在线程内将项目添加到 NSMutableArray

Question

我想用线程扫描照片库，当我的应用程序逻辑正常时，我想将PHAsset 添加到finalarray：

NSMutableArray <PHAsset *> *finalarray = [[NSMutableArray alloc] init];

for (NSMutableArray *photoArray in arrayOfArrays) {
    dispatch_group_enter(aGroup);
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
        for (PHAsset *asset in photoArray) {
            [[PHImageManager defaultManager] requestImageDataForAsset:asset
                                                              options:options
                                                        resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {

                //Make some logic

                if (logic) {
                    [finalarray addObject:asset];
                }
            }];
        }
        dispatch_group_leave(aGroup);
    });
}

arrayOfArrays 是PHAsset 的数组。

我的代码运行良好，但有时我会遇到SIGABRT 崩溃，并且我会在代码控制台中看到此日志：

malloc: Incorrect checksum for freed object 0x1206d5968: probably modified after being freed.
Corrupt value: 0x100017580
malloc: *** set a breakpoint in malloc_error_break to debug
malloc: Incorrect checksum for freed object 0x1206d5968: probably modified after being freed.
Corrupt value: 0x100017580

Answer 1

如果您有多个线程更新一个属性，您必须同步它们的访问。你可以使用NSLock:

NSMutableArray <PHAsset *> *finalarray = [[NSMutableArray alloc] init];
NSLock *lock = [[NSLock alloc] init];

for (NSMutableArray *photoArray in arrayOfArrays) {
    dispatch_group_enter(aGroup);
    for (PHAsset *asset in photoArray) {
        [[PHImageManager defaultManager] requestImageDataForAsset:asset
                                                          options:options
                                                    resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {

            //Make some logic

            if (logic) {
                [lock lock];
                [finalarray addObject:asset];
                [lock unlock];
                dispatch_group_leave(aGroup);
            }
        }];
    }
}

或者您可以使用 GCD 队列：

NSMutableArray <PHAsset *> *finalarray = [[NSMutableArray alloc] init];
dispatch_queue_t queue = dispatch_queue_create("...", NULL);

for (NSMutableArray *photoArray in arrayOfArrays) {
    dispatch_group_enter(aGroup);
    for (PHAsset *asset in photoArray) {
        [[PHImageManager defaultManager] requestImageDataForAsset:asset
                                                          options:options
                                                    resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {

            //Make some logic

            if (logic) {
                dispatch_async(queue, ^{
                    [finalarray addObject:asset];
                    dispatch_group_leave(aGroup);
                });
            }
        }];
    }
}

注意，上面我假设您正在异步获取图像，在这种情况下您不需要使用全局队列，但您需要确保调用 dispatch_group_leave inside requestImageDataForAsset .

但是，无论如何，请确保在从多个线程访问属性时同步访问（使用 GCD 队列或某些锁）。