Replace Semaphore with AtomicInteger

Since we are only utilizing the non-blocking operations of Semaphore,
Its better to use AtomicInteger to avoid all the extra overhead.

Change-Id: I219b3b35468fe11ef5bf063f671b5f6415630a0c

src/main/java/com/googlesource/gerrit/plugins/quota/TaskQuotaWithPermits.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/quota/TaskQuotaWithPermits.java b/src/main/java/com/googlesource/gerrit/plugins/quota/TaskQuotaWithPermits.java
index 027ddcf..ea414ca 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/quota/TaskQuotaWithPermits.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/quota/TaskQuotaWithPermits.java
@@ -1,20 +1,25 @@
 package com.googlesource.gerrit.plugins.quota;
 
 import com.google.gerrit.server.git.WorkQueue;
-import java.util.concurrent.Semaphore;
+import java.util.concurrent.atomic.AtomicInteger;
 
 public abstract class TaskQuotaWithPermits implements TaskQuota {
-  protected final Semaphore permits;
+  protected final AtomicInteger permits;
 
   public TaskQuotaWithPermits(int maxPermits) {
-    this.permits = new Semaphore(maxPermits);
+    this.permits = new AtomicInteger(maxPermits);
   }
 
   public boolean isReadyToStart(WorkQueue.Task<?> task) {
-    return permits.tryAcquire();
+    if (permits.decrementAndGet() >= 0) {
+      return true;
+    }
+
+    permits.incrementAndGet();
+    return false;
   }
 
   public void onStop(WorkQueue.Task<?> task) {
-    permits.release();
+    permits.incrementAndGet();
   }
 }