public class

IntAllocator

extends Object
java.lang.Object
   ↳ com.rabbitmq.utility.IntAllocator

Class Overview

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

Concurrent 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() was expensive in this scheme, whereas in the present implementation it is O(1), as is #free().
Although allocate() is slightly slower than O(1) and in the worst case could be O(N), the use of the #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.

Summary

Public Constructors
IntAllocator(int bottom, int top)
Creates an IntAllocator allocating integer IDs within the inclusive range [bottom, top].
Public Methods
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()
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

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)

Public Methods

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

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

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

public String toString ()