Class: ConditionVariable

Inherits:

Object

• Object
• ConditionVariable

Defined in:

lib/thread.rb,
thread.c

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

• #broadcast ⇒ Object

  Wakes up all threads waiting for this condition.

• #initialize ⇒ ConditionVariable constructor

  Creates a new ConditionVariable.

• #marshal_dump ⇒ Object
• #marshal_load ⇒ Object

  for marshalling mutexes and condvars.

• #signal ⇒ Object

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

• #wait ⇒ Object

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

Constructor Details

#initialize ⇒ ConditionVariable

Creates a new ConditionVariable

# File 'lib/thread.rb', line 187

def initialize
  @waiters = []
end

Instance Method Details

#broadcast ⇒ Object

Wakes up all threads waiting for this condition.

# File 'lib/thread.rb', line 220

/*
 * Document-method: broadcast
 * call-seq: broadcast
 *
 * Wakes up all threads waiting for this condition.
 *
 */

static VALUE
rb_condvar_broadcast(VALUE self)
{
    ConditionVariable *condvar;

    Data_Get_Struct(self, ConditionVariable, condvar);
  
    thread_exclusive(wake_all, (VALUE)&condvar->waiting);
    rb_thread_schedule();

    return self;
}

#marshal_dump ⇒ Object

#marshal_load ⇒ Object

for marshalling mutexes and condvars

# File 'thread.c'

/* for marshalling mutexes and condvars */

static VALUE
dummy_load(VALUE self, VALUE string)
{
    return Qnil;
}

#signal ⇒ Object

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

# File 'lib/thread.rb', line 208

def signal
  begin
    t = @waiters.shift
    t.run if t
  rescue ThreadError
    retry
  end
end

#wait ⇒ Object

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

# File 'lib/thread.rb', line 194

def wait(mutex)
  begin
    mutex.exclusive_unlock do
      @waiters.push(Thread.current)
      Thread.stop
    end
  ensure
    mutex.lock
  end
end