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

Method Summary

Modifier and Type	Method and 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 Detail

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 Detail

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