371 lines
14 KiB
Java
371 lines
14 KiB
Java
/*
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* Copyright 2014 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package io.netty.util.internal;
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import io.netty.util.internal.logging.InternalLogger;
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import io.netty.util.internal.logging.InternalLoggerFactory;
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import java.lang.Thread.UncaughtExceptionHandler;
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import java.security.SecureRandom;
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import java.util.Random;
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import java.util.concurrent.BlockingQueue;
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import java.util.concurrent.LinkedBlockingQueue;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicLong;
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/**
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* A random number generator isolated to the current thread. Like the
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* global {@link java.util.Random} generator used by the {@link
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* java.lang.Math} class, a {@code ThreadLocalRandom} is initialized
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* with an internally generated seed that may not otherwise be
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* modified. When applicable, use of {@code ThreadLocalRandom} rather
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* than shared {@code Random} objects in concurrent programs will
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* typically encounter much less overhead and contention. Use of
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* {@code ThreadLocalRandom} is particularly appropriate when multiple
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* tasks (for example, each a {@link io.netty.util.internal.chmv8.ForkJoinTask}) use random numbers
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* in parallel in thread pools.
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*
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* <p>Usages of this class should typically be of the form:
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* {@code ThreadLocalRandom.current().nextX(...)} (where
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* {@code X} is {@code Int}, {@code Long}, etc).
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* When all usages are of this form, it is never possible to
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* accidently share a {@code ThreadLocalRandom} across multiple threads.
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*
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* <p>This class also provides additional commonly used bounded random
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* generation methods.
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*
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* //since 1.7
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* //author Doug Lea
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*/
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@SuppressWarnings("all")
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public final class ThreadLocalRandom extends Random {
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private static final InternalLogger logger = InternalLoggerFactory.getInstance(ThreadLocalRandom.class);
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private static final AtomicLong seedUniquifier = new AtomicLong();
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private static volatile long initialSeedUniquifier =
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SystemPropertyUtil.getLong("io.netty.initialSeedUniquifier", 0);
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private static final Thread seedGeneratorThread;
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private static final BlockingQueue<byte[]> seedQueue;
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private static final long seedGeneratorStartTime;
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private static volatile long seedGeneratorEndTime;
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static {
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if (initialSeedUniquifier == 0) {
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// Try to generate a real random number from /dev/random.
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// Get from a different thread to avoid blocking indefinitely on a machine without much entropy.
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seedGeneratorThread = new Thread("initialSeedUniquifierGenerator") {
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@Override
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public void run() {
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final SecureRandom random = new SecureRandom(); // Get the real random seed from /dev/random
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final byte[] seed = random.generateSeed(8);
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seedGeneratorEndTime = System.nanoTime();
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seedQueue.add(seed);
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}
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};
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seedGeneratorThread.setDaemon(true);
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seedGeneratorThread.setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
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@Override
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public void uncaughtException(Thread t, Throwable e) {
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logger.debug("An exception has been raised by {}", t.getName(), e);
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}
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});
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seedQueue = new LinkedBlockingQueue<byte[]>();
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seedGeneratorStartTime = System.nanoTime();
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seedGeneratorThread.start();
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} else {
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seedGeneratorThread = null;
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seedQueue = null;
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seedGeneratorStartTime = 0L;
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}
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}
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public static void setInitialSeedUniquifier(long initialSeedUniquifier) {
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ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
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}
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public static long getInitialSeedUniquifier() {
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// Use the value set via the setter.
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long initialSeedUniquifier = ThreadLocalRandom.initialSeedUniquifier;
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if (initialSeedUniquifier != 0) {
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return initialSeedUniquifier;
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}
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synchronized (ThreadLocalRandom.class) {
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initialSeedUniquifier = ThreadLocalRandom.initialSeedUniquifier;
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if (initialSeedUniquifier != 0) {
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return initialSeedUniquifier;
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}
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// Get the random seed from the generator thread with timeout.
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final long timeoutSeconds = 3;
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final long deadLine = seedGeneratorStartTime + TimeUnit.SECONDS.toNanos(timeoutSeconds);
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boolean interrupted = false;
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for (;;) {
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final long waitTime = deadLine - System.nanoTime();
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try {
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final byte[] seed;
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if (waitTime <= 0) {
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seed = seedQueue.poll();
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} else {
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seed = seedQueue.poll(waitTime, TimeUnit.NANOSECONDS);
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}
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if (seed != null) {
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initialSeedUniquifier =
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((long) seed[0] & 0xff) << 56 |
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((long) seed[1] & 0xff) << 48 |
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((long) seed[2] & 0xff) << 40 |
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((long) seed[3] & 0xff) << 32 |
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((long) seed[4] & 0xff) << 24 |
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((long) seed[5] & 0xff) << 16 |
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((long) seed[6] & 0xff) << 8 |
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(long) seed[7] & 0xff;
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break;
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}
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} catch (InterruptedException e) {
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interrupted = true;
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logger.warn("Failed to generate a seed from SecureRandom due to an InterruptedException.");
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break;
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}
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if (waitTime <= 0) {
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seedGeneratorThread.interrupt();
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logger.warn(
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"Failed to generate a seed from SecureRandom within {} seconds. " +
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"Not enough entropy?", timeoutSeconds
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);
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break;
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}
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}
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// Just in case the initialSeedUniquifier is zero or some other constant
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initialSeedUniquifier ^= 0x3255ecdc33bae119L; // just a meaningless random number
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initialSeedUniquifier ^= Long.reverse(System.nanoTime());
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ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
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if (interrupted) {
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// Restore the interrupt status because we don't know how to/don't need to handle it here.
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Thread.currentThread().interrupt();
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// Interrupt the generator thread if it's still running,
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// in the hope that the SecureRandom provider raises an exception on interruption.
