Cache: change to a Singleton object so it is only loaded from disk once

lib/rscons.rb

@@ -23,7 +23,7 @@ module Rscons
 
   # Remove all generated files
   def self.clean
-    cache = Cache.new
+    cache = Cache.instance
     # remove all built files
     cache.targets.each do |target|
       FileUtils.rm_f(target)
@@ -35,7 +35,7 @@ module Rscons
         Dir.rmdir(directory) rescue nil
       end
     end
-    Cache.clear
+    cache.clear
   end
 
   # Return whether the given path is an absolute filesystem path or not

lib/rscons/cache.rb

@@ -2,6 +2,7 @@ require "digest/md5"
 require "fileutils"
 require "json"
 require "set"
+require "singleton"
 require "rscons/version"
 
 module Rscons
@@ -50,30 +51,25 @@ module Rscons
   #     },
   #   }
   class Cache
-    #### Constants
+    include Singleton
 
     # Name of the file to store cache information in
     CACHE_FILE = ".rsconscache"
 
-    #### Class Methods
-
-    # Remove the cache file
-    def self.clear
-      FileUtils.rm_f(CACHE_FILE)
-    end
-
-    #### Instance Methods
-
     # Create a Cache object and load in the previous contents from the cache
     # file.
     def initialize
-      @cache = JSON.load(File.read(CACHE_FILE)) rescue {}
+      initialize!
-      unless @cache.is_a?(Hash)
+    end
-        $stderr.puts "Warning: #{CACHE_FILE} was corrupt. Contents:\n#{@cache.inspect}"
+
-        @cache = {}
+    # Remove the cache file.
-      end
+    def clear
-      @cache["targets"] ||= {}
+      FileUtils.rm_f(CACHE_FILE)
-      @cache["directories"] ||= {}
+      initialize!
+    end
+
+    # Clear the cached file checksums.
+    def clear_checksum_cache!
       @lookup_checksums = {}
     end
 
@@ -194,9 +190,21 @@ module Rscons
       @cache["directories"].keys
     end
 
-    # Private Instance Methods
     private
 
+    # Create a Cache object and load in the previous contents from the cache
+    # file.
+    def initialize!
+      @cache = JSON.load(File.read(CACHE_FILE)) rescue {}
+      unless @cache.is_a?(Hash)
+        $stderr.puts "Warning: #{CACHE_FILE} was corrupt. Contents:\n#{@cache.inspect}"
+        @cache = {}
+      end
+      @cache["targets"] ||= {}
+      @cache["directories"] ||= {}
+      @lookup_checksums = {}
+    end
+
     # Return a file's checksum, or the previously calculated checksum for
     # the same file
     # @param file [String] The file name.

lib/rscons/environment.rb

@@ -172,7 +172,8 @@ module Rscons
     # called after the block returns.
     def process
       clean_target_paths!
-      cache = Cache.new
+      cache = Cache.instance
+      cache.clear_checksum_cache!
       targets_processed = {}
       process_target = proc do |target|
         targets_processed[target] ||= begin

spec/rscons/cache_spec.rb

@@ -5,14 +5,11 @@ module Rscons
     end
 
     def build_from(cache)
-      JSON.should_receive(:load).and_return(cache)
+      JSON.stub(:load) do
-      Cache.new
+        cache
-    end
+      end
-
+      Cache.instance.tap do |cache|
-    describe ".clear" do
+        cache.send(:initialize!)
-      it "removes the cache file" do
-        FileUtils.should_receive(:rm_f).with(Cache::CACHE_FILE)
-        Cache.clear
       end
     end
 
@@ -21,11 +18,21 @@ module Rscons
         it "prints a warning and defaults to an empty hash" do
           JSON.should_receive(:load).and_return("string")
           $stderr.should_receive(:puts).with(/Warning:.*was.corrupt/)
-          Cache.new.instance_variable_get(:@cache).is_a?(Hash).should be_true
+          c = Cache.instance
+          c.send(:initialize!)
+          c.instance_variable_get(:@cache).is_a?(Hash).should be_true
         end
       end
     end
 
+    describe "#clear" do
+      it "removes the cache file" do
+        FileUtils.should_receive(:rm_f).with(Cache::CACHE_FILE)
+        JSON.stub(:load) {{}}
+        Cache.instance.clear
+      end
+    end
+
     describe "#write" do
       it "should fill in 'version' and write to file" do
         cache = {}

spec/rscons/environment_spec.rb

@@ -140,7 +140,8 @@ module Rscons
         env.Program("a.out", "main.c")
 
         cache = "cache"
-        Cache.should_receive(:new).and_return(cache)
+        Cache.should_receive(:instance).and_return(cache)
+        cache.should_receive(:clear_checksum_cache!)
         env.should_receive(:run_builder).with(anything, "a.out", ["main.c"], cache, {}).and_return(true)
         cache.should_receive(:write)
 
@@ -153,7 +154,8 @@ module Rscons
         env.Object("main.o", "other.cc")
 
         cache = "cache"
-        Cache.should_receive(:new).and_return(cache)
+        Cache.should_receive(:instance).and_return(cache)
+        cache.should_receive(:clear_checksum_cache!)
         env.should_receive(:run_builder).with(anything, "main.o", ["other.cc"], cache, {}).and_return("main.o")
         env.should_receive(:run_builder).with(anything, "a.out", ["main.o"], cache, {}).and_return("a.out")
         cache.should_receive(:write)
@@ -167,7 +169,8 @@ module Rscons
         env.Object("main.o", "other.cc")
 
         cache = "cache"
-        Cache.should_receive(:new).and_return(cache)
+        Cache.should_receive(:instance).and_return(cache)
+        cache.should_receive(:clear_checksum_cache!)
         env.should_receive(:run_builder).with(anything, "main.o", ["other.cc"], cache, {}).and_return(false)
         cache.should_receive(:write)
 

spec/rscons_spec.rb

@@ -2,7 +2,7 @@ describe Rscons do
   describe ".clean" do
     it "removes all build targets and created directories" do
       cache = "cache"
-      Rscons::Cache.should_receive(:new).and_return(cache)
+      Rscons::Cache.should_receive(:instance).and_return(cache)
       cache.should_receive(:targets).and_return(["build/a.out", "build/main.o"])
       FileUtils.should_receive(:rm_f).with("build/a.out")
       FileUtils.should_receive(:rm_f).with("build/main.o")
@@ -18,7 +18,7 @@ describe Rscons do
       Dir.should_receive(:rmdir).with("build")
       File.should_receive(:directory?).with("other").and_return(true)
       Dir.should_receive(:entries).with("other").and_return([".", "..", "other.file"])
-      Rscons::Cache.should_receive(:clear)
+      cache.should_receive(:clear)
 
       Rscons.clean
     end