Lwt_switchSourceLwt switches
Switch has two goals:
For example, consider the following interface:
type id
val free : id -> unit Lwt.t
val f : unit -> id Lwt.t
val g : unit -> id Lwt.t
val h : unit -> id Lwt.tNow you want to call f, g and h in parallel. You can simply do:
lwt idf = f () and idg = g () and idh = h () in
...However, one may want to handle possible failures of f (), g () and h (), and disable all allocated resources if one of these three threads fails. This may be hard since you have to remember which one failed and which one returned correctly.
Now if we change the interface a little bit:
val f : ?switch : Lwt_switch.t -> unit -> id Lwt.t
val g : ?switch : Lwt_switch.t -> unit -> id Lwt.t
val h : ?switch : Lwt_switch.t -> unit -> id Lwt.tthe code becomes:
Lwt_switch.with_switch (fun switch ->
lwt idf = f ~switch ()
and idg = g ~switch ()
and idh = h ~switch () in
...
)Type of switches.
with_switch fn is fn switch, where switch is a fresh switch that is turned off when the callback thread finishes (whether it succeeds or fails).
is_on switch returns true if the switch is currently on, and false otherwise.
turn_off switch turns off the switch. It calls all registered hooks, waits for all of them to terminate, then returns. If one of the hooks failed, it will fail with the exception raised by the hook. If the switch is already off, it does nothing.
Exception raised when trying to add a hook to a switch that is already off.
check switch does nothing if switch is None or contains an switch that is currently on, and raises Off otherwise.