src/xgselect.c

   1 /* Function for handling the GLib event loop.
   2
   3 Copyright (C) 2009-2017 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 (at
  10 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 <https://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 "lisp.h"
  29 #include "blockinput.h"
  30 #include "systime.h"
  31
  32 /* `xg_select' is a `pselect' replacement.  Why do we need a separate function?
  33    1. Timeouts.  Glib and Gtk rely on timer events.  If we did pselect
  34       with a greater timeout then the one scheduled by Glib, we would
  35       not allow Glib to process its timer events.  We want Glib to
  36       work smoothly, so we need to reduce our timeout to match Glib.
  37    2. Descriptors.  Glib may listen to more file descriptors than we do.
  38       So we add Glib descriptors to our pselect pool, but we don't change
  39       the value returned by the function.  The return value  matches only
  40       the descriptors passed as arguments, making it compatible with
  41       plain pselect.  */
  42
  43 int
  44 xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
  45            struct timespec *timeout, sigset_t *sigmask)
  46 {
  47   fd_set all_rfds, all_wfds;
  48   struct timespec tmo;
  49   struct timespec *tmop = timeout;
  50
  51   GMainContext *context;
  52   bool have_wfds = wfds != NULL;
  53   GPollFD gfds_buf[128];
  54   GPollFD *gfds = gfds_buf;
  55   int gfds_size = ARRAYELTS (gfds_buf);
  56   int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
  57   bool context_acquired = false;
  58   int i, nfds, tmo_in_millisec, must_free = 0;
  59   bool need_to_dispatch;
  60
  61   context = g_main_context_default ();
  62   context_acquired = g_main_context_acquire (context);
  63   /* FIXME: If we couldn't acquire the context, we just silently proceed
  64      because this function handles more than just glib file descriptors.
  65      Note that, as implemented, this failure is completely silent: there is
  66      no feedback to the caller.  */
  67
  68   if (rfds) all_rfds = *rfds;
  69   else FD_ZERO (&all_rfds);
  70   if (wfds) all_wfds = *wfds;
  71   else FD_ZERO (&all_wfds);
  72
  73   n_gfds = (context_acquired
  74             ? g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
  75                                     gfds, gfds_size)
  76             : -1);
  77
  78   if (gfds_size < n_gfds)
  79     {
  80       /* Avoid using SAFE_NALLOCA, as that implicitly refers to the
  81          current thread.  Using xnmalloc avoids thread-switching
  82          problems here.  */
  83       gfds = xnmalloc (n_gfds, sizeof *gfds);
  84       must_free = 1;
  85       gfds_size = n_gfds;
  86       n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
  87                                      gfds, gfds_size);
  88     }
  89
  90   for (i = 0; i < n_gfds; ++i)
  91     {
  92       if (gfds[i].events & G_IO_IN)
  93         {
  94           FD_SET (gfds[i].fd, &all_rfds);
  95           if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
  96         }
  97       if (gfds[i].events & G_IO_OUT)
  98         {
  99           FD_SET (gfds[i].fd, &all_wfds);
 100           if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
 101           have_wfds = true;
 102         }
 103     }
 104
 105   if (must_free)
 106     xfree (gfds);
 107
 108   if (n_gfds >= 0 && tmo_in_millisec >= 0)
 109     {
 110       tmo = make_timespec (tmo_in_millisec / 1000,
 111                            1000 * 1000 * (tmo_in_millisec % 1000));
 112       if (!timeout || timespec_cmp (tmo, *timeout) < 0)
 113         tmop = &tmo;
 114     }
 115
 116   fds_lim = max_fds + 1;
 117   nfds = thread_select (pselect, fds_lim,
 118                         &all_rfds, have_wfds ? &all_wfds : NULL, efds,
 119                         tmop, sigmask);
 120   if (nfds < 0)
 121     retval = nfds;
 122   else if (nfds > 0)
 123     {
 124       for (i = 0; i < fds_lim; ++i)
 125         {
 126           if (FD_ISSET (i, &all_rfds))
 127             {
 128               if (rfds && FD_ISSET (i, rfds)) ++retval;
 129               else ++our_fds;
 130             }
 131           else if (rfds)
 132             FD_CLR (i, rfds);
 133
 134           if (have_wfds && FD_ISSET (i, &all_wfds))
 135             {
 136               if (wfds && FD_ISSET (i, wfds)) ++retval;
 137               else ++our_fds;
 138             }
 139           else if (wfds)
 140             FD_CLR (i, wfds);
 141
 142           if (efds && FD_ISSET (i, efds))
 143             ++retval;
 144         }
 145     }
 146
 147   /* If Gtk+ is in use eventually gtk_main_iteration will be called,
 148      unless retval is zero.  */
 149 #ifdef USE_GTK
 150   need_to_dispatch = retval == 0;
 151 #else
 152   need_to_dispatch = true;
 153 #endif
 154   if (need_to_dispatch && context_acquired)
 155     {
 156       int pselect_errno = errno;
 157       /* Prevent g_main_dispatch recursion, that would occur without
 158          block_input wrapper, because event handlers call
 159          unblock_input.  Event loop recursion was causing Bug#15801.  */
 160       block_input ();
 161       while (g_main_context_pending (context))
 162         g_main_context_dispatch (context);
 163       unblock_input ();
 164       errno = pselect_errno;
 165     }
 166
 167   if (context_acquired)
 168     g_main_context_release (context);
 169
 170   /* To not have to recalculate timeout, return like this.  */
 171   if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
 172     {
 173       retval = -1;
 174       errno = EINTR;
 175     }
 176
 177   return retval;
 178 }
 179 #endif /* HAVE_GLIB */