package lwt
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lwt.unix
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package lwt
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Main loop and event queue
This module controls the ``main-loop'' of Lwt.
val run : 'a Lwt.t -> 'arun p calls the Lwt scheduler repeatedly until p resolves, and returns the value of p if it is fulfilled. If p is rejected with an exception, that exception is raised.
Every native or bytecode program that uses Lwt should always use this function for evaluating a promise at the top level (such as its main function or main loop), otherwise promises that depend on I/O operations will not be resolved.
Example:
let main () = Lwt_io.write_line Lwt_io.stdout "hello world"
let () = Lwt_main.run @@ main ()When targeting JavaScript, Lwt_main.run is not available, but neither it's necessary since the JS environment automatically takes care of the I/O considerations.
On Unix, calling Lwt_main.run installs a SIGCHLD handler, which is needed for the implementations of Lwt_unix.waitpid and Lwt_unix.wait4. As a result, programs that call Lwt_main.run and also use non-Lwt system calls need to handle those system calls failing with EINTR.
Note that you should avoid using run inside threads
- The calling threads will not resume before
runreturns. - Successive invocations of
runare serialized: an invocation ofrunwill not terminate before all subsequent invocations are terminated.
Note also that it is not safe to call run in a function registered with Pervasives.at_exit, use the at_exit function of this module instead.
val yield : unit -> unit Lwt.tyield () is a threads which suspends itself and then resumes as soon as possible and terminates.
module type Hooks = sig ... endHook sequences. Each module of this type is a set of hooks, to be run by Lwt at certain points during execution. See modules Enter_iter_hooks, Leave_iter_hooks, and Exit_hooks.
module Enter_iter_hooks : Hooks with type 'return_value kind = 'return_valueHooks, of type unit -> unit, that are called before each iteration of the Lwt main loop.
module Leave_iter_hooks : Hooks with type 'return_value kind = 'return_valueHooks, of type unit -> unit, that are called after each iteration of the Lwt main loop.
module Exit_hooks : Hooks with type 'return_value kind = 'return_value Lwt.tPromise-returning hooks, of type unit -> unit Lwt.t, that are called at process exit. Exceptions raised by these hooks are ignored.
val enter_iter_hooks : (unit -> unit) Lwt_sequence.tval leave_iter_hooks : (unit -> unit) Lwt_sequence.tval exit_hooks : (unit -> unit Lwt.t) Lwt_sequence.tval at_exit : (unit -> unit Lwt.t) -> unitLwt_main.at_exit hook is the same as ignore (Lwt_main.Exit_hooks.add_first hook).