ThreadLocalRandom.java

/*
 * Copyright 2000-2014 JetBrains s.r.o.
 *
 * 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.intellij.util.containers;

import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

class ThreadLocalRandom {
  public static int getProbe() {
    return tlr.get().threadLocalRandomProbe;
  }

  public static void localInit() {
    int p = probeGenerator.addAndGet(PROBE_INCREMENT);
    int probe = (p == 0) ? 1 : p; // skip 0
    long seed = mix64(seeder.getAndAdd(SEEDER_INCREMENT));
    Tlr t = tlr.get();
    t.threadLocalRandomProbe = probe;
    t.threadLocalRandomSeed = seed;
  }

  /**
   * Pseudo-randomly advances and records the given probe value for the
   * given thread.
   */
  static int advanceProbe(int probe) {
    probe ^= probe << 13;   // xorshift
    probe ^= probe >>> 17;
    probe ^= probe << 5;
    tlr.get().threadLocalRandomProbe = probe;
    return probe;
  }

  static class Tlr {
    /**
     * The current seed for a ThreadLocalRandom
     */
    long threadLocalRandomSeed;

    /**
     * Probe hash value; nonzero if threadLocalRandomSeed initialized
     */
    int threadLocalRandomProbe;
  }

  private static final ThreadLocal<Tlr> tlr = new ThreadLocal<Tlr>() {
    @Override
    protected Tlr initialValue() {
      return new Tlr();
    }
  };
  private static final AtomicInteger probeGenerator = new AtomicInteger();
  /**
   * The increment for generating probe values
   */
  private static final int PROBE_INCREMENT = 0x9e3779b9;

  /**
   * The increment of seeder per new instance
   */
  private static final long SEEDER_INCREMENT = 0xbb67ae8584caa73bL;

  /**
   * The next seed for default constructors.
   */
  private static final AtomicLong seeder = new AtomicLong(/*initialSeed()*/);

  private static long mix64(long z) {
    z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
    z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
    return z ^ (z >>> 33);
  }
}