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# encoding: utf-8
require "amq/bit_set"
module AMQ
# Simple bitset-based integer allocator, heavily inspired by com.rabbitmq.utility.IntAllocator class
# in the RabbitMQ Java client.
#
# Unlike monotonically incrementing identifier, this allocator is suitable for very long running programs
# that aggressively allocate and release channels.
class IntAllocator
#
# API
#
# @return [Integer] Number of integers in the allocation range
attr_reader :number_of_bits
# @return [Integer] Upper boundary of the integer range available for allocation
attr_reader :hi
# @return [Integer] Lower boundary of the integer range available for allocation
attr_reader :lo
# @param [Integer] lo Lower boundary of the integer range available for allocation
# @param [Integer] hi Upper boundary of the integer range available for allocation
# @raise [ArgumentError] if upper boundary is not greater than the lower one
def initialize(lo, hi)
raise ArgumentError.new "upper boundary must be greater than the lower one (given: hi = #{hi}, lo = #{lo})" unless hi > lo
@hi = hi
@lo = lo
@number_of_bits = hi - lo
@range = Range.new(1, @number_of_bits)
@free_set = BitSet.new(@number_of_bits)
end # initialize(hi, lo)
# Attempts to allocate next available integer. If allocation succeeds, allocated value is returned.
# Otherwise, -1 is returned.
#
# Current implementation of this method is O(n), where n is number of bits in the range available for
# allocation.
#
# @return [Integer] Allocated integer if allocation succeeded. -1 otherwise.
def allocate
if n = @free_set.next_clear_bit
if n < @hi - 1 then
@free_set.set(n)
n + 1
else
-1
end
else
-1
end
end # allocate
# Releases previously allocated integer. If integer provided as argument was not previously allocated,
# this method has no effect.
#
# @return [NilClass] nil
def free(reservation)
@free_set.unset(reservation-1)
end # free(reservation)
alias release free
# @return [Boolean] true if provided argument was previously allocated, false otherwise
def allocated?(reservation)
@free_set.get(reservation-1)
end # allocated?(reservation)
# Releases the whole allocation range
def reset
@free_set.clear
end # reset
protected
end # IntAllocator
end # AMQ
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