--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/java/suikwasha/distributedalgorithm/simulator/Synchronizer.java	Fri Oct 19 00:05:41 2012 +0900
@@ -0,0 +1,48 @@
+package suikwasha.distributedalgorithm.simulator;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class Synchronizer
+{
+	private AtomicLong counter;
+	private CountDownLatch latch;
+	
+	public Synchronizer()
+	{
+		counter = new AtomicLong();
+		latch = new CountDownLatch(1);
+	}
+	
+	public long countup() throws IllegalStateException
+	{
+		// double checking , is it effective?
+		if(latch.getCount() != 0){
+			long value = counter.incrementAndGet();
+			if(latch.getCount() != 0){
+				return value;
+			}
+		}
+		
+		throw new IllegalStateException("latch.getCount() == 0");
+	}
+	
+	public long countdown() throws IllegalStateException
+	{
+		long value = counter.decrementAndGet();
+		if(value < 0){
+			throw new IllegalStateException("counter < 0");
+		}
+		
+		if(value == 0){
+			latch.countDown();
+		}
+		
+		return value;
+	}
+	
+	public void await() throws InterruptedException
+	{
+		latch.await();
+	}
+}