Module Lwt_pipe.Maybe_bounded

Maybe_bounded are pipes that may or may not be bounded. This is decided when createing the pipe and can be queried with the bounded function.

type 'a t

Type of queues holding values of type 'a.

val create : ?bound:(int * ('a -> int)) -> unit -> 'a t

create ~bound:(max_size, compute_size) () is an empty queue that can hold max bound "bytes" of data, using compute_size to compute the number of "bytes" in a datum. I.e., it is equivalent to Bounded.create ~max_size ~compute_size but the functions below make no assumptions about the bound leading to a slightly different interface and potentially worse performances.

create (), with the bound argument no set, is an empty queue that is unbounded. I.e., it is equivalent to Unbounded.create () but the functions below make no assumptions about the bound leading to a slightly different interface and potentially worse performances.

val bounded : 'a t -> bool

bounded t is true iff t was created with a set bound.

val push : 'a t -> 'a -> unit Lwt.t

push q v is a promise that is pending until there is enough space in q to accommodate v. When this happens v is added to the end of q and the promise resolves.

If there is enough space in q to accommodate v when the call is made, then the v is added immediately and an already resolved promise is returned.

Note that if several writes are stuck because the pipe is full. These writes will succeed in an order that might be different from the order the write attempts were made. Specifically, when pushing elements of different computed sizes, smaller pushes may be resolved earlier if enough space is freed.

  • raises {!Closed}

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

val pop : 'a t -> 'a Lwt.t

pop q is a promise that is pending until there is an 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.

val pop_with_timeout : unit Lwt.t -> 'a t -> 'a option Lwt.t

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.

val pop_all : 'a t -> 'a list Lwt.t

pop_all q is a promise that is pending until there is an 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 an element 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.

val pop_all_now : 'a t -> 'a list

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.

val peek : 'a t -> 'a Lwt.t

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.

val peek_all_now : 'a t -> 'a list

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.

val push_now : 'a t -> 'a -> bool

push_now q v either

  • adds v at the ends of q immediately and returns true, or
  • if q is full, returns false.
  • raises Closed

    if q is closed.

val pop_now : 'a t -> 'a option

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.

val length : 'a t -> int

length q is the number of elements in q.

val is_empty : 'a t -> bool

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

val close : 'a t -> unit

close q the write-end of q:

  • Pending and 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.

val is_closed : 'a t -> bool
val push_overhead : int

The number of bytes used in the internal representation to hold an element in the queue.