[Insight-developers] Using kwsys/Process.h functions

[Brad King]

kent williams wrote:
> I just wrote some code to do coarse-grained parallelism using the
> kwsysProcess functions.  I run two external programs at the same time on a
> multiprocessor.
> 
> It worked as advertised except for one thing: If I ran a process
> synchronously -- i.e. I didn't set kwsysProcess_Option_Detach -- and then
> called kwsysProcess_GetExitValue, the exit code returned was always 1, even
> if the program successfully executed.
> 
> If I ran the program detached, the correct exit code was returned.
> 
> My work around was to run all processes detached, but call
> kwsysProcess_GetExitValue to block and wait for the process synchronously if
> needed.
> 
> Since kwsysProcess is used in Cmake, I assume it has been thoroughly tested,
> and I'm just missing something. Am I?

It's used not just by CMake, but also by CTest to run every test on all
the dashboard machines.  It's pretty well tested :)

Are you calling kwsysProcess_WaitForExit before getting the result?

Here is typical usage:

  kwsysProcess* kp = kwsysProcess_New();
  kwsysProcess_SetCommand(kp, cmd);
  kwsysProcess_Execute(kp);
  kwsysProcess_WaitForExit(kp, 0);
  switch(kwsysProcess_GetState(kp))
    {
    case kwsysProcess_State_Exited:
      {
      int retVal = kwsysProcess_GetExitValue(kp);
      } break;
    /* ... handle other cases ... */
    }
  kwsysProcess_Delete(kp);

FYI, once the process is detatched you cannot get the exit value because
the structure has dropped all references to the child.  It's meant for
starting daemons.

-Brad