一、信号量的介绍
https://www.jianshu.com/p/24ffa819379c
https://www.jianshu.com/p/56c4838aa3e0
二、信号量的使用
- 1、使用场景一：首先通过网络请求一获取用户useid，之后用userid为参数发起网络请求二。
#pragma mark - 网络请求一
- (void)getuserId:(dispatch_semaphore_t)semaphore{
AFHTTPSessionManager *sessionmanger=[[AFHTTPSessionManager alloc]init];
sessionmanger.responseSerializer=[AFHTTPResponseSerializer serializer];
[sessionmanger POST:@"https://www.baidu.com/" parameters:nil constructingBodyWithBlock:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"请求成功1%@", [NSThread currentThread]);
useid=@"1234";
dispatch_semaphore_signal(semaphore);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"%@",error);
dispatch_semaphore_signal(semaphore);
}];
}
#pragma mark - 网络请求二
- (void)requestwithuserid:(NSString *)userid{
NSDictionary *parms=[NSMutableDictionary dictionary];
[parms setValue:userid forKey:@"userid"];
AFHTTPSessionManager *sessionmanger=[[AFHTTPSessionManager alloc]init];
sessionmanger.responseSerializer=[AFHTTPResponseSerializer serializer];
[sessionmanger POST:@"https://www.baidu.com/" parameters:userid constructingBodyWithBlock:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"请求成功2");
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"%@",error);
}];
}
#pragma mark - 使用信号量实现
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_semaphore_t semaphore= dispatch_semaphore_create(0); // 创建信号量
[self getuserId:semaphore];//获取用户useid
dispatch_semaphore_wait(semaphore,DISPATCH_TIME_FOREVER);//当前信号量为0，一直等待阻塞线程
[self requestwithuserid:useid];
}
command+R运行一下，没有任何反应。
原因分析：线程卡住了。代码执行到dispatch_semaphore_wait(semaphore,DISPATCH_TIME_FOREVER)因为信号量为0，当前线程会被阻塞。而当前线程是主线程，网络请求一成功后回调到主线程，因为主线程被阻塞 造成信号量无法释放，一直卡住。
解决方案就是开启一个异步的线程
- (void)viewDidLoad {
[super viewDidLoad];
//创建一个并行队列
dispatch_queue_t queque = dispatch_queue_create("GoyakodCreated", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queque, ^{
dispatch_semaphore_t semaphore= dispatch_semaphore_create(0); // 创建信号量
[self getuserId:semaphore];
dispatch_semaphore_wait(semaphore,DISPATCH_TIME_FOREVER);
[self requestwithuserid:useid];
});
}
- 2、使用场景二：从客户端有顺序的一张张上传图片
dispatch_queue_t queque = dispatch_queue_create("GoyakodCreated", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queque, ^{
for (NSInteger i=0;i<imageArray.count;i++) {
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
[[AFHttpRequest shareRequest] unifiedPicConversionWithchannelNo:@"" businessNum:@"" serialNum:serialNum sendType:@"" picName:picName picDirection:@"" picIoStr:picBase64Str serverSuccessFn:^(id dict) {
dispatch_semaphore_signal(semaphore);
} serverFailureFn:^(NSError *error) {
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
}
});
- 3、使用场景三：控制线程并发数
//定义一个信号量，初始化为10
dispatch_semaphore_t semaphore = dispatch_semaphore_create(10);
//同时执行100个任务
for (int i = 0; i < 100; i++)
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//当前信号量-1
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
NSLog(@"任务%d执行",i+1);
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:kUrlString]];
dispatch_async(dispatch_get_main_queue(), ^{
//TODO:刷新界面
});
//当前信号量+1
dispatch_semaphore_signal(semaphore);
});
}
开始初始化一个信号量，默认为10，然后同时执行100个任务，所以每次最大并发是10。dispatch_semaphore_wait表示是当前的信号量减去1，因为已经启动一个任务，所以通过这个方法来修改信号量的值。同样，当当前任务执行完后，要释放信号量，使当前信号量加1，所以用dispatch_semaphore_signal方法
- 4、使用场景四：多个网络请求后刷新UI
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
dispatch_group_t group = dispatch_group_create();
// 创建信号量
semaphore = dispatch_semaphore_create(0);
// 创建全局并行
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_async(group, queue, ^{
[self request1];
});
dispatch_group_async(group, queue, ^{
[self request2];
});
dispatch_group_notify(group, queue, ^{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
//在这里 进行请求后的方法，回到主线程
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"更新UI");
});
});
NSLog(@"12344");
}
- (void)request1{
AFHTTPSessionManager *manger=[[AFHTTPSessionManager alloc]init];
manger.responseSerializer=[AFHTTPResponseSerializer serializer];
[manger POST:@"https://www.baidu.com" parameters:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"请求成功1");
dispatch_semaphore_signal(semaphore);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(semaphore);
}];
}
- (void)request2{
AFHTTPSessionManager *manger=[[AFHTTPSessionManager alloc]init];
manger.responseSerializer=[AFHTTPResponseSerializer serializer];
[manger POST:@"https://www.baidu.com" parameters:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"请求成功2");
dispatch_semaphore_signal(semaphore);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(semaphore);
}];
}
或者这样
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
dispatch_group_t group = dispatch_group_create();
// 创建全局并行
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_async(group, queue, ^{
[self request1];
});
dispatch_group_async(group, queue, ^{
[self request2];
});
dispatch_group_notify(group, queue, ^{
//在这里 进行请求后的方法，回到主线程
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"更新UI");
});
});
NSLog(@"12344");
}
- (void)request1{
// 创建信号量
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
AFHTTPSessionManager *manger=[[AFHTTPSessionManager alloc]init];
manger.responseSerializer=[AFHTTPResponseSerializer serializer];
[manger POST:@"https://www.baidu.com" parameters:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"请求成功1");
NSLog(@"%ld", dispatch_semaphore_signal(semaphore));
;
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(semaphore);
NSLog(@"%@",semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
}
- (void)request2{
// 创建信号量
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
AFHTTPSessionManager *manger=[[AFHTTPSessionManager alloc]init];
manger.responseSerializer=[AFHTTPResponseSerializer serializer];
[manger POST:@"https://www.baidu.com" parameters:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"请求成功2");
dispatch_semaphore_signal(semaphore);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
}
@end
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