File: README

# README

Path: | README
Last Update: | Wed Mar 03 05:48:31 -0700 2010

## Synopsis

System Timer, a timer based on underlying SIGALRM system timers, is a solution to Ruby processes which hang beyond the time limit when accessing external resources. This is useful when timeout.rb, which relies on green threads, does not work consistently.

More background on:

- ph7spot.com/articles/system_timer
- davidvollbracht.com/2008/6/2/30-days-of-teach-day-1-systemtimer

## Usage

      require 'systemtimer'

      SystemTimer.timeout_after(5) do

        # Something that should be interrupted if it takes too much time...
        # ... even if blocked on a system call!

      end

## Requirements

SystemTimer only works on UNIX platforms (Mac OS X, Linux, Solaris, BSD, …). You can install the gem on Microsoft Windows, but you will only get a convenience shell wrapping a simple call to timeout.rb under the cover.

## Install

        sudo gem install systemtimer

## Authors

- David Vollbracht <davidvollbracht.com>
- Philippe Hanrigou <ph7spot.com>

## Copyright

Copyright: | (C) 2008 David Vollbracht & Philippe Hanrigou

## Description

While deploying Rails application in production our team discovered that some web service call would not timeout way beyond their defined limit, progressively freezing our Mongrel cluster until we restarted the servers. A closer analysis revealed that the native thread in charge of of the web service call was never scheduled, "stucked" on the service call. As it turn out the timeout library bundled with Ruby 1.8 (MRI) relies on green-threads to perform its magic… so the magic had no chance to happen in this scenario.

Based on an original idea by Kurtis Seebaldt <kseebaldt.blogspot.com>, David Vollbracht and Philippe Hanrigou pair programmed an alternative implementation based on system timers (the `SIGALRM` POSIX signal): This design guarantees proper timeout behavior even when crossing-boundaries and accessing system/external resources. Special care has been taken to interfere as little as possible with other processes that might also rely on `SIGALRM`, in particular MySQL.

This implementation is not intended to be drop-in replacement to timeout.rb, just a way to wrap sensitive call to system resources.

You can find more details on SystemTimer and how to use it at ph7spot.com/articles/system_timer

## License

(The Ruby License)

Copyright: | (C) 2008 David Vollbracht & Philippe Hanrigou

SystemTimer is copyrighted free software by David Vollbracht and Philippe Hanrigou. You can redistribute it and/or modify it under either the terms of the GPL (see COPYING file), or the conditions below:

      1. You may make and give away verbatim copies of the source form of the
         software without restriction, provided that you duplicate all of the
         original copyright notices and associated disclaimers.

      2. You may modify your copy of the software in any way, provided that
         you do at least ONE of the following:

           a) place your modifications in the Public Domain or otherwise
              make them Freely Available, such as by posting said
              modifications to Usenet or an equivalent medium, or by allowing
                  the author to include your modifications in the software.

           b) use the modified software only within your corporation or
              organization.

           c) rename any non-standard executables so the names do not conflict
                  with standard executables, which must also be provided.

           d) make other distribution arrangements with the author.

      3. You may distribute the software in object code or executable
         form, provided that you do at least ONE of the following:

           a) distribute the executables and library files of the software,
              together with instructions (in the manual page or equivalent)
              on where to get the original distribution.

           b) accompany the distribution with the machine-readable source of
              the software.

           c) give non-standard executables non-standard names, with
              instructions on where to get the original software distribution.

           d) make other distribution arrangements with the author.

      4. You may modify and include the part of the software into any other
         software (possibly commercial).  But some files in the distribution
         are not written by the author, so that they are not under this terms.

         They are gc.c(partly), utils.c(partly), regex.[ch], st.[ch] and some
         files under the ./missing directory.  See each file for the copying
         condition.

      5. The scripts and library files supplied as input to or produced as
         output from the software do not automatically fall under the
         copyright of the software, but belong to whomever generated them,
         and may be sold commercially, and may be aggregated with this
         software.

      6. THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
         IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
         WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
         PURPOSE.

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