io.netty.util.internal.ThreadLocalRandom Maven / Gradle / Ivy
/*
* Copyright 2014 The Netty Project
*
* The Netty Project licenses this file to you 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.
*/
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package io.netty.util.internal;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.lang.Thread.UncaughtExceptionHandler;
import java.security.SecureRandom;
import java.util.Random;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
/**
* A random number generator isolated to the current thread. Like the
* global {@link java.util.Random} generator used by the {@link
* java.lang.Math} class, a {@code ThreadLocalRandom} is initialized
* with an internally generated seed that may not otherwise be
* modified. When applicable, use of {@code ThreadLocalRandom} rather
* than shared {@code Random} objects in concurrent programs will
* typically encounter much less overhead and contention. Use of
* {@code ThreadLocalRandom} is particularly appropriate when multiple
* tasks (for example, each a {@link io.netty.util.internal.chmv8.ForkJoinTask}) use random numbers
* in parallel in thread pools.
*
* Usages of this class should typically be of the form:
* {@code ThreadLocalRandom.current().nextX(...)} (where
* {@code X} is {@code Int}, {@code Long}, etc).
* When all usages are of this form, it is never possible to
* accidently share a {@code ThreadLocalRandom} across multiple threads.
*
*
This class also provides additional commonly used bounded random
* generation methods.
*
* //since 1.7
* //author Doug Lea
*/
@SuppressWarnings("all")
public final class ThreadLocalRandom extends Random {
private static final InternalLogger logger = InternalLoggerFactory.getInstance(ThreadLocalRandom.class);
private static final AtomicLong seedUniquifier = new AtomicLong();
private static volatile long initialSeedUniquifier;
private static final Thread seedGeneratorThread;
private static final BlockingQueue seedQueue;
private static final long seedGeneratorStartTime;
private static volatile long seedGeneratorEndTime;
static {
initialSeedUniquifier = SystemPropertyUtil.getLong("io.netty.initialSeedUniquifier", 0);
if (initialSeedUniquifier == 0) {
boolean secureRandom = SystemPropertyUtil.getBoolean("java.util.secureRandomSeed", false);
if (secureRandom) {
seedQueue = new LinkedBlockingQueue();
seedGeneratorStartTime = System.nanoTime();
// Try to generate a real random number from /dev/random.
// Get from a different thread to avoid blocking indefinitely on a machine without much entropy.
seedGeneratorThread = new Thread("initialSeedUniquifierGenerator") {
@Override
public void run() {
final SecureRandom random = new SecureRandom(); // Get the real random seed from /dev/random
final byte[] seed = random.generateSeed(8);
seedGeneratorEndTime = System.nanoTime();
long s = ((long) seed[0] & 0xff) << 56 |
((long) seed[1] & 0xff) << 48 |
((long) seed[2] & 0xff) << 40 |
((long) seed[3] & 0xff) << 32 |
((long) seed[4] & 0xff) << 24 |
((long) seed[5] & 0xff) << 16 |
((long) seed[6] & 0xff) << 8 |
(long) seed[7] & 0xff;
seedQueue.add(s);
}
};
seedGeneratorThread.setDaemon(true);
seedGeneratorThread.setUncaughtExceptionHandler(new UncaughtExceptionHandler() {
@Override
public void uncaughtException(Thread t, Throwable e) {
logger.debug("An exception has been raised by {}", t.getName(), e);
}
});
seedGeneratorThread.start();
} else {
initialSeedUniquifier = mix64(System.currentTimeMillis()) ^ mix64(System.nanoTime());
seedGeneratorThread = null;
seedQueue = null;
seedGeneratorStartTime = 0L;
}
} else {
seedGeneratorThread = null;
seedQueue = null;
seedGeneratorStartTime = 0L;
}
}
public static void setInitialSeedUniquifier(long initialSeedUniquifier) {
ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
}
public static long getInitialSeedUniquifier() {
// Use the value set via the setter.
long initialSeedUniquifier = ThreadLocalRandom.initialSeedUniquifier;
if (initialSeedUniquifier != 0) {
return initialSeedUniquifier;
}
synchronized (ThreadLocalRandom.class) {
initialSeedUniquifier = ThreadLocalRandom.initialSeedUniquifier;
if (initialSeedUniquifier != 0) {
return initialSeedUniquifier;
}
// Get the random seed from the generator thread with timeout.
final long timeoutSeconds = 3;
final long deadLine = seedGeneratorStartTime + TimeUnit.SECONDS.toNanos(timeoutSeconds);
boolean interrupted = false;
for (;;) {
final long waitTime = deadLine - System.nanoTime();
try {
final Long seed;
if (waitTime <= 0) {
seed = seedQueue.poll();
} else {
seed = seedQueue.poll(waitTime, TimeUnit.NANOSECONDS);
}
if (seed != null) {
initialSeedUniquifier = seed;
break;
}
} catch (InterruptedException e) {
interrupted = true;
logger.warn("Failed to generate a seed from SecureRandom due to an InterruptedException.");
break;
}
if (waitTime <= 0) {
seedGeneratorThread.interrupt();
logger.warn(
"Failed to generate a seed from SecureRandom within {} seconds. " +
"Not enough entropy?", timeoutSeconds
);
break;
}
}
// Just in case the initialSeedUniquifier is zero or some other constant
initialSeedUniquifier ^= 0x3255ecdc33bae119L; // just a meaningless random number
initialSeedUniquifier ^= Long.reverse(System.nanoTime());
ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
if (interrupted) {
// Restore the interrupt status because we don't know how to/don't need to handle it here.
