Suspend Thread when Finished

[Pettor]

Hi,

I am creating a GUI in Win32 using C-system functions (non-MFC) and would be very grateful for some tips or directions regarding some threading problem i have.

DESCRIPTION: Just as any Win32 i have a WndProc that controlls the GUI. In this GUI there is a "Thread On/Off"-button that simply starts a thread when pushed, and once pushed again suspends (maybe destroy?) it.

The Thread is an infinite loop just doing the same procedure over and over again. Because the procedure here is calling some safety critical functions, there is a mutex that is taken and later released.

QUESTION: The problem is that when the button is pressed to suspend the thread it needs to tell the thread to finish it's current loop (it can't just stop in this procedure) and later release the mutex. When the button is once again pressed the procedure should be starting from the begging. I have some code to show:


GUI Controller (WndProc):

case WM_COMMAND:

    wmId    = LOWORD(wParam);
    wmEvent = HIWORD(wParam);

    switch (wmId)
    {
        // The button is pressed
        case IDC_WHEEL_POLL_AND_SEND:

            // The Thread doesn't exist
	    if(pollAndSendThread == NULL)
	    {

	        // Create the Thread
	        pollAndSendThread = CreateThread(
		    NULL,
		    NULL,
		    PollnSend,
		    (LPVOID) hWnd,
		    0,
		    NULL);

                // Do some GUI changes
		SetWindowText(GetDlgItem(hWnd, IDC_WHEEL_POLL_AND_SEND_STATUS_TEXT), "On");
	    }

	    // ResumeThread returns precious value of suspend count, if 0 then suspend cause it was already running
	    else if(ResumeThread(pollAndSendThread) == 0 )
	    {
	        // Thread was suspended and mutex need to be released and Thread procedure finished
	    }
	    else
	        SetWindowText(GetDlgItem(hWnd, IDC_WHEEL_POLL_AND_SEND_STATUS_TEXT), "On");

	    return TRUE;

The Thread:

This is only a simple skeleton for how the thread is going to be. What need to be done is that when the button above is pressed, this thread moves down to the sleep and only then gets suspended, so the procedure is finished and mutex released.

//Poll and send function to be threaded
DWORD WINAPI PollnSend(LPVOID lpParam){

    HRESULT hr;
    DIJOYSTATE2 pJoyState2;

    while(true) 
    {
        // "Take" the mutex
        DWORD dwWaitResult = WaitForSingleObject((*g_pJoystick).getMutex(), INFINITE);
		
	switch(dwWaitResult)
	{
	    //Got access to the mutex
	    case WAIT_OBJECT_0:

	    try
	    {
	        // Simulate critical work that
		std::cout << "Thread Doing critical work";
		Sleep(4000);
	    }

	    // Catch possible errors
	    catch(...)
	    {
	        std::cout << "Catch";
	    }

	    ReleaseMutex((*g_pJoystick).getMutex());

	    break;
	    case WAIT_ABANDONED:
	        std::cout << "Wait abanonded";
	}

        Sleep(5);
    }
    return true;
}

I am very grateful for any help! It's possible something quite easy, but i want it to be done in the correct way (Threading can easily be dangerous and our updates every 5 millisecond so if crash is possible it will happen!).

Regards,

[THEARTOFWEB]

I am not really sure:

#include <windowsx.h>

// Declare

void Cls_OnCommand(HWND hwnd, int message, HWND hwndCtl, UINT codeNotify);
void method_IDC_WHEEL_POLL_AND_SEND(HWND hwnd);

// Global

volatile bool stopThreadFlag = false;
HANDLE pollAndSendThread == NULL;

(...)

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	switch(message)
	{
		HANDLE_MSG (hwnd, WM_CREATE, Cls_OnCreate);
		HANDLE_MSG (hwnd, WM_COMMAND, Cls_OnCommand);
		HANDLE_MSG (hwnd, WM_DESTROY, Cls_OnDestroy);
		// ...other messages
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}

(...)

void Cls_OnCommand(HWND hwnd, int message, HWND hwndCtl, UINT codeNotify)
{
	switch (message)
	{
		case IDC_WHEEL_POLL_AND_SEND:
			method_IDC_WHEEL_POLL_AND_SEND(hwnd);
			break;

		case ...
		break;
	}
}

(...)

void method_IDC_WHEEL_POLL_AND_SEND(HWND hWnd)
{
	// The Thread doesn't exist
	if(pollAndSendThread == NULL)
	{
		stopThreadFlag = false;

		// Create the Thread
		pollAndSendThread = CreateThread(NULL,NULL,PollnSend,(LPVOID) hWnd,0,NULL);

		// Do some GUI changes
		SetWindowText(GetDlgItem(hWnd, IDC_WHEEL_POLL_AND_SEND_STATUS_TEXT), "On");
	}

	    // ResumeThread
	else if(ResumeThread(pollAndSendThread) == 0 )
	{
		stopThreadFlag = true;
		// Thread was suspended
	}
	else
	{
		SetWindowText(GetDlgItem(hWnd, IDC_WHEEL_POLL_AND_SEND_STATUS_TEXT), "On");
	}

}

(...)

//Poll and send function to be threaded
DWORD WINAPI PollnSend(LPVOID lpParam){

	HRESULT hr;
	DIJOYSTATE2 pJoyState2;

	while(1) 
	{

		if(stopThreadFlag)
			break;

		// "Take" the mutex
		DWORD dwWaitResult = WaitForSingleObject((*g_pJoystick).getMutex(), INFINITE);
		
		switch(dwWaitResult)
		{
			//Got access to the mutex
			case WAIT_OBJECT_0:

			try
			{
				// Simulate critical work that
				std::cout << "Thread Doing critical work";
				Sleep(4000);
			}

			// Catch possible errors
			catch(...)
			{
				std::cout << "Catch";
			}

			ReleaseMutex((*g_pJoystick).getMutex());

			break;

			case WAIT_ABANDONED:
			std::cout << "Wait abanonded";
		}

		Sleep(5);
	}
	return true;
}

[Pettor]

Thank you for your answer,

You solution should be working, even if I am somewhat afraid it might have side effects? It also require us to only have one Thread running, which shouldn't be a problem (we only use 1 thread right now) but I don't know what changes will be made in the future. However it's a good solution and I will test it for side effects.

You also made some really good points in modulating the GUI which I liked (HANDLE_MSG). This makes the GUI more flexible and separated, very nice

Regards,