Timer

Versatile Timer class which relies on Crystal scheduler.

Basic example:

Timer.new(1.second) do
  puts "1 second has passed!"
end

sleep

Example with select:

channel = Channel(Nil).new

select
when channel.receive
  puts "Never happens"
when Timer.new(1.second)
  puts "Timeout!"
end

sleep # Will print "Timeout!" after 1 second

You can #postpone and #reschedule a timer. The latter has bigger performance impact if rescheduling at an earlier moment of time.

at = Time.utc_now + 5.minutes

timer = Timer.new(at) do
  puts "Triggered"
end

# OK, will trigger in 6 minutes from now
timer.postpone(1.minute)

# ditto
timer.reschedule(Time.utc_now + 6.minutes)

# Worse performance but still acceptable
timer.reschedule(Time.utc_now + 1.minute)

Note that a timer can be scheduled at a moment in the past, which means that it would run immediately after given control by the Crystal scheduler.

You can also #trigger a timer (still calling the block in another fiber) or #cancel it completely.