Module Picos_aux_mpmcq

Lock-free multi-producer, multi-consumer queue.

🏎️ This data structure is optimized for use as a building block of the ready queue of a (mostly) fair (i.e. mostly FIFO) multi-threaded scheduler. For example, one could use a queue per thread, to reduce contention, and have threads attempt to pop fibers from the queues of other threads when their local queues are empty. It is also possible to use only a single shared queue, but that will result in very high contention as this queue is not relaxed.

API

type !'a t

A multi-producer, multi-consumer queue.

val create : ?padded:bool -> unit -> 'a t

create () returns a new empty multi-producer, multi-consumer queue.

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

push queue value adds the value to the tail of the queue.

val push_head : 'a t -> 'a -> unit

push_head queue value adds the value to the head of the queue.

exception Empty

Raised by pop_exn in case it finds the queue empty.

val pop_exn : 'a t -> 'a

pop_exn queue tries to remove the value at the head of the queue. Returns the removed value or raises Empty in case the queue was empty.

  • raises Empty

    in case the queue was empty.

val length : 'a t -> int

length queue returns the length or the number of values in the queue.

val is_empty : 'a t -> bool

is_empty queue is equivalent to length queue = 0.

Examples

An example top-level session:

# let q : int Picos_aux_mpmcq.t =
    Picos_aux_mpmcq.create ()
val q : int Picos_aux_mpmcq.t = <abstr>

# Picos_aux_mpmcq.push q 42
- : unit = ()

# Picos_aux_mpmcq.push_head q 76
- : unit = ()

# Picos_aux_mpmcq.length q
- : int = 2

# Picos_aux_mpmcq.push q 101
- : unit = ()

# Picos_aux_mpmcq.pop_exn q
- : int = 76

# Picos_aux_mpmcq.pop_exn q
- : int = 42

# Picos_aux_mpmcq.pop_exn q
- : int = 101

# Picos_aux_mpmcq.pop_exn q
Exception: Picos_aux_mpmcq.Empty.