dispatch_group实践，AFN3.0多个网络请求
dispatch_group实践，AFN3.0多个网络请求
在实际开发过程中经常会有在一个页面有多个网络请求，页面UI需要在所有网络请求全部回来的情况下更新。先简单看一个具体的问题：
页面有三个网络请求a、b、c。三个网络请求都成功的情况下刷新UI，有一个失败就认为请求失败，不进行UI刷新。
目前想到的方法
- 添加
标识进行判断是否所有的网络请求都是成功的 - 通过
信号量判断 - 直接使用
dispatch_group（当然也可以结合信号量）
这里就简单使用dispatch_group来实践一下：
先简单了解一下必须的东西
常用方法
1、
dispatch_group_create创建一个调度任务组2、
dispatch_group_async把一个任务异步提交到任务组里3、
dispatch_group_enter/dispatch_group_leave这种方式用在不使用dispatch_group_async来提交任务，且必须配合使用4、
dispatch_group_notify用来监听任务组事件的执行完毕5、
dispatch_group_wait设置等待时间
实现一个dispatch_group_async 简单的例子
基本需求和文章前面的需求差不多，task 1、task 2、task 3、task 4四个任务，task 4要在task 1、task 2、task 3执行完成之后在执行。
先看一下代码：
- (void)testDisGroup {
dispatch_queue_t demoQuene = dispatch_queue_create("demoQuene", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
NSLog(@"\n\nmain thread %@\n\n",[NSThread currentThread]);
dispatch_group_async(group, demoQuene, ^{
sleep(arc4random_uniform(5));
NSLog(@"task 1 %@",[NSThread currentThread]);
});
dispatch_group_async(group, demoQuene, ^{
sleep(arc4random_uniform(5));
NSLog(@"task 2 %@",[NSThread currentThread]);
});
dispatch_group_async(group, demoQuene, ^{
sleep(arc4random_uniform(5));
NSLog(@"task 3 %@",[NSThread currentThread]);
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"task 4 %@",[NSThread currentThread]);
});
}看一下结果：
当然task 1、task 2、task 3完成的顺序不是固定，最后是task 4，需要看系统怎么分配资源。
升级一下dispatch_group_async 的例子
在上面任务的基础上添加一个需求，就是task 2、task 3要有一个顺序，比如task 2要在task 3执行完成之后才能执行。
看一下代码（当然实现的方案很多，这只是个例子）：
- (void)testDisGroup {
dispatch_queue_t demoQueneCONCURRENT = dispatch_queue_create("demoQuene", DISPATCH_QUEUE_CONCURRENT);
dispatch_queue_t demoQueneSERIAL = dispatch_queue_create("demoQuene", DISPATCH_QUEUE_SERIAL);
dispatch_group_t group = dispatch_group_create();
NSLog(@"\n\nmain thread %@\n\n",[NSThread currentThread]);
dispatch_group_async(group, demoQueneCONCURRENT, ^{
sleep(arc4random_uniform(5));
NSLog(@"task 1 %@",[NSThread currentThread]);
});
dispatch_group_async(group, demoQueneSERIAL, ^{
sleep(arc4random_uniform(5));
NSLog(@"task 3 %@",[NSThread currentThread]);
});
dispatch_group_async(group, demoQueneSERIAL, ^{
sleep(arc4random_uniform(5));
NSLog(@"task 2 %@",[NSThread currentThread]);
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"task 4 %@",[NSThread currentThread]);
});
}执行结果:
另一个结果：
当然这个结果也存在多种情况，不变的是task 4要在task 1、task 2、task 3执行完成之后在执行，task 2要在task 3执行完成之后才能执行。其他的顺序是不确定的。
使用dispatch_group_enter/dispatch_group_leave 复写一下第一个例子
-(void)testDisGroupEnterAndLeave {
dispatch_queue_t demoQueneCONCURRENT = dispatch_queue_create("demoQuene2", DISPATCH_QUEUE_CONCURRENT);
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_async(demoQueneCONCURRENT, ^{
NSLog(@"task 1 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_async(demoQueneCONCURRENT, ^{
NSLog(@"task 2 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_async(demoQueneCONCURRENT, ^{
NSLog(@"task 3 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
dispatch_group_leave(group);
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"task 4 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
});
}运行结果：
另一结果：
使用dispatch_group_enter/dispatch_group_leave 复写一下第二个例子
上代码：
-(void)testDisGroupEnterAndLeave {
dispatch_queue_t demoQueneCONCURRENT = dispatch_queue_create("demoQuene2", DISPATCH_QUEUE_CONCURRENT);
dispatch_queue_t demoQueneSERIAL = dispatch_queue_create("demoQuene3", DISPATCH_QUEUE_SERIAL);
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_async(demoQueneCONCURRENT, ^{
NSLog(@"task 1 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_async(demoQueneSERIAL, ^{
NSLog(@"task 3 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
dispatch_group_leave(group);
