Type of queues holding values of type 'a.

create () is an empty unbounded queue.

push q v: v is added immediately to q.

Note that pushing never needs to wait for room to be available inside the pipe. As a result, push returns unit. This is unlike Bounded.push, where Bounded.push may need to wait for some space to be freed inside the pipe and thus returns unit Lwt.t.

• raises {!Closed}

  if q is closed.

pop q is a promise that is pending until there is at least one element in q. When this happens an element is removed and the promise is fulfilled with it.

If there is already an element in q when the call is made, the element is removed immediately and an already resolved promise is returned.

• raises {!Closed}

  if q is empty and closed. More specifically, the promise is rejected with Closed if q is empty and closed.

pop_with_timeout t q is a promise that behaves similarly to pop q except that it resolves with None if t resolves before there is an element in q to pop.

Note that there can be multiple promises that are awaiting for an element to pop from the queue. As a result, it is possible that pop_with_timeout is fulfilled with None even though values have been pushed to the q.

t is canceled (i.e., it fails with Canceled) if an element is returned.

• raises {!Closed}

  if q is empty and closed. More specifically, the promise is rejected with Closed if q is empty and closed.

pop_all q is a promise that is pending until there is at least one element in q. When this happens, all the elements of q are removed and the promise is fulfilled with the list of elements (in the order in which they were inserted).

If there is already one or more elements in q when the call is made, the elements are removed immediately and an already resolved promise is returned.

• raises {!Closed}

  if q is empty and closed. More specifically, the promise is rejected with Closed if q is empty and closed.

In practice, this function returns a promise that either:

• is pending and will resolve with a single-element list,
• is already resolved with a list of at least one element,
• or will be rejected with Closed.

pop_all_now q removes and returns all the elements in q (in the order in which they were inserted). If q is empty, [] is returned.

• raises {!Closed}

  if q is empty and closed.

peek q returns the same value as pop q but does not remove the returned element.

• raises {!Closed}

  if q is empty and closed. More specifically, the promise is rejected with Closed if q is empty and closed.

peek_all_now q returns the elements in the q (oldest first), or [] if empty. It does not remove elements from q.

• raises {!Closed}

  if q is empty and closed.

pop_now q may remove and return the first element in q if q contains at least one element.

• raises Closed

  if q is closed.

length q is the number of elements in q.

is_empty q is true if q is empty, false otherwise.

close q the write-end of q:

• Future write attempts will fail with Closed.
• If there is data left in the pipe, then future read attempts will be resolved until the remaining data is drained, after which further reads will fail with Closed.
• If there is no data left in the pipe, then pending and future reads will fail with Closed.

The close function is idempotent.

is_closed q is true if close q has been called. It is false otherwise.