GCD同步若干个异步调用

原理

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...
//        });
//    });

}