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glib/gmain: timerfd for sub-msec poll timeout
When using poll() directly, the best we can get is 1 millisecond timing intervals. This allows using a timerfd(2) in conjunction with g_source_set_ready_time(). Fixes https://gitlab.gnome.org/GNOME/glib/-/issues/3277
This commit is contained in:
Christian Hergert
parent
fe461fd1ad
commit
bf989aa1b3
142
glib/gmain.c
142
glib/gmain.c
@ -54,6 +54,9 @@
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#ifdef HAVE_EVENTFD
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#include <sys/eventfd.h>
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#endif
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#ifdef HAVE_TIMERFD
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#include <sys/timerfd.h>
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#endif
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#endif
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#include <signal.h>
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@ -189,7 +192,7 @@ struct _GMainContext
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GHashTable *sources; /* guint -> GSource */
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GPtrArray *pending_dispatches;
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gint timeout; /* Timeout for current iteration */
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gint64 timeout; /* Timeout for current iteration */
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guint next_id;
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GQueue source_lists;
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@ -204,6 +207,11 @@ struct _GMainContext
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GPollFD wake_up_rec;
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#ifdef HAVE_TIMERFD
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GPollFD timerfd_rec;
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struct itimerspec timerfd_spec;
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#endif
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/* Flag indicating whether the set of fd's changed during a poll */
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gboolean poll_changed;
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@ -322,7 +330,7 @@ static gboolean g_main_context_prepare_unlocked (GMainContext *context,
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gint *priority);
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static gint g_main_context_query_unlocked (GMainContext *context,
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gint max_priority,
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gint *timeout,
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gint64 *timeout,
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GPollFD *fds,
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gint n_fds);
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static gboolean g_main_context_check_unlocked (GMainContext *context,
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@ -331,7 +339,7 @@ static gboolean g_main_context_check_unlocked (GMainContext *context,
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gint n_fds);
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static void g_main_context_dispatch_unlocked (GMainContext *context);
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static void g_main_context_poll_unlocked (GMainContext *context,
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int timeout,
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gint64 timeout,
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int priority,
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GPollFD *fds,
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int n_fds);
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@ -563,6 +571,11 @@ g_main_context_unref (GMainContext *context)
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g_wakeup_free (context->wakeup);
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g_cond_clear (&context->cond);
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#ifdef HAVE_TIMERFD
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if (context->timerfd_rec.fd > -1)
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close (context->timerfd_rec.fd);
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#endif
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g_free (context);
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/* And now finally get rid of our references to the sources. This will cause
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@ -659,6 +672,20 @@ g_main_context_new_with_flags (GMainContextFlags flags)
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g_wakeup_get_pollfd (context->wakeup, &context->wake_up_rec);
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g_main_context_add_poll_unlocked (context, 0, &context->wake_up_rec);
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#ifdef HAVE_TIMERFD
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{
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int tfd = timerfd_create (CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
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if (tfd > -1)
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{
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context->timerfd_rec.fd = tfd;
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context->timerfd_rec.events = G_IO_IN;
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context->timerfd_rec.revents = 0;
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g_main_context_add_poll_unlocked (context, 0, &context->timerfd_rec);
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}
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}
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#endif
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G_LOCK (main_context_list);
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main_context_list = g_slist_append (main_context_list, context);
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@ -3681,7 +3708,7 @@ g_main_context_prepare_unlocked (GMainContext *context,
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g_source_iter_init (&iter, context, TRUE);
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while (g_source_iter_next (&iter, &source))
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{
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gint source_timeout = -1;
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gint64 source_timeout_usec = -1;
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if (SOURCE_DESTROYED (source) || SOURCE_BLOCKED (source))
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continue;
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@ -3699,14 +3726,20 @@ g_main_context_prepare_unlocked (GMainContext *context,
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if (prepare)
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{
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gint64 begin_time_nsec G_GNUC_UNUSED;
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gint source_timeout_msec = -1;
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context->in_check_or_prepare++;
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UNLOCK_CONTEXT (context);
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begin_time_nsec = G_TRACE_CURRENT_TIME;
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result = (* prepare) (source, &source_timeout);
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TRACE (GLIB_MAIN_AFTER_PREPARE (source, prepare, source_timeout));
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result = (* prepare) (source, &source_timeout_msec);
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TRACE (GLIB_MAIN_AFTER_PREPARE (source, prepare, source_timeout_msec));
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if (source_timeout_msec > 0)
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source_timeout_usec = source_timeout_msec * 1000;
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else
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source_timeout_usec = source_timeout_msec;
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g_trace_mark (begin_time_nsec, G_TRACE_CURRENT_TIME - begin_time_nsec,
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"GLib", "GSource.prepare",
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@ -3730,18 +3763,13 @@ g_main_context_prepare_unlocked (GMainContext *context,
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if (source->priv->ready_time <= context->time)
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{
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source_timeout = 0;
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source_timeout_usec = 0;
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result = TRUE;
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}
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else
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else if (source_timeout_usec < 0 ||
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(source->priv->ready_time < context->time + source_timeout_usec))
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{
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gint64 timeout;
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/* rounding down will lead to spinning, so always round up */
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timeout = (source->priv->ready_time - context->time + 999) / 1000;
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if (source_timeout < 0 || timeout < source_timeout)
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source_timeout = MIN (timeout, G_MAXINT);
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source_timeout_usec = MAX (0, source->priv->ready_time - context->time);
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}
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}
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@ -3763,13 +3791,13 @@ g_main_context_prepare_unlocked (GMainContext *context,
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current_priority = source->priority;
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context->timeout = 0;
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}
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if (source_timeout >= 0)
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if (source_timeout_usec >= 0)
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{
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if (context->timeout < 0)
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context->timeout = source_timeout;
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context->timeout = source_timeout_usec;
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else
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context->timeout = MIN (context->timeout, source_timeout);
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context->timeout = MIN (context->timeout, source_timeout_usec);
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}
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}
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g_source_iter_clear (&iter);
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@ -3811,6 +3839,7 @@ g_main_context_query (GMainContext *context,
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GPollFD *fds,
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gint n_fds)
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{