930710 - Using Createprocess Function, How Can I Limit It To Only One Instance?

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hi i run another program from inside my program by using CreateProcess function. it works properly, but i like to go further:
1. i want no separate task bar icon appear for the child program.
2. the program in executed by clicking on a toolbar icon in my program. i want if it clicked again, the child program gets activated instead of being executed again. now two separate child programs appear.
how can i?
thx

Posted 2-Oct-14 0:54am

ilostmyid2

Updated 6-Oct-14 1:36am

v2

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Comments

[no name] 2-Oct-14 6:59am

What programming language is "Windows"? Create a mutex, if the "Windows" programming language supports that.

ilostmyid2 2-Oct-14 7:16am

sorry, it's in C++. i've no control over the child application. i've no access to its source. it's not my program.

Richard MacCutchan 2-Oct-14 10:08am

1. I don't think you can do that.
2. After clicking the "activate child" button, disable it so it cannot be called again, or keep a flag somewhere to prevent it being activated a second time.

ilostmyid2 2-Oct-14 10:11am

2. good idea, but i can't find out when the child program is closed so that i may enable it again.

Richard MacCutchan 2-Oct-14 10:16am

Don't you get a pointer or something from CreateProcess that you can use to find out when it closes?

ilostmyid2 2-Oct-14 10:20am

yes, i do. indeed it returns the handle to the new process and its process id as well as these info about its primary thread. but how can it help?

Richard MacCutchan 2-Oct-14 10:55am

See http://msdn.microsoft.com/en-gb/library/windows/desktop/ms687032(v=vs.85).aspx.

ilostmyid2 3-Oct-14 1:07am

thanks
such a management seems somehow complicated.
isn't there an easier way to check it?
let's concentrate on what i really want. i'm going to execute a program or if it's already running (by my program or user), bring it to front.

Richard MacCutchan 3-Oct-14 3:43am

such a management seems somehow complicated.
No one said it was easy. You do not have much choice other than to use the tools and interfaces that Microsoft make available. I don't know of any other ways but you could try some more Google research.

ilostmyid2 4-Oct-14 0:51am

this may help only if the only one who may execute the program be my own program. it doesn't help when the program is already running, even before my program. i want to bring it to front in such a case. it's enough that it be running. in such a case, i don't want to execute it again.

Richard MacCutchan 4-Oct-14 3:33am

Then you need some way to identify the program so you can tell if it is running. And if you do not have access to its source then it's difficult to know what to suggest.

ilostmyid2 4-Oct-14 11:25am

in task manager we see list of all running programs/processes. we may also bring a specific program to front. this is exactly what i need to do in my program.

Richard MacCutchan 5-Oct-14 3:11am

You still need some way to identify the program you are interested in. Getting the list of programs is just a matter of using one of the Windows API functions, see http://stackoverflow.com/questions/10819575/how-to-list-active-application-windows-using-c-sharp.

ilostmyid2 5-Oct-14 16:11pm

thanks for the link. but it's for C#, not C/C++.

Richard MacCutchan 6-Oct-14 5:35am

Your question is tagged "Windows", with no specific language. Also, the EnumWindows function is a C/C++ function, check the documentation on MSDN.

2 solutions

Solution 1

CreateProcess fills properly the out parameter lpProcessInformation, that is a pointer to a PROCESS_INFORMATION[^] struct, defined this way:

C

typedef struct _PROCESS_INFORMATION {
  HANDLE hProcess;
  HANDLE hThread;
  DWORD  dwProcessId;
  DWORD  dwThreadId;
} PROCESS_INFORMATION, *LPPROCESS_INFORMATION;

Passing the hProcess member of this struct to GetExitCodeProcess[^] you obtain the info you are searching for (e.g. STILL_ACTIVE if the child process is still running).

Read carefully the documentation.

Posted 6-Oct-14 2:48am

CPallini

Comments

ilostmyid2 6-Oct-14 9:45am

then i should end the process? this way, i need to first execute the program and then figure out that it has been running. what i want is to prevent it to be executed again. there should be an IN parameter for this purpose, like a flag to specify it should be run as single-instance.

CPallini 6-Oct-14 9:48am

"then i should end the process?"
Nope, on button click you have just to verify if there is already a child process running. If it is the case then you don't start a new child instance.

ilostmyid2 6-Oct-14 11:02am

this is true only if my process has created the child process. if the process has been running before my process, or after my process but has been brought up by a user, then i can't check it.

CPallini 6-Oct-14 11:13am

Yes, that's true. If you are indeed in such more complex scenarios then your life is more troubled and possibly the EnumWindows function is on your way.

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ilostmyid2 · Accepted Answer · 2014-10-07T19:04:00

thanks
based on your cooperation and my investigations the following code was resulted. i would expect such an answer.
good luck! :)

C++

struct handle_data
{
	unsigned long process_id;
	HWND best_handle;
};

BOOL is_main_window(HWND handle)
{   
	return GetWindow(handle, GW_OWNER) == (HWND)0 && IsWindowVisible(handle);
}

BOOL CALLBACK enum_windows_callback(HWND handle, LPARAM lParam)
{
	handle_data& data = *(handle_data*)lParam;
	unsigned long process_id = 0;
	GetWindowThreadProcessId(handle, &process_id);
	if (data.process_id != process_id || !is_main_window(handle))
		return TRUE;
	data.best_handle = handle;
	return FALSE;   
}

HWND find_main_window(unsigned long process_id)
{
	handle_data data;
	data.process_id = process_id;
	data.best_handle = 0;
	EnumWindows(enum_windows_callback, (LPARAM)&data);
	return data.best_handle;
}

CString file_name(LPCSTR path)
{
	int len = strlen(path);
	for (int i = len - 1; i >= 0; i--)
		if (path[i] == '\\')
			return path + i + 1;
	return "";
}

// check whether the program is running. if so, it also brings it to front.
// prog may be something like "devenv.exe".
bool is_running(LPCSTR prog)
{
	void *buf = NULL;
	int estimatedRequiredBufSize = 300;
	DWORD requiredBufSize;
	while (true)
	{
		buf = realloc(buf, estimatedRequiredBufSize);
		VERIFY(EnumProcesses((DWORD *) buf, estimatedRequiredBufSize, &requiredBufSize));
		if (estimatedRequiredBufSize == requiredBufSize)
			estimatedRequiredBufSize *= 2;
		else
			break;
	}
	DWORD *pProcessIds = (DWORD *) buf;
	int numProcesses = requiredBufSize / sizeof(DWORD);
	for (int i=0; i<numprocesses;>	{
		HANDLE hProcess = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pProcessIds[i]);
		if (hProcess)
		{
			char path[_MAX_PATH];
			DWORD size = sizeof(path) - 1, wholeSize = size;
			VERIFY(QueryFullProcessImageName(hProcess, 0, path, &size));
			ASSERT(size < wholeSize);
			if (file_name(path) == prog)
			{
				HWND hWnd = find_main_window(pProcessIds[i]);
				VERIFY(SetForegroundWindow(hWnd));
				free(pProcessIds);
				return true;
			}
		}
	}
	free(pProcessIds);
	return false;
}