From 15f0b88446699bdeaffaf20c42bb31950b50aacc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kjetil=20=C3=98rbekk?= <kjetil.orbekk@gmail.com>
Date: Wed, 2 May 2012 12:52:21 +0200
Subject: Add CyclicCountDownLatch.
(You may not want to use this.)
---
.../java/com/orbekk/util/CyclicCountDownLatch.java | 88 ++++++++++++++++++++++
1 file changed, 88 insertions(+)
create mode 100644 same/src/main/java/com/orbekk/util/CyclicCountDownLatch.java
(limited to 'same/src/main')
diff --git a/same/src/main/java/com/orbekk/util/CyclicCountDownLatch.java b/same/src/main/java/com/orbekk/util/CyclicCountDownLatch.java
new file mode 100644
index 0000000..a7ce7c4
--- /dev/null
+++ b/same/src/main/java/com/orbekk/util/CyclicCountDownLatch.java
@@ -0,0 +1,88 @@
+/**
+ * Copyright 2012 Kjetil Ørbekk <kjetil.orbekk@gmail.com>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.orbekk.util;
+
+import java.util.concurrent.locks.AbstractQueuedSynchronizer;
+
+/** This class provides something of a cyclic version of a CountDownLatch.
+ *
+ * The latch resets when await() completes. It may ignore calls to countDown()
+ * that occur before await() returns (it is not accumulative).
+ *
+ * Use this class with caution.
+ */
+public class CyclicCountDownLatch {
+ private static class Sync extends AbstractQueuedSynchronizer {
+ final int count;
+
+ public Sync(int count) {
+ this.count = count;
+ setState(count);
+ }
+
+ @Override protected boolean tryReleaseShared(int unused) {
+ boolean success = false;
+ while (!success) {
+ int expect = getState();
+ int update = Math.max(expect - 1, 0);
+ success = compareAndSetState(expect, update);
+ }
+ return getState() <= 0;
+ }
+
+ @Override protected int tryAcquireShared(int unused) {
+ boolean success = false;
+ while (!success) {
+ int expect = getState();
+ if (expect > 0) {
+ break;
+ }
+ int update = count;
+ success = compareAndSetState(expect, update);
+ }
+
+ if (success) {
+ // Non-exclusive success. Other threads may attempt to acquire.
+ return 1;
+ } else {
+ // Failure.
+ return -1;
+ }
+ }
+
+ public int getCount() {
+ return getState();
+ }
+ }
+
+ private final Sync sync;
+
+ public CyclicCountDownLatch(int count) {
+ sync = new Sync(count);
+ }
+
+ public void await() throws InterruptedException {
+ sync.acquireSharedInterruptibly(-1);
+ }
+
+ public void countDown() {
+ sync.releaseShared(-1);
+ }
+
+ public int getCount() {
+ return sync.getCount();
+ }
+}
--
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