heartbeat

heartbeat.rb

# we're using the TmpIO class
# -*- encoding: binary -*-
# :stopdoc:
require 'tmpdir'
# some versions of Ruby had a broken Tempfile which didn't work
# well with unlinked files.  This one is much shorter, easier
# to understand, and slightly faster.
class TmpIO < File

  # creates and returns a new File object.  The File is unlinked
  # immediately, switched to binary mode, and userspace output
  # buffering is disabled
  def self.new
    fp = begin
      super("#{Dir::tmpdir}/#{rand}", RDWR|CREAT|EXCL, 0600)
    rescue Errno::EEXIST
      retry
    end
    unlink(fp.path)
    fp.binmode
    fp.sync = true
    fp
  end

  # for easier env["rack.input"] compatibility with Rack <= 1.1
  def size
    stat.size
  end unless File.method_defined?(:size)
end
# end

#
# EXAMPLE
#
# usage :  worker = Worker.new(worker_nr, Unicorn::TmpIO.new)
# p TmpIO.new
# p TmpIO.new

#
# Worker class
# 
class Worker < Struct.new(:nr, :tmp, :switched)
  # worker objects may be compared to just plain Integers
  def ==(other_nr) # :nodoc:
    nr == other_nr
  end  
end

#
# EXAMPLE
#
# we create some workers
w1 = Worker.new 1, TmpIO.new
w2 = Worker.new 2, TmpIO.new

# The chmod will use either ‘1’ or ‘0’ each time this gets executed.
# (Assign ‘0’ to the local variable ‘m’, compare it to ‘0’. If it matches (m == 0), m = 1, otherwise m = 0. 
# A one line toggle.)

# this one should be stale
p w1.tmp.chmod(m = 0 == m ? 1 : 0)
sleep 5
# this one should be ok
p w2.tmp.chmod(m = 0 == m ? 1 : 0)

WORKERS = []
WORKERS << w1
WORKERS << w2

# Here’s what the master does to check the worker’s status
# Even though the file is unlinked it still has metadata associated with it. 
# Using the file’s #ctime we can check when the file was last mode changed, 
# and thus when the worker was last alive.
timeout = 3
WORKERS.each do |worker|
  stat = worker.tmp.stat
  unless (diff = (Time.now - stat.ctime)) <= timeout
    p "Worker #{worker.nr} has gone stale and needs to be respawned"
  else
    p "Worker #{worker.nr} is not stale"
  end
end