ConditionVariable objects augment class Mutex. Using condition variables, it is possible to suspend while in the middle of a critical section until a resource becomes available.

Example:

require 'thread'

mutex = Mutex.new
resource = ConditionVariable.new

a = Thread.new {
  mutex.synchronize {
    # Thread 'a' now needs the resource
    resource.wait(mutex)
    # 'a' can now have the resource
  }
}

b = Thread.new {
  mutex.synchronize {
    # Thread 'b' has finished using the resource
    resource.signal
  }
}
Methods
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Class Public methods
new()

Creates a new ConditionVariable

Source: show | on GitHub 

# File ../ruby/lib/thread.rb, line 54
def initialize
  @waiters = []
  @waiters_mutex = Mutex.new
end
Instance Public methods
broadcast()

Wakes up all threads waiting for this lock.

Source: show | on GitHub 

# File ../ruby/lib/thread.rb, line 96
def broadcast
  # TODO: incomplete
  waiters0 = nil
  @waiters_mutex.synchronize do
    waiters0 = @waiters.dup
    @waiters.clear
  end
  for t in waiters0
    begin
      t.run
    rescue ThreadError
    end
  end
  self
end
signal()

Wakes up the first thread in line waiting for this lock.

Source: show | on GitHub 

# File ../ruby/lib/thread.rb, line 83
def signal
  begin
    t = @waiters_mutex.synchronize { @waiters.shift }
    t.run if t
  rescue ThreadError
    retry
  end
  self
end
wait(mutex, timeout=nil)

Releases the lock held in mutex and waits; reacquires the lock on wakeup.

If timeout is given, this method returns after timeout seconds passed, even if no other thread doesn't signal.

Source: show | on GitHub 

# File ../ruby/lib/thread.rb, line 65
def wait(mutex, timeout=nil)
  begin
    # TODO: mutex should not be used
    @waiters_mutex.synchronize do
      @waiters.push(Thread.current)
    end
    mutex.sleep timeout
  ensure
    @waiters_mutex.synchronize do
      @waiters.delete(Thread.current)
    end
  end
  self
end