嵌套完井块的NSBlockOperation

Question

应该有一个具有完成块的方法来执行：

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

               }];

我需要使用NSOperation (而不是GCD调度块，因为我需要更多地控制操作流和取消)来实现这个并发。

现在，假设要执行一个正常的完成块，我可以使用NSBlockOperation如下

- (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;
}

所以把它叫做

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

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

    }];

相反，存在异步代码的问题是：

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];

如果我执行嵌套调用，如

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

           }];

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

}];

此NSOperation将立即结束，因为insert:completion:方法将在具有完成块的调用之后返回。

那么，如何序列化此执行，以便在执行嵌套的insert:completion:完成块之后调用insert:completion:？

使用@Mozilla的解决方案更新了，我推出了一个自定义NSBlockOperation，用于在上面添加一些属性：

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

还有这个

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];

这里我不喜欢的是引用我的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];
        });
}