GCD处理多线程同步操作 韩俊强的博客

原文地址: http://blog.csdn.net/qq_31810357/article/details/78906308 未经许可,严禁转载!

GCD使用 dispatch_group_notify、dispatch_group_enter、dispatch_group_leave处理多线程同步操作

一、简介

dispatch_group_enter：通知group，下面的任务马上要放到group中执行。

dispatch_group_leave：通知group，任务完成了，该任务要从group中移除。

通常两者穿插于任务中;

二、测试

- (void)syncActionTest
{
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_enter(group);

    //模拟多线程耗时操作
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        sleep(3);
        NSLog(@"%@----Block1结束",[NSThread currentThread]);
        dispatch_group_leave(group);
    });
    NSLog(@"%@----1结束",[NSThread currentThread]);

    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        sleep(3);
        NSLog(@"%@----Block2结束",[NSThread currentThread]);
        dispatch_group_leave(group);
    });
    NSLog(@"%@----2结束",[NSThread currentThread]);

    dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"%@---全部结束",[NSThread currentThread]);
        });
    });
}

三、应用

常见如 : 多图片上传, 在上传完所有图片后将imgUrl数组上传到服务器

dispatch_group_t group = dispatch_group_create();

    __weak DespritionViewController *weakSelf = self;

    for (UIImage *image in self.arrDataSources) {

        dispatch_group_enter(group);

        [ZDUserHttpRequest uploadImage:image andType:@"1" completion:^(NSString *picUrl) {

            dispatch_group_leave(group);

            if (picUrl) {
                [weakSelf.picUrlArr addObject:picUrl];
            } else {
                [SVProgressHUD showErrorWithStatus:@"上传失败,请重试"];
            }
        } failed:^(NSURLSessionDataTask *task, NSError *error) {
            dispatch_group_leave(group);
        }];
    }
    dispatch_group_notify(group, dispatch_get_global_queue(0, 0), ^{
        dispatch_async(dispatch_get_main_queue(), ^{

            do something...
        });
    });

结论:

在开启了多线程执行任务时，若使用了dispatch_group_notify、dispatch_group_enter、dispatch_group_leave，也能有效的保证了等所有的子线程任务处理完后，有一个处理最后结果的地方。