I have no interest whatsoever in termination notifications - only in launch
notifications. Once I know my child process is, in fact, running and I have its
pid, I want the whole mess including the NSTask to go away. And as I mentioned
before, the entire thing has to complete within one-routine. This code runs in
a method which returns whether or not the child has been launched - so I can't
use the notifications which only come in after the main event loop has been run
later.
Erg
________________________________
From: Greg Guerin <glgue...@amug.org>
To: list-cocoa-dev <cocoa-dev@lists.apple.com>
Sent: Tuesday, June 9, 2009 9:43:51 AM
Subject: Re: [NSTask] -launch return
Erg Consultant wrote:
> [ launchTask launch ];
>
> // Wait 'til is running...
>
> while( ![ launchTask isRunning ] )
> {
> ; // Spin
> }
This approach seems misguided.
The docs for -launch say an NSInvalidArgumentException is raised if a new
process can't be created. So if you're not getting an
NSInvalidArgumentException, then logic suggests that the child process has been
launched.
Next, since NSTask is almost certainly using one of the Posix forking functions
to create the child process, then it's certain that if the process is created,
it has a process-id. So the whole premise of having to wait for another
condition in order to have a process-id is misguided.
Worse, the spin-loop could hang forever. That's because there's no guarantee
that the process hasn't terminated between -launch and -isRunning. It might
have terminated for a reason you didn't expect. You also don't know how the
scheduler will run things, so the parent process could be delayed in its
return, and/or the child could exit very quickly. Death by race condition in a
spin-lock.
Your code releases the NSTask after getting its pid. However, the docs for
NSTaskDidTerminateNotification in the NSTask reference say that the
notification won't be sent for a released task. It's unclear whether you
intend the NSTask to be long-lived or short-lived, or whether you expect to
receive this notification later.
-- GG
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