run 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.

Note that you should avoid using run inside threads

• The calling threads will not resume before run returns.
• Successive invocations of run are serialized: an invocation of run will 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.

yield () is a threads which suspends itself and then resumes as soon as possible and terminates.

Hook 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.

Hooks, of type unit -> unit, that are called before each iteration of the Lwt main loop.

Hooks, of type unit -> unit, that are called after each iteration of the Lwt main loop.

Promise-returning hooks, of type unit -> unit Lwt.t, that are called at process exit. Exceptions raised by these hooks are ignored.

• deprecated

  Use module Enter_iter_hooks.

• deprecated

  Use module Leave_iter_hooks.

• deprecated

  Use module Exit_hooks.

Lwt_main.at_exit hook is the same as ignore (Lwt_main.Exit_hooks.add_first hook).