libubox: How to terminate uloop orderly?

[Peter Seiderer]

Hello Alexander,

On Tue, 17 May 2022 12:37:00 +0300, Alexandru Ardelean <ardeleanalex at gmail.com> wrote:

> On Tue, May 17, 2022 at 12:06 PM Koch, Alexander via openwrt-devel
> <openwrt-devel at lists.openwrt.org> wrote:
> >
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> > ---------- Forwarded message ----------
> > From: "Koch, Alexander" <akoch at initse.com>
> > To: "openwrt-devel at lists.openwrt.org" <openwrt-devel at lists.openwrt.org>
> > Cc:
> > Bcc:
> > Date: Tue, 17 May 2022 09:04:13 +0000
> > Subject: libubox: How to terminate uloop orderly?
> > Hi openwrt-devel,
> >
> > I'm writing a small daemon in C that talks to a specific IC and shall offer its
> > functionality to other OpenWRT components via ubus.
> >
> > It spawns a separate pthread for all ubus related things, which ends up calling
> > `uloop_run()`. So far everything works fine and I can see all objects exposed by
> > my daemon on the bus.
> >
> > The issue I'm facing now is that I cannot seem to find a way of orderly shutting
> > down the daemon, as the thread calling `uloop_run()` never returns from it. I've
> > tried calling `uloop_end()` as well as replacing `uloop_run()` by
> > `uloop_run_timeout(10)` but that didn't help.
>
> I never thought/knew that uloop_run() & threads mixed well.
> I never tried it too much either.
>
> I always thought of uloop_run() being the main process loop and then
> "maybe" starting some threads from there.
> And I think uloop is kind of designed to be more single-process than
> multi-process.
>
> So, if you have one uloop somewhere and try to do some uloop calls in
> a thread, it's kind of race-y and potentially buggy.
> Also because they work on the same main loop data.
>
> >
> > So I'm wondering: what is the correct way to terminate the uloop?
> >
> > One thing that does seem to work is sending the thread a SIGTERM via
> > `pthread_kill()`. But that makes `uloop_run()` return a non-zero value (15) and,
> > as signals are delivered to the entire process, can have side-effects on other
> > parts of the daemon, so I'd prefer to avoid this method.
> >

Despite the mentioned multi-threading problems with this approach
one option to stop the uloop_run() call from another thread is by
calling:

	 uloop_handle_sigint(SIGTERM)

But needs a patched libubox to get public access to this method, e.g.:

diff --git a/uloop.c b/uloop.c
index 8517366..b7cc764 100644
--- a/uloop.c
+++ b/uloop.c
@@ -402,7 +402,7 @@ static void uloop_signal_wake(void)
 } while (1);
 }

-static void uloop_handle_sigint(int signo)
+void uloop_handle_sigint(int signo)
 {
 uloop_status = signo;
 uloop_cancelled = true;
diff --git a/uloop.h b/uloop.h
index 36084f5..ab061a5 100644
--- a/uloop.h
+++ b/uloop.h
@@ -112,4 +112,7 @@ static inline int uloop_run(void)
 }
 void uloop_done(void);

+
+void uloop_handle_sigint(int signo);
+
 #endif


Regards,
Peter


> >
> > Thanks in advance for any hints!
> >
> >
> > Best regards,
> >
> > Alex
> >
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