bug#18861: Acknowledgement (25.0.50; gfile-based file notifications are not immediate)

[Dima Kogan <dima@secretsauce.net>]

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Control: tags -1 + patch

Hi. A glib maintainer responded to the bug report, and it turns out
emacs was using glib slightly incorrectly. I'm attaching a patch to fix
the issue, as suggested by the maintainer.

With this patch, the pselect() call in emacs does see the glib
notification as it should. There is still an issue (also in glib) where
this notification comes about 1 second after the actual file system
activity, so I'm keeping this bug open. The glib bug tracker entry about
THIS problem is here:

 https://bugzilla.gnome.org/show_bug.cgi?id=739322


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From eb3579400f098a7cb43f55e48262c2939ff33254 Mon Sep 17 00:00:00 2001
From: Dima Kogan <dima@secretsauce.net>
Date: Tue, 28 Oct 2014 14:29:01 -0700
Subject: [PATCH] xg_select() now acquires the glib context before querying it

Prior to this patch we were calling g_main_context_query() without calling
g_main_context_acquire(). This resulted in the file descriptors returned by
g_main_context_query() missing activity. I.e. something would happen in glib,
but a select() on the file descriptors would keep blocking.

We now acquire the context, which makes select() return on activity, as it
should.

This is emacs and glib bugs:

 http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18861
 https://bugzilla.gnome.org/show_bug.cgi?id=739274
---
 src/xgselect.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/xgselect.c b/src/xgselect.c
index bf889a9..a830b7d 100644
--- a/src/xgselect.c
+++ b/src/xgselect.c
@@ -55,11 +55,20 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
   GPollFD *gfds = gfds_buf;
   int gfds_size = ARRAYELTS (gfds_buf);
   int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
+  bool context_acquired = false;
   int i, nfds, tmo_in_millisec;
   bool need_to_dispatch;
   USE_SAFE_ALLOCA;
 
   context = g_main_context_default ();
+  if( g_main_context_acquire(context) != TRUE )
+    {
+      // we couldn't acquire the context. I let this function proceed because it
+      // handles more than just glib file descriptors
+      retval = -1;
+    }
+  else
+    context_acquired = true;
 
   if (rfds) all_rfds = *rfds;
   else FD_ZERO (&all_rfds);
@@ -152,6 +161,9 @@ xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
       errno = pselect_errno;
     }
 
+  if (context_acquired)
+    g_main_context_release(context);
+
   /* To not have to recalculate timeout, return like this.  */
   if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
     {
-- 
2.0.0