Multithreading with the Windows API

I am trying to create a multithreaded program using the windows API. Here is what I have so far:

Code:

//Definitions////////////////////////////////////////////////////////////////////////////// //Define this to allow multithreading #define _MT /////////////////////////////////////////////////////////////////////////////////////////// //Include files//////////////////////////////////////////////////////////////////////////// #include <windows.h> #include <stdio.h> #include <commctrl.h> #include "resource.h" #include "diologs.h" /////////////////////////////////////////////////////////////////////////////////////////// //Global variables///////////////////////////////////////////////////////////////////////// //All puropose counter variable int i; //Thread handles HANDLE mainDialogProc_Handle; //Main diolog //Thread IDs LPDWORD mainDialogProc_ID; //Main diolog /////////////////////////////////////////////////////////////////////////////////////////// //Main function. Serves as entry point for other application threads/////////////////////// bool main(void) { printf("%d\n",GetLastError()); mainDialogProc_Handle = CreateThread( (LPSECURITY_ATTRIBUTES) NULL, //Security attributes for thread. Default is fine here (DWORD) 0, //Initial thread stack size. Again, default is fine (LPTHREAD_START_ROUTINE) &DialogThread, //Pointer to thread function (LPVOID) NULL, //Argument for new thread. Not implemented here (DWORD) NULL, //Creation flags. None neccesary here (LPDWORD) mainDialogProc_ID); //Pointer to receive thread ID printf("%d\n",GetLastError()); if(!mainDialogProc_Handle) { printf("Error: Could not create DialogThread\n"); } return FALSE; } ///////////////////////////////////////////////////////////////////////////////////////////

Also, here is my code for the function in diologs.h that the thread should be going into (although I'm sure none of this is actually getting executed.)

Code:

DWORD WINAPI DialogThread(LPVOID lParam) { DialogBoxParam( GetModuleHandle(NULL), MAKEINTRESOURCE(IDD_DLG_MAIN), NULL, (DLGPROC)MainDialogProc, 0); return FALSE; }

This code does absolutely nothing execpt display my two printf functions calls. The weird thing about this mess is that I'm getting a Class does not exist error on my first call to the GetLastError function before my code even makes any calls to the Windows API. After the call to the CreateThread function though, no error occurs, and I actually get a handle to my thread, but it just never excecutes. Can anyone explain why this code won't work, and also why I'm getting that error if the two things aren't related.

Try this:

Code:

mainDialogProc_Handle = CreateThread( (LPSECURITY_ATTRIBUTES) NULL, //Security attributes for thread. Default is fine here (DWORD) 0, //Initial thread stack size. Again, default is fine (LPTHREAD_START_ROUTINE) DialogThread, //Pointer to thread function *CHANGED* (LPVOID) NULL, //Argument for new thread. Not implemented here (DWORD) NULL, //Creation flags. None neccesary here (LPDWORD) mainDialogProc_ID); //Pointer to receive thread ID

I don't think that's it, but try it anyway.

Also, place a MessageBox() call in DialogThread() just to notify you if it makes it that far.

Quote:

The weird thing about this mess is that I'm getting a Class does not exist error on my first call to the GetLastError function before my code even makes any calls to the Windows API.

I would assume that this is just a coincidence. Class does not exist may be a default value, or just some garbage that was sitting there when the program executed. Whatever the reason is, it doesn't matter, because you aren't actually really checking for an error at that stage. I would just take the call out of your code.

Quote:

Originally posted by bennyandthejets
Try this:

Code:

mainDialogProc_Handle = CreateThread( (LPSECURITY_ATTRIBUTES) NULL, //Security attributes for thread. Default is fine here (DWORD) 0, //Initial thread stack size. Again, default is fine (LPTHREAD_START_ROUTINE) DialogThread, //Pointer to thread function *CHANGED* (LPVOID) NULL, //Argument for new thread. Not implemented here (DWORD) NULL, //Creation flags. None neccesary here (LPDWORD) mainDialogProc_ID); //Pointer to receive thread ID

I don't think that's it, but try it anyway.

Nope, I already tried that and it didn't help.

Quote:

Originally posted by bennyandthejets
Also, place a MessageBox() call in DialogThread() just to notify you if it makes it that far.

I already did this with a printf call, that's why I said I was sure the code simply wasn't excecuting.

Quote:

Originally posted by bennyandthejets
I would assume that this is just a coincidence. Class does not exist may be a default value, or just some garbage that was sitting there when the program executed. Whatever the reason is, it doesn't matter, because you aren't actually really checking for an error at that stage. I would just take the call out of your code.

The default value is 0 for that function and it always started as 0 before I introduced the multithreading code. Oh, and the printf's were just temporary to check for what the problem was, I wasn't planning on leaving them in.

Hmmm. I just noticed that you pass a dead pointer to CreateThread(). That may be affecting things, but I'm not sure. You should create an actual DWORD, not a pointer to one:

Code:

//Thread IDs DWORD mainDialogProc_ID; //Main diolog

Code:

mainDialogProc_Handle = CreateThread( (LPSECURITY_ATTRIBUTES) NULL, //Security attributes for thread. Default is fine here (DWORD) 0, //Initial thread stack size. Again, default is fine (LPTHREAD_START_ROUTINE) DialogThread, //Pointer to thread function (LPVOID) NULL, //Argument for new thread. Not implemented here (DWORD) NULL, //Creation flags. None neccesary here &mainDialogProc_ID); //Pointer to receive thread ID *CHANGED*

Give that a shot.

Nope, no effect.

EDIT: And trying both suggestions at once didn't work either :\

Add this right after CreateThread():

Code:

WaitForSingleObject(mainDialogProc_ID,INFINITE);

I suspect the process may be terminating before the thread even starts.

Hey, it worked. Well, except you tried to pass it the thread ID instead of handle but I fixed that ;). So does that mean the problem was the CreateThread function doesn't wait till the thread is fully created to continue executing the thread you created it in?

Stupid me:p passed the ID.

Yes, the problem lies in CreateThread() returning before DialogThread() has had time to run. Normally, you wouldn't terminate the process straight away, because that would defeat the purpose of multithreading. When your program becomes a bit larger, and doesn't quit straight away, you'll be able to remove WaitForSingleObject(). Remember to consider asychronous operation; that is, use mutex objects or some other crazy thing to ensure that only one thread accesses some particular data at a time. Ie, global variables.