Package com.rabbitmq.utility

Class IntAllocator

java.lang.Object
com.rabbitmq.utility.IntAllocator
public class IntAllocator extends Object

A class for allocating integers from a given range that uses a BitSet representation of the free integers.

Concurrency Semantics:

This class is not thread safe.

Implementation notes:

This was originally an ordered chain of non-overlapping Intervals, together with a fixed size array cache for freed integers.

reserve(int) was expensive in this scheme, whereas in the present implementation it is O(1), as is free(int).

Although allocate() is slightly slower than O(1) and in the worst case could be O(N), the use of a "lastIndex" field for starting the next scan for free integers means this is negligible.

The data representation overhead is O(N) where N is the size of the allocation range. One long is used for every 64 integers in the range.

Very little Object creation and destruction occurs in use.

  • Constructor Summary

    Constructors
    Constructor
    Description
    IntAllocator(int bottom, int top)
    Creates an IntAllocator allocating integer IDs within the inclusive range [bottom, top].

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    allocate()
    Allocate an unallocated integer from the range, or return -1 if no more integers are available.
    void
    free(int reservation)
    Make the provided integer available for allocation again.
    boolean
    reserve(int reservation)
    Attempt to reserve the provided ID as if it had been allocated.
    String
    toString()
     

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • IntAllocator

      public IntAllocator(int bottom, int top)
      Creates an IntAllocator allocating integer IDs within the inclusive range [bottom, top].
      Parameters:
      bottom - lower end of range
      top - upper end of range (inclusive)

  • Method Details

    • allocate

      public int allocate()
      Allocate an unallocated integer from the range, or return -1 if no more integers are available.
      Returns:
      the allocated integer, or -1

    • free

      public void free(int reservation)
      Make the provided integer available for allocation again. This operation runs in O(1) time. No error checking is performed, so if you double free or free an integer that was not originally allocated the results are undefined.
      Parameters:
      reservation - the previously allocated integer to free

    • reserve

      public boolean reserve(int reservation)
      Attempt to reserve the provided ID as if it had been allocated. Returns true if it is available, false otherwise. This operation runs in O(1) time.
      Parameters:
      reservation - the integer to be allocated, if possible
      Returns:
      true if allocated, false if already allocated

    • toString

      public String toString()
      Overrides:
      toString in class Object