C thread not behaving correctly - simple code

Question

I am creating a new thread in c using _beginthreadex. I have written the following code. same code written in two versions, first version is working properly but second one is not working.

working code

main.c

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

extern void func(unsigned (__stdcall *SecondThreadFunc)( void* ));

int main()
{ 
    func(NULL);
}

second.c

#include<Windows.h>

//when thread start routine is declared in the same file new thread is running fine...
//but if this routine is moved to main.c and passed as parameter to func new thread is not working
unsigned __stdcall SecondThreadFunc( void* pArguments )
{
    printf( "In second thread...\n ");
    return 0;
} 


void func(unsigned (__stdcall *SecondThreadFunc)( void* ))
{
    HANDLE hThread;
    printf( "Creating second thread...\n" );

    // Create the second thread.
    hThread = (HANDLE)_beginthreadex( NULL, 0, &SecondThreadFunc, NULL, 0, NULL );

    // Wait until second thread terminates.
    WaitForSingleObject( hThread, INFINITE );
}

Not working code(Below)

main.c

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


extern void func(unsigned (__stdcall *SecondThreadFunc)( void* ));

unsigned __stdcall SecondThreadFunc( void* pArguments )
{
    printf( "In second thread...\n ");
    return 0;
} 

int main()
{ 
    func(SecondThreadFunc);
}

second.c

#include<Windows.h>

void func(unsigned (__stdcall *SecondThreadFunc)( void* ))
{
    HANDLE hThread;
    printf( "Creating second thread...\n" );

    // Create the second thread.
    hThread = (HANDLE)_beginthreadex( NULL, 0, &SecondThreadFunc, NULL, 0, NULL );

    // Wait until second thread terminates.
    WaitForSingleObject( hThread, INFINITE );
}

I am getting access violation inside _beginthreadex while calling SecondThreadFunc. Can some help me out. Thanks in advance.

printf() etc stdio functions are not thread safe.

Lundin
– Lundin

2011-01-26 13:50:51 +00:00
Commented Jan 26, 2011 at 13:50 — Lundin
– Lundin, Commented Jan 26, 2011 at 13:50

CAFxX · Accepted Answer · 2011-01-26 10:02:53Z

1

In the not working code you should have (pay attention to the &s):

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

edited Jan 26, 2011 at 10:02

answered Jan 26, 2011 at 9:13

CAFxX

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3 Comments

Vineel Kumar Reddy Over a year ago

both are function calls but why the above correction is working... in c function pointer need not use & when passing to a function. Is that correct?

caf Over a year ago

@Vineel Kumar Reddy: The change to the func() call is unnecessary, for the reason you state. The second change, however, is necessary - the SecondThreadFunc in func() is a function pointer value, so when you take its address you get the address of a function pointer, not the address of a function. In this case, SecondThreadFunc and *SecondThreadFunc are the equivalent expressions.

Vineel Kumar Reddy Over a year ago

U r awesome though i have been programming in c from 6 year this is really a very subtle example. Thanks a lot

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