I think either you or Stevens misunderstands something, and it certainly isn't Stevens.

First of all if you look at Run commands in parallel you will see a use of wait that I would support.

Now let us get at the misunderstanding. What you are quoting Stevens talking about is handling SIGCHILD signals. He is very much correct that you should not do that with wait. The right way to be careful is with waitpid. And indeed the problem is particularly bad in Perl.

I agree with all that.

But that is very different from saying that wait itself should be deprecated. Go back to the example I gave you. You see there that it is used carefully. Signals are not being used to track children, rather you are carefully launching children, keeping track of them, and matching children to reaped processes. So what if you block? The desired behaviour is to block!

But, you say, we should just use a signal handler, right?

Wrong.

Perl's signal handling is not very good. First of all while a signal is being handled, if you get a second one you can dump core. Oops. There are various times in normal operation when a signal can cause you to dump core. Double oops. And Perl's signal handling is based on SysV semantics - not BSD or POSIX.

So even while I agree with everything that Stevens wrote, it is irrelevant since I don't trust signals in Perl. When you don't trust signals then you have to step back and ask yourself, "Do I really want to block?" And if you do, then wait is probably just fine and dandy. When you are talking about signal handlers, it is not good. But for its little niche it is fine.

Now if you disagree with anything I just said, saying it here is the wrong thing to do. Instead get the current development version of Perl, download it, go into the documentation, and start submitting patches to p5p.

In reply to RE (tilly) 4: For all your forking needs.. by tilly
in thread For all your forking needs.. by reyjrar

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