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Class: Thread::Queue

Relationships & Source Files
Inherits: Object
Defined in: thread_sync.c,
thread_sync.c,
thread_sync.rb

Overview

The Queue class implements multi-producer, multi-consumer queues. It is especially useful in threaded programming when information must be exchanged safely between multiple threads. The Queue class implements all the required locking semantics.

The class implements FIFO (first in, first out) type of queue. In a FIFO queue, the first tasks added are the first retrieved.

Example:

queue = Thread::Queue.new

producer = Thread.new do
  5.times do |i|
    sleep rand(i) # simulate expense
    queue << i
    puts "#{i} produced"
  end
end

consumer = Thread.new do
  5.times do |i|
    value = queue.pop
    sleep rand(i/2) # simulate expense
    puts "consumed #{value}"
  end
end

consumer.join

Class Method Summary

  • .new ⇒ Queue constructor

    Creates a new queue instance, optionally using the contents of an enumerable for its initial state.

Instance Attribute Summary

Instance Method Summary

Constructor Details

.new ⇒ Queue .new(enumerable) ⇒ Queue

Creates a new queue instance, optionally using the contents of an enumerable for its initial state.

Example:

q = Thread::Queue.new
#=> #<Thread::Queue:0x00007ff7501110d0>
q.empty?
#=> true

q = Thread::Queue.new([1, 2, 3])
#=> #<Thread::Queue:0x00007ff7500ec500>
q.empty?
#=> false
q.pop
#=> 1
[ GitHub ] 

  


# File 'thread_sync.c', line 970



static VALUE
rb_queue_initialize(int argc, VALUE *argv, VALUE self)
{
    VALUE initial;
    struct rb_queue *q = queue_ptr(self);
    if ((argc = rb_scan_args(argc, argv, "01", &initial)) == 1) {
        initial = rb_to_array(initial);
    }
    RB_OBJ_WRITE(self, queue_list(q), ary_buf_new());
    ccan_list_head_init(queue_waitq(q));
    if (argc == 1) {
        rb_ary_concat(q->que, initial);
    }
    return self;
}


  







Instance Attribute Details



  

    #closed?  ⇒ Boolean  (readonly)  



  

    

Returns true if the queue is closed.


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1051



static VALUE
rb_queue_closed_p(VALUE self)
{
    return RBOOL(queue_closed_p(self));
}


  








  

    #empty?  ⇒ Boolean  (readonly)  



  

    

Returns true if the queue is empty.


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1174



static VALUE
rb_queue_empty_p(VALUE self)
{
    return RBOOL(queue_length(self, queue_ptr(self)) == 0);
}


  







Instance Method Details



  

    

      #push(object)  
      #enq(object)  
      #<<(object)  
    

    Also known as: #push, #enq
  



  

    

Pushes the given object to the queue.


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1067



static VALUE
rb_queue_push(VALUE self, VALUE obj)
{
    return queue_do_push(self, queue_ptr(self), obj);
}


  








  

    #clear  
  



  

    

Removes all objects from the queue.


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1186



static VALUE
rb_queue_clear(VALUE self)
{
    struct rb_queue *q = queue_ptr(self);

    rb_ary_clear(check_array(self, q->que));
    return self;
}


  








  

    #close    



  

    

Closes the queue. A closed queue cannot be re-opened.



After the call to close completes, the following are true:


  • 

    #closed? will return true
    

  • 

    close will be ignored.
    

  • 

    calling enq/push/<< will raise a ::ClosedQueueError.
    

  • 

    when #empty? is false, calling deq/pop/shift will return an object from the queue as usual.
    

  • 

    when #empty? is true, deq(false) will not suspend the thread and will return nil. deq(true) will raise a ::ThreadError.
    




::ClosedQueueError is inherited from ::StopIteration, so that you can break loop block.



Example:



q = Thread::Queue.new
Thread.new{
  while e = q.deq # wait for nil to break loop
    # ...
  end
}
q.close


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1030



static VALUE
rb_queue_close(VALUE self)
{
    struct rb_queue *q = queue_ptr(self);

    if (!queue_closed_p(self)) {
        FL_SET(self, QUEUE_CLOSED);

        wakeup_all(queue_waitq(q));
    }

    return self;
}


  








  

    #deq(non_block = false, timeout: nil)  
  



  

    

Alias for #pop.


  



  [ GitHub ]


  

  


# File 'thread_sync.rb', line 20



alias_method :deq, :pop


  








  

    

      #push(object)  
      #enq(object)  
      #<<(object)  
    

  



  

    

Alias for #<<.


  









  

    #freeze    



  

    

The queue can’t be frozen, so this method raises an exception:



Thread::Queue.new.freeze # Raises TypeError (cannot freeze #<Thread::Queue:0x...>)


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1219



static VALUE
rb_queue_freeze(VALUE self)
{
    rb_raise(rb_eTypeError, "cannot freeze " "%+"PRIsVALUE, self);
    UNREACHABLE_RETURN(self);
}


  








  

    

      #length  
      #size  
    

    Also known as: #size
  



  

    

Returns the length of the queue.


  





  


  [ GitHub ]


  

  


# File 'thread_sync.c', line 1204



static VALUE
rb_queue_length(VALUE self)
{
    return LONG2NUM(queue_length(self, queue_ptr(self)));
}


  








  

    #marshal_dump  
  

  

    This method is for internal use only.
  

  [ GitHub ]


  

  


# File 'thread_sync.c', line 1630



static VALUE
undumpable(VALUE obj)
{
    rb_raise(rb_eTypeError, "can't dump %"PRIsVALUE, rb_obj_class(obj));
    UNREACHABLE_RETURN(Qnil);
}


  








  

    #num_waiting  
  



  

    

Returns the number of threads waiting on the queue.


  



  [ GitHub ]


  

  


# File 'thread_sync.c', line 1232



static VALUE
rb_queue_num_waiting(VALUE self)
{
    struct rb_queue *q = queue_ptr(self);

    return INT2NUM(q->num_waiting);
}


  








  

    #pop(non_block = false, timeout: nil)      Also known as: #deq, #shift
  



  

    

Retrieves data from the queue.



If the queue is empty, the calling thread is suspended until data is pushed onto the queue. If non_block is true, the thread isn’t suspended, and ::ThreadError is raised.



If timeout seconds have passed and no data is available nil is returned. If timeout is 0 it returns immediately.


  



  [ GitHub ]


  

  


# File 'thread_sync.rb', line 14



def pop(non_block = false, timeout: nil)
  if non_block && timeout
    raise ArgumentError, "can't set a timeout if non_block is enabled"
  end
  Primitive.rb_queue_pop(non_block, timeout)
end


  








  

    

      #push(object)  
      #enq(object)  
      #<<(object)  
    

  



  

    

Alias for #<<.


  





  








  

    #shift(non_block = false, timeout: nil)  
  



  

    

Alias for #pop.


  



  [ GitHub ]


  

  


# File 'thread_sync.rb', line 21



alias_method :shift, :pop


  








  

    

      #length  
      #size  
    

  



  

    

Alias for #length.