Thanks for giving me something to chew on. I modified your script to run some of these corner cases and everything seems to behave correctly. I'm confused however why your script correctly collects all children when my attempt killed the shell but not the badly behaved grandchild. My code was something like (it has since been deleted, single-threaded version): 

my $pid = open my $calc, '-|', "$command 2>&1" or die "Pipe failed on 
+open: $!\n";
local $SIG{ALRM} = sub {
    kill 9, $pid;
    die "Calculation call failed to return with $timeout seconds\n";
};
alarm $timeout;
local $/; # Slurp
my $content = <$calc>;
close $calc;
alarm 0;

[download]

Is there an obvious behavioral difference? I'm pretty sure this is very close to what I had between Re: killing a program called with system() if it takes too long? and Re^2: Killing children's of children.

In reply to Re^2: Handling badly behaved system calls in threads by kennethk
in thread Handling badly behaved system calls in threads by kennethk

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