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|
#
# Attempt to load the Redis-library.
#
# Without this we cannot connect to our queue.
#
%w( redis ).each do |library|
begin
require library
rescue LoadError
puts("Failed to load the #{library} library - queue access will fail!")
end
end
module Custodian
#
# An abstraction layer for our queue.
#
class QueueType
#
# Retrieve a job from the queue.
#
def fetch(_timeout)
raise 'Subclasses must implement this method!'
end
#
# Add a new job to the queue.
#
def add(_job_string)
raise 'Subclasses must implement this method!'
end
#
# Get the size of the queue
#
def size?
raise 'Subclasses must implement this method!'
end
#
# Empty the queue
#
def flush!
raise 'Subclasses must implement this method!'
end
end
#
# This is a simple queue which uses Redis for storage.
#
class RedisQueueType < QueueType
#
# Connect to the server on localhost, unless QUEUE_ADDRESS is set.
#
def initialize
host = ENV['QUEUE_ADDRESS'] || '127.0.0.1'
@redis = Redis.new(:host => host)
end
#
# Fetch a job from the queue.
#
# The timeout is used to specify the period we wait for a new job, and
# we pause that same period between fetches.
#
def fetch(timeout = 1)
job = nil
loop do
job = @redis.zrange('zset', '0', '0')
if !job.empty?
# We only have one entry in our array
job = job[0]
# Remove from the queue
@redis.zrem('zset', job)
return job
else
sleep(timeout)
end
end
end
#
# Add a new job to the queue - this can stall for the case where the
# job is already pending.
#
def add(test)
@redis.watch('zset')
#
# Count the number of times we attempt to add the test
#
attempts = 0
added = false
#
# This is run in a loop, as we have to wait until both
#
# (a) the score is missing
# (b) the zadd function succeeds
#
while (attempts < 40) do
#
# Only update if no score is set
#
if !@redis.zscore('zset', test)
#
# If MULTI returns nil, the transaction failed, so we need to try
# again.
#
break unless @redis.multi do |r|
@redis.zadd('zset', Time.now.to_f, test)
added = true
end.nil?
end
#
# This could be tighter..
#
sleep 0.1
#
# Bump the count of attempts.
#
attempts += 1
end
#
# Do we need to unwatch here?
#
@redis.unwatch
#
# Return the success/fail
#
return added
end
#
# How many jobs in the queue?
#
def size?
@redis.scard('custodian_queue')
end
#
# Empty the queue, discarding all pending jobs.
#
def flush!
@redis.del('custodian_queue')
end
end
end
|
