Re: Thread deadlock misery

"PaulH" <>
13 Mar 2007 08:20:06 -0700
I used the critical section because I read in another post on this
group that it might be necessary despite the Interlocked() operation
being atomic. In this case it obviously doesn't help me any, so I'll
remove it. Thanks!

The Sleep() call in the transmit thread is to regulate the number of
transmissions per second. The Sleep() call in the StatCalc thread is
to regulate the number of statistical samples per second.

Below is some actual code from my transmit thread. After it sends
about 300 frames, this thread halts.

/// count of frames sent
volatile long m_nSentFrames;

// Method public static CMainFrame::TransmitThread
/// @brief Transmit unicast frames to a client at a specified rate.
/// @param TFP - [in] allocated pointer to the parameters
/// @return DWORD WINAPI - 0
/*static*/ DWORD WINAPI CMainFrame::TransmitThread( TTCB* TFP )
    std::auto_ptr< TTCB > pATFP( TFP );

    WSAData wsaData = { 0 };
    WSAStartup( MAKEWORD( 2, 2 ), &wsaData );

    // Get the address info for the DUT
    struct addrinfo *DUTAddr = NULL,
                    hints = { 0 };
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_protocol = IPPROTO_UDP;
    char cPort[ 10 ] = { 0 };
    _itoa_s( TFP->port, cPort, 9, 10 );
    if( getaddrinfo( pATFP->TFP.address, cPort, &hints, &DUTAddr ) !=
0 )
        // error handling

    // open a UDP, DGRAM socket for the connection
    if( DUTSocket < 0 )
        // error handling

    // create an empty buffer to pad the frames to the appropriate
    std::vector< char > buffer( pATFP->TFP.size );
    WSABUF wsaBuf = { pATFP->TFP.size, &buffer.front() };

    // Throw unicast frames at the given rate & size to the DUT
    CMainFrame* pParent = reinterpret_cast< CMainFrame* >( pATFP-

pParent );

    while( pATFP->pParent->m_bRunning )
        DWORD dwStartTime = GetTickCount();
        DWORD sent = 0;
        if( WSASendTo( DUTSocket,
                       sizeof( SOCKADDR ),
                       NULL ) < 0 )
            // error handling
        InterlockedIncrement( &pParent->m_nSentFrames );
        DWORD dwSleepTime = ( 1000 / pATFP->TFP.FPS ) -
( GetTickCount() - dwStartTime );
        if( dwSleepTime > 0 )
            Sleep( dwSleepTime );

    // Test finished successfully, cleanup
    closesocket( DUTSocket );
    freeaddrinfo( DUTAddr );
    return 0;

If you can tell where I'm going wrong here, please let me know.

On Mar 12, 5:29 pm, "Doug Harrison [MVP]" <> wrote:

On 12 Mar 2007 15:12:30 -0700, "PaulH" <> wrote:

I have an application with 4 threads GUI, Transmit, Receive, and
StatCalc. The transmit and receive threads both update a counter
variable, and the StatCalc thread periodically updates some statistics
based on those two counters. Unfortunately, the Transmit and StatCalc
threads deadlock and only the receive thread runs.

The GUI thread initiates the Transmit, Receive, and StatCalc threads
virtually simultaneously.

Below is some pseudo-code of what I'm doing

While(TRUE) {
send a frame;

receive some frames;
InterlockedExchangeAdd(&ReceiveCounter, framecount);
wait for next frame;

While(TRUE) {
//wait for the Transmit and Receive threads to generate data
calculate statistics;

//reset the counters
InterlockedExchange(&TransmitCounter, 0);
InterlockedExchange(&ReceiveCounter, 0);

If anybody see a way to prevent these threads from dead locking, let
me know.

In order for a deadlock to occur, there must be a circular wait. There is
none in what you've shown. In addition, you're guarding individual
InterlockedXXX function calls with a mutex, and this is unnecessary. The
whole point of the InterlockedXXX functions is to obviate mutexes under
these conditions. The problem is thus in code you haven't shown, perhaps in
the code that receives or transmits. Also, why are you calling Sleep?

Doug Harrison
Visual C++ MVP

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