/*
* Copyright 2013 Ben Manes. All Rights Reserved.
*
* 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.benmanes.caffeine.testing;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicReferenceArray;
import com.google.common.util.concurrent.ThreadFactoryBuilder;
import com.google.common.util.concurrent.Uninterruptibles;
/**
* A testing harness for concurrency related executions.
* <p/>
* This harness will ensure that all threads execute at the same time, records
* the full execution time, and optionally retrieves the responses from each
* thread. This harness can be used for performance tests, investigations of
* lock contention, etc.
* <p/>
* This code was adapted from <tt>Java Concurrency in Practice</tt>, using an
* example of a {@link CountDownLatch} for starting and stopping threads in
* timing tests.
*
* @author ben.manes@gmail.com (Ben Manes)
*/
public final class ConcurrentTestHarness {
private static final Executor executor = Executors.newCachedThreadPool(
new ThreadFactoryBuilder().setPriority(Thread.MIN_PRIORITY).setDaemon(true).build());
private ConcurrentTestHarness() {}
/** Executes the task using the shared thread pool. */
public static void execute(Runnable task) {
executor.execute(task);
}
/**
* Executes a task, on N threads, all starting at the same time.
*
* @param nThreads the number of threads to execute
* @param task the task to execute in each thread
* @return the execution time for all threads to complete, in nanoseconds
*/
public static long timeTasks(int nThreads, Runnable task) {
return timeTasks(nThreads, Executors.callable(task)).executionTime();
}
/**
* Executes a task, on N threads, all starting at the same time.
*
* @param nThreads the number of threads to execute
* @param task the task to execute in each thread
* @return the result of each task and the full execution time, in nanoseconds
*/
public static <T> TestResult<T> timeTasks(int nThreads, Callable<T> task) {
CountDownLatch startGate = new CountDownLatch(1);
CountDownLatch endGate = new CountDownLatch(nThreads);
AtomicReferenceArray<T> results = new AtomicReferenceArray<T>(nThreads);
for (int i = 0; i < nThreads; i++) {
final int index = i;
executor.execute(() -> {
try {
startGate.await();
try {
results.set(index, task.call());
} finally {
endGate.countDown();
}
} catch (Exception e) {
throw new RuntimeException(e);
}
});
}
long start = System.nanoTime();
startGate.countDown();
Uninterruptibles.awaitUninterruptibly(endGate);
long end = System.nanoTime();
return new TestResult<T>(end - start, toList(results));
}
/**
* Migrates the data from the atomic array to a {@link List} for easier
* consumption.
*
* @param data the per-thread results from the test
* @return the per-thread results as a standard collection
*/
private static <T> List<T> toList(AtomicReferenceArray<T> data) {
List<T> list = new ArrayList<>(data.length());
for (int i = 0; i < data.length(); i++) {
list.add(data.get(i));
}
return list;
}
/**
* The results of the test harness's execution.
*
* @param <T> the data type produced by the task
*/
public static final class TestResult<T> {
private final long executionTime;
private final List<T> results;
public TestResult(long executionTime, List<T> results) {
this.executionTime = executionTime;
this.results = results;
}
/**
* The test's execution time, in nanoseconds.
*
* @return The time to complete the test.
*/
public long executionTime() {
return executionTime;
}
/**
* The results from executing the tasks.
*
* @return The outputs from the tasks.
*/
public List<T> results() {
return results;
}
}
}