asyncio.cpp

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        // Also WaitForNext will refuse to block if this is set
        // unless m_bWaiting is also set which it will be when we release
        // the critsec if there are any outstanding).
        m_bFlushing = TRUE;

        CAsyncRequest * preq;
        while((preq = GetWorkItem()) != 0)
        {
            preq->Cancel();
            PutDoneItem(preq);
        }

        // now wait for any outstanding requests to complete
        if(m_cItemsOut > 0)
        {
            // can be only one person waiting
            ASSERT(!m_bWaiting);

            // this tells the completion routine that we need to be
            // signalled via m_evAllDone when all outstanding items are
            // done. It also tells WaitForNext to continue blocking.
            m_bWaiting = TRUE;
        }
        else
        {
            // all done

            // force m_evDone set so that even if list is empty,
            // WaitForNext will not block
            // don't do this until we are sure that all
            // requests are on the done list.
            m_evDone.Set();
            return S_OK;
        }
    }

    ASSERT(m_bWaiting);

    // wait without holding critsec
    for(;;)
    {
        m_evAllDone.Wait();
        {
            // hold critsec to check
            CAutoLock lock(&m_csLists);

            if(m_cItemsOut == 0)
            {
                // now we are sure that all outstanding requests are on
                // the done list and no more will be accepted
                m_bWaiting = FALSE;

                // force m_evDone set so that even if list is empty,
                // WaitForNext will not block
                // don't do this until we are sure that all
                // requests are on the done list.
                m_evDone.Set();

                return S_OK;
            }
        }
    }
}


// end a flushing state
HRESULT
CAsyncIo::EndFlush()
{
    CAutoLock lock(&m_csLists);

    m_bFlushing = FALSE;

    ASSERT(!m_bWaiting);

    // m_evDone might have been set by BeginFlush - ensure it is
    // set IFF m_listDone is non-empty
    if(m_listDone.GetCount() > 0)
    {
        m_evDone.Set();
    }
    else
    {
        m_evDone.Reset();
    }

    return S_OK;
}


// start the thread
HRESULT
CAsyncIo::StartThread(void)
{
    if(m_hThread)
    {
        return S_OK;
    }

    // clear the stop event before starting
    m_evStop.Reset();

    DWORD dwThreadID;
    m_hThread = CreateThread(NULL,
                            0,
                            InitialThreadProc,
                            this,
                            0,
                            &dwThreadID);
    if(!m_hThread)
    {
        DWORD dwErr = GetLastError();
        return HRESULT_FROM_WIN32(dwErr);
    }

    return S_OK;
}


// stop the thread and close the handle
HRESULT
CAsyncIo::CloseThread(void)
{
    // signal the thread-exit object
    m_evStop.Set();

    if(m_hThread)
    {
        WaitForSingleObject(m_hThread, INFINITE);
        CloseHandle(m_hThread);
        m_hThread = NULL;
    }

    return S_OK;
}


// manage the list of requests. hold m_csLists and ensure
// that the (manual reset) event hevList is set when things on
// the list but reset when the list is empty.
// returns null if list empty
CAsyncRequest*
CAsyncIo::GetWorkItem()
{
    CAutoLock lck(&m_csLists);
    CAsyncRequest * preq  = m_listWork.RemoveHead();

    // force event set correctly
    if(m_listWork.GetCount() == 0)
    {
        m_evWork.Reset();
    }

    return preq;
}


// get an item from the done list
CAsyncRequest*
CAsyncIo::GetDoneItem()
{
    CAutoLock lock(&m_csLists);
    CAsyncRequest * preq  = m_listDone.RemoveHead();

    // force event set correctly if list now empty
    // or we're in the final stages of flushing
    // Note that during flushing the way it's supposed to work is that
    // everything is shoved on the Done list then the application is
    // supposed to pull until it gets nothing more
    //
    // Thus we should not set m_evDone unconditionally until everything
    // has moved to the done list which means we must wait until
    // cItemsOut is 0 (which is guaranteed by m_bWaiting being TRUE).

    if(m_listDone.GetCount() == 0 &&
        (!m_bFlushing || m_bWaiting))
    {
        m_evDone.Reset();
    }

    return preq;
}


// put an item on the work list - fail if bFlushing
HRESULT
CAsyncIo::PutWorkItem(CAsyncRequest* pRequest)
{
    CAutoLock lock(&m_csLists);
    HRESULT hr;

    if(m_bFlushing)
    {
        hr = VFW_E_WRONG_STATE;
    }
    else if(m_listWork.AddTail(pRequest))
    {
        // event should now be in a set state - force this
        m_evWork.Set();

        // start the thread now if not already started
        hr = StartThread();

    }
    else
    {
        hr = E_OUTOFMEMORY;
    }

    return(hr);
}


// put an item on the done list - ok to do this when
// flushing
HRESULT
CAsyncIo::PutDoneItem(CAsyncRequest* pRequest)
{
    ASSERT(CritCheckIn(&m_csLists));

    if(m_listDone.AddTail(pRequest))
    {
        // event should now be in a set state - force this
        m_evDone.Set();
        return S_OK;
    }
    else
    {
        return E_OUTOFMEMORY;
    }
}


// called on thread to process any active requests
void
CAsyncIo::ProcessRequests(void)
{
    // lock to get the item and increment the outstanding count
    CAsyncRequest * preq = NULL;

    for(;;)
    {
        {
            CAutoLock lock(&m_csLists);

            preq = GetWorkItem();
            if(preq == NULL)
            {
                // done
                return;
            }

            // one more item not on the done or work list
            m_cItemsOut++;

            // release critsec
        }

        preq->Complete();

        // regain critsec to replace on done list
        {
            CAutoLock l(&m_csLists);

            PutDoneItem(preq);

            if(--m_cItemsOut == 0)
            {
                if(m_bWaiting)
                    m_evAllDone.Set();
            }
        }
    }
}


// the thread proc - assumes that DWORD thread param is the
// this pointer
DWORD
CAsyncIo::ThreadProc(void)
{
    HANDLE ahev[] = {m_evStop, m_evWork};

    for(;;)
    {
        DWORD dw = WaitForMultipleObjects(2,
                                          ahev,
                                          FALSE,
                                          INFINITE);
        if(dw == WAIT_OBJECT_0+1)
        {
            // requests need processing
            ProcessRequests();
        }
        else
        {
            // any error or stop event - we should exit
            return 0;
        }
    }
}


// perform a synchronous read request on this thread.
// may not be aligned - so we will have to buffer.
HRESULT
CAsyncIo::SyncRead(
                LONGLONG llPos,
                LONG lLength,
                BYTE * pBuffer)
{
    if(IsAligned(llPos) &&
        IsAligned(lLength) &&
        IsAligned((LONG) pBuffer))
    {
        LONG cbUnused;
        return SyncReadAligned(llPos, lLength, pBuffer, &cbUnused, NULL);
    }

    // not aligned with requirements - use buffered file handle.
    //!!! might want to fix this to buffer the data ourselves?

    CAsyncRequest request;

    HRESULT hr = request.Request(this,
                                m_pStream,
                                llPos,
                                lLength,
                                FALSE,
                                pBuffer,
                                NULL,
                                0);

    if(FAILED(hr))
    {
        return hr;
    }

    return request.Complete();
}


//  Return the alignment
HRESULT
CAsyncIo::Alignment(LONG *pAlignment)
{
    CheckPointer(pAlignment,E_POINTER);

    *pAlignment = Alignment();
    return S_OK;
}