Package com.github.benmanes.caffeine.cache

Class StripedBuffer<E>

  • All Implemented Interfaces:
    Buffer<E>
    Direct Known Subclasses:
    BoundedBuffer
    abstract class StripedBuffer<E>
extends java.lang.Object
implements Buffer<E>
    A base class providing the mechanics for supporting dynamic striping of bounded buffers. This implementation is an adaption of the numeric 64-bit Striped64 class, which is used by atomic counters. The approach was modified to lazily grow an array of buffers in order to minimize memory usage for caches that are not heavily contended on.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      (package private) static int ATTEMPTS
      The maximum number of attempts when trying to expand the table.
      (package private) static int MAXIMUM_TABLE_SIZE
      The bound on the table size.
      (package private) static int NCPU
      Number of CPUS.
      (package private) static long PROBE  
      (package private) Buffer<E> @Nullable [] table
      Table of buffers.
      (package private) static long TABLE_BUSY  
      (package private) int tableBusy
      Spinlock (locked via CAS) used when resizing and/or creating Buffers.

    • Constructor Summary

      Constructors 
      Constructor Description
      StripedBuffer()  

    • Method Summary

      All Methods Static Methods Instance Methods Abstract Methods Concrete Methods 
      Modifier and Type Method Description
      (package private) static int advanceProbe​(int probe)
      Pseudo-randomly advances and records the given probe value for the given thread.
      (package private) boolean casTableBusy()
      CASes the tableBusy field from 0 to 1 to acquire lock.
      protected abstract Buffer<E> create​(E e)
      Creates a new buffer instance after resizing to accommodate a producer.
      void drainTo​(java.util.function.Consumer<E> consumer)
      Drains the buffer, sending each element to the consumer for processing.
      (package private) void expandOrRetry​(E e, boolean wasUncontended)
      Handles cases of updates involving initialization, resizing, creating new Buffers, and/or contention.
      (package private) static int getProbe()
      Returns the probe value for the current thread.
      int offer​(E e)
      Inserts the specified element into this buffer if it is possible to do so immediately without violating capacity restrictions.
      int reads()
      Returns the number of elements that have been read from the buffer.
      int writes()
      Returns the number of elements that have been written to the buffer.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

      • Methods inherited from interface com.github.benmanes.caffeine.cache.Buffer

        size

    • Field Detail

      • TABLE_BUSY

        static final long TABLE_BUSY

      • PROBE

        static final long PROBE

      • NCPU

        static final int NCPU
        Number of CPUS.

      • MAXIMUM_TABLE_SIZE

        static final int MAXIMUM_TABLE_SIZE
        The bound on the table size.

      • ATTEMPTS

        static final int ATTEMPTS
        The maximum number of attempts when trying to expand the table.
        See Also:
        Constant Field Values

      • table

        transient volatile Buffer<E> @Nullable [] table
        Table of buffers. When non-null, size is a power of 2.

      • tableBusy

        transient volatile int tableBusy
        Spinlock (locked via CAS) used when resizing and/or creating Buffers.

    • Constructor Detail

      • StripedBuffer

        StripedBuffer()

    • Method Detail

      • casTableBusy

        final boolean casTableBusy()
        CASes the tableBusy field from 0 to 1 to acquire lock.

      • getProbe

        static final int getProbe()
        Returns the probe value for the current thread. Duplicated from ThreadLocalRandom because of packaging restrictions.

      • advanceProbe

        static final int advanceProbe​(int probe)
        Pseudo-randomly advances and records the given probe value for the given thread. Duplicated from ThreadLocalRandom because of packaging restrictions.

      • create

        protected abstract Buffer<E> create​(E e)
        Creates a new buffer instance after resizing to accommodate a producer.
        Parameters:
        e - the producer's element
        Returns:
        a newly created buffer populated with a single element

      • offer

        public int offer​(E e)
        Description copied from interface: Buffer
        Inserts the specified element into this buffer if it is possible to do so immediately without violating capacity restrictions. The addition is allowed to fail spuriously if multiple threads insert concurrently.
        Specified by:
        offer in interface Buffer<E>
        Parameters:
        e - the element to add
        Returns:
        1 if the buffer is full, -1 if the CAS failed, or 0 if added

      • drainTo

        public void drainTo​(java.util.function.Consumer<E> consumer)
        Description copied from interface: Buffer
        Drains the buffer, sending each element to the consumer for processing. The caller must ensure that a consumer has exclusive read access to the buffer.
        Specified by:
        drainTo in interface Buffer<E>
        Parameters:
        consumer - the action to perform on each element

      • reads

        public int reads()
        Description copied from interface: Buffer
        Returns the number of elements that have been read from the buffer.
        Specified by:
        reads in interface Buffer<E>
        Returns:
        the number of elements read from this buffer

      • writes

        public int writes()
        Description copied from interface: Buffer
        Returns the number of elements that have been written to the buffer.
        Specified by:
        writes in interface Buffer<E>
        Returns:
        the number of elements written to this buffer

      • expandOrRetry

        final void expandOrRetry​(E e,
                         boolean wasUncontended)
        Handles cases of updates involving initialization, resizing, creating new Buffers, and/or contention. See above for explanation. This method suffers the usual non-modularity problems of optimistic retry code, relying on rechecked sets of reads.
        Parameters:
        e - the element to add
        wasUncontended - false if CAS failed before call