ruby 32 lines · 7 steps

A thread-safe throttle in Ruby

A Throttle class that rate-limits actions per key using a monotonic clock and a mutex for safe concurrent access.

Explained by highlit

Intermediate concurrency rate-limiting mutex monotonic-clock

1class Throttle
def initialize(interval)
  @interval = interval
  @mutex = Mutex.new
  @last_called = {}
end
7 
def call(key = :default)
  now = Process.clock_gettime(Process::CLOCK_MONOTONIC)
10 
  @mutex.synchronize do
    last = @last_called[key]
    return false if last && now - last < @interval
    @last_called[key] = now
  end
16 
  yield
  true
end
20 
def remaining(key = :default)
  last = @mutex.synchronize { @last_called[key] }
  return 0.0 unless last
24 
  elapsed = Process.clock_gettime(Process::CLOCK_MONOTONIC) - last
  [@interval - elapsed, 0.0].max
end
28 
def reset(key = :default)
  @mutex.synchronize { @last_called.delete(key) }
end
32end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1A monotonic clock avoids the bugs that wall-clock time introduces when the system clock jumps.
2Guarding shared state with a mutex keeps the check-and-update sequence atomic across threads.
3Keying timestamps by a value lets one throttle independently rate-limit many distinct actions.

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