函數介紹
一。dispatch_semaphore_create(M)
創建一個值為M的信號量
dispatch_semaphore_wait(信號量，等待時間)
如果該信號量的值大於0，則使其信號量的值-1，否則，阻塞線程直到該信號量的值大於0或者達到等待時間。
dispatch_semaphore_signal(信號量)
釋放信號量，使得該信號量的值加1
dispatch_group_t group = dispatch_group_create();
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
dispatch_queue_t queue = dispatch_queue_create(NULL, DISPATCH_QUEUE_SERIAL);
for (int j = 0; j < 4; j ++) {
dispatch_group_async(group, queue, ^{
if (j == 0) {
[self loadOne:semaphore];
}else if (j == 1){
[self loadTwe:semaphore];
}else if (j == 2){
[self loadThree:semaphore];
}else{
[self loadFour:semaphore];
}
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
});
}
dispatch_group_notify(group, queue, ^{
//所有請求返回數據后執行
NSLog(@"完成");
});
- (void)loadOne:(dispatch_semaphore_t)group
{
//完成
dispatch_semaphore_signal(group);
}
二。使用GCD的dispatch_group_t
創建一個dispatch_group_t
每次網絡請求前先dispatch_group_enter,請求回調后再dispatch_group_leave，enter和leave必須配合使用，有幾次enter就要有幾次leave，否則group會一直存在。
當所有enter的block都leave后，會執行dispatch_group_notify的block。
dispatch_group_t downloadGroup = dispatch_group_create();
NSString *requestURL11 = [NSString stringWithFormat:@"%@api/index/index?",MYURL];
dispatch_group_enter(downloadGroup);
[[HttpRequest sharedInstance] postWithURLString:requestURL11 headStr:nil parameters:nil success:^(id responseObject) {
NSLog(@"success11");
dispatch_group_leave(downloadGroup);
} failure:^(id failure) {
NSLog(@"failure111");
}];
NSString *requestURL22 = [NSString stringWithFormat:@"%@api/recommend/index?",MYURL];
dispatch_group_enter(downloadGroup);
[[HttpRequest sharedInstance] postWithURLString:requestURL22 headStr:nil parameters:nil success:^(id responseObject) {
NSLog(@"success22");
dispatch_group_leave(downloadGroup);
} failure:^(id failure) {
NSLog(@"failure22");
}];
dispatch_group_notify(downloadGroup, dispatch_get_main_queue(), ^{
NSLog(@"end");
});
三。