Thread: Threading problem

Greetings!

I learnt little bit about multithreading, and tried to create a program with 2 threads. But the program won’t work. It seems like the thread function won’t execute. When I tried to debug into dirWatch(), the execution pointer doesn’t seems to enter the function. Though CreateThread() doesn’t return NULL and I don’t get any error messages. (I'm running this on WinXP)
Here what it looks like so far:

Code:

......
......

// Thread function

void WINAPI dirWatch(char dir[256]){

.......
.......

}

void main(){

........
........
........

lstrcpy(dir,temp);
// Create 1st thread
if(CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)dirWatch,dir,0,NULL)==NULL)
	MessageBox(NULL,"CreateThread() failed.", "Message",0);

.........
.........
.........

lstrcpy(dir,temp);
// Create 2nd thread
if(CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)dirWatch,dir,0,NULL)==NULL)
	MessageBox(NULL,"CreateThread() failed.", "Message",0);
.......
.......

}

What I’m doing wrong here please?

Thanks for reading.

Your thread procedure is prototyped wrong, it should be:

Code:

DWORD WINAPI dirWatch(LPVOID lParam) {
   char *dir = (char*)lParam;
   ...

Make sure that the string you are passing (dir in your case) is allocated with malloc if you are using C or new if you are using C++, and don't forget to free that memory in your thread procedure. The reason you do this is so that multiple threads are not using the same memory at the same time.

Oh, and change void main to int main before someone else here yells at you

I changed the code the way you pointed out. But I don’t know why, it still doesn’t work.
new code:

Code:

// Thread function
	......
DWORD WINAPI dirWatch(LPVOID lParam){
	char *dir = (char*)lParam;
	......
	delete[] dir;
}

void main(){
	......
	char *dir = new char[256];
	......
	lstrcpy(dir,temp);
	// Create 1st thread
	if(CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)dirWatch,dir,0,NULL)==NULL)
		MessageBox(NULL,"CreateThread() failed.", "Message",0);
	.........
		
	dir = new char[256];
	.........
	lstrcpy(dir,temp);
	// Create 2nd thread
	if(CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)dirWatch,dir,0,NULL)==NULL)
		MessageBox(NULL,"CreateThread() failed.", "Message",0);
	.......
}

I assume that in the real code dir Watch is actually dirWatch (or it wouldn't compile)?

Apart from that the code looks ok..you've put a breakpoint in dirWatch and it never gets hit?

Yes, it's dirWatch.
And yes, the breakpoint in dirWatch never get hit. The program just ends without executing dirWatch. Why is that?

Does your main function end after you create your threads or do you wait?
(It should wait).

Your program will exit when main returns, even if other threads are still executing or just starting to execute. The easiest way to prevent this is to store the thread handles returned by CreateThread and wait on them before returning from main. A thread handle is set to the signaled state when the thread exits. The WaitForSingleObject function will return when the object passed to it is in the signaled state or the timeout expires.

Code:

   hThread1 = CreateThread(...);

   ...

   WaitForSingleObject(hThread1, INFINITE);
   WaitForSingleObject(hThread2, INFINITE);
   return 0;

Thanks.