directshow 中 x Objects left active 问题的解决(转载)

“x Objects left active“
这是很多人开发direct show时遇到的一个错误，我也被它困扰过很长一段时间，直到最近才找到解决的办法。
假设出错的代码是这样的：

 

#include "stdafx.h"

#include <dshow.h>
#include <stdio.h>
#include <qedit.h>
#include <streams.h>     // DirectShow (includes windows.h)

void runthread(void)
{
    IGraphBuilder *pGraph = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent   *pEvent = NULL;
    IBaseFilter *pSampleGrabber1 = NULL,*pSampleGrabber2 = NULL;

    // Initialize the COM library.
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr))
    {
        printf("ERROR - Could not initialize COM library");
        return;
    }

    // Create the filter graph manager and query for interfaces.
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IGraphBuilder, (void **)&pGraph);
    if (FAILED(hr))
    {
        printf("ERROR - Could not create the Filter Graph Manager.");
        return;
    }

    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);

    hr = pGraph->RenderFile(L"C:/DXSDK/Samples/Media/CLOCKTXT.avi",NULL);

    // Create Filters
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IBaseFilter, (void **)&pSampleGrabber1);
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, 
        IID_IBaseFilter, (void **)&pSampleGrabber2);


    // Add filters to Filter Graph
    hr = pGraph->AddFilter(pSampleGrabber1,L"filter3");
    hr = pGraph->AddFilter(pSampleGrabber2,L"filter4");

///////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////
{
    IEnumFilters *pEnumFilter = NULL;
    IBaseFilter *pFilter = NULL;
    IEnumPins *pEnumPin = NULL;
    IPin *pPin = NULL;
    FILTER_INFO FilterInfo;
    PIN_INFO PinInfo;

    pGraph->EnumFilters(&pEnumFilter);
    while (pEnumFilter->Next(1,&pFilter,NULL) == S_OK)
    {
        pFilter->QueryFilterInfo(&FilterInfo);
        printf("filter name : %10ws ",FilterInfo.achName);
        pFilter->EnumPins(&pEnumPin);
        int i=0,j=0;
        while (pEnumPin->Next(1,&pPin,NULL) == S_OK)
        {
            // Check pin info
            pPin->QueryPinInfo(&PinInfo);
            printf("..filter pin : %10ws ",PinInfo.achName);
            //printf("..filter pin : %10ws ",pPin->QueryId);
            if (PinInfo.dir == PINDIR_INPUT) printf("..Pin is Input ");
                else printf("..Pin is Output ");

            // Check Connect
            AM_MEDIA_TYPE pmt;
            ZeroMemory(&pmt,sizeof(AM_MEDIA_TYPE));
            if (pPin->ConnectionMediaType(&pmt) != S_OK)
                printf("..this pin is not connected. ");
                        
            // Check Render
            if (PinInfo.dir == PINDIR_INPUT 
                    && pmt.majortype == MEDIATYPE_Video)
                i = 1;
            if (PinInfo.dir == PINDIR_INPUT 
                    && pmt.majortype == MEDIATYPE_Audio)
                i = 2;
            j++;
        }
        if (j == 1 && i ==1) printf("..this is a video render. ");
        if (j == 1 && i ==2) printf("..this is a audio render. ");
        pEnumPin->Release();
    }
    pEnumFilter->Release();
}
//return;*/
///////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////
/*    if (SUCCEEDED(hr))
    {
        // Run the graph.
        hr = pControl->Run();
        if (SUCCEEDED(hr))
        {
            // Wait for completion.
            long evCode;
            pEvent->WaitForCompletion(INFINITE, &evCode);
        }
    }
*/
    pSampleGrabber1->Release();
    pSampleGrabber2->Release();

    pControl->Release();
    pEvent->Release();
    pGraph->Release();
    CoUninitialize();
}

void main()
{
    runthread();
}

这段程序先建立一个用来渲染文件的filtergraph,然后建立两个SampleGrabber Filter，并将其加入filtergraph。请注意，这两个filter只是加入了filtergraph，而没有于其中任何一个filter连接。
接下来，程序例遍整个filtergraph,显示filter的名字、pin的名字、pin的连接情况，并根据filter拥有的已连接的input pin数目和pin的媒体类型来判断该filter是否是一个renderer（尽管这并非十分科学）。

看起来程序并没有错，可我们在调试时却得到了这样的结果：
Executable:***.exe Pid *** Tid ***.Module qedit.dll, 6 objects left active!
这就是说，我们还有未释放的资源。
当然，你可以将这条消息屏蔽掉，而且你的程序也不会出现太大的问题，至少眼前来说是如此。

