The Thread::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 Thread::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
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;
}
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
static VALUE
rb_queue_clear(VALUE self)
{
struct rb_queue *q = queue_ptr(self);
rb_ary_clear(check_array(self, q->que));
return self;
}
Removes all objects from the queue.
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;
}
Closes the queue. A closed queue cannot be re-opened.
After the call to close completes, the following are true:
-
closed?will return true -
closewill 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 aThreadError.
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
static VALUE
rb_queue_closed_p(VALUE self)
{
return RBOOL(queue_closed_p(self));
}
Returns true if the queue is closed.
static VALUE
rb_queue_empty_p(VALUE self)
{
return RBOOL(queue_length(self, queue_ptr(self)) == 0);
}
Returns true if the queue is empty.
static VALUE
rb_queue_freeze(VALUE self)
{
rb_raise(rb_eTypeError, "cannot freeze " "%+"PRIsVALUE, self);
UNREACHABLE_RETURN(self);
}
The queue can’t be frozen, so this method raises an exception:
Thread::Queue.new.freeze # Raises TypeError (cannot freeze #<Thread::Queue:0x...>)
static VALUE
rb_queue_length(VALUE self)
{
return LONG2NUM(queue_length(self, queue_ptr(self)));
}
Returns the length of the queue.
static VALUE
rb_queue_num_waiting(VALUE self)
{
struct rb_queue *q = queue_ptr(self);
return INT2NUM(q->num_waiting);
}
Returns the number of threads waiting on the queue.
# File tmp/rubies/ruby-3.4.0-preview1/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
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.
static VALUE
rb_queue_push(VALUE self, VALUE obj)
{
return queue_do_push(self, queue_ptr(self), obj);
}
Pushes the given object to the queue.