iOS 网络请求顺序处理（信号量，group）
2022-05-12 本文已影响0人
心猿意码_
一、日常开发中，会经常遇到这样的需求：
- 网络请求A返回成功后，调用网络请求B，网络请求B结果返回成功后调用网络请求C（即：A—>B—>C）。
- 循环调用网络请求A，确保每次请求返回成功后继续调用网络请求A（即：A—>A—>A）。
- 网络请求A和B返回成功后，调用网路请求C（即：A&B—>C）。
二、以上三种需求，分别在此列举下示例：
- 在GCD中跟信号量有关的三个函数如下：：
//创建时，值为<0返回null；值为0时，当前线程无法直接执行wait，需等待signal信号+1后执行wait
dispatch_semaphore_t sema = dispatch_semaphore_create(0); semaphore
//发送一个信号 +1
dispatch_semaphore_signal(sema);
//等待信号（signal）>0执行
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
A—>B—>C：
信号量处理
- (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（异常）:
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
循环请求：
信号量处理
- (void)viewDidLoad {
[super viewDidLoad];
dispatch_async(dispatch_get_global_queue(0, 0), ^{
for (NSInteger i = 0; i < 3; i ++) {
NSLog(@"开始====%ld",i);
[self loadListMenuWithFinishIndex:i];
}
});
}
- (void)loadListMenuWithFinishIndex:(NSInteger)index{
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) {
dispatch_semaphore_signal(sema);
NSLog(@"结束======%ld",index);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
dispatch_semaphore_signal(sema);
NSLog(@"结束======%ld", index);
}];
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
}
打印结果:
2022-05-12 10:45:15.329772+0800 SemaphoreDemo[13910:3299813] 开始====0
2022-05-12 10:45:15.439159+0800 SemaphoreDemo[13910:3299720] 结束======0
2022-05-12 10:45:15.439178+0800 SemaphoreDemo[13910:3299813] 开始====1
2022-05-12 10:45:15.444384+0800 SemaphoreDemo[13910:3299720] 结束======1
2022-05-12 10:45:15.444405+0800 SemaphoreDemo[13910:3299813] 开始====2
2022-05-12 10:45:15.464591+0800 SemaphoreDemo[13910:3299720] 结束======2
多个网络请求都完成之后进行某操作（A&B—>C）:
Group处理
#import "AFNetworking.h"
@interface ViewController ()
@property (nonatomic,strong)dispatch_group_t group;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.group = dispatch_group_create();
NSLog(@"开始====%@",@"A");
[self loadListFinishMark:@"A"];
NSLog(@"开始====%@",@"B");
[self loadListFinishMark:@"B"];
// 完成A&B后执行C请求
dispatch_group_notify(self.group, dispatch_get_main_queue(), ^{
NSLog(@"开始====%@",@"C");
[self loadListFinishCMark];
});
}
#pragma mark - Group Request
- (void)loadListFinishMark:(NSString *)mark{
// enter 与 leave 一一对应
dispatch_group_enter(self.group);
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) {
NSLog(@"结束======%@",mark);
dispatch_group_leave(self.group);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"结束======%@", mark);
dispatch_group_leave(self.group);
}];
}
- (void)loadListFinishCMark{
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) {
NSLog(@"结束======C");
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"结束======C");
}];
}
打印结果：
2022-05-12 10:52:32.505854+0800 SemaphoreDemo[14680:3307180] 开始====A
2022-05-12 10:52:32.508026+0800 SemaphoreDemo[14680:3307180] 开始====B
2022-05-12 10:52:32.626408+0800 SemaphoreDemo[14680:3307180] 结束======B
2022-05-12 10:52:32.626604+0800 SemaphoreDemo[14680:3307180] 结束======A
2022-05-12 10:52:32.627107+0800 SemaphoreDemo[14680:3307180] 开始====C
2022-05-12 10:52:32.631006+0800 SemaphoreDemo[14680:3307180] 结束======C
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