Module Terminator
In: lib/terminator.rb

Terminator

Synopsis

An external timeout mechanism based on processes and signals. Safe for system calls. Safe for minors. but not very safe for misbehaving, downtrodden zombied out processes.

Description

Terminator is a solution to the problem of ‘how am I meant to kill a system call in Ruby!?’

Ruby (at least MRI) uses green threads to "multitask". This means that there is really only ever one ruby process running which then splits up it‘s processor time between all of it‘s threads internally.

The processor then only has to deal with one ruby process and the ruby process deals with all it‘s threads. There are pros and cons to this method, but that is not the point of this library.

The point is, that if you make a system call to an external resource from ruby, then the kernel will go and make that call for ruby and NOT COME BACK to ruby until that system call completes or fails. This can take a very long time and is why your feeble attempts at using ruby‘s internal "Timeout" command has failed miserably at timing out your external web service, database or network connections.

You see, Ruby just doesn‘t get a chance to do anything as the kernel goes "I‘m not going to talk to you again until your system calls complete". Sort of a no win situation for Ruby.

That‘s where Terminator comes in. Like Arnie, he will come back. No matter what, and complete his mission, unless he gets aborted before his timeout, you can trust Terminator to thoroughly and without remorse, nuke your misbehaving and timing out ruby processes efficiently, and quickly.

How it Works

Basically we create a new terminator ruby process, separate to the existing running ruby process that has a simple command of sleep for x seconds, and then do a process TERM on the PID of the original ruby process that created it.

If your process finishes before the timeout, it will kill the Terminator first.

So really it is a race of who is going to win?

Word of warning though. Terminator is not subtle. Don‘t expect it to split hairs. Trying to give a process that takes about 1 second to complete, a 2 second terminator… well… odds are 50/50 on who is going to make it.

If you have a 1 second process, give it 3 seconds to complete. Arnie doesn‘t much care for casualties of war.

Another word of warning, if using Terminator inside a loop, it is possible to exceed your open file limit. I have safely tested looping 1000 times

URIS

Usage

The terminator library is simple to use.

 require 'terminator'
 Terminator.terminate(1) do
   sleep 4
   puts("I will never print")
 end
 #=> Terminator::Error: Timeout out after 1s

The above code snippet will raise a Terminator::Error as the terminator‘s timeout is 2 seconds and the block will take at least 4 to complete.

You can put error handling in with a simple begin / rescue block:

 require 'terminator'
 begin
   Terminator.terminate(1) do
     sleep 4
     puts("I will never print")
   end
 rescue
   puts("I got terminated, but rescued myself.")
 end
 #=> I got terminated, but rescued myself.

The standard action on termination is to raise a Terminator::Error, however, this is just an anonymous object that is called, so you can pass your own trap handling by giving the terminator a lambda as an argument.

 require 'terminator'
 custom_trap = lambda { eval("raise(RuntimeError, 'Oops... I failed...')") }
 Terminator.terminate(:seconds => 1, :trap => custom_trap) do
   sleep 10
 end
 #=> RuntimeError: (eval):1:in `irb_binding': Oops... I failed...

Methods

terminate  

Classes and Modules

Class Terminator::Error

Constants

Version = '0.4.4'

Public Instance methods

Terminator.terminate has two ways you can call it. You can either just specify:

 Terminator.terminate(seconds) { code_to_execute }

where seconds is an integer number greater than or equal to 1. If you pass a float in on seconds, Terminator will call to_i on it and convert it to an integer. This is because Terminator is not a precise tool, due to it calling a new ruby instance, and spawning a new process, relying on split second accuracy is a folly.

If you want to pass in the block, please use:

 Terminator.terminate(:seconds => seconds, :trap => block) { code_to_execute }

Where block is an anonymous method that gets called when the timeout occurs.

[Validate]