Lwt_main.run p
calls the Lwt scheduler, performing I/O until p
resolves. Lwt_main.run p
returns the value in p
if p
is fulfilled. If p
is rejected with an exception instead, Lwt_main.run p
raises that exception.
Every native and bytecode program that uses Lwt should call this function at its top level. It implements the Lwt main loop.
Example:
let main () = Lwt_io.write_line Lwt_io.stdout "hello world"
let () = Lwt_main.run (main ())
Lwt_main.run
is not available when targeting JavaScript, because the environment (such as Node.js or the browser's script engine) implements the I/O loop.
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
.
Nested calls to Lwt_main.run
are not allowed. That is, do not call Lwt_main.run
in a callback triggered by a promise that is resolved by an outer invocation of Lwt_main.run
. If your program makes such a call, Lwt_main.run
will raise Failure
. This should be considered a logic error (i.e., code making such a call is inherently broken).
It is not safe to call Lwt_main.run
in a function registered with Pervasives.at_exit
, use Lwt_main.at_exit
instead.