package fiber

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State variables

A "state variable" Svar.t differs from Ivar.t in that it can be updated multiple times. It is particularly useful if you'd like to observe the state of a process by subscribing to "interesting" (from your perspective) events.

For example, a build system can have a complex state machine, switching between states like "waiting for source file changes", "building", etc., by calling Svar.write on the corresponding state variable. If you don't care about most of the states but would like to observe all errors, you can use Svar.wait ~until:is_error to be woken up when an error happens. Other observers may have different preferences, expressed with different until predicates. You can also use the non-blocking Svar.read if you'd like to use polling instead.

type 'a t

'a t is a state variable holding the value of type 'a

val create : 'a -> 'a t

create init creates a new state variable initialized with init

val read : 'a t -> 'a

read t returns the current value of t

val wait : 'a t -> until:('a -> bool) -> unit fiber

wait t ~until waits until t's value satisfies the predicate until. If the current value satisfies it, wait returns immediately, otherwise, the caller is blocked.

val write : 'a t -> 'a -> unit fiber

write t a sets the current value of t to a