callback never invoked

Marc Lehmann schmorp at
Sun Oct 25 15:28:51 CET 2020

On Sun, Oct 18, 2020 at 02:46:44PM +0500, rustahm <rustahm at> wrote:
> libev++ to watch a directory of files and call the callback function as
> soon as inotify gives at least one relevant event. And I don't want libev++
> to block my main program, that's why I tried to use it with NOWAIT.

All event libraries block at least one thread. You coulöd move that into
something other than your main thread, but that complicates things so I would
not reocmmend that.

> Am I doing it totally wrong? Is libev++ a right tool for the task?

I am not sure what you are trying to achieve, but libev (not libev++) does
kind of impose event-based programming on the user. You could use it
differently, but that would be very advanced, and possibly also painful.

So if you can't use an event-based approach and do you work in callbacks,
libev (or any other event library) would be the wrong tool.

> If I add ev_run(EV_A_ 0); to engage_watcher() I get use of undeclared
> identifier 'loop'.

You cna either use "ev_run (ev_default_loop (), 0)" or, if you have more
than one loop, pass the "struct ev_loop *" around. There is also a macro
you can use "ev_run (EV_DEFAULT_UC_ 0)" that is faster than calling
ev_default_loop if the loop is guartanteed to be initialiased already.

> and run the program but it gets blocked until I change a file in the
> directory being watched.

Yes, that's how it works. You need to cal ev_run in your main program and
do your work in callbacks, always returning to the main loop.

                The choice of a       Deliantra, the free code+content MORPG
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