problem with Processess

  • Thread starter Thread starter Sudhakar
  • Start date Start date
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Sudhakar

Hi,

I want to start a independent process from another process. Let me
explain my problem,

I have a "process A" running. Process B has to be started just before the
process A ends and the invocation of process B has to be triggered from
inside the process A.
So, when the process B started, process A would have been terminated but the
process B should not be stopped.

Please suggest how I can achieve this is VC++ ?

Thanks,
Sud
 
I have a "process A" running. Process B has to be started just before the
process A ends and the invocation of process B has to be triggered from
inside the process A.
So, when the process B started, process A would have been terminated but the
process B should not be stopped.

Please suggest how I can achieve this is VC++ ?
Click to expand...

Processes are (largely) independent under Win32 so the instigator
process won't normally close the spawned process when it closes. Use
whichever API is most appropriate to your circumstance - CreateProcess
or ShellExecute.

Dave
 
I want to start a independent process from another process. Let me
explain my problem,

I have a "process A" running. Process B has to be started just before the
process A ends and the invocation of process B has to be triggered from
inside the process A.
So, when the process B started, process A would have been terminated but
the
process B should not be stopped.

Please suggest how I can achieve this is VC++ ?
Click to expand...

Call CreateProcess, ShellExecute or system before process A exits
 
Sudhakar said:
Hi,

I want to start a independent process from another process. Let me
explain my problem,

I have a "process A" running. Process B has to be started just before the
process A ends and the invocation of process B has to be triggered from
inside the process A.
So, when the process B started, process A would have been terminated but
the
process B should not be stopped.

Please suggest how I can achieve this is VC++ ?
Click to expand...

In addition to what's already been said, if you need to guarantee that
process A has already exited (because you're replacing it with an updated
version, for example) then you'll need to wait in process B:

in Process A
event = CreateEvent(... some unique name ...);
processB = CreateProcess(exeB, put processA pid in arg list);
wakeReason = WaitForMultipleObjects({processB, event});
if (wakeReason was event) ExitProcess();
else if (wakeReason was processB) MessageBox("ProcessB couldn't be
started");

in Process B
event = OpenEvent(... same unique name ...);
processA = OpenProcess(... pid parsed from args ...);
SetEvent(event);
WaitForSingleObject(processA);
.... now processA is definitely dead ...

This method takes care of the race conditions (what if Process A goes to
sleep between CreateProcess and ExitProcess), (what if another process
reuses Process A's PID before Process B calls OpenProcess) as well as the
case where Process B dies during startup and never sets the event.
 
Thanks Ben for the solution. It worked

Ben Voigt said:
In addition to what's already been said, if you need to guarantee that
process A has already exited (because you're replacing it with an updated
version, for example) then you'll need to wait in process B:

in Process A
event = CreateEvent(... some unique name ...);
processB = CreateProcess(exeB, put processA pid in arg list);
wakeReason = WaitForMultipleObjects({processB, event});
if (wakeReason was event) ExitProcess();
else if (wakeReason was processB) MessageBox("ProcessB couldn't be
started");

in Process B
event = OpenEvent(... same unique name ...);
processA = OpenProcess(... pid parsed from args ...);
SetEvent(event);
WaitForSingleObject(processA);
... now processA is definitely dead ...

This method takes care of the race conditions (what if Process A goes to
sleep between CreateProcess and ExitProcess), (what if another process
reuses Process A's PID before Process B calls OpenProcess) as well as the
case where Process B dies during startup and never sets the event.
Click to expand...
 
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