GCD同步若干个异步调用

来源：互联网发布：地暖品牌知乎编辑：程序博客网时间：2024/05/17 05:06

应用场景
根据若干个url异步加载多张图片，然后在都下载完成后合成一张整图

原理

使用Dispatch Group追加block到Global Group Queue,这些block如果全部执行完毕，就会执行Main ，Dispatch Queue中的结束处理的block

实现

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);dispatch_group_t group = dispatch_group_create();dispatch_group_async(group, queue, ^{ /*加载图片1 */ });dispatch_group_async(group, queue, ^{ /*加载图片2 */ });dispatch_group_async(group, queue, ^{ /*加载图片3 */ });dispatch_group_notify(group, dispatch_get_main_queue(), ^{    // 合并图片});

实例

// 用整除3，余数1，余数2，模拟图片加载，最终添加到总的数组模拟图片合成- (void)synchronizeGroupWithAsynchronousCall {    __block  NSMutableArray *mArray1, *mArray2, *mArray3, *array;    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    dispatch_group_t group = dispatch_group_create();    dispatch_group_async(group, queue, ^{ /*加载图片1 */        mArray1 = [NSMutableArray array];        for (int i = 0; i <= 30; i++) {            if (i % 3 == 0) {                printf("----%d\n", i);                [mArray1 addObject:@(i)];            }        }        NSLog(@"----thread%@", [NSThread currentThread]);    });    dispatch_group_async(group, queue, ^{ /*加载图片2 */        mArray2 = [NSMutableArray array];        for (int i = 0; i <= 30; i++) {            if (i % 3 == 1) {                printf("++++%d\n", i);                [mArray2 addObject:@(i)];            }        }        NSLog(@"++++thread%@", [NSThread currentThread]);    });    dispatch_group_async(group, queue, ^{ /*加载图片3 */        mArray3 = [NSMutableArray array];        for (int i = 0; i <= 30; i++) {            if (i % 3 == 2) {                printf("~~~~%d\n", i);                [mArray3 addObject:@(i)];            }        }        NSLog(@"~~~~thread%@", [NSThread currentThread]);    });    dispatch_group_notify(group, dispatch_get_main_queue(), ^{        // 合并图片        array = [NSMutableArray array];        [array addObjectsFromArray:mArray1];        [array addObjectsFromArray:mArray2];        [array addObjectsFromArray:mArray3];        for (NSNumber *num in array) {            NSLog(@"num = %@", num);        }        NSLog(@"thread%@", [NSThread currentThread]);    });//    dispatch_group_notify(group, queue, ^{//        // 如果这里还有基于上面两个任务的结果继续执行一些代码，建议还是放到子线程中，等代码执行完毕后在回到主线程//        //        // 回到主线程//        dispatch_async(dispatch_get_main_queue(), ^{//            // 执行相关代码...//        });//    });}

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