OpenProcess() returns different handles

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7 total messages Started by Wiebe Vos Sun, 09 Apr 2006 20:36

#3968

Author: Wiebe Vos
Date: Sun, 09 Apr 2006 20:36

14 lines
1248 bytes

BCB6 + WinXP(Pro)

//
PROCESS_INFORMATION  processInfo;
//
I sucessfully launch an app with CreateProcess(...)
However thereafter OpenProcess ( PROCESS_ALL_ACCESS,  true, 
processInfo.dwProcessId)
returns a handle that differs from processInfo.hProcess
(In fact it returns a different handle each time when called.)
Why?

Thanks in advance,
Wiebe

Re: OpenProcess() returns different handles

#3969

Author: Eric Noel
Date: Sun, 09 Apr 2006 20:54

13 lines
1406 bytes

Wiebe Vos wrote:
> I sucessfully launch an app with CreateProcess(...)
> However thereafter OpenProcess ( PROCESS_ALL_ACCESS,  true, 
> processInfo.dwProcessId)
> returns a handle that differs from processInfo.hProcess
> (In fact it returns a different handle each time when called.)
> Why?

WAD. Think of it as if you were opening a file handle - you can open the 
same file multiple times, each handle can have different access, and be 
used independently. Same idea in this case for your process handle.

- Eric

Re: OpenProcess() returns different handles

#3970

Author: Wiebe Vos
Date: Mon, 10 Apr 2006 08:15

7 lines
1164 bytes

Thanks,
I want to use the returned handle to check if the program is (still) alive
and be able to kill it.
However GetExitCodeProcess ( returnedHandle, &exitCode) gives exitCode=0.
How can I get the appropriate handle to do so, when I have the processId?

Wiebe

Re: OpenProcess() returns different handles

#3971

Author: Wiebe Vos
Date: Mon, 10 Apr 2006 08:22

2 lines
1055 bytes

BTW. It is a console program. (no window)
Wiebe

Re: OpenProcess() returns different handles

#3972

Author: Wiebe Vos
Date: Mon, 10 Apr 2006 09:20

7 lines
1297 bytes

Never mind.
The dwDesiredAccess parameter in OpenProcess() deals with that.
FWIW:
PROCESS_QUERY_INFORMATION gives the handle to determine the program status.
PROCESS_TERMINATE gives the license to kill.

Wiebe

Re: OpenProcess() returns different handles

#3974

Author: Bob Gonder
Date: Mon, 10 Apr 2006 16:37

32 lines
2077 bytes

Wiebe Vos wrote:

>I want to use the returned handle to check if the program is (still) alive
>and be able to kill it.

The hProcess member of the PROCESS_INFORMATION structure you passed to
CreateProcess() should give you that handle.

{Note: I am not recommending this code. It is for illustration
purposes only}

    if( CreateProcess( 0, command, 0, 0, FALSE, NORMAL_PRIORITY_CLASS,
		 0, 0, &si, &pi ) )
    {
	CloseHandle( pi.hThread ); 
	do{
		WaitForSingleObject( pi.hProcess, 100);
		GetExitCodeProcess ( pi.hProcess, &exitCode);
	}while( exitCode == STILL_ACTIVE );

	CloseHandle( pi.hProcess ); 
    };

>However GetExitCodeProcess ( returnedHandle, &exitCode) gives exitCode=0.

Did you check the return value of the function itself?

	if( ! GetExitCodeProcess ( pi.hProcess, &exitCode) )
		ReportError( "GetExitCodeProcess", GetLastError() );

One also wonders why you ask for the handle to be inheritable (true)?
> OpenProcess ( PROCESS_ALL_ACCESS,  true, processInfo.dwProcessId)

Re: OpenProcess() returns different handles

#3977

Author: Wiebe Vos
Date: Mon, 10 Apr 2006 18:40

16 lines
1431 bytes

Hi Bob,

> The hProcess member of the PROCESS_INFORMATION structure you passed to
   CreateProcess() should give you that handle.
   Correct. However thereafter the launched app is bound to be terminated
and/or
   "replaced".

> ...why you ask for the handle to be inheritable (true)?
   No specific reason. Taken from an example.

As indicated in my earlier response, I managed to find a solution.

Thanks for your help,

Wiebe

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