signal handling calls Lwt_main.run

[edwintorok]

See cleanup.ml, it calls Lwt_main.run when handling a signal.
I think this is very fragile and could lock up under some situations, reading the Lwt_main.run documentation it says:

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. 

So if we get a signal while the main Lwt_main.run is running the one inside the signal handler wouldn't run at all.

Unfortunately the Lwt documentation is not very clear on how to resolve Lwt promises when triggered from a signal handler, but perhaps the right thing to do would be to use Lwt.async (...) (provided we have an exception handler set up for asynchronous exceptions).

[gaborigloi]

I'm not quite sure about the order in which things happen when we catch the signal
If the Lwt main loop is still running, then we do not need Lwt_main.run
Otherwise, if it is not running at that point, it's safe to run it.