[squeak-dev] OSProcess question

David T. Lewis lewis at mail.msen.com
Mon Mar 10 23:37:49 UTC 2008

On Mon, Mar 10, 2008 at 11:13:42AM -0700, Andreas Raab wrote:
> We have a situation where some code reliably locks up when used like here:
>  p := OSProcess command: 'chmod +x ', path.
>  [p isComplete] whileFalse.
> This hangs quite reliably in the second line and I'm *assuming* that we 
> need to yield/delay execution while waiting. Is this correct? I was 
> trying to trace through the code paths which update the runState but it 
> wasn't immediately clear where this comes from.

Hi Andreas,

Yes, you should add a delay in the loop, or use this (which adds the
delay for you):

  p := OSProcess waitForCommand: 'chmod +x ', path

The run state of an external OS process is updated by a separate Squeak
process (evaluate "OSProcess accessor grimReaperProcess"), so you need
to wait for the grimReaperProcess to react to the external process
exit notification. On Unix, this is a SIGCHLD, which is caught by OSPP,
which sends #signalSemaphoreWithIndex:, which wakes up the grimReaperProcess,
which calls #primitiveReapChildProcess to clean up and obtain the child
exit status. After all of this has happened, #isComplete will answer

BTW, you can receive direct notification of a change in run state for
an external OS process (ExternalOSProcess>>update:), but this executes
in the context of the grimReaperProcess, so use this with care.


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