# Thread, external processes, and trap **URL:** \ **Category:** Ruby\ **Created:** [September 11, 2006, 5:55am UTC](https://www.ruby-forum.com/t/thread-external-processes-and-trap/68252 "2006-09-11T05:55:09Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![James\_Mills](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/d78d45/32.png) [@James\_Mills](https://www.ruby-forum.com/u/James_Mills)\ **Post date:** [September 11, 2006, 5:55am UTC](https://www.ruby-forum.com/t/thread-external-processes-and-trap/68252/1 "2006-09-11T05:55:09Z")
Hello list. I have what I hope is a simple newbie problem. I have a ruby program that is acting as a “controller” between a remote application and an external process. Basically the controller receives a command from the remote application, does some quick formatting, then connects to the remote process via an admin interface and sends the command. In order to ensure that I have an external process to send information to, I spawn it and watch it from within the ruby controller. I also want to keep an eye on it and re-spawn it if needed. So basically I used Thread.new twice. The first thread is the process “watcher” which spans the actual process thread. Once it does this, the watcher thread sleeps until the process thread exits. If the process does exit for some reason, the watcher thread will respawn it a configurable number of times. This actually works pretty good, in and of itself. The problem comes when I introduce a SIGINT trap in the main body of my code. The INT trap simply cleans up the running threads and exits. This also works fine by itself. The problem is when I try and use ^C to exit the program _after_ I’ve already respawned the process thread. Here are a few scenarios: 1. watcher and proc threads up and running with no respawns. ^C is pressed - App exits as expected 2. watcher and proc threads up and running. I kill the external process manually - The watcher thread catches the fact that the process thread is no longer running and respawns it 3. watcher and proc threads up and running. I kill the external process manually, and the watcher respawns it. I press ^C - The process thread is killed and the watcher catches and respawns it! The trap code is never executed!!! This problem has really frustrated me, and I hope the list can give me a hand. This is my first app using Threads, so go easy… Thanks, ~james ---
**Author:** ![James\_Mills](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/d78d45/32.png) [@James\_Mills](https://www.ruby-forum.com/u/James_Mills)\ **Post date:** [September 11, 2006, 7:41am UTC](https://www.ruby-forum.com/t/thread-external-processes-and-trap/68252/2 "2006-09-11T07:41:17Z")
James Mills wrote: > In order to ensure that I have an external process to send information > to, I spawn it and watch it from within the ruby controller. I also > want to keep an eye on it and re-spawn it if needed. So basically I > used Thread.new twice. The first thread is the process “watcher” > which spans the actual process thread. Once it does this, the watcher > thread sleeps until the process thread exits. If the process does > exit for some reason, the watcher thread will respawn it a > configurable number of times. > 1. watcher and proc threads up and running. I kill the external > process manually, and the watcher respawns it. I press ^C - The > process thread is killed and the watcher catches and respawns it! The > trap code is never executed!!! That’s probably because a) the trap block is executed in the context of the watcher thread and b) exit uses an exception to terminate the process: robert@fussel /cygdrive/c/Temp $ ruby -e ‘begin exit; rescue Exception =\> e; p e end’ #\ robert@fussel /cygdrive/c/Temp $ ruby -e ‘puts SystemExit.ancestors’ SystemExit Exception Object Kernel I guess you catch Exception in your watcher and not something more specific. You should probably either catch more selective or check the exception and act accordingly in your watcher thread. Kind regards ``` robert ```