/*
    * 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:
    *
    *   https://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
   * https://creativecommons.org/publicdomain/zero/1.0/
   */
  
  package io.netty.util.internal;
  
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  
  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.
   *
   * <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
   * accidentally share a {@code ThreadLocalRandom} across multiple threads.
   *
   * <p>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<Long> 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<Long>();
                  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
      */
     @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)
      * @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) {
         checkPositive(n, "n");
 
         // 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) {
         checkPositive(n, "n");
         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;
 }