同步Objective-C中的異步任務

Question

我試圖使用GCDAsyncSocket向我的iDevice客戶端發送一些圖像文件（幾乎100MB）。我想同步發送數據包到客戶端。我的意思是在發送100MB數據給第一個客戶端迭代到下一個客戶端之後。但是因爲異步性質GCDAsyncSocket我不知道如何序列化這些包發送。

我無法使用信號量，因爲在發送圖像之前，我會與每個客戶端協商以瞭解應發送的圖像，然後嘗試發送這些圖像。我找不到一個乾淨的方式來等待和發出信號。

- (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]; 
} 

這是AsyncSocket寫入數據是如何工作的：

- (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. 
} 

所以沒有任何人有任何想法我怎麼能同步這個任務？

UPDATE

的套接字連接我用GCDAsyncSocket一個大量使用代表團事件通知。（GCDAsyncSocket.h和GCDAsyncSocket.m）（與completionHandler沒有方法）。

我寫了一個名爲TCPClient的類，它處理套接字連接和數據包發送，並將其設置爲初始化套接字的委託。 寫入數據包後，代理方法- (void)socket:(GCDAsyncSocket *)sock didWriteDataWithTag:(long)tag被調用。它只會通知我一些數據已經寫入。在這裏我不能根據書面數據來決定撥打dispatch_group_leave。所以依靠委託方法是沒用的。

我已經修改[client.socket寫數據：緩衝withTimeout：-1.0標籤：0] GCDAsyncSocket.h和.m文件接受completionBlock：使用這種方法[client.socket writeData:buffer withTimeout:-1.0 tag:0 completionBlock:completionBlock] 幫助我解決同步異步任務。

// 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"); 
        } 

       }]; 

但問題是更新GCDAsyncsocket後，我的代碼可能會中斷。 這裏我正在尋找整潔的方式來添加完成處理程序到GCDAsyncsocket而不直接修改它。比如創建一個包裝器或使用Objective-C運行時的特性。 你有什麼想法嗎？

Answer 1

你可以用調度組完成。對於具有完成塊中的異步任務：

//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 
} 

可選地用於與代表一個任務：

@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); 
}