其实问题个根源在这里：

pGraph->EnumFilters(&pEnumFilter);
while (pEnumFilter->Next(1,&pFilter,NULL) == S_OK)
{....}
pEnumFilter->Release();

看看DirectShow关于Enumerating Filters的说明，你会找到这样一句：
“Note the places where the function calls Release on an interface to decrement the reference count.“
也就是说，pEnumFilter->Next返回的pFilter指向的接口是一个新申请的接口，而系统并不自己释放它，只就需要我们来做了：

pGraph->EnumFilters(&pEnumFilter);
while (pEnumFilter->Next(1,&pFilter,NULL) == S_OK)
{
....
    pFilter->Release();
}
pEnumFilter->Release();

类似情况也出现在pFilter->QueryFilterInfo和pEnumPin->Next(1,&pPin,NULL)中。所以我们必须手动释放其中接口指针指向的接口。
修改之后的代码：

 

#include "stdafx.h"

#include <dshow.h>
#include <stdio.h>
#include <qedit.h>
#include <streams.h>     // DirectShow (includes windows.h)

void runthread(void)
{
    IGraphBuilder *pGraph = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent   *pEvent = NULL;
    IBaseFilter *pSampleGrabber1 = NULL,*pSampleGrabber2 = NULL;

    // Initialize the COM library.
    HRESULT hr = CoInitialize(NULL);
    if (FAILED(hr))
    {
        printf("ERROR - Could not initialize COM library");
        return;
    }

    // Create the filter graph manager and query for interfaces.
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IGraphBuilder, (void **)&pGraph);
    if (FAILED(hr))
    {
        printf("ERROR - Could not create the Filter Graph Manager.");
        return;
    }

    hr = pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);

    hr = pGraph->RenderFile(L"C:/DXSDK/Samples/Media/CLOCKTXT.avi",NULL);

    // Create Filters
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, 
                        IID_IBaseFilter, (void **)&pSampleGrabber1);
    hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, 
        IID_IBaseFilter, (void **)&pSampleGrabber2);


    // Add filters to Filter Graph
    hr = pGraph->AddFilter(pSampleGrabber1,L"filter3");
    hr = pGraph->AddFilter(pSampleGrabber2,L"filter4");

///////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////
{
    IEnumFilters *pEnumFilter = NULL;
    IBaseFilter *pFilter = NULL;
    IEnumPins *pEnumPin = NULL;
    IPin *pPin = NULL;
    FILTER_INFO FilterInfo;
    PIN_INFO PinInfo;

    pGraph->EnumFilters(&pEnumFilter);
    while (pEnumFilter->Next(1,&pFilter,NULL) == S_OK)
    {
        pFilter->QueryFilterInfo(&FilterInfo);
        printf("filter name : %10ws ",FilterInfo.achName);
        pFilter->EnumPins(&pEnumPin);
        int i=0,j=0;
        while (pEnumPin->Next(1,&pPin,NULL) == S_OK)
        {
            // Check pin info
            pPin->QueryPinInfo(&PinInfo);
            printf("..filter pin : %10ws ",PinInfo.achName);
            //printf("..filter pin : %10ws ",pPin->QueryId);
            if (PinInfo.dir == PINDIR_INPUT) printf("..Pin is Input ");
                else printf("..Pin is Output ");

            // Check Connect
            AM_MEDIA_TYPE pmt;
            ZeroMemory(&pmt,sizeof(AM_MEDIA_TYPE));
            if (pPin->ConnectionMediaType(&pmt) != S_OK)
                printf("..this pin is not connected. ");
                        
            // Check Render
            if (PinInfo.dir == PINDIR_INPUT 
                    && pmt.majortype == MEDIATYPE_Video)
                i = 1;
            if (PinInfo.dir == PINDIR_INPUT 
                    && pmt.majortype == MEDIATYPE_Audio)
                i = 2;
            j++;
            pPin->Release();
        }
        if (j == 1 && i ==1) printf("..this is a video render. ");
        if (j == 1 && i ==2) printf("..this is a audio render. ");

        pEnumPin->Release();
        if (FilterInfo.pGraph!=NULL) 
        {
            int k=FilterInfo.pGraph->Release();
            printf("%d ",k);
        }
        pFilter->Release();
    }
    pEnumFilter->Release();
}
//return;*/
///////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////
/*    if (SUCCEEDED(hr))
    {
        // Run the graph.
        hr = pControl->Run();
        if (SUCCEEDED(hr))
        {
            // Wait for completion.
            long evCode;
            pEvent->WaitForCompletion(INFINITE, &evCode);
        }
    }
*/
    pSampleGrabber1->Release();
    pSampleGrabber2->Release();

    pControl->Release();
    pEvent->Release();
    pGraph->Release();
    CoUninitialize();
}

void main()
{
    runthread();

}