src/xgselect.c

   1 /* Function for handling the GLib event loop.
   2
   3 Copyright (C) 2009-2015 Free Software Foundation, Inc.
   4
   5 This file is part of GNU Emacs.
   6
   7 GNU Emacs is free software: you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation, either version 3 of the License, or
  10 (at your option) any later version.
  11
  12 GNU Emacs is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include <config.h>
  21
  22 #include "xgselect.h"
  23
  24 #ifdef HAVE_GLIB
  25
  26 #include <glib.h>
  27 #include <errno.h>
  28 #include <stdbool.h>
  29 #include <timespec.h>
  30 #include "frame.h"
  31 #include "blockinput.h"
  32
  33 /* `xg_select' is a `pselect' replacement.  Why do we need a separate function?
  34    1. Timeouts.  Glib and Gtk rely on timer events.  If we did pselect
  35       with a greater timeout then the one scheduled by Glib, we would
  36       not allow Glib to process its timer events.  We want Glib to
  37       work smoothly, so we need to reduce our timeout to match Glib.
  38    2. Descriptors.  Glib may listen to more file descriptors than we do.
  39       So we add Glib descriptors to our pselect pool, but we don't change
  40       the value returned by the function.  The return value  matches only
  41       the descriptors passed as arguments, making it compatible with
  42       plain pselect.  */
  43
  44 int
  45 xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
  46            struct timespec const *timeout, sigset_t const *sigmask)
  47 {
  48   fd_set all_rfds, all_wfds;
  49   struct timespec tmo;
  50   struct timespec const *tmop = timeout;
  51
  52   GMainContext *context;
  53   int have_wfds = wfds != NULL;
  54   GPollFD gfds_buf[128];
  55   GPollFD *gfds = gfds_buf;
  56   int gfds_size = ARRAYELTS (gfds_buf);
  57   int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
  58   bool context_acquired = false;
  59   int i, nfds, tmo_in_millisec;
  60   bool need_to_dispatch;
  61   USE_SAFE_ALLOCA;
  62
  63   context = g_main_context_default ();
  64   context_acquired = g_main_context_acquire (context);
  65   /* FIXME: If we couldn't acquire the context, we just silently proceed
  66      because this function handles more than just glib file descriptors.
  67      Note that, as implemented, this failure is completely silent: there is
  68      no feedback to the caller.  */
  69
  70   if (rfds) all_rfds = *rfds;
  71   else FD_ZERO (&all_rfds);
  72   if (wfds) all_wfds = *wfds;
  73   else FD_ZERO (&all_wfds);
  74
  75   n_gfds = (context_acquired
  76             ? g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
  77                                     gfds, gfds_size)
  78             : -1);
  79
  80   if (gfds_size < n_gfds)
  81     {
  82       SAFE_NALLOCA (gfds, sizeof *gfds, n_gfds);
  83       gfds_size = n_gfds;
  84       n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
  85                                      gfds, gfds_size);
  86     }
  87
  88   for (i = 0; i < n_gfds; ++i)
  89     {
  90       if (gfds[i].events & G_IO_IN)
  91         {
  92           FD_SET (gfds[i].fd, &all_rfds);
  93           if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
  94         }
  95       if (gfds[i].events & G_IO_OUT)
  96         {
  97           FD_SET (gfds[i].fd, &all_wfds);
  98           if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
  99           have_wfds = 1;
 100         }
 101     }
 102
 103   SAFE_FREE ();
 104
 105   if (n_gfds >= 0 && tmo_in_millisec >= 0)
 106     {
 107       tmo = make_timespec (tmo_in_millisec / 1000,
 108                            1000 * 1000 * (tmo_in_millisec % 1000));
 109       if (!timeout || timespec_cmp (tmo, *timeout) < 0)
 110         tmop = &tmo;
 111     }
 112
 113   fds_lim = max_fds + 1;
 114   nfds = pselect (fds_lim, &all_rfds, have_wfds ? &all_wfds : NULL,
 115                   efds, tmop, sigmask);
 116
 117   if (nfds < 0)
 118     retval = nfds;
 119   else if (nfds > 0)
 120     {
 121       for (i = 0; i < fds_lim; ++i)
 122         {
 123           if (FD_ISSET (i, &all_rfds))
 124             {
 125               if (rfds && FD_ISSET (i, rfds)) ++retval;
 126               else ++our_fds;
 127             }
 128           else if (rfds)
 129             FD_CLR (i, rfds);
 130
 131           if (have_wfds && FD_ISSET (i, &all_wfds))
 132             {
 133               if (wfds && FD_ISSET (i, wfds)) ++retval;
 134               else ++our_fds;
 135             }
 136           else if (wfds)
 137             FD_CLR (i, wfds);
 138
 139           if (efds && FD_ISSET (i, efds))
 140             ++retval;
 141         }
 142     }
 143
 144   /* If Gtk+ is in use eventually gtk_main_iteration will be called,
 145      unless retval is zero.  */
 146 #ifdef USE_GTK
 147   need_to_dispatch = retval == 0;
 148 #else
 149   need_to_dispatch = true;
 150 #endif
 151   if (need_to_dispatch)
 152     {
 153       int pselect_errno = errno;
 154       /* Prevent g_main_dispatch recursion, that would occur without
 155          block_input wrapper, because event handlers call
 156          unblock_input.  Event loop recursion was causing Bug#15801.  */
 157       block_input ();
 158       while (g_main_context_pending (context))
 159         g_main_context_dispatch (context);
 160       unblock_input ();
 161       errno = pselect_errno;
 162     }
 163
 164   if (context_acquired)
 165     g_main_context_release (context);
 166
 167   /* To not have to recalculate timeout, return like this.  */
 168   if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
 169     {
 170       retval = -1;
 171       errno = EINTR;
 172     }
 173
 174   return retval;
 175 }
 176 #endif /* HAVE_GLIB */