How to Use _beginthreadex() and _endthreadex()

• The C Run-Time (CRT), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 5.0, 6.0

SUMMARY

This article shows by example how to use the thread handle returned by _beginthreadex() with the synchronization API WaitForSingleObject() in multithreaded applications.

When developing a multithreaded Win32-based application with Visual C++, you need to use the CRT thread functions to create any threads that call CRT functions. To create and terminate threads, use either _beginthread() and _endthread() or _beginthreadex() and _endthreadex(). If you use the Win32 APIs CreateThread() and EndThread() instead, some of the CRT functions used in the thread will not work. You need to use the CRT functions to both create and end the threads or you lose the memory that the CRT allocates for the thread.

MORE INFORMATION

The _beginthreadex() function gives you more control over how the thread is created than _beginthread() does. The _endthreadex() function is also more flexible. For example, with _beginthreadex(), you can use security information, set the initial state of the thread (running or suspended), and get the thread identifier of the newly created thread. You are also able to use the thread handle returned by _beginthreadex() with the synchronization APIs, which you cannot do with _beginthread().

It is safer to use _beginthreadex() than _beginthread(). If the thread spawned by _beginthread() exits quickly, the handle returned to the caller of _beginthread() may be invalid, or worse yet, point to another thread. However, the handle returned by _beginthreadex() has to be closed by the caller of _beginthreadex(), so it's guaranteed to be a valid handle if _beginthreadex() did not return an error.

NOTE: The _beginthreadex() and _endthreadex() functions are not available in Visual C++, 32-bit Edition, version 1.0.

The following sample code demonstrates how you can use the thread handle returned by _beginthreadex() with the synchronization API WaitForSingleObject(). The main thread waits for the second thread to terminate before it continues. When the second thread calls _endthreadex(), it causes its thread object to go to the signaled state. This allows the primary thread to continue running. This cannot be done with _beginthread() and _endthread(), because _endthread() calls the Win32 API CloseHandle(), destroying the thread object before it can be set to the signaled state.

Sample Code

/* Compile options needed: Default options for a multithreaded console
   application. You need to compile the code as a .CPP file.
*/ 

#include <windows.h>
#include <stdio.h>
#include <process.h>

unsigned Counter;

unsigned __stdcall SecondThreadFunc( void* pArguments )
{
    printf( "In second thread...\n" );

    while ( Counter < 1000000 )
        Counter++;

    _endthreadex( 0 );
    return 0;
}

void main()
{
    HANDLE hThread;
    unsigned threadID;

    printf( "Creating second thread...\n" );

    // Create the second thread.

    hThread = (HANDLE)_beginthreadex( NULL, 0, &SecondThreadFunc, NULL, 0,
        &threadID );

    // Wait until second thread has terminated. If you comment out the line
    // below, Counter will not be correct because the thread has not
    // terminated, and Counter most likely has not been incremented to
    // 1000000 yet.

    WaitForSingleObject( hThread, INFINITE );

    printf( "Counter should be 1000000; it is-> %d\n", Counter );

    // Destroy the thread object.

    CloseHandle( hThread );
} 

REFERENCES

For more information on these functions and multithreading, please see the following sources:

• Visual C++ Run-Time Library Reference, Part 2, Run-Time Reference; the descriptions of _beginthread/_beginthreadex and _endthread/_endthreadex.



• Win32 Programmer's Reference, Volume 2: Chapter 43, "Processes and Threads," and Chapter 44, "Synchronization."

Keywords : kbcode kbprg kbCRT kbVC200 kbVC210 kbVC220 kbVC400 kbVC500 kbVC600
Version : WinNT:2.0,2.1,2.2,4.0,5.0
Platform : NT WINDOWS
Issue type : kbhowto