Bulletproofing Servers

perlknight has asked for the wisdom of the Perl Monks concerning the following question:

All I am reading Network Programming with Perl by Lincoln Stein. I am having trouble on page 443, "Handling HUP and other Signals", here's a snip of the code which I am having trouble with,

sub reap_child {
   while ( (my $child = waitpid(-1,WHNOHANG)) > 0) {
      $CHILDREN{$child}->($child) if ref $CHILDREN{$child} eq 'CODE';
      delete $CHILDREN{$child};
   }
}
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what's does this line do, $CHILDREN{$child}->($child) if ref $CHILDREN{$child} eq 'CODE'? Is it saying $CHILDREN{$child} = $child if ref $CHILDREN{$child} eq 'CODE'? What does the value 'CODE' means?

sub kill_children {
   kill TERM => keys %CHILDREN;
   sleep while %CHILDREN;
}
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what does </code>"kill TERM => keys %CHILDREN;"</code> mean? Send a Kill TERM signal to all children pid? Not use to seing "TERM => (value ... values + n". Thanks.

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Re: Bulletproofing Servers by jwest (Friar) on Jul 19, 2002 at 19:24 UTC
To your first question, it means: If the value of the hash %CHILDREN at key $child is a reference to a block of 'CODE' (a subroutine), then call that code reference with the value of $child as its first parameter. `kill TERM => keys %CHILDREN` is very much like you suspect. To be clearer, it could be written as: `kill('TERM', keys(%CHILDREN));` kill takes a signal as the first parameter, and a list of pids to send the signal to as the rest of its parameters. --jwest -><- -><- -><- -><- -><- All things are Perfect To every last Flaw And bound in accord With Eris's Law - HBT; The Book of Advice, 1:7	[reply] [d/l] [select]
Re: Bulletproofing Servers by talexb (Chancellor) on Jul 19, 2002 at 19:25 UTC
`if ref $CHILDREN{$child} eq 'CODE';` I believe this checks to see if the reference type of `$CHILDREN{$child}` is CODE -- that is, is it a coderef. `kill TERM => keys %CHILDREN;` Again, from the reference section of v3 of the Camel, `kill` takes a SIGNAL and a LIST. The `=>` is a substitue for a comma. ps I'm not crazy about the use of ALL CAPS variable names, but am I gonna argue with Lincoln Stein? --t. alex "Mud, mud, glorious mud. Nothing quite like it for cooling the blood!" --Michael Flanders and Donald Swann	[reply] [d/l] [select]