Re: [Qemu-devel] [PATCH 3/9] chardev: use a child source for qio input source

[Marc-André Lureau]

Hi

On Thu, Apr 4, 2019 at 5:18 PM KONRAD Frederic
<address@hidden> wrote:
>
> Hi guys,
>
> We have some random delays with gdbstub since this commit under Windows.
> Basically while debugging the next command can sometimes take more than 5
> seconds while it usually tooks 30ms before. It is not target dependent I see
> that happening with sparc, ppc, riscv, etc.. but only on Windows host.
>
> Does that ring a bell?

No, is this with a socket chardev or other kind?

Could you check the chardev behaviour with the HMP monitor for ex:
qemu -chardev socket,id=foo,server,host=localhost,port=9999 -monitor chardev:foo

Is this also taking a few seconds to reply?

Have you checked running tests/test-char on windows? Is this also
taking long (>2sec)?

>
> Cheers,
> Fred
>
> Le 8/28/18 à 12:23 AM, Marc-André Lureau a écrit :
> > GLib child source were added with version 2.28. We can use them now
> > that we bumped our requirement to 2.40.
> >
> > Signed-off-by: Marc-André Lureau <address@hidden>
> > ---
> >   chardev/char-io.c | 48 +++++------------------------------------------
> >   1 file changed, 5 insertions(+), 43 deletions(-)
> >
> > diff --git a/chardev/char-io.c b/chardev/char-io.c
> > index f81052481a..8ced184160 100644
> > --- a/chardev/char-io.c
> > +++ b/chardev/char-io.c
> > @@ -33,7 +33,6 @@ typedef struct IOWatchPoll {
> >       IOCanReadHandler *fd_can_read;
> >       GSourceFunc fd_read;
> >       void *opaque;
> > -    GMainContext *context;
> >   } IOWatchPoll;
> >
> >   static IOWatchPoll *io_watch_poll_from_source(GSource *source)
> > @@ -55,47 +54,24 @@ static gboolean io_watch_poll_prepare(GSource *source,
> >           iwp->src = qio_channel_create_watch(
> >               iwp->ioc, G_IO_IN | G_IO_ERR | G_IO_HUP | G_IO_NVAL);
> >           g_source_set_callback(iwp->src, iwp->fd_read, iwp->opaque, NULL);
> > -        g_source_attach(iwp->src, iwp->context);
> > -    } else {
> > -        g_source_destroy(iwp->src);
> > +        g_source_add_child_source(source, iwp->src);
> >           g_source_unref(iwp->src);
> > +    } else {
> > +        g_source_remove_child_source(source, iwp->src);
> >           iwp->src = NULL;
> >       }
> >       return FALSE;
> >   }
> >
> > -static gboolean io_watch_poll_check(GSource *source)
> > -{
> > -    return FALSE;
> > -}
> > -
> >   static gboolean io_watch_poll_dispatch(GSource *source, GSourceFunc 
> > callback,
> >                                          gpointer user_data)
> >   {
> > -    abort();
> > -}
> > -
> > -static void io_watch_poll_finalize(GSource *source)
> > -{
> > -    /* Due to a glib bug, removing the last reference to a source
> > -     * inside a finalize callback causes recursive locking (and a
> > -     * deadlock).  This is not a problem inside other callbacks,
> > -     * including dispatch callbacks, so we call io_remove_watch_poll
> > -     * to remove this source.  At this point, iwp->src must
> > -     * be NULL, or we would leak it.
> > -     *
> > -     * This would be solved much more elegantly by child sources,
> > -     * but we support older glib versions that do not have them.
> > -     */
> > -    IOWatchPoll *iwp = io_watch_poll_from_source(source);
> > -    assert(iwp->src == NULL);
> > +    return G_SOURCE_CONTINUE;
> >   }
> >
> >   static GSourceFuncs io_watch_poll_funcs = {
> >       .prepare = io_watch_poll_prepare,
> > -    .check = io_watch_poll_check,
> >       .dispatch = io_watch_poll_dispatch,
> > -    .finalize = io_watch_poll_finalize,
> >   };
> >
> >   GSource *io_add_watch_poll(Chardev *chr,
> > @@ -115,7 +91,6 @@ GSource *io_add_watch_poll(Chardev *chr,
> >       iwp->ioc = ioc;
> >       iwp->fd_read = (GSourceFunc) fd_read;
> >       iwp->src = NULL;
> > -    iwp->context = context;
> >
> >       name = g_strdup_printf("chardev-iowatch-%s", chr->label);
> >       g_source_set_name((GSource *)iwp, name);
> > @@ -126,23 +101,10 @@ GSource *io_add_watch_poll(Chardev *chr,
> >       return (GSource *)iwp;
> >   }
> >
> > -static void io_remove_watch_poll(GSource *source)
> > -{
> > -    IOWatchPoll *iwp;
> > -
> > -    iwp = io_watch_poll_from_source(source);
> > -    if (iwp->src) {
> > -        g_source_destroy(iwp->src);
> > -        g_source_unref(iwp->src);
> > -        iwp->src = NULL;
> > -    }
> > -    g_source_destroy(&iwp->parent);
> > -}
> > -
> >   void remove_fd_in_watch(Chardev *chr)
> >   {
> >       if (chr->gsource) {
> > -        io_remove_watch_poll(chr->gsource);
> > +        g_source_destroy(chr->gsource);
> >           chr->gsource = NULL;
> >       }
> >   }
> >