content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * 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.alibaba.nacos.client.naming.utils;
  
  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.
   * <p>
   * <p>
   * 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.
   * <p>
   * <p>
   * This class also provides additional commonly used bounded random generation methods.
   * <p>
   * //since 1.7 //author Doug Lea
   */
  @SuppressWarnings("all")
  public class ThreadLocalRandom extends Random {
  
      private static final AtomicLong seedUniquifier = new AtomicLong();
  
      private static volatile long initialSeedUniquifier;
  
      public static void setInitialSeedUniquifier(long initialSeedUniquifier) {
          ThreadLocalRandom.initialSeedUniquifier = initialSeedUniquifier;
      }
  
      public static synchronized long getInitialSeedUniquifier() {
          // Use the value set via the setter.
          long initialSeedUniquifier = ThreadLocalRandom.initialSeedUniquifier;
          // Otherwise, generate one.
          if (initialSeedUniquifier == 0) {
              // Try to generate a real random number from /dev/random.
              // Get from a different thread to avoid blocking indefinitely on a machine without much entrophy.
              final BlockingQueue<Long> queue = new LinkedBlockingQueue<Long>();
              Thread generatorThread = new Thread("initialSeedUniquifierGenerator") {
                  @Override
                  public void run() {
                      SecureRandom random = new SecureRandom(); // Get the real random seed from /dev/random
                      queue.add(random.nextLong());
                  }
              };
              generatorThread.start();
  
              // Get the random seed from the thread with timeout.
              final long timeoutSeconds = 3;
              final long deadLine = System.nanoTime() + TimeUnit.SECONDS.toNanos(timeoutSeconds);
              for (; ; ) {
                  long waitTime = deadLine - System.nanoTime();
                  if (waitTime <= 0) {
                      break;
                  }
  
                  try {
                      Long result = queue.poll(waitTime, TimeUnit.NANOSECONDS);
                      if (result != null) {
                          initialSeedUniquifier = result;
                          break;
                      }
                  } catch (InterruptedException ignore) {
                      // Ignore
                  }
              }
  
              // 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;
          }
  
          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)) {
                  return next ^ System.nanoTime();
              }
          }
      }
  
      // 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 = false;
  
      // 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;
      }
  
      /**
       * The actual ThreadLocal
       */
      private static final ThreadLocal<ThreadLocalRandom> localRandom = new ThreadLocal<ThreadLocalRandom>() {
          @Override
          protected ThreadLocalRandom initialValue() {
              return new ThreadLocalRandom();
          }
      };
  
      /**
       * Returns the current thread's {@code ThreadLocalRandom}.
       *
       * @return the current thread's {@code ThreadLocalRandom}
       */
      public static ThreadLocalRandom current() {
          return localRandom.get();
      }
  
      /**
       * Throws {@code UnsupportedOperationException}. Setting seeds in this generator is not supported.
       *
       * @throws UnsupportedOperationException always
       */
      @Override
      public void setSeed(long seed) {
          if (initialized) {
              throw new UnsupportedOperationException();
          }
          rnd = (seed ^ multiplier) & mask;
      }
  
      @Override
      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)
       * @return the next value
       * @throws IllegalArgumentException if least greater than or equal to bound
       */
      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;
  }
  