ios - 带有嵌套补全 block 的NSBlockOperation

Question

假设有一个带有完成块的方法可以执行:

[container insert:data
               completion:^(NSDictionary *result, NSError *error) {

               }];

我需要使用 NSOperation使其并发(比 GCD调度块更多，因为我需要对操作流程和取消进行更多控制)。

现在，假设执行正常的完成块，我可以使用 NSBlockOperation

- (NSOperation *)executeBlock:(void (^)(void))block
                    inQueue:(NSOperationQueue *)queue
                    completion:(void (^)(BOOL finished))completion
{
    NSOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:block];
    NSOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
        completion(blockOperation.isFinished);
    }];

    [completionOperation addDependency:blockOperation];

    [[NSOperationQueue currentQueue] addOperation:completionOperation];
    [queue addOperation:blockOperation];

    return blockOperation;
}

所以称它为

[self executeBlock:^{
        /// my sync code

    }   inQueue:operationQueue
        completion:^(BOOL finished) {

    }];

问题是那里有异步代码:

void (^completionBlock)() = ^void() {
        // this is the NSOperation completion block where sync code is executed
    };

和

    void (^insertCompletionBlock)(NSDictionary *, NSError *) = ^void(NSDictionary *result, NSError *error) {
      // this is the insert api completion block 
   };

所以有

[container insert:data completion:insertCompletionBlock];

如果我像这样打一个嵌套电话

[self executeBlock:^{
    [container insert:data
           completion:^(NSDictionary *result, NSError *error) {

           }];

}   inQueue:operationQueue
    completion:^(BOOL finished) {

}];

该 NSOperation将立即结束，因为 insert:completion:方法将在其调用完成后返回。

那么，如何序列化此执行以便在执行 NSBlockOperation的嵌套完成块之后调用 insert:completion:？

[更新]
使用@Mozilla的解决方案
我想出了一个自定义的 NSBlockOperation，用于在其上添加一些属性:

@interface MyCloudOperation: NSBlockOperation
@property(nonatomic,strong) id result;
@property(nonatomic,strong) NSError *error;
@end
@implementation MXMCloudOperation
@end

和这个

MyCloudOperation *blockOp=[[MyCloudOperation alloc] init];
    __weak MXMCloudOperation *weakBlockOp=blockOp;
    [blockOp setCompletionBlock:^{
        if(completion) completion(weakBlockOp.result,weakBlockOp.error);
    }];
    [blockOp addExecutionBlock:^{
        dispatch_semaphore_t mutex = dispatch_semaphore_create(0);
        void (^insertCompletionBlock)(NSDictionary *, NSError *) = ^void(NSDictionary *result, NSError *error) {
            if(error) {
                weakBlockOp.error=error;
                NSLog(@"Error saving to %@ data\n%@", containerName,
                      error.localizedDescription);
            } else {
                weakBlockOp.result=result;
                NSLog(@"Data %@ sent", result);
            }
            dispatch_semaphore_signal(mutex);
        };
        [container insert:data completion:insertCompletionBlock];
        dispatch_semaphore_wait(mutex, DISPATCH_TIME_FOREVER);
    }];
    [operationQueue addOperation:blockOp];

我在这里不喜欢引用我的 NSBlockOperation来传递完成处理程序的参数，但是我现在没有找到更好的解决方案。

Answer 1

我通过使用dispatch_semaphore_t解决了这个问题。

- (void)saveWebDataInternal:(ResponseModel *)data completion:(void(^)(NSArray *))completion
{
        NSBlockOperation *op = [[NSBlockOperation alloc] init];

        op.completionBlock = ^{
            dispatch_async(dispatch_get_main_queue(), ^{
                [self loadCachedDataInternal:completion];
            });
        };

        [op addExecutionBlock:^{
            dispatch_semaphore_t mutex = dispatch_semaphore_create(0);

            [self.cacheDAO asyncImport:data completion:^{
                dispatch_semaphore_signal(mutex);
            }];

            dispatch_semaphore_wait(mutex, DISPATCH_TIME_FOREVER);
        }];

        // start operation
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            [op start];
        });
}