Class: ConditionVariable

Inherits:
Object
  • Object
show all
Defined in:
lib/rubysl/thread/thread.rb

Overview

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
  }
}

Instance Method Summary collapse

Constructor Details

#initialize ⇒ ConditionVariable

Creates a new ConditionVariable



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# File 'lib/rubysl/thread/thread.rb', line 46

def initialize
  @waiters = []
end

Instance Method Details

#broadcast ⇒ Object

Wakes up all threads waiting for this lock.



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# File 'lib/rubysl/thread/thread.rb', line 101

def broadcast
  Rubinius.lock(self)
  begin
    @waiters.shift << true until @waiters.empty?
  ensure
    Rubinius.unlock(self)
  end
  self
end

#signal ⇒ Object

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



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# File 'lib/rubysl/thread/thread.rb', line 88

def signal
  Rubinius.lock(self)
  begin
    @waiters.shift << true unless @waiters.empty?
  ensure
    Rubinius.unlock(self)
  end
  self
end

#wait(mutex, timeout = nil) ⇒ Object

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



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# File 'lib/rubysl/thread/thread.rb', line 53

def wait(mutex, timeout=nil)
  Rubinius.lock(self)

  begin
    wchan = Rubinius::Channel.new

    begin
      mutex.unlock
      @waiters.push wchan
      Rubinius.unlock(self)
      signaled = wchan.receive_timeout timeout
    ensure
      mutex.lock
      Rubinius.lock(self)

      unless signaled or @waiters.delete(wchan)
        # we timed out, but got signaled afterwards (e.g. while waiting to
        # acquire @lock), so pass that signal on to the next waiter
        @waiters.shift << true unless @waiters.empty?
      end
    end

    if timeout
      !!signaled
    else
      self
    end
  ensure
    Rubinius.unlock(self)
  end
end