Thread.currentThread().interrupt();
// Interrupt the generator thread if it's still running,
// in the hope that the SecureRandom provider raises an exception on interruption.
seedGeneratorThread.interrupt();
}
if (seedGeneratorEndTime == 0) {
seedGeneratorEndTime = System.nanoTime();
}
return initialSeedUniquifier;
}
}
private static long newSeed() {
for (;;) {
final long current = seedUniquifier.get();
final long actualCurrent = current != 0? current : getInitialSeedUniquifier();
// L'Ecuyer, "Tables of Linear Congruential Generators of Different Sizes and Good Lattice Structure", 1999
final long next = actualCurrent * 181783497276652981L;
if (seedUniquifier.compareAndSet(current, next)) {
if (current == 0 && logger.isDebugEnabled()) {
if (seedGeneratorEndTime != 0) {
logger.debug(String.format(
"-Dio.netty.initialSeedUniquifier: 0x%016x (took %d ms)",
actualCurrent,
TimeUnit.NANOSECONDS.toMillis(seedGeneratorEndTime - seedGeneratorStartTime)));
} else {
logger.debug(String.format("-Dio.netty.initialSeedUniquifier: 0x%016x", actualCurrent));
}
}
return next ^ System.nanoTime();
}
}
}
// Borrowed from
// http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/main/java/util/concurrent/ThreadLocalRandom.java
private static long mix64(long z) {
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
return z ^ (z >>> 33);
}
// same constants as Random, but must be redeclared because private
private static final long multiplier = 0x5DEECE66DL;
private static final long addend = 0xBL;
private static final long mask = (1L << 48) - 1;
/**
* The random seed. We can't use super.seed.
*/
private long rnd;
/**
* Initialization flag to permit calls to setSeed to succeed only
* while executing the Random constructor. We can't allow others
* since it would cause setting seed in one part of a program to
* unintentionally impact other usages by the thread.
*/
boolean initialized;
// Padding to help avoid memory contention among seed updates in
// different TLRs in the common case that they are located near
// each other.
private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
/**
* Constructor called only by localRandom.initialValue.
*/
ThreadLocalRandom() {
super(newSeed());
initialized = true;
}
/**
* Returns the current thread's {@code ThreadLocalRandom}.
*
* @return the current thread's {@code ThreadLocalRandom}
*/
public static ThreadLocalRandom current() {
return InternalThreadLocalMap.get().random();
}
/**
* Throws {@code UnsupportedOperationException}. Setting seeds in
* this generator is not supported.
*
* @throws UnsupportedOperationException always
*/
public void setSeed(long seed) {
if (initialized) {
throw new UnsupportedOperationException();
}
rnd = (seed ^ multiplier) & mask;
}
protected int next(int bits) {
rnd = (rnd * multiplier + addend) & mask;
return (int) (rnd >>> (48 - bits));
}
/**
* Returns a pseudorandom, uniformly distributed value between the
* given least value (inclusive) and bound (exclusive).
*
* @param least the least value returned
* @param bound the upper bound (exclusive)
* @throws IllegalArgumentException if least greater than or equal
* to bound
* @return the next value
*/
public int nextInt(int least, int bound) {
if (least >= bound) {
throw new IllegalArgumentException();
}
return nextInt(bound - least) + least;
}
/**
* Returns a pseudorandom, uniformly distributed value
* between 0 (inclusive) and the specified value (exclusive).
*
* @param n the bound on the random number to be returned. Must be
* positive.
* @return the next value
* @throws IllegalArgumentException if n is not positive
*/
public long nextLong(long n) {
if (n <= 0) {
throw new IllegalArgumentException("n must be positive");
}
// Divide n by two until small enough for nextInt. On each
// iteration (at most 31 of them but usually much less),
// randomly choose both whether to include high bit in result
// (offset) and whether to continue with the lower vs upper
// half (which makes a difference only if odd).
long offset = 0;
while (n >= Integer.MAX_VALUE) {
int bits = next(2);
long half = n >>> 1;
long nextn = ((bits & 2) == 0) ? half : n - half;
if ((bits & 1) == 0) {
offset += n - nextn;
}
n = nextn;
}
return offset + nextInt((int) n);
}
/**
* Returns a pseudorandom, uniformly distributed value between the
* given least value (inclusive) and bound (exclusive).
*
* @param least the least value returned
* @param bound the upper bound (exclusive)
* @return the next value
* @throws IllegalArgumentException if least greater than or equal
* to bound
*/
public long nextLong(long least, long bound) {
if (least >= bound) {
throw new IllegalArgumentException();
}
return nextLong(bound - least) + least;
}
/**
* Returns a pseudorandom, uniformly distributed {@code double} value
* between 0 (inclusive) and the specified value (exclusive).
*
* @param n the bound on the random number to be returned. Must be
* positive.
* @return the next value
* @throws IllegalArgumentException if n is not positive
*/
public double nextDouble(double n) {
if (n <= 0) {
throw new IllegalArgumentException("n must be positive");
}
return nextDouble() * n;
}
/**
* Returns a pseudorandom, uniformly distributed value between the
* given least value (inclusive) and bound (exclusive).
*
* @param least the least value returned
* @param bound the upper bound (exclusive)
* @return the next value
* @throws IllegalArgumentException if least greater than or equal
* to bound
*/
public double nextDouble(double least, double bound) {
if (least >= bound) {
throw new IllegalArgumentException();
}
return nextDouble() * (bound - least) + least;
}
private static final long serialVersionUID = -5851777807851030925L;
}