CreateProcess going away indefinitely

This is a discussion on CreateProcess going away indefinitely within the C++ Programming forums, part of the General Programming Boards category; Here's my cry for help: Within a DLL I am calling CreateProcess to run an exe which brings up a ...

  1. #1
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    CreateProcess going away indefinitely

    Here's my cry for help:

    Within a DLL I am calling CreateProcess to run an exe which brings up a window which requires user interaction. My problem is that the first time this call is made the window will not appear until the user clicks on something else on the Desktop - the taskbar, another window, the start menu, etc. - only then will the window we're waiting on appear. The second time this is run the window comes up on its own.

    Another odditiy: If the .exe is run on its own without being called from within the DLL it comes up immediately, with no delay whether it is the first time running or the hundredth.

    Does anyone have a suggestion for fixing this behavior so that I can make the exe call from the DLL, having it run as if it were NOT being called from the DLL? I am working in various versions of Windows (98/ME/XP).

    Thanks in advance!!

  2. #2
    Registered User Codeplug's Avatar
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    Post the code which calls CreateProcess().

    gg

  3. #3
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    Post Here's the code that calls CreateProcess:

    First LaunchScanner is called, then WaitForImage. If anything like a MessageBox call is stuck in after the CreateProcess, the scanner program comes up immediately - is there something else that I can call which will have the same effect, without displaying something like a MessageBox on the screen?

    Code:
    CString CFilterModuleDllApp::GetScannerProgram() {
    	CHAR windowsDirectory[MAX_LOADSTRING];
    	CHAR orexAppPath[MAX_LOADSTRING];
    	CHAR executable[MAX_LOADSTRING];
    
    	GetWindowsDirectory(windowsDirectory, MAX_LOADSTRING);
    	LoadString(m_hInstance, OREX_SCANPATH, orexAppPath, MAX_LOADSTRING);
    	strcpy(executable, windowsDirectory);
    	strcat(executable, "\\");
    	strcat(executable, orexAppPath);
    	return CString(executable);
    }
    
    int CFilterModuleDllApp::LaunchScanner() {
    	PROCESS_INFORMATION	scan_procinfo;
    	STARTUPINFO			scan_startup;
    
    	scan_startup.cb = sizeof(STARTUPINFO);
    	scan_startup.lpReserved = NULL;
    	scan_startup.lpDesktop = NULL;
    	scan_startup.lpTitle = NULL;
    	scan_startup.dwFlags = 0;
    	scan_startup.cbReserved2 = 0;
    	scan_startup.lpReserved2 = 0;
    
    	if (!CreateProcess(GetScannerProgram(), NULL, NULL, NULL, TRUE, REALTIME_PRIORITY_CLASS,
    		               NULL, NULL, &scan_startup, &scan_procinfo)) {
    		return -500;
    	}
    	return 0;
    }
    
    int CFilterModuleDllApp::WaitForImage(int *width, int *height, int *xPixelSize, int *yPixelSize) {
    	CHAR interfacename[MAX_LOADSTRING];
    	CHAR tempbuf[MAX_LOADSTRING];
    	CHAR compbuf[MAX_LOADSTRING];
    	CString pixelSizeLookup;
    	CString pixelSizeTranslation;
    	LoadString(m_hInstance, OREX_INI, interfacename, MAX_LOADSTRING);
    	LoadString(m_hInstance, OREX_CLOSE, tempbuf, MAX_LOADSTRING);
    	LoadString(m_hInstance, OREX_CLOSE, compbuf, MAX_LOADSTRING);
    	for(;!strcmp(tempbuf,compbuf);) {
    		if (GetPrivateProfileString("SCANNER STATUS", "Scanner Status", "",
    			                        tempbuf, MAX_LOADSTRING, interfacename) == 0) {
    			return -20;
    		}
    	}
    
    	LoadString(m_hInstance, OREX_OPEN, tempbuf, MAX_LOADSTRING);
    	LoadString(m_hInstance, OREX_OPEN, compbuf, MAX_LOADSTRING);
    	for(;!strcmp(tempbuf,compbuf);) {
    		if (GetPrivateProfileString("SCANNER STATUS", "Scanner Status", "",
    			                        tempbuf, MAX_LOADSTRING, interfacename) == 0) {
    			return -20;
    		}
    	}
    
    	LoadString(m_hInstance, OREX_CLOSE, compbuf, MAX_LOADSTRING);
    	if (!strcmp(compbuf,tempbuf)) {
    		return 0;
    	}
    
    	if (GetPrivateProfileString("SCANNER STATUS", "Image Width", "",
    		                        tempbuf, MAX_LOADSTRING, interfacename) == 0) {
    		return -21;
    	}
    	*width = atoi(tempbuf);
    
    	if (GetPrivateProfileString("SCANNER STATUS", "Image Height", "",
    		                        tempbuf, MAX_LOADSTRING, interfacename) == 0) {
    		return -22;
    	}
    	*height = atoi(tempbuf);
    
