Class: Strand::ConditionVariable

Inherits:
Object
  • Object
show all
Defined in:
lib/strand/condition_variable.rb

Overview

Provides for Strands (Fibers) what Ruby’s ConditionVariable provides for Threads.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ ConditionVariable

Create a new condition variable.



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# File 'lib/strand/condition_variable.rb', line 6

def initialize
  @waiters = []
end

Instance Method Details

#signal ⇒ Object

Asynchronously resume a fiber waiting on this condition variable. The waiter is not resumed immediately, but on the next tick of EM’s reactor loop.

cond = Strand::ConditionVariable.new
Strand.new{ puts 1; cond.wait; puts 2 }
puts 3
cond.signal
puts 4
# output is...
1
3
4
2



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# File 'lib/strand/condition_variable.rb', line 66

def signal
  # If there are no waiters, do nothing.
  return if @waiters.empty?

  # Find a waiter to wake up.
  waiter = @waiters.shift

  # Resume it on next tick.
  EM.next_tick{ waiter.resume }
end

#wait(timeout = nil) ⇒ Object

Wait until signaled. Returns true upon returning.

x = nil
cond = Strand::ConditionVariable.new
Strand.new{ cond.wait; x = 1; cond.signal }
puts x # => nil
cond.signal
cond.wait # => true
puts x # => 1

If timeout is a number, then returns false if timed out or true if signaled.

x = nil
cond = Strand::ConditionVariable.new
Strand.new{ cond.wait; x = 1; cond.signal }
puts x # => nil
cond.wait(0.01) # => false
puts x # => nil



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# File 'lib/strand/condition_variable.rb', line 25

def wait(timeout = nil)
  # Get the fiber that called us.
  fiber = Fiber.current

  # Add the fiber to the list of waiters.
  @waiters << fiber

  # Setup the timer if they specified a timeout
  timer = EM::Timer.new(timeout){ fiber.resume(:timeout) } if timeout

  # Wait for signal or timeout.
  if Fiber.yield == :timeout
    # Timeout occurred.

    # Remove from list of waiters.
    @waiters.delete(fiber)

    false
  else
    # Ok we were signaled.

    # Cancel the timer if there is one.
    timer.cancel if timer

    true
  end

end