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module Gitlab
# JobWaiter can be used to wait for a number of Sidekiq jobs to complete.
#
# Its use requires the cooperation of the sidekiq jobs themselves. Set up the
# waiter, then start the jobs, passing them its `key`. Their `perform` methods
# should look like:
#
# def perform(args, notify_key)
# # do work
# ensure
# ::Gitlab::JobWaiter.notify(notify_key, jid)
# end
#
# The JobWaiter blocks popping items from a Redis array. All the sidekiq jobs
# push to that array when done. Once the waiter has popped `count` items, it
# knows all the jobs are done.
class JobWaiter
def self.notify(key, jid)
Gitlab::Redis::SharedState.with { |redis| redis.lpush(key, jid) }
end
attr_reader :key, :jobs_remaining, :finished
# jobs_remaining - the number of jobs left to wait for
def initialize(jobs_remaining)
@key = "gitlab:job_waiter:#{SecureRandom.uuid}"
@jobs_remaining = jobs_remaining
@finished = []
end
# Waits for all the jobs to be completed.
#
# timeout - The maximum amount of seconds to block the caller for. This
# ensures we don't indefinitely block a caller in case a job takes
# long to process, or is never processed.
def wait(timeout = 10)
deadline = Time.now.utc + timeout
Gitlab::Redis::SharedState.with do |redis|
# Fallback key expiry: allow a long grace period to reduce the chance of
# a job pushing to an expired key and recreating it
redis.expire(key, [timeout * 2, 10.minutes.to_i].max)
while jobs_remaining > 0
# Redis will not take fractional seconds. Prefer waiting too long over
# not waiting long enough
seconds_left = (deadline - Time.now.utc).ceil
# Redis interprets 0 as "wait forever", so skip the final `blpop` call
break if seconds_left <= 0
list, jid = redis.blpop(key, timeout: seconds_left)
break unless list && jid # timed out
@finished << jid
@jobs_remaining -= 1
end
# All jobs have finished, so expire the key immediately
redis.expire(key, 0) if jobs_remaining == 0
end
finished
end
end
end
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