Extract formula locks into a class

Library/Homebrew/formula.rb

@@ -1,6 +1,7 @@
 require 'download_strategy'
 require 'dependency_collector'
 require 'formula_support'
+require 'formula_lock'
 require 'hardware'
 require 'bottles'
 require 'patches'
@@ -241,19 +242,12 @@ class Formula
   end
 
   def lock
-    HOMEBREW_CACHE_FORMULA.mkpath
-    lockpath = HOMEBREW_CACHE_FORMULA/"#{@name}.brewing"
-    @lockfile = lockpath.open(File::RDWR | File::CREAT)
-    unless @lockfile.flock(File::LOCK_EX | File::LOCK_NB)
-      raise OperationInProgressError, @name
-    end
+    @lock = FormulaLock.new(name)
+    @lock.lock
   end
 
   def unlock
-    unless @lockfile.nil?
-      @lockfile.flock(File::LOCK_UN)
-      @lockfile.close
-    end
+    @lock.unlock unless @lock.nil?
   end
 
   def == b

Library/Homebrew/formula_lock.rb

@@ -0,0 +1,40 @@
+class FormulaLock
+  LOCKDIR = HOMEBREW_CACHE_FORMULA
+
+  def initialize(name)
+    @name = name
+    @path = LOCKDIR.join("#{@name}.brewing")
+  end
+
+  def lock
+    LOCKDIR.mkpath
+    @lockfile = get_or_create_lockfile
+    unless @lockfile.flock(File::LOCK_EX | File::LOCK_NB)
+      raise OperationInProgressError, @name
+    end
+  end
+
+  def unlock
+    unless @lockfile.nil? || @lockfile.closed?
+      @lockfile.flock(File::LOCK_UN)
+      @lockfile.close
+    end
+  end
+
+  def with_lock
+    lock
+    yield
+  ensure
+    unlock
+  end
+
+  private
+
+  def get_or_create_lockfile
+    if @lockfile.nil? || @lockfile.closed?
+      @path.open(File::RDWR | File::CREAT)
+    else
+      @lockfile
+    end
+  end
+end

Library/Homebrew/keg.rb

@@ -1,4 +1,5 @@
 require 'extend/pathname'
+require 'formula_lock'
 
 class Keg < Pathname
   def initialize path
@@ -62,18 +63,7 @@ class Keg < Pathname
   end
 
   def lock
-    HOMEBREW_CACHE_FORMULA.mkpath
-    path = HOMEBREW_CACHE_FORMULA/"#{fname}.brewing"
-    file = path.open(File::RDWR | File::CREAT)
-    unless file.flock(File::LOCK_EX | File::LOCK_NB)
-      raise OperationInProgressError, fname
-    end
-    yield
-  ensure
-    unless file.nil?
-      file.flock(File::LOCK_UN)
-      file.close
-    end
+    FormulaLock.new(fname).with_lock { yield }
   end
 
   def linked_keg_record

Library/Homebrew/test/test_formula_lock.rb

@@ -0,0 +1,21 @@
+require 'testing_env'
+require 'formula_lock'
+
+class FormulaLockTests < Test::Unit::TestCase
+  def setup
+    @lock = FormulaLock.new("foo")
+    @lock.lock
+  end
+
+  def teardown
+    @lock.unlock
+  end
+
+  def test_locking_file_with_existing_lock_raises_error
+    assert_raises(OperationInProgressError) { FormulaLock.new("foo").lock }
+  end
+
+  def test_locking_existing_lock_suceeds
+    assert_nothing_raised { @lock.lock }
+  end
+end