waitgroup

lib/channel/waitgroup.rb

@@ -0,0 +1,38 @@
+class WaitGroup
+  def initialize
+    @mutex = Mutex.new
+    @count = 0
+    @waiting = []
+  end
+
+  def add(count)
+    sync! { @count += count }
+  end
+
+  def done
+    sync! do
+      fail 'negative count' if done?
+      @count -= 1
+      wake!
+    end
+  end
+
+  private def done?
+    @count == 0
+  end
+
+  def wait
+    sync! do
+      @waiting << Thread.current
+      @mutex.sleep until done?
+    end
+  end
+
+  private def wake!
+    @waiting.each { |t| t.wakeup if t.alive? }
+  end
+
+  private def sync!(&block)
+    @mutex.synchronize(&block)
+  end
+end