iOS多线程初级

dispatch_group_t group= dispatch_group_create(); 创建队列

以下两组要成对出现，

dispatch_group_enter(group); 将任务添加到group中

dispatch_group_leave(group);  代表该任务结束，从group中移除

上述队列中任务执行完之后再执行

dispatch_group_notify(group, dispatch_get_main_queue()）;

使用场景如下

dispatch_group_t group= dispatch_group_create();
            dispatch_group_enter(group);
            [dataSource refreshDataWithCompletion:^(BOOL success, NSError *error) {

                NSlog(@"Block1");

                dispatch_group_leave(group);
            }];
            dispatch_group_enter(group);
            [dataStore refreshRealTimePriceWithCompletionBlock:^(NPMQueryRealtimePriceResponse *response) {

                NSlog(@"Block2");

dispatch_group_leave(group); }]; dispatch_group_notify(group, dispatch_get_main_queue(), ^{

               NSlog(@"Block3“);

});

实验证明，Block1与Block2无执行先后顺序，Block3在Block1Block2都执行完之后打印。