_group_async(group, queue, ^{
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/satinApi?type=1&page=1" param:nil success:^(id data) {
// 信号量📶+1
dispatch_semaphore_signal(semaphore);
NSLog(@"2请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
// 信号量📶+1
dispatch_semaphore_signal(semaphore);
}];
});
dispatch_group_notify(group, queue, ^{
// 信号量 -1 为0时wait会阻塞线程
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"信号量为0");
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/satinCommentApi?id=27610708&page=1" param:nil success:^(id data) {
NSLog(@"3请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
}];
});
打印结果1或2请求结束后才会请求3
2018-09-03 21:49:47.309334+0800 信号量[20350:707280] 2请求成功
2018-09-03 21:49:48.299139+0800 信号量[20350:707280] 1请求成功
2018-09-03 21:49:48.299139+0800 信号量[20350:707371] 信号量为0
2018-09-03 21:49:48.640118+0800 信号量[20350:707280] 3请求成功
#2
dispatch_queue_t queue = dispatch_queue_create("ben", NULL);
dispatch_async(queue, ^{
NSLog(@"current1:%@",[NSThread currentThread]);
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/journalismApi" param:nil success:^(id data) {
dispatch_semaphore_signal(semaphore);
NSLog(@"1请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); //等待信号,当信号总量少于0 的时候就会一直等待 ,否则就可以正常的执行,并让信号总量-1
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/satinApi?type=1&page=1" param:nil success:^(id data) {
dispatch_semaphore_signal(semaphore);
NSLog(@"2请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); //等待信号,当信号总量少于0 的时候就会一直等待 ,否则就可以正常的执行,并让信号总量-1
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/satinCommentApi?id=27610708&page=1" param:nil success:^(id data) {
NSLog(@"3请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
}];
});
打印结果顺序执行1,2,3
2018-09-03 21:52:34.881525+0800 信号量[20448:711755] 1请求成功
2018-09-03 21:52:35.659227+0800 信号量[20448:711755] 2请求成功
2018-09-03 21:52:35.951249+0800 信号量[20448:711755] 3请求成功
遇到的坑
NSLog(@"current1:%@",[NSThread currentThread]);
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/satinApi?type=1&page=1" param:nil success:^(id data) {
dispatch_semaphore_signal(semaphore);
NSLog(@"2请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
dispatch_semaphore_signal(semaphore);
}];
NSLog(@"你会来这儿吗1");
NSLog(@"current1:%@",[NSThread currentThread]);
// #######阻塞了主线程
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); //等待信号,当信号总量少于0 的时候就会一直等待 ,否则就可以正常的执行,并让信号总量-1
NSLog(@"你会来这儿吗2");
[ATBaseRequest getRequestWithMethod:@"https://www.apiopen.top/satinCommentApi?id=27610708&page=1" param:nil success:^(id data) {
NSLog(@"3请求成功");
} failure:^(NSInteger resultId, NSString *errorMsg) {
}];
打印你会发现卡在了NSLog(@"你会来这儿吗1"); 这里
原因:阻塞了主线程。
2018-09-03 21:56:36.863662+0800 信号量[20583:717991] current1:<NSThread: 0x604000076680>{number = 1, name = main}
2018-09-03 21:56:36.961266+0800 信号量[20583:717991] 你会来这儿吗1
2018-09-03 21:56:36.961413+0800 信号量[20583:717991] current1:<NSThread: 0x604000076680>{number = 1, name = main}
demo传送门:GitHub
作者：本本的开心牧场
链接：https://www.jianshu.com/p/72843289ad5d
來源：简书
简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。
