同步Objective-C中的异步任务

Question

我试图使用GCDAsyncSocket向我的iDevice客户端发送一些图像文件（几乎100MB）。我想同步发送数据包到客户端。我的意思是在发送100MB数据给第一个客户端迭代到下一个客户端之后。但是因为异步性质GCDAsyncSocket我不知道如何序列化这些包发送。

我无法使用信号量，因为在发送图像之前，我会与每个客户端协商以了解应发送的图像，然后尝试发送这些图像。我找不到一个干净的方式来等待和发出信号。

- (void)sendImagesToTheClients:clients 
{ 
    ... 
    //negotiating with client to know which images should sent 
    ... 

    for(Client* client in clients) 
    { 
     packet = [packet addImages: images]; 
     [self sendPacket:packet toClient:client]; 
    } 
} 

- (void)sendPacket:packet toClient:client 
{ 
// Initialize Buffer 
    NSMutableData *buffer = [[NSMutableData alloc] init]; 
    NSData *bufferData = [NSKeyedArchiver archivedDataWithRootObject:packet]; 

    uint64_t headerLength = [bufferData length]; 
    [buffer appendBytes:&headerLength length:sizeof(uint64_t)]; 
    [buffer appendBytes:[bufferData bytes] length:[bufferData length]]; 

    // Write Buffer 
    [client.socket writeData:buffer withTimeout:-1.0 tag:0]; 
} 

这是AsyncSocket写入数据是如何工作的：

- (void)writeData:(NSData *)data withTimeout:(NSTimeInterval)timeout tag:(long)tag 
{ 
    if ([data length] == 0) return; 

    GCDAsyncWritePacket *packet = [[GCDAsyncWritePacket alloc] initWithData:data timeout:timeout tag:tag]; 

    dispatch_async(socketQueue, ^{ @autoreleasepool { 

     LogTrace(); 

     if ((flags & kSocketStarted) && !(flags & kForbidReadsWrites)) 
     { 
      [writeQueue addObject:packet]; 
      [self maybeDequeueWrite]; 
     } 
    }}); 

    // Do not rely on the block being run in order to release the packet, 
    // as the queue might get released without the block completing. 
} 

所以没有任何人有任何想法我怎么能同步这个任务？

UPDATE

的套接字连接我用GCDAsyncSocket一个大量使用代表团事件通知。（GCDAsyncSocket.h和GCDAsyncSocket.m）（与completionHandler没有方法）。

我写了一个名为TCPClient的类，它处理套接字连接和数据包发送，并将其设置为初始化套接字的委托。 写入数据包后，代理方法- (void)socket:(GCDAsyncSocket *)sock didWriteDataWithTag:(long)tag被调用。它只会通知我一些数据已经写入。在这里我不能根据书面数据来决定拨打dispatch_group_leave。所以依靠委托方法是没用的。

我已经修改[client.socket写数据：缓冲withTimeout：-1.0标签：0] GCDAsyncSocket.h和.m文件接受completionBlock：使用这种方法[client.socket writeData:buffer withTimeout:-1.0 tag:0 completionBlock:completionBlock] 帮助我解决同步异步任务。

// perform your async task 
      dispatch_async(self.socketQueue, ^{ 
       [self sendPacket:packet toClient:client withCompletion:^(BOOL finished, NSError *error) 
       { 
        if (finished) { 
         NSLog(@"images file sending finished"); 
         //leave the group when you're done 
         dispatch_group_leave(group); 
        } 
        else if (!finished && error) 
        { 
         NSLog(@"images file sending FAILED"); 
        } 

       }]; 

但问题是更新GCDAsyncsocket后，我的代码可能会中断。 这里我正在寻找整洁的方式来添加完成处理程序到GCDAsyncsocket而不直接修改它。比如创建一个包装器或使用Objective-C运行时的特性。 你有什么想法吗？

Answer 1

你可以用调度组完成。对于具有完成块中的异步任务：

//create & enter the group 
dispatch_group_t group = dispatch_group_create(); 
dispatch_group_enter(group); 

// perform your async task 
dispatch_async(socketQueue, ^{ 

    //leave the group when you're done 
    dispatch_group_leave(group); 
}); 

// wait for the group to complete 
// (you can use DISPATCH_TIME_FOREVER to wait forever) 
long status = dispatch_group_wait(group, 
        dispatch_time(DISPATCH_TIME_NOW,NSEC_PER_SEC * COMMAND_TIMEOUT)); 

// check to see if it timed out, or comepleted 
if (status != 0) { 
    // timed out 
} 

可选地用于与代表一个任务：

@property (nonatomic) dispatch_group_t group; 

-(BOOL)doWorkSynchronously { 

    self.group = dispatch_group_create(); 
    dispatch_group_enter(self.group); 

    [object doAsyncWorkWithDelegate:self]; 

    long status = dispatch_group_wait(self.group, 
         dispatch_time(DISPATCH_TIME_NOW,NSEC_PER_SEC * COMMAND_TIMEOUT)); 

    // A 
    if (status != 0) { 
     // timed out 
     return NO 
    } 

    return YES; 
} 

-(void)asyncWorkCompleted {} 

    // after this call, control should jump back to point A in the doWorkSynchronously method 
    dispatch_group_leave(self.group); 
}