[AETHER-38] Moves T3 utils to ONOS utils
Change-Id: I8eebc7934df2018507742b187bb64ee9b425fca7
diff --git a/utils/misc/src/main/java/org/onlab/util/Generator.java b/utils/misc/src/main/java/org/onlab/util/Generator.java
new file mode 100644
index 0000000..223de5d
--- /dev/null
+++ b/utils/misc/src/main/java/org/onlab/util/Generator.java
@@ -0,0 +1,154 @@
+/*
+ * Copyright 2020-present Open Networking Foundation
+ *
+ * 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 org.onlab.util;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Generator class that yields instances of T type objects as soon as they are ready.
+ *
+ * @param <T> type of the object.
+ */
+public abstract class Generator<T> implements Iterable<T> {
+
+ private class Condition {
+ private boolean isSet;
+
+ synchronized void set() {
+ isSet = true;
+ notifyAll();
+ }
+
+ synchronized void await() throws InterruptedException {
+ try {
+
+ if (isSet) {
+ return;
+ }
+
+ while (!isSet) {
+ wait();
+ }
+ } finally {
+ isSet = false;
+ }
+ }
+ }
+
+ private static ThreadGroup threadGroup;
+
+ private Thread producer;
+ private boolean hasFinished;
+ private final Condition itemAvailableOrHasFinished = new Condition();
+ private final Condition itemRequested = new Condition();
+ private T nextItem;
+ private boolean nextItemAvailable;
+ private RuntimeException exceptionRaisedByProducer;
+
+ @Override
+ public Iterator<T> iterator() {
+ return new Iterator<T>() {
+ @Override
+ public boolean hasNext() {
+ return waitForNext();
+ }
+
+ @Override
+ public T next() {
+ if (!waitForNext()) {
+ throw new NoSuchElementException();
+ }
+ nextItemAvailable = false;
+ return nextItem;
+ }
+
+ @Override
+ public void remove() {
+ throw new UnsupportedOperationException();
+ }
+
+ private boolean waitForNext() {
+ if (nextItemAvailable) {
+ return true;
+ }
+ if (hasFinished) {
+ return false;
+ }
+ if (producer == null) {
+ startProducer();
+ }
+ itemRequested.set();
+ try {
+ itemAvailableOrHasFinished.await();
+ } catch (InterruptedException e) {
+ hasFinished = true;
+ producer.interrupt();
+ try {
+ producer.join();
+ } catch (InterruptedException e1) {
+ // Interrupting the broken thread
+ Thread.currentThread().interrupt();
+ throw new IllegalStateException(e1);
+ }
+ }
+ if (exceptionRaisedByProducer != null) {
+ throw exceptionRaisedByProducer;
+ }
+ return !hasFinished;
+ }
+ };
+ }
+
+ protected abstract void run() throws InterruptedException;
+
+ /**
+ * Makes available the next item.
+ *
+ * @param element the next item
+ * @throws InterruptedException if await fails
+ */
+ public void yield(T element) throws InterruptedException {
+ nextItem = element;
+ nextItemAvailable = true;
+ itemAvailableOrHasFinished.set();
+ itemRequested.await();
+ }
+
+ private void startProducer() {
+ assert producer == null;
+ synchronized (this) {
+ if (threadGroup == null) {
+ threadGroup = new ThreadGroup("onos-generator");
+ }
+ }
+ producer = new Thread(threadGroup, () -> {
+ try {
+ itemRequested.await();
+ Generator.this.run();
+ } catch (InterruptedException e) {
+ // Remaining steps in run() will shut down thread.
+ } catch (RuntimeException e) {
+ exceptionRaisedByProducer = e;
+ }
+ hasFinished = true;
+ itemAvailableOrHasFinished.set();
+ });
+ producer.setDaemon(true);
+ producer.start();
+ }
+}