1 files changed, 155 insertions, 0 deletions
diff --git a/lib/rake/thread_pool.rb b/lib/rake/thread_pool.rb
new file mode 100644
index 0000000000..983a67a514
--- /dev/null
+++ b/lib/rake/thread_pool.rb
@@ -0,0 +1,155 @@
+require 'thread'
+require 'set'
+
+require 'rake/promise'
+
+module Rake
+
+  class ThreadPool              # :nodoc: all
+
+    # Creates a ThreadPool object.
+    # The parameter is the size of the pool.
+    def initialize(thread_count)
+      @max_active_threads = [thread_count, 0].max
+      @threads = Set.new
+      @threads_mon = Monitor.new
+      @queue = Queue.new
+      @join_cond = @threads_mon.new_cond
+
+      @history_start_time = nil
+      @history = []
+      @history_mon = Monitor.new
+      @total_threads_in_play = 0
+    end
+
+    # Creates a future executed by the +ThreadPool+.
+    #
+    # The args are passed to the block when executing (similarly to
+    # <tt>Thread#new</tt>) The return value is an object representing
+    # a future which has been created and added to the queue in the
+    # pool. Sending <tt>#value</tt> to the object will sleep the
+    # current thread until the future is finished and will return the
+    # result (or raise an exception thrown from the future)
+    def future(*args, &block)
+      promise = Promise.new(args, &block)
+      promise.recorder = lambda { |*stats| stat(*stats) }
+
+      @queue.enq promise
+      stat :queued, :item_id => promise.object_id
+      start_thread
+      promise
+    end
+
+    # Waits until the queue of futures is empty and all threads have exited.
+    def join
+      @threads_mon.synchronize do
+        begin
+          stat :joining
+          @join_cond.wait unless @threads.empty?
+          stat :joined
+        rescue Exception => e
+          stat :joined
+          $stderr.puts e
+          $stderr.print "Queue contains #{@queue.size} items. Thread pool contains #{@threads.count} threads\n"
+          $stderr.print "Current Thread #{Thread.current} status = #{Thread.current.status}\n"
+          $stderr.puts e.backtrace.join("\n")
+          @threads.each do |t|
+            $stderr.print "Thread #{t} status = #{t.status}\n"
+            # 1.8 doesn't support Thread#backtrace
+            $stderr.puts t.backtrace.join("\n") if t.respond_to? :backtrace
+          end
+          raise e
+        end
+      end
+    end
+
+    # Enable the gathering of history events.
+    def gather_history          #:nodoc:
+      @history_start_time = Time.now if @history_start_time.nil?
+    end
+
+    # Return a array of history events for the thread pool.
+    #
+    # History gathering must be enabled to be able to see the events
+    # (see #gather_history). Best to call this when the job is
+    # complete (i.e. after ThreadPool#join is called).
+    def history                 # :nodoc:
+      @history_mon.synchronize { @history.dup }.
+        sort_by { |i| i[:time] }.
+        each { |i| i[:time] -= @history_start_time }
+    end
+
+    # Return a hash of always collected statistics for the thread pool.
+    def statistics              #  :nodoc:
+      {
+        :total_threads_in_play => @total_threads_in_play,
+        :max_active_threads => @max_active_threads,
+      }
+    end
+
+    private
+
+    # processes one item on the queue. Returns true if there was an
+    # item to process, false if there was no item
+    def process_queue_item      #:nodoc:
+      return false if @queue.empty?
+
+      # Even though we just asked if the queue was empty, it
+      # still could have had an item which by this statement
+      # is now gone. For this reason we pass true to Queue#deq
+      # because we will sleep indefinitely if it is empty.
+      promise = @queue.deq(true)
+      stat :dequeued, :item_id => promise.object_id
+      promise.work
+      return true
+
+      rescue ThreadError # this means the queue is empty
+      false
+    end
+
+    def start_thread # :nodoc:
+      @threads_mon.synchronize do
+        next unless @threads.count < @max_active_threads
+
+        t = Thread.new do
+          begin
+            while @threads.count <= @max_active_threads
+              break unless process_queue_item
+            end
+          ensure
+            @threads_mon.synchronize do
+              @threads.delete Thread.current
+              stat :ended, :thread_count => @threads.count
+              @join_cond.broadcast if @threads.empty?
+            end
+          end
+        end
+        @threads << t
+        stat :spawned, :new_thread => t.object_id, :thread_count => @threads.count
+        @total_threads_in_play = @threads.count if @threads.count > @total_threads_in_play
+      end
+    end
+
+    def stat(event, data=nil) # :nodoc:
+      return if @history_start_time.nil?
+      info = {
+        :event  => event,
+        :data   => data,
+        :time   => Time.now,
+        :thread => Thread.current.object_id,
+      }
+      @history_mon.synchronize { @history << info }
+    end
+
+    # for testing only
+
+    def __queue__ # :nodoc:
+      @queue
+    end
+
+    def __threads__ # :nodoc:
+      @threads.dup
+    end
+  end
+
+end