Re: Multithread heap assertion failure

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Thu, 09 Aug 2007 10:07:20 -0400
Zhiguo wrote:

HI, all of you,

I have created a Win32 console project with MFC support(shared dll) to
test my multithread programming.
When run, a "Debug assertion failure" occures at the following

I cannot figure out why the exception occurs. Can you shed some light
on me?

Any help appreciated. Thansk in advance.


The only source file is as follows:

#include <afx.h>
#include <afxmt.h>
#include <afxwin.h>
#include <windows.h>

#include <iostream>
using namespace std;

class CTestThread: public CWinThread{
    virtual ~CTestThread(){}

    int Run(){
        cout << "run..." << endl;
        return 1;

    BOOL InitInstance(){
        cout << "init..." << endl;
        return TRUE;

    int ExitInstance(){
        cout << "exit inst..." << endl;
        return 0;

int main(){
    int nWorkerNum = 2;
    CTestThread * m_pThread = new CTestThread[nWorkerNum];
    HANDLE * m_pThreadHandle = new HANDLE[nWorkerNum];
    for(int i = 0; i < nWorkerNum; i ++){
        m_pThreadHandle[i] = m_pThread[i].m_hThread;
    WaitForMultipleObjects(nWorkerNum, m_pThreadHandle, TRUE, INFINITE);
    cout << "Press any key to conitnue..." << endl;
    char c; cin >> c;

When you exit from the thread CWinThread normally does

  delete this;

If the thread runs and exits very quickly this makes your
m_pThread[i].m_hThread use an invalid pointer.

You can avoid this problem like this:

m_pThread[i].m_bAutoDelete = FALSE;
m_pThreadHandle[i] = m_pThread[i].m_hThread;

With this change you also should delete m_pThread[i] after
WaitForMultipleObjects returns.

Scott McPhillips [MVP VC++]

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