Class ThreadLocalRandom

  • All Implemented Interfaces:
    java.io.Serializable

    public final class ThreadLocalRandom
    extends java.util.Random
    A random number generator isolated to the current thread. Like the global Random generator used by the Math class, a ThreadLocalRandom is initialized with an internally generated seed that may not otherwise be modified. When applicable, use of ThreadLocalRandom rather than shared Random objects in concurrent programs will typically encounter much less overhead and contention. Use of ThreadLocalRandom is particularly appropriate when multiple tasks (for example, each a io.netty.util.internal.chmv8.ForkJoinTask) use random numbers in parallel in thread pools.

    Usages of this class should typically be of the form: ThreadLocalRandom.current().nextX(...) (where X is Int, Long, etc). When all usages are of this form, it is never possible to accidentally share a ThreadLocalRandom across multiple threads.

    This class also provides additional commonly used bounded random generation methods. //since 1.7 //author Doug Lea

    See Also:
    Serialized Form
    • Constructor Summary

      Constructors 
      Constructor Description
      ThreadLocalRandom()
      Constructor called only by localRandom.initialValue.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static ThreadLocalRandom current()
      Returns the current thread's ThreadLocalRandom.
      static long getInitialSeedUniquifier()  
      private static long mix64​(long z)  
      private static long newSeed()  
      protected int next​(int bits)  
      double nextDouble​(double n)
      Returns a pseudorandom, uniformly distributed double value between 0 (inclusive) and the specified value (exclusive).
      double nextDouble​(double least, double bound)
      Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
      int nextInt​(int least, int bound)
      Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
      long nextLong​(long n)
      Returns a pseudorandom, uniformly distributed value between 0 (inclusive) and the specified value (exclusive).
      long nextLong​(long least, long bound)
      Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
      static void setInitialSeedUniquifier​(long initialSeedUniquifier)  
      void setSeed​(long seed)
      Throws UnsupportedOperationException.
      • Methods inherited from class java.util.Random

        doubles, doubles, doubles, doubles, ints, ints, ints, ints, longs, longs, longs, longs, nextBoolean, nextBytes, nextDouble, nextFloat, nextGaussian, nextInt, nextInt, nextLong
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • seedUniquifier

        private static final java.util.concurrent.atomic.AtomicLong seedUniquifier
      • initialSeedUniquifier

        private static volatile long initialSeedUniquifier
      • seedGeneratorThread

        private static final java.lang.Thread seedGeneratorThread
      • seedQueue

        private static final java.util.concurrent.BlockingQueue<java.lang.Long> seedQueue
      • seedGeneratorStartTime

        private static final long seedGeneratorStartTime
      • seedGeneratorEndTime

        private static volatile long seedGeneratorEndTime
      • rnd

        private long rnd
        The random seed. We can't use super.seed.
      • initialized

        boolean initialized
        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.
      • pad0

        private long pad0
      • pad1

        private long pad1
      • pad2

        private long pad2
      • pad3

        private long pad3
      • pad4

        private long pad4
      • pad5

        private long pad5
      • pad6

        private long pad6
      • pad7

        private long pad7
    • Constructor Detail

      • ThreadLocalRandom

        ThreadLocalRandom()
        Constructor called only by localRandom.initialValue.
    • Method Detail

      • setInitialSeedUniquifier

        public static void setInitialSeedUniquifier​(long initialSeedUniquifier)
      • getInitialSeedUniquifier

        public static long getInitialSeedUniquifier()
      • newSeed

        private static long newSeed()
      • mix64

        private static long mix64​(long z)
      • current

        public static ThreadLocalRandom current()
        Returns the current thread's ThreadLocalRandom.
        Returns:
        the current thread's ThreadLocalRandom
      • setSeed

        public void setSeed​(long seed)
        Throws UnsupportedOperationException. Setting seeds in this generator is not supported.
        Overrides:
        setSeed in class java.util.Random
        Throws:
        java.lang.UnsupportedOperationException - always
      • next

        protected int next​(int bits)
        Overrides:
        next in class java.util.Random
      • nextInt

        public int nextInt​(int least,
                           int bound)
        Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
        Parameters:
        least - the least value returned
        bound - the upper bound (exclusive)
        Returns:
        the next value
        Throws:
        java.lang.IllegalArgumentException - if least greater than or equal to bound
      • nextLong

        public long nextLong​(long n)
        Returns a pseudorandom, uniformly distributed value between 0 (inclusive) and the specified value (exclusive).
        Parameters:
        n - the bound on the random number to be returned. Must be positive.
        Returns:
        the next value
        Throws:
        java.lang.IllegalArgumentException - if n is not positive
      • nextLong

        public long nextLong​(long least,
                             long bound)
        Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
        Parameters:
        least - the least value returned
        bound - the upper bound (exclusive)
        Returns:
        the next value
        Throws:
        java.lang.IllegalArgumentException - if least greater than or equal to bound
      • nextDouble

        public double nextDouble​(double n)
        Returns a pseudorandom, uniformly distributed double value between 0 (inclusive) and the specified value (exclusive).
        Parameters:
        n - the bound on the random number to be returned. Must be positive.
        Returns:
        the next value
        Throws:
        java.lang.IllegalArgumentException - if n is not positive
      • nextDouble

        public double nextDouble​(double least,
                                 double bound)
        Returns a pseudorandom, uniformly distributed value between the given least value (inclusive) and bound (exclusive).
        Parameters:
        least - the least value returned
        bound - the upper bound (exclusive)
        Returns:
        the next value
        Throws:
        java.lang.IllegalArgumentException - if least greater than or equal to bound