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Parallel programming on the go
/*
* 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.github.dm.jrt.runner;
import com.github.dm.jrt.util.WeakIdentityHashMap;
import org.jetbrains.annotations.NotNull;
import java.lang.ref.WeakReference;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.concurrent.TimeUnit;
/**
* Runner implementation throttling the number of running executions so to keep it under a specified
* limit.
*
* Created by davide-maestroni on 07/18/2015.
*/
class ThrottlingRunner implements Runner {
private final WeakIdentityHashMap> mExecutions =
new WeakIdentityHashMap>();
private final int mMaxRunning;
private final Object mMutex = new Object();
private final LinkedList mQueue = new LinkedList();
private final Runner mRunner;
private int mRunningCount;
/**
* Constructor.
*
* @param wrapped the wrapped instance.
* @param maxExecutions the maximum number of running executions.
* @throws java.lang.IllegalArgumentException if the specified max number is less than 1.
*/
@SuppressWarnings("ConstantConditions")
ThrottlingRunner(@NotNull final Runner wrapped, final int maxExecutions) {
if (wrapped == null) {
throw new NullPointerException("the wrapped runner must not be null");
}
if (maxExecutions < 1) {
throw new IllegalArgumentException(
"the maximum number of running executions must be at least 1, while it was: "
+ maxExecutions);
}
mRunner = wrapped;
mMaxRunning = maxExecutions;
}
public void cancel(@NotNull final Execution execution) {
ThrottlingExecution throttlingExecution = null;
synchronized (mMutex) {
final Iterator iterator = mQueue.iterator();
while (iterator.hasNext()) {
final PendingExecution pendingExecution = iterator.next();
if (pendingExecution.mExecution == execution) {
iterator.remove();
}
}
final WeakReference executionReference =
mExecutions.get(execution);
if (executionReference != null) {
throttlingExecution = executionReference.get();
}
}
if (throttlingExecution != null) {
mRunner.cancel(throttlingExecution);
}
}
public boolean isExecutionThread() {
return mRunner.isExecutionThread();
}
public void run(@NotNull final Execution execution, final long delay,
@NotNull final TimeUnit timeUnit) {
ThrottlingExecution throttlingExecution = null;
synchronized (mMutex) {
final LinkedList queue = mQueue;
if ((mRunningCount + queue.size()) >= mMaxRunning) {
queue.add(new PendingExecution(execution, delay, timeUnit));
} else {
throttlingExecution = getThrottlingExecution(execution);
}
}
if (throttlingExecution != null) {
mRunner.run(throttlingExecution, delay, timeUnit);
}
}
@NotNull
private ThrottlingExecution getThrottlingExecution(@NotNull final Execution execution) {
final WeakReference executionReference = mExecutions.get(execution);
ThrottlingExecution throttlingExecution =
(executionReference != null) ? executionReference.get() : null;
if (throttlingExecution == null) {
throttlingExecution = new ThrottlingExecution(execution);
if (execution.mayBeCanceled()) {
mExecutions.put(execution,
new WeakReference(throttlingExecution));
}
}
return throttlingExecution;
}
/**
* Pending execution implementation.
*/
private class PendingExecution extends TemplateExecution {
private final long mDelay;
private final Execution mExecution;
private final TimeUnit mTimeUnit;
/**
* Constructor.
*
* @param execution the execution.
* @param delay the execution delay.
* @param timeUnit the delay time unit.
*/
private PendingExecution(@NotNull final Execution execution, final long delay,
@NotNull final TimeUnit timeUnit) {
mExecution = execution;
mDelay = delay;
mTimeUnit = timeUnit;
}
public void run() {
final ThrottlingExecution throttlingExecution;
synchronized (mMutex) {
throttlingExecution = getThrottlingExecution(mExecution);
}
mRunner.run(throttlingExecution, mDelay, mTimeUnit);
}
}
/**
* Execution used to dequeue and run pending executions, when the maximum running count allows
* it.
*/
private class ThrottlingExecution implements Execution {
private final Execution mExecution;
/**
* Constructor.
*
* @param execution the execution.
*/
private ThrottlingExecution(@NotNull final Execution execution) {
mExecution = execution;
}
public boolean mayBeCanceled() {
return mExecution.mayBeCanceled();
}
public void run() {
final int maxRunning = mMaxRunning;
final Execution execution = mExecution;
final LinkedList queue = mQueue;
synchronized (mMutex) {
if (mRunningCount >= maxRunning) {
queue.addFirst(new PendingExecution(execution, 0, TimeUnit.MILLISECONDS));
return;
}
++mRunningCount;
}
try {
execution.run();
} finally {
PendingExecution pendingExecution = null;
synchronized (mMutex) {
if ((--mRunningCount < maxRunning) && !queue.isEmpty()) {
pendingExecution = queue.removeFirst();
}
}
if (pendingExecution != null) {
pendingExecution.run();
}
}
}
}
}