Queue

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 type of queue. In a FIFO queue, the first tasks added are the first retrieved.

Example:

queue = 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

Public Class Methods

new() click to toggle source

Creates a new queue instance.

 
               static VALUE
rb_queue_initialize(VALUE self)
{
    struct rb_queue *q = queue_ptr(self);
    RB_OBJ_WRITE(self, &q->que, ary_buf_new());
    list_head_init(queue_waitq(q));
    return self;
}

Public Instance Methods

<<(p1) click to toggle source

Alias for: push

clear() click to toggle source

Removes all objects from the queue.

 
               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 click to toggle source

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

 
               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;
}

closed? click to toggle source

Returns true if the queue is closed.

 
               static VALUE
rb_queue_closed_p(VALUE self)
{
    return queue_closed_p(self) ? Qtrue : Qfalse;
}

deq(*args) click to toggle source

Alias for: pop

empty? click to toggle source

Returns true if the queue is empty.

 
               static VALUE
rb_queue_empty_p(VALUE self)
{
    return queue_length(self, queue_ptr(self)) == 0 ? Qtrue : Qfalse;
}

enq(p1) click to toggle source

Alias for: push

length click to toggle source

size

Returns the length of the queue.

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

Also aliased as: size

num_waiting() click to toggle source

Returns the number of threads waiting on the queue.

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

    return INT2NUM(q->num_waiting);
}

pop(non_block=false) click to toggle source

deq(non_block=false)

shift(non_block=false)

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.

 
               static VALUE
rb_queue_pop(int argc, VALUE *argv, VALUE self)
{
    int should_block = queue_pop_should_block(argc, argv);
    return queue_do_pop(self, queue_ptr(self), should_block);
}

Also aliased as: deq, shift

push(object) click to toggle source

enq(object)

<<(object)

Pushes the given object to the queue.

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

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