Module Lwt

module Lwt: sig .. end

Module Lwt: cooperative light-weight threads.

type 'a t

The type of threads returning a result of type 'a.

val return : 'a -> 'a t

return e is a thread whose return value is the value of the expression e.

val fail : exn -> 'a t

fail e is a thread that fails with the exception e.

val bind : 'a t -> ('a -> 'b t) -> 'b t

bind t f is a thread which first waits for the thread t to terminate and then, if the thread succeeds, behaves as the application of function f to the return value of t. If the thread t fails, bind t f also fails, with the same exception.

The expression bind t (fun x -> t') can intuitively be read as let x = t in t'.

Note that bind is also often used just for synchronization purpose: t' will not execute before t is terminated.

The result of a thread can be bound several time.

val (>>=) : 'a t -> ('a -> 'b t) -> 'b t

t >>= f is an alternative notation for bind t f.

val catch : (unit -> 'a t) -> (exn -> 'a t) -> 'a t

catch t f is a thread that behaves as the thread t () if this thread succeeds. If the thread t () fails with some exception, catch t f behaves as the application of f to this exception.

val try_bind : (unit -> 'a t) -> ('a -> 'b t) -> (exn -> 'b t) -> 'b t

try_bind t f g behaves as bind (t ()) f if t does not fail. Otherwise, it behaves as the application of g to the exception associated to t ().

val choose : 'a t list -> 'a t

choose l behaves as the first thread in l to terminate. If several threads are already terminated, one is choosen at random.

val ignore_result : 'a t -> unit

ignore_result t start the thread t and ignores its result value if the thread terminates sucessfully. However, if the thread t fails, the exception is raised instead of being ignored. You should use this function if you want to start a thread and don't care what its return value is, nor when it terminates (for instance, because it is looping). Note that if the thread t yields and later fails, the exception will not be raised at this point in the program.

val wait : unit -> 'a t

wait () is a thread which sleeps forever (unless it is resumed by one of the functions wakeup, wakeup_exn below). This thread does not block the execution of the remainder of the program (except of course, if another thread tries to wait for its termination).

Execution order A thread executes as much as possible. Switching to another thread is always explicit.

Exception handling

You must use "fail e" instead of "raise e" if you want the exception to be wrapped into the thread.
The construction try t with ... will not caught the exception associated to the thread t if this thread fails. You should use catch instead.