Add lock to avoid builds running in parallel

When one build is running, we don't want a second one
to run as well as the two builds could step on each
other toes. This change adds a locking mechanism that
waits for the current build to finish before starting
the next build.

Gemfile

@@ -19,8 +19,9 @@ gem "server.rb", path: "./packages/ruby/server"
 
 ##
 # Everything else
-gem "ryo.rb", "~> 0.3", github: "0x1eef/ryo.rb", tag: "v0.3.0"
-gem "test-cmd.rb", "~> 0.3", github: "0x1eef/test-cmd.rb", tag: "v0.3.0"
+gem "ryo.rb", github: "0x1eef/ryo.rb", tag: "v0.3.0"
+gem "test-cmd.rb", github: "0x1eef/test-cmd.rb", tag: "v0.3.0"
+gem "lockf.rb", github: "0x1eef/lockf.rb", tag: "v0.12.0"
 gem "standard", "~> 1.24"
 gem "paint", "~> 2.3"
 gem "dotenv", "~> 2.8"

Gemfile.lock

@@ -1,3 +1,10 @@
+GIT
+  remote: https://github.com/0x1eef/lockf.rb.git
+  revision: fd79284a8d3af8562654742a23b39288a0e4e24f
+  tag: v0.12.0
+  specs:
+    lockf.rb (0.12.0)
+
 GIT
   remote: https://github.com/0x1eef/nanoc-gzip.rb.git
   revision: 3bb1719ad11d983a25945c1017df76aa2f6b8540
@@ -172,6 +179,7 @@ PLATFORMS
 DEPENDENCIES
   dotenv (~> 2.8)
   listen (~> 3.0)
+  lockf.rb!
   memoize (~> 1.3)
   nanoc (~> 4.12)
   nanoc-gzip.rb!
@@ -180,11 +188,11 @@ DEPENDENCIES
   paint (~> 2.3)
   rainpress (~> 1.0)
   rake
-  ryo.rb (~> 0.3)!
+  ryo.rb!
   sass (~> 3.7)
   server.rb!
   standard (~> 1.24)
-  test-cmd.rb (~> 0.3)!
+  test-cmd.rb!
 
 BUNDLED WITH
    2.4.10

tasks/nanoc.rake

@@ -1,34 +1,63 @@
 # frozen_string_literal: true
 
+require "fileutils"
+require "lockf"
 build_dir = Ryo.from(YAML.load_file("./nanoc.yaml")).output_dir
+lockp = File.join Dir.getwd, "tmp", "build.lock"
+FileUtils.touch(lockp)
+lockf = LockFile.new(lockp)
+
 namespace :nanoc do
   task :compile do
+    warn "[build] Acquire lock..."
+    lockf.lock
     ENV["SASS_PATH"] = "./src/css/"
     sh "bundle exec nanoc co"
+  rescue Interrupt
+    warn "SIGINT: exit"
+    exit
+  ensure
+    warn "[build] Release lock..."
+    lockf.release
   end
 
   task :clean do
+    warn "[build] Acquire lock..."
+    lockf.lock
     sh "rm -rf #{build_dir}"
+  ensure
+    warn "[build] Release lock..."
+    lockf.release
   end
 
   task :clean_css do
+    warn "[build] Acquire lock..."
+    lockf.lock
     cssdir = File.join(build_dir, "css")
-    if Dir.exist?(cssdir)
-      sh "rm -rf #{cssdir}"
-    end
+    sh "rm -rf #{cssdir}" if Dir.exist?(cssdir)
+  ensure
+    warn "[build] Release lock..."
+    lockf.release
   end
 
-  task watch: [:compile] do
+  task watch: ['build'] do
+    warn "[build] Acquire lock..."
+    lockf.lock
     require "listen"
     Listen.to File.join(Dir.getwd, "src"), force_polling: true do
       sh "rake build"
     end.start
     sleep
+  rescue Interrupt
+    warn "SIGINT: exit"
+    warn "[build] Release lock..."
+    lockf.release
+    exit
   end
 end
 
 desc "Build the website"
-task build: ["nanoc:clean_css", "nanoc:compile"]
+task build: ["nanoc:compile"]
 
 desc "Trigger a build when src/ is modified"
 task "build:watch" => "nanoc:watch"