});
dispatch_group_enter(group);
dispatch_async(demoQueneSERIAL, ^{
NSLog(@"task 2 %@",[NSThread currentThread]);
sleep(arc4random_uniform(5));
dispatch_group_leave(group);
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"task 4 %@ \n\n\n.",[NSThread currentThread]);
sleep(arc4random_uniform(5));
});
}结果（两次结果写在一起了）：
开始实战
还是文章开始的那道题现在看一下
页面有三个网络请求a、b、c。三个网络请求都成功的情况下刷新UI，有一个失败就认为请求失败，不进行UI刷新。
@interface TestThread () {
dispatch_group_t _group;
}
@end
@implementation TestThread
- (void)p_loadBannerData {
dispatch_group_enter(_group);
AdvBannerApi *bannerApi = [[AdvBannerApi alloc] initWithAdvType:AdvTypeBanner];
[bannerApi startWithSuccessBlock:^(ApiResult * _Nullable result) {
NSLog(@"task 1 success");
dispatch_group_leave(_group);
} failureBlock:^(NSError * _Nullable error) {
NSLog(@"task 1 failure");
dispatch_group_leave(_group);
}];
}
- (void)p_loadCourseListData {
dispatch_group_enter(_group);
QualityCourseApi *courseApi = [[QualityCourseApi alloc] initWithStart:@"0"
count:@"20"];
[courseApi startWithSuccessBlock:^(ApiResult * _Nullable result) {
NSLog(@"task 2 success");
dispatch_group_leave(_group);
} failureBlock:^(NSError * _Nullable error) {
NSLog(@"task 2 failure");
dispatch_group_leave(_group);
}];
}
- (void)p_loadLivingLessonData {
dispatch_group_enter(_group);
LessonForecastApi *api = [[LessonForecastApi alloc] init];
[api startWithSuccessBlock:^(ApiResult * _Nullable result) {
NSLog(@"task 3 success");
dispatch_group_leave(_group);
} failureBlock:^(NSError * _Nullable error) {
NSLog(@"task 3 failure");
dispatch_group_leave(_group);
}];
}
- (void)reloadUI {
NSLog(@"task 4");
}
-(void)disGroupEnterAndLeave {
_group = dispatch_group_create();
[self p_loadBannerData];
[self p_loadCourseListData];
[self p_loadLivingLessonData];
dispatch_group_notify(_group, dispatch_get_main_queue(), ^{
NSLog(@"run task 4 %@",[NSThread currentThread]);
[self reloadUI];
});
}
@end看一下结果：
其他的写法就一一实现了。现在看一下错误的写法
@interface TestThread () {
dispatch_group_t _group;
}
@end
@implementation TestThread
- (void)p_loadBannerData {
AdvBannerApi *bannerApi = [[AdvBannerApi alloc] initWithAdvType:AdvTypeBanner];
[bannerApi startWithSuccessBlock:^(ApiResult * _Nullable result) {
NSLog(@"task 1 success");
} failureBlock:^(NSError * _Nullable error) {
NSLog(@"task 1 failure");
}];
}
- (void)p_loadCourseListData {
QualityCourseApi *courseApi = [[QualityCourseApi alloc] initWithStart:@"0"
count:@"20"];
[courseApi startWithSuccessBlock:^(ApiResult * _Nullable result) {
NSLog(@"task 2 success");
} failureBlock:^(NSError * _Nullable error) {
NSLog(@"task 2 failure");
}];
}
- (void)p_loadLivingLessonData {
LessonForecastApi *api = [[LessonForecastApi alloc] init];
[api startWithSuccessBlock:^(ApiResult * _Nullable result) {
NSLog(@"task 3 success");
} failureBlock:^(NSError * _Nullable error) {
NSLog(@"task 3 failure");
}];
}
- (void)reloadUI {
NSLog(@"task 4");
}
-(void)disGroup {
dispatch_queue_t demoQueneCONCURRENT = dispatch_queue_create("demoQuene", DISPATCH_QUEUE_CONCURRENT);
_group = dispatch_group_create();
dispatch_group_async(_group, demoQueneCONCURRENT, ^{
[self p_loadBannerData];
});
dispatch_group_async(_group, demoQueneCONCURRENT, ^{
[self p_loadCourseListData];
});
dispatch_group_async(_group, demoQueneCONCURRENT, ^{
[self p_loadLivingLessonData];
});
dispatch_group_notify(_group, dispatch_get_main_queue(), ^{
NSLog(@"run task 4 %@",[NSThread currentThread]);
[self reloadUI];
});
}
@end看一下结果：
很显然结果是错误的,
task 4最先得出了结果，主要因为
dispatch_group_async(_group, demoQueneCONCURRENT, ^{
});开启了一个新线程，然后
[self p_loadBannerData];网络请求又开启了一个线程。
dispatch_group_async(_group, demoQueneCONCURRENT, ^{
});开启的3个新线程执行完之后执行task 4。网络耗时的操作才执行。然后就………………错了。