    	// look up the pixel size for the width, height
    	pixelSizeLookup.Format("%d,%d", *width, *height);
    	pixelSizeTranslation = GetProfileString("PixelSize", pixelSizeLookup);
    	
    	// extract the x and y pixel sizes from the results
    	int pos = pixelSizeTranslation.Find(",");
    	*xPixelSize = atoi(pixelSizeTranslation.Mid(0, pos));
    	*yPixelSize = atoi(pixelSizeTranslation.Mid(pos + 1));
    
    	return 1;
    }

  4. #4
    Registered User Codeplug's Avatar
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    Try this - I'll look at the rest later if this doesn't fix it.
    Code:
    PROCESS_INFORMATION scan_procinfo = {0};
    STARTUPINFO         scan_startup = {0};
    gg

  5. #5
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    No joy

    I wish I could report that your suggestion fixed the problem, but it didn't seem to change anything. Thanks, though!

  6. #6
    Registered User Codeplug's Avatar
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    Try these suggestions individually:
    - use NORMAL_PRIORITY_CLASS to rule that out as being the cause (for whatever reason)
    - use GetScannerProgram() as the second parameter and make the first NULL (this is what I normally do).
    - don't inherit handles - set 5th parameter to FALSE

    If those don't work, try this:
    Code:
    STARTUPINFO si = {0};
    si.cb = sizeof(STARTUPINFO);
    si.dwFlags = STARTF_USESHOWWINDOW;
    si.wShowWindow = SW_SHOWNORMAL;
    Also, you have a handle leak.
    You are responsible for closing the handles in the PROCESS_INFORMATION strcuture:
    Code:
    CloseHandle(scan_procinfo.hProcess);
    CloseHandle(scan_procinfo.hThread);
    gg

  7. #7
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    Well, LaunchScanner has the suggested changes in it - I tried all of the suggestions above, still no change in behavior. Is there no call that I can make that will yield to the O/S in a manner similar to MessageBox, but without the visuals?

    Code:
    int CFilterModuleDllApp::LaunchScanner() {
    	PROCESS_INFORMATION scan_procinfo = {0};
    	STARTUPINFO         scan_startup = {0};
    	CHAR		*executable;
    	CString		strexec;
    
    	scan_startup.cb = sizeof(STARTUPINFO);
    	scan_startup.lpReserved = NULL;
    	scan_startup.lpDesktop = NULL;
    	scan_startup.lpTitle = NULL;
    	scan_startup.dwFlags = 0;
    	scan_startup.cbReserved2 = 0;
    	scan_startup.lpReserved2 = 0;
    	strexec = GetScannerProgram();
    	int length = strexec.GetLength();
    	executable = strexec.GetBuffer(length);
    	STARTUPINFO si = {0};
    	si.cb = sizeof(STARTUPINFO);
    	si.dwFlags = STARTF_USESHOWWINDOW;
    	si.wShowWindow = SW_SHOWNORMAL;
    
    
    	if (!CreateProcess(NULL, executable, NULL, NULL, FALSE, NORMAL_PRIORITY_CLASS,
    		               NULL, NULL, &si, &scan_procinfo)) {
    		CloseHandle(scan_procinfo.hProcess);
    		CloseHandle(scan_procinfo.hThread);
    		return -500;
    	}
    
    	CloseHandle(scan_procinfo.hProcess);
    	CloseHandle(scan_procinfo.hThread);
    	return 0;
    }

  8. #8
    Registered User Codeplug's Avatar
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    Do you have the code for that application? If so, how does it create and show its main window?

    Do you get the same behavior when calling CreateProcess() from an exe instead of a DLL?

    What OS are you testing on? Same behavior on multiple OS's?

    You don't have to close handles if CreateProcess() fails.

    gg

  9. #9
    Yes, my avatar is stolen anonytmouse's Avatar
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    I think I may have experienced the same problem a while back.

    When the parent program spawned the child process with CreateProcess it did not come to the foreground. Instead it stayed in the background until clicked on.

    It seems that Windows does not bring the new process to the foreground if the parent process does not pump its message loop or exit within a given time period.

    Wierdly enough, this rule does not seem to apply if the parent process was launched from the console, even though it is not a console program.

    The solution would seem to be to do what the call to MessageBox is doing. That is to pump the message loop straight after you spawn the process.

    Here is the stock standard DoEvents implementation:
    Code:
    void DoEvents(void) {
    
    	MSG Msg; 
    
    	while ( PeekMessage(&Msg,NULL,0,0,PM_REMOVE) ) {
    		TranslateMessage(&Msg); 
    		DispatchMessage(&Msg);
    	}
    }
    As a side note, you probably want to put a short Sleep() call in those loops.

  10. #10
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    Cool Hooray! Happy New Year!

    That did the trick - thank you!!

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