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/* Function for handling the GLib event loop.
Copyright (C) 2009-2021 Free Software Foundation, Inc.
This file is part of GNU Emacs.
GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
#include <config.h>
#include "xgselect.h"
#ifdef HAVE_GLIB
#include <glib.h>
#include <errno.h>
#include "lisp.h"
#include "blockinput.h"
#include "systime.h"
static ptrdiff_t threads_holding_glib_lock;
static GMainContext *glib_main_context;
void release_select_lock (void)
{
#if GNUC_PREREQ (4, 7, 0)
if (__atomic_sub_fetch (&threads_holding_glib_lock, 1, __ATOMIC_ACQ_REL) == 0)
g_main_context_release (glib_main_context);
#else
if (--threads_holding_glib_lock == 0)
g_main_context_release (glib_main_context);
#endif
}
static void acquire_select_lock (GMainContext *context)
{
#if GNUC_PREREQ (4, 7, 0)
if (__atomic_fetch_add (&threads_holding_glib_lock, 1, __ATOMIC_ACQ_REL) == 0)
{
glib_main_context = context;
while (!g_main_context_acquire (context))
{
/* Spin. */
}
}
#else
if (threads_holding_glib_lock++ == 0)
{
glib_main_context = context;
while (!g_main_context_acquire (context))
{
/* Spin. */
}
}
#endif
}
/* `xg_select' is a `pselect' replacement. Why do we need a separate function?
1. Timeouts. Glib and Gtk rely on timer events. If we did pselect
with a greater timeout then the one scheduled by Glib, we would
not allow Glib to process its timer events. We want Glib to
work smoothly, so we need to reduce our timeout to match Glib.
2. Descriptors. Glib may listen to more file descriptors than we do.
So we add Glib descriptors to our pselect pool, but we don't change
the value returned by the function. The return value matches only
the descriptors passed as arguments, making it compatible with
plain pselect. */
int
xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
struct timespec *timeout, sigset_t *sigmask)
{
fd_set all_rfds, all_wfds;
struct timespec tmo;
struct timespec *tmop = timeout;
GMainContext *context;
bool have_wfds = wfds != NULL;
GPollFD gfds_buf[128];
GPollFD *gfds = gfds_buf;
int gfds_size = ARRAYELTS (gfds_buf);
int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
int i, nfds, tmo_in_millisec, must_free = 0;
bool need_to_dispatch;
context = g_main_context_default ();
acquire_select_lock (context);
if (rfds) all_rfds = *rfds;
else FD_ZERO (&all_rfds);
if (wfds) all_wfds = *wfds;
else FD_ZERO (&all_wfds);
n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
gfds, gfds_size);
if (gfds_size < n_gfds)
{
/* Avoid using SAFE_NALLOCA, as that implicitly refers to the
current thread. Using xnmalloc avoids thread-switching
problems here. */
gfds = xnmalloc (n_gfds, sizeof *gfds);
must_free = 1;
gfds_size = n_gfds;
n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
gfds, gfds_size);
}
for (i = 0; i < n_gfds; ++i)
{
if (gfds[i].events & G_IO_IN)
{
FD_SET (gfds[i].fd, &all_rfds);
if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
}
if (gfds[i].events & G_IO_OUT)
{
FD_SET (gfds[i].fd, &all_wfds);
if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
have_wfds = true;
}
}
if (must_free)
xfree (gfds);
if (n_gfds >= 0 && tmo_in_millisec >= 0)
{
tmo = make_timespec (tmo_in_millisec / 1000,
1000 * 1000 * (tmo_in_millisec % 1000));
if (!timeout || timespec_cmp (tmo, *timeout) < 0)
tmop = &tmo;
}
fds_lim = max_fds + 1;
nfds = thread_select (pselect, fds_lim,
&all_rfds, have_wfds ? &all_wfds : NULL, efds,
tmop, sigmask);
if (nfds < 0)
retval = nfds;
else if (nfds > 0)
{
for (i = 0; i < fds_lim; ++i)
{
if (FD_ISSET (i, &all_rfds))
{
if (rfds && FD_ISSET (i, rfds)) ++retval;
else ++our_fds;
}
else if (rfds)
FD_CLR (i, rfds);
if (have_wfds && FD_ISSET (i, &all_wfds))
{
if (wfds && FD_ISSET (i, wfds)) ++retval;
else ++our_fds;
}
else if (wfds)
FD_CLR (i, wfds);
if (efds && FD_ISSET (i, efds))
++retval;
}
}
/* If Gtk+ is in use eventually gtk_main_iteration will be called,
unless retval is zero. */
#ifdef USE_GTK
need_to_dispatch = retval == 0;
#else
need_to_dispatch = true;
#endif
if (need_to_dispatch)
{
acquire_select_lock (context);
int pselect_errno = errno;
/* Prevent g_main_dispatch recursion, that would occur without
block_input wrapper, because event handlers call
unblock_input. Event loop recursion was causing Bug#15801. */
block_input ();
while (g_main_context_pending (context))
g_main_context_dispatch (context);
unblock_input ();
errno = pselect_errno;
release_select_lock ();
}
/* To not have to recalculate timeout, return like this. */
if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
{
retval = -1;
errno = EINTR;
}
return retval;
}
#endif /* HAVE_GLIB */
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