Requires: An elegant solution to race conditions

Question

I have the following code:

class TimeOutException
{};

template <typename T>
class MultiThreadedBuffer
{
public:
    MultiThreadedBuffer()
    {
        InitializeCriticalSection(&m_csBuffer);
        m_evtDataAvail = CreateEvent(NULL, TRUE, FALSE, NULL);
    }
    ~MultiThreadedBuffer()
    {
        CloseHandle(m_evtDataAvail);
        DeleteCriticalSection(&m_csBuffer);
    }
    void LockBuffer()
    {
        EnterCriticalSection(&m_csBuffer);
    }
    void UnlockBuffer()
    {
        LeaveCriticalSection(&m_csBuffer);
    }
    void Add(T val)
    {
        LockBuffer();
        m_buffer.push_back(val);
        SetEvent(m_evtDataAvail);
        UnlockBuffer();
    }
    T Get(DWORD timeout)
    {
        T val;
        if (WaitForSingleObject(m_evtDataAvail, timeout) == WAIT_OBJECT_0) {
            LockBuffer();

            if (!m_buffer.empty()) {
                val = m_buffer.front();
                m_buffer.pop_front();
            }

            if (m_buffer.empty()) {
                ResetEvent(m_evtDataAvail);
            }

            UnlockBuffer();
        } else {
            throw TimeOutException();
        }
        return val;
    }
    bool IsDataAvail()
    {
        return (WaitForSingleObject(m_evtDataAvail, 0) == WAIT_OBJECT_0);
    }
    std::list<T> m_buffer;
    CRITICAL_SECTION m_csBuffer;
    HANDLE m_evtDataAvail;
};

Unit testing shows that this code works fine when used on a single thread, if the default T constructor and copy / assign statements are not thrown. Since I am writing T, this is acceptable.

My problem is the Get method. If there is no data (i.e. M_evtDataAvail is not set), then several threads may block the WaitForSingleObject call. When new data becomes available, it all gets to the Lock () call. Only one will pass and can receive data and move on. After unlocking (), another thread may move and detect that there is no data. Currently, it will return the default object.

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Answer 1

auto- reset reset. , , , . . auto- reset, FALSE CreateEvent API. , , .. , - , . RAII, , .

Answer 2

Semaphore Event. 0 1 ReleaseSemaphore , Add. , WaitForSingleObject Get , .

Answer 3

, , , auto- reset. , WaitForsingleevent , LockBuffer, . WaitForSingleEvent . - , ...

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