From: Gregory Colvin (gregory.colvin_at_[hidden])
Date: 2004-06-22 22:11:43
On Jun 22, 2004, at 4:31 PM, Stefan Seefeld wrote:
> Gregory Colvin wrote:
>> Normally you don't want to leak resources, which may or may not
>> zombies. And even if zombies are involved, reclaiming them need not
>> require a signal handler, which was my original point.
> oh ? Any call to fork()
On systems that have fork().
> should be accompagnied by a call to wait()
> (or one of its cousins such as 'waitpid()').
On systems that have wait().
> The only question is whether
> that has to happen synchronously or asynchronously.
And that question could be answered by the process library, or left
to the user.
> Calling 'wait()' synchronously basically means to block right after
> has been called untill the child process terminates. One technique that
> uses this approach is to detach the subprocess, i.e. to fork twice,
> and while
> the grand-child carries out the actual task, the child finishes
Which won't work if the parent cares about the child's exit() value?
> The much more frequent situation is to call it asynchronously, i.e.
> the call
> would be either executed from inside the SIGCHLD handler or somehow
> by it (such as a semaphore, which is reentrant).
Which was the implementation Angus first suggested, which a few of
us pointed out was unsafe as written. I meant to suggest the choice
could be left to the user.
You can also avoid blocking with a separate thread to do the wait(),
or by calling waitpid() with WNOHANG in a polling loop.
> Do I miss something ?
No, I think we agree on what the possibilities are for Posix.
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