Add monitor command for running loops under a supervisor

Author: kovyrin

README.rdoc

@@ -75,6 +75,12 @@ This is it! To manage your loop, just run one of the following commands:
 
     $ ./script/loops start
 
+* To run all enabled non-disabled loops with logging mirrored to console (this method does not
+  create any pid files and never releases control of the terminal, so it is the perfect way of running
+  loops under the control of a supervisor like supervisord/runit/upstart/systemd):
+
+    $ ./script/loops monitor
+
 * To run all enabled loops in background:
 
     $ ./script/loops start -d
@@ -83,6 +89,10 @@ This is it! To manage your loop, just run one of the following commands:
 
     $ ./script/loops start hello_world -d
 
+* To run specific loop in foreground with logging mirrored to console:
+
+    $ ./script/loops monitor hello_world
+
 * To see all possible options:
 
     $ ./script/loops help

lib/loops/cli.rb

@@ -18,6 +18,7 @@ class CLI
     register_command :start
     register_command :stop
     register_command :stats
+    register_command :monitor
 
     # @return [Array<String>]
     #   The +Array+ of (unparsed) command-line options.

lib/loops/cli/options.rb

@@ -295,6 +295,10 @@ def start_engine!
     start                            Start all loops except ones marked with disabled:true in config
     start loop1 [loop2]              Start only loops specified
     stop                             Stop daemonized loops monitor
+    monitor                          Start and monitor all enabled loops
+                                     (use this with supervisord, runit, upstart or systemd)
+    monitor loop1 [loop2]            Start and monitor only loops specified
+                                     (use this with supervisord, runit, upstart or systemd)
     stats                            Print loops memory statistics
     debug loop                       Debug specified loop
     help                             Show this message

lib/loops/commands/monitor_command.rb

@@ -0,0 +1,14 @@
+class Loops::Commands::MonitorCommand < Loops::Command
+  def execute
+    # Mirror logging to console
+    Loops.logger.write_to_console = true
+
+    # Set process name
+    $0 = "loops monitor: #{options[:args].join(' ') rescue 'all'}\0"
+
+    # Start loops and let the monitor process take over
+    puts "Starting loops in monitor mode..."
+    engine.start_loops!(options[:args])
+    puts "Monitoring loop is finished, exiting now..."
+  end
+end

lib/loops/engine.rb

@@ -9,6 +9,7 @@ def initialize
     load_config
   end
 
+  #-------------------------------------------------------------------------------------------------
   def load_config
     # load and parse with erb
     raw_config = File.read(Loops.config_file)
@@ -25,11 +26,14 @@ def load_config
     Loops.logger.colorful_logs = @global_config['colorful_logs'] || @global_config['colourful_logs']
   end
 
+  #-------------------------------------------------------------------------------------------------
   def start_loops!(loops_to_start = [])
-    @running_loops = []
+    enabled_loops = []
+
+    # Initialize process manager
     @pm = Loops::ProcessManager.new(global_config, Loops.logger)
 
-    # Start all loops
+    # Start all enabled loops
     loops_config.each do |name, loop_config|
       # Do not load the loop if it is disabled
       next if loop_config['disabled']
@@ -44,22 +48,26 @@ def start_loops!(loops_to_start = [])
 
       # Start the loop
       start_loop(name, klass, loop_config)
-      @running_loops << name
+      enabled_loops << name
     end
 
     # Do not continue if there is nothing to run
-    if @running_loops.empty?
+    if enabled_loops.empty?
       puts 'WARNING: No loops to run! Exiting...'
       return
     end
 
-    # Start monitoring loop
+    # Set up signals to shut down when received an external signal to stop
     setup_signals
+
+    # Start process monitoring loop
     @pm.monitor_workers
 
+    # Done, exiting now
     info 'Loops are stopped now!'
   end
 
+  #-------------------------------------------------------------------------------------------------
   def debug_loop!(loop_name)
     @pm = Loops::ProcessManager.new(global_config, Loops.logger)
     loop_config = loops_config[loop_name] || {}