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Tests passing means a good time to commit

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1 parent d9af5aa commit a0caf67d78f7805f20886956c1a6febd0443475f Jacob Harris committed Apr 13, 2010
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  1. +199 −18 LICENSE
  2. +19 −1 README.rdoc
  3. +4 −3 Rakefile
  4. +132 −0 lib/lifeline.rb
  5. +1 −0 test/helper.rb
  6. +100 −3 test/test_lifeline.rb
@@ -1,20 +1,201 @@
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@@ -1,6 +1,24 @@
= lifeline
-Description goes here.
+Methods for creating lifeline tasks. This allows you to write cron jobs that
+restart processes that die while ensuring the code is only executing only once
+(avoiding the duplication that sometimes happens using the 'daemons') gem.
+Both a generic lifeline method is provided as well as methods to create 3
+lifeline rake tasks for managing lifelines.
+== The Lifeline Approach
+== Examples
+ Lifeline.lifeline do
+ # some code you want to run in only a single process
+ end
+ Lifeline.define_lifeline_tasks("appname") do
+ # some code you want to run in a single lifeline
+ end
+ > rake -T appname
== Note on Patches/Pull Requests
@@ -6,12 +6,13 @@ begin do |gem| = "lifeline"
gem.summary = %Q{A cron-based alternative to running daemon scripts}
- gem.description = %Q{TODO: longer description of your gem}
+ gem.description = %Q{A cron-based alternative to running daemon scripts} = ""
gem.homepage = ""
- gem.authors = ["The New York Times"]
- gem.add_development_dependency "thoughtbot-shoulda", ">= 0"
+ gem.authors = ["Jacob Harris", "Ben Koski", "Matt Todd"]
+ gem.add_development_dependency "shoulda", ">= 0"
gem.add_development_dependency "yard", ">= 0"
+ gem.add_development_dependency "mocha", ">= 0"
# gem is a Gem::Specification... see for additional settings
@@ -0,0 +1,132 @@
+require 'rake'
+require 'rake/tasklib'
+module Lifeline
+ ##
+ # @private
+ def get_process_list
+ processes = %x{ps ax -o pid,command}
+ return nil if processes.nil?
+ processes.split(/\n/).map do |p|
+ if p =~ /^(\d+)\s(.+)$/
+ {:pid => $1.to_i, :command => $2.strip}
+ end
+ end.compact
+ end
+ ##
+ # A method for executing a block of code only if there is no other process with the same command running. This is useful if you want
+ # to have a perpetually running daemon that only executes once at a time. It uses the process name returned by ps ax to see if there is
+ # a process with the same command name but a different PID already executing. If so, it terminates without running the block. NOTE: since it
+ # uses the command name returned from <tt>ps ax</tt>, it us up to to you to name the process containing this code with a distinctly unique name. If two
+ # separate Rails projects both have a <tt>rake lifeline</tt> task they WILL interfere with each other. I'd suggest prefixing with the project name (ie,
+ # <tt>doc_viewer:lifeline</tt>) to be sure
+ #
+ # @param &block a block which is executed if there is not already a lifeline running.
+ # @raise [ArgumentError] if you do not pass in a block argument
+ def lifeline
+ if !block_given?
+ raise ArgumentError, "You must pass in a block to be the body of the run rake task"
+ end
+ my_pid = $$
+ processes = get_process_list
+ if processes.nil? || processes.empty?
+ raise "No processes being returned by get_process_list. Aborting!"
+ end
+ myself = processes.detect {|p| p[:pid] == my_pid}
+ if myself.nil?
+ raise "Unable to find self in process list. This is bizarre to say the least. Exiting"
+ end
+ # there isn't already another process running with the same command
+ if !processes.any? {|p| p[:pid] != my_pid && p[:command] == myself[:command]}
+ yield
+ end
+ end
+ # Define rake tasks for running, starting, and terminating
+ class LifelineRakeTask < ::Rake::TaskLib
+ # The namespace to define the tasks in
+ # @return [String] the namespace for the tasks
+ attr_accessor :namespace
+ ##
+ # Creates 3 new tasks for the lifeline in the namespace specified. These
+ # tasks are
+ # * run - a task for running the code provided in the block
+ # * lifeline - a lifeline task for running the run task if it's not already running
+ # * terminate - a task for terminating all lifelines.
+ #
+ # @param [String, Symbol] name the namespace of the rake tasks
+ # @param [optional, Hash] opts Additional options for the method
+ # @option opts [Array<String, Symbol>] :prereqs ([]) If there any any rake tasks that should be prerequisites of the :run task, specify them here (For Rails, you would do :prereqs => :environment)
+ # @param a block that defines the body of the run task
+ def initialize(namespace, opts={}, &block)
+ if !block_given?
+ raise ArgumentError, "You must pass in a block to be the body of the run rake task"
+ end
+ @namespace = namespace
+ define_run_task(opts, &block)
+ define_lifeline_task
+ define_terminate_task
+ end
+ protected
+ def run_task_name
+ "#{namespace}:run"
+ end
+ def define_run_task(opts={}, &block)
+ desc "Runs the #{namespace}:run task"
+ task_arg = if opts[:prereqs]
+ {run_task_name => opts[:prereqs]}
+ else
+ run_task_name
+ end
+ task(task_arg, &block)
+ end
+ def define_lifeline_task
+ desc "A lifeline task for executing only one process of #{namespace}:run at a time"
+ task("#{namespace}:lifeline") do
+ lifeline do
+ Rake::Task["#{namespace}:run"].invoke
+ end
+ end
+ end
+ def define_terminate_task
+ desc "Terminates any running #{namespace}:lifeline tasks"
+ task("#{namespace}:terminate") do
+ unless (process = %x{ps aux | grep "#{namespace}:lifeline" | grep ruby | grep -v grep}.chomp).empty?
+ runner_pid = process.gsub(/(\s+)/, ' ').split(' ')[1]
+ puts %x{kill -9 #{runner_pid}}
+ end
+ end
+ end
+ end
+ ##
+ # A method that defines 3 rake tasks for doing lifelines:
+ # * <tt>namespace:run</tt> runs the specified block
+ # * <tt>namespace:lifeline</tt> a lifeline for executing only a single copy of <tt>namespace:run</tt> at a time
+ # * <tt>namespace:terminate</tt> a task for terminating the lifelines
+ #
+ # @param [String,Symbol] namespace the namespace to define the 3 tasks in
+ # @param &block a block which defines the body of the namespace:run method
+ #
+ # @raise [ArgumentError] if you do not pass in a block argument
+ def define_lifeline_tasks(namespace, &block)
+, &block)
+ end
Oops, something went wrong. Retry.

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