Make assets watchers run as singletons

CHANGELOG.rst

@@ -5,6 +5,11 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+Common: Make asset watchers run as singletons (so they won't start if the
+watcher is already running in another shell).
+
+Common: Make rake provide better error messages if packages are missing.
+
 Common: Repairs development documentation generation by sphinx.
 
 LMS: Problem rescoring.  Added options on the Grades tab of the

Gemfile

@@ -4,3 +4,4 @@ gem 'sass', '3.1.15'
 gem 'bourbon', '~> 1.3.6'
 gem 'colorize', '~> 0.5.8'
 gem 'launchy', '~> 2.1.2'
+gem 'sys-proctable', '~> 0.9.3'

rakefile

@@ -1,9 +1,11 @@
-require 'json'
-require 'rake/clean'
-require './rakefiles/helpers.rb'
-
-Dir['rakefiles/*.rake'].each do |rakefile|
-    import rakefile
+begin
+    require 'json'
+    require 'rake/clean'
+    require './rakelib/helpers.rb'
+rescue LoadError => error
+    puts "Import faild (#{error})"
+    puts "Please run `bundle install` to bootstrap ruby dependencies"
+    exit 1
 end
 
 # Build Constants

rakefiles/assets.rake → rakelib/assets.rake

@@ -55,8 +55,9 @@ def sass_cmd(watch=false, debug=false)
           "#{watch ? '--watch' : '--update'} -E utf-8 #{sass_watch_paths.join(' ')}"
 end
 
+# This task takes arguments purely to pass them via dependencies to the preprocess task
 desc "Compile all assets"
-multitask :assets => 'assets:all'
+task :assets, [:system, :env] => 'assets:all'
 
 namespace :assets do
 
@@ -80,8 +81,9 @@ namespace :assets do
     {:xmodule => [:install_python_prereqs],
      :coffee => [:install_node_prereqs, :'assets:coffee:clobber'],
      :sass => [:install_ruby_prereqs, :preprocess]}.each_pair do |asset_type, prereq_tasks|
+        # This task takes arguments purely to pass them via dependencies to the preprocess task
         desc "Compile all #{asset_type} assets"
-        task asset_type => prereq_tasks do
+        task asset_type, [:system, :env] => prereq_tasks do |t, args|
             cmd = send(asset_type.to_s + "_cmd", watch=false, debug=false)
             if cmd.kind_of?(Array)
                 cmd.each {|c| sh(c)}
@@ -90,7 +92,8 @@ namespace :assets do
             end
         end
 
-        multitask :all => asset_type
+        # This task takes arguments purely to pass them via dependencies to the preprocess task
+        multitask :all, [:system, :env] => asset_type
         multitask :debug => "assets:#{asset_type}:debug"
         multitask :_watch => "assets:#{asset_type}:_watch"
 
@@ -111,9 +114,9 @@ namespace :assets do
             task :_watch => (prereq_tasks + ["assets:#{asset_type}:debug"]) do
                 cmd = send(asset_type.to_s + "_cmd", watch=true, debug=true)
                 if cmd.kind_of?(Array)
-                    cmd.each {|c| background_process(c)}
+                    cmd.each {|c| singleton_process(c)}
                 else
-                    background_process(cmd)
+                    singleton_process(cmd)
                 end
             end
         end

rakefiles/helpers.rb → rakelib/helpers.rb

@@ -1,4 +1,6 @@
 require 'digest/md5'
+require 'sys/proctable'
+require 'colorize'
 
 def find_executable(exec)
     path = %x(which #{exec}).strip
@@ -84,6 +86,16 @@ def background_process(*command)
     end
 end
 
+# Runs a command as a background process, as long as no other processes
+# tagged with the same tag are running
+def singleton_process(*command)
+    if Sys::ProcTable.ps.select {|proc| proc.cmdline.include?(command.join(' '))}.empty?
+        background_process(*command)
+    else
+        puts "Process '#{command.join(' ')} already running, skipping".blue
+    end
+end
+
 def environments(system)
     Dir["#{system}/envs/**/*.py"].select{|file| ! (/__init__.py$/ =~ file)}.map do |env_file|
         env_file.gsub("#{system}/envs/", '').gsub(/\.py/, '').gsub('/', '.')

rakefiles/prereqs.rake → rakelib/prereqs.rake

@@ -1,5 +1,3 @@
-require './rakefiles/helpers.rb'
-
 PREREQS_MD5_DIR = ENV["PREREQ_CACHE_DIR"] || File.join(REPO_ROOT, '.prereqs_cache')
 
 CLOBBER.include(PREREQS_MD5_DIR)