Module `Event`

First-class synchronous communication.

This module implements synchronous inter-thread communications over channels. As in John Reppy's Concurrent ML system, the communication events are first-class values: they can be built and combined independently before being offered for communication.

type 'a channel: The type of communication channels carrying values of type 'a.

val new_channel : unit -> 'a channel: Return a new channel.

type +'a event: The type of communication events returning a result of type 'a.

val send : 'a channel -> 'a -> unit event: send ch v returns the event consisting in sending the value v over the channel ch. The result value of this event is ().

val receive : 'a channel -> 'a event: receive ch returns the event consisting in receiving a value from the channel ch. The result value of this event is the value received.

val always : 'a -> 'a event: always v returns an event that is always ready for synchronization. The result value of this event is v.

val choose : 'a event list -> 'a event: choose evl returns the event that is the alternative of all the events in the list evl.

val wrap : 'a event -> ('a -> 'b) -> 'b event: wrap ev fn returns the event that performs the same communications as ev, then applies the post-processing function fn on the return value.

val wrap_abort : 'a event -> (unit -> unit) -> 'a event: wrap_abort ev fn returns the event that performs the same communications as ev, but if it is not selected the function fn is called after the synchronization.

val guard : (unit -> 'a event) -> 'a event: guard fn returns the event that, when synchronized, computes fn() and behaves as the resulting event. This allows events with side-effects to be computed at the time of the synchronization operation.

val sync : 'a event -> 'a: ``Synchronize'' on an event: offer all the communication possibilities specified in the event to the outside world, and block until one of the communications succeed. The result value of that communication is returned.

val select : 'a event list -> 'a: ``Synchronize'' on an alternative of events. select evl is shorthand for sync(choose evl).

val poll : 'a event -> 'a option: Non-blocking version of Event.sync: offer all the communication possibilities specified in the event to the outside world, and if one can take place immediately, perform it and return Some r where r is the result value of that communication. Otherwise, return None without blocking.