SizedQueue Basic Usage

sized_queue.rb

require 'thread'

# Create a SizedQueue with a buffer capacity of just one.
queue = SizedQueue.new 1

# Add four symbols to the SizedQueue. (A SizedQueue is thread-safe just like a
# Queue.)
Thread.new { queue << :of }
Thread.new { queue << :earl }
Thread.new { queue << :and }
Thread.new { queue << :midge }

# With a SizedQueue capcity of one, three of the four are waiting enqueue
# (queued, waiting to get into the queue (inception two levels deep)) and the
# remaining one is in the queue buffer itself.
queue.max
#=> 1
queue.num_waiting
#=> 3

# If the SizedQueue capacity is increased dynamically, elements in the enqueue
# will scootch over into the queue buffer.
queue.max = 3
#=> 3
queue.num_waiting
#=> 1

# Likewise, if the SizedQueue is decremented by an element, one of the enqueue
# will hop into the queue buffer.
queue.shift
#=> :of
queue.num_waiting
#=> 0

# So now there is a SizedQueue with a fixed buffer capacity of three, which is
# full with nothing enqueue.
queue.shift
#=> :earl
queue.shift
#=> :and
queue.shift
#=> :midge

# Once the queue is empty, trying to decrement an element will block until an
# element is added to the queue.
queue.shift