Re: Re: Taming multiple external processes

Ah... the $pid assignment did get frobbed. After re-adding that, your example works fine. But applying it to my task fails. The server process appears to hang on the open2 call. The child process is started, according to ps, but never starts reading input (according to its STDERR output). When I kill the open() process, the whole server dies with open2: close(main::PIPE) failed: at ./testserver3 line 30, which seems to say that the PIPE handle couldn't be closed in the parent.

This is somewhat frustrating.

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Re: Re: Re: Taming multiple external processes by tilly (Archbishop) on Jan 02, 2004 at 15:56 UTC
You may have copied part of it slightly wrong. When I used a local variable and a named string in open2, it really was important that I did so. If you read the documentation for IPC::Open2 you'll see that I'm trying to get Perl to dup the filehandle directly. That is important because a close will fail there because your first process already has unread data that it wants PIPE to read before it exits. If that isn't the problem, then you should make your own private copy of IPC::Open3, be sure that you are loading that version (eg with a use lib), and then start inserting debugging statements to figure out where and when it is doing the close. Also I will warn you. Depending on how app1 is coded, figuring out how to kill it might not work for you. After all when it forks, its kids might be talking to their STDOUT, which means that the second process in the pipeline is still being talked to. And if the kids ignore the signal when dad dies... Another thing to re-check. Does app1 really talk on STDOUT? If it talks on STDERR, or changes its behaviour when it finds itself not on a terminal, it could be very confusing. The output of `app1 arguments here \| cat 2> /dev/null` at the shell might be revealing. (That calls it with output hooked to a pipe, and hides STDERR.)	[reply] [d/l]
Re: Re: Re: Re: Taming multiple external processes by 87C751 (Acolyte) on Jan 02, 2004 at 20:25 UTC
It appears that the manner in which app1 is coded may be the culprit. If I change from a network stream to a local file as input, the problem disappears, and even the simple `open(FH,"app1 args \| app2 args \|");` form works as expected (all children and the enclosing shell are killed when I close FH). Thus I'm off to visit app1's source. Many thanks for the guidance.	[reply] [d/l]