somic · December 3, 2008 17:46 · Dec 3, 2008
diff --git a/forking_supervisor.rb b/forking_supervisor.rb
@@ -0,0 +1,78 @@
+#!/usr/bin/env ruby
+#
+# forking supervisor - forks workers and replaces dead workers.
+# start it in one console, send signals to it from another console.
+#
+
+require 'rubygems'
+require 'daemons/daemonize'
+
+
+def logit(msg)
+  if $worker
+    puts "#{Time.now} worker[#{$$}] #{msg}"
+  else
+    puts "#{Time.now} supervisor[#{$$}] #{msg}"
+  end
+end
+
+def myworker
+  # this is your worker, it does something useful
+  loop {
+    logit "ping"
+    sleep 20
+  }
+end
+
+def start_worker_daemon
+  p = Process.fork { $worker = true; myworker }
+  logit "started worker pid=#{p}"
+  p
+end
+
+
+if __FILE__ == $0
+    # starts supervisor
+    Daemonize.daemonize(logfile_name="/tmp/my.log", app_name="foo") if
+      ARGV[0] == '-d'   # do you want supervisor as a daemon?
+
+    logit "started"
+    pids = Array.new
+    workers = 3     # how many workers would you like today?
+    logit "workers = #{workers}"
+    $shutdown = false
+
+    Signal.trap("TERM") {
+      $shutdown = true
+      if $worker
+        # can do some worker cleanup here
+        logit "Caught SIGTERM. Exiting."
+      else
+        logit "caught SIGTERM. Signaling child processes: #{pids.inspect}"
+        pids.each { |pid|
+          logit "sending SIGTERM to pid=#{pid}"
+          Process.kill('TERM', pid)
+          Process.waitpid(pid)
+          logit "pid=#{pid} died."
+        }
+        logit "All child processes died."
+        # can do some supervisor cleanup here
+      end
+      exit
+    }
+
+    Signal.trap('CLD') {
+      unless $shutdown
+        pids.delete(Process.wait)
+        pids << start_worker_daemon
+      end
+    }
+
+    while pids.size < workers
+      pids << start_worker_daemon
+    end
+
+    loop { sleep 0x1000000 } rescue exit
+
+end
+