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seedGeneratorThread.interrupt();
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}
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if (seedGeneratorEndTime == 0) {
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seedGeneratorEndTime = System.nanoTime();
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}
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return initialSeedUniquifier;
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}
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}
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private static long newSeed() {
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for (;;) {
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final long current = seedUniquifier.get();
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final long actualCurrent = current != 0? current : getInitialSeedUniquifier();
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// L'Ecuyer, "Tables of Linear Congruential Generators of Different Sizes and Good Lattice Structure", 1999
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final long next = actualCurrent * 181783497276652981L;
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if (seedUniquifier.compareAndSet(current, next)) {
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if (current == 0 && logger.isDebugEnabled()) {
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if (seedGeneratorEndTime != 0) {
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logger.debug(String.format(
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"-Dio.netty.initialSeedUniquifier: 0x%016x (took %d ms)",
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actualCurrent,
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TimeUnit.NANOSECONDS.toMillis(seedGeneratorEndTime - seedGeneratorStartTime)));
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} else {
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logger.debug(String.format("-Dio.netty.initialSeedUniquifier: 0x%016x", actualCurrent));
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}
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}
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return next ^ System.nanoTime();
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}
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}
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}
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// same constants as Random, but must be redeclared because private
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private static final long multiplier = 0x5DEECE66DL;
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private static final long addend = 0xBL;
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private static final long mask = (1L << 48) - 1;
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/**
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* The random seed. We can't use super.seed.
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*/
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private long rnd;
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/**
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* Initialization flag to permit calls to setSeed to succeed only
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* while executing the Random constructor. We can't allow others
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* since it would cause setting seed in one part of a program to
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* unintentionally impact other usages by the thread.
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*/
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boolean initialized;
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// Padding to help avoid memory contention among seed updates in
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// different TLRs in the common case that they are located near
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// each other.
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private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
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/**
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* Constructor called only by localRandom.initialValue.
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*/
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ThreadLocalRandom() {
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super(newSeed());
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initialized = true;
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}
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/**
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* Returns the current thread's {@code ThreadLocalRandom}.
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*
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* @return the current thread's {@code ThreadLocalRandom}
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*/
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public static ThreadLocalRandom current() {
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return InternalThreadLocalMap.get().random();
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}
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/**
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* Throws {@code UnsupportedOperationException}. Setting seeds in
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* this generator is not supported.
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*
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* @throws UnsupportedOperationException always
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*/
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public void setSeed(long seed) {
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if (initialized) {
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throw new UnsupportedOperationException();
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}
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rnd = (seed ^ multiplier) & mask;
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}
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protected int next(int bits) {
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rnd = (rnd * multiplier + addend) & mask;
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return (int) (rnd >>> (48 - bits));
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}
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/**
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* Returns a pseudorandom, uniformly distributed value between the
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* given least value (inclusive) and bound (exclusive).
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*
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* @param least the least value returned
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* @param bound the upper bound (exclusive)
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* @throws IllegalArgumentException if least greater than or equal
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* to bound
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* @return the next value
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*/
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public int nextInt(int least, int bound) {
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if (least >= bound) {
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throw new IllegalArgumentException();
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}
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return nextInt(bound - least) + least;
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}
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/**
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* Returns a pseudorandom, uniformly distributed value
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* between 0 (inclusive) and the specified value (exclusive).
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*
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* @param n the bound on the random number to be returned. Must be
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* positive.
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* @return the next value
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* @throws IllegalArgumentException if n is not positive
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*/
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public long nextLong(long n) {
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if (n <= 0) {
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throw new IllegalArgumentException("n must be positive");
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}
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// Divide n by two until small enough for nextInt. On each
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// iteration (at most 31 of them but usually much less),
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// randomly choose both whether to include high bit in result
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// (offset) and whether to continue with the lower vs upper
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// half (which makes a difference only if odd).
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long offset = 0;
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while (n >= Integer.MAX_VALUE) {
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int bits = next(2);
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long half = n >>> 1;
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long nextn = ((bits & 2) == 0) ? half : n - half;
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if ((bits & 1) == 0) {
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offset += n - nextn;
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}
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n = nextn;
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}
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return offset + nextInt((int) n);
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}
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/**
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* Returns a pseudorandom, uniformly distributed value between the
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* given least value (inclusive) and bound (exclusive).
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*
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* @param least the least value returned
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* @param bound the upper bound (exclusive)
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* @return the next value
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* @throws IllegalArgumentException if least greater than or equal
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* to bound
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*/
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public long nextLong(long least, long bound) {
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if (least >= bound) {
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throw new IllegalArgumentException();
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}
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return nextLong(bound - least) + least;
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}
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/**
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* Returns a pseudorandom, uniformly distributed {@code double} value
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* between 0 (inclusive) and the specified value (exclusive).
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*
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* @param n the bound on the random number to be returned. Must be
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* positive.
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* @return the next value
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* @throws IllegalArgumentException if n is not positive
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*/
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public double nextDouble(double n) {
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if (n <= 0) {
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throw new IllegalArgumentException("n must be positive");
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}
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return nextDouble() * n;
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}
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/**
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* Returns a pseudorandom, uniformly distributed value between the
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* given least value (inclusive) and bound (exclusive).
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*
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* @param least the least value returned
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* @param bound the upper bound (exclusive)
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* @return the next value
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* @throws IllegalArgumentException if least greater than or equal
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* to bound
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*/
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public double nextDouble(double least, double bound) {
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if (least >= bound) {
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throw new IllegalArgumentException();
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}
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return nextDouble() * (bound - least) + least;
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}
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private static final long serialVersionUID = -5851777807851030925L;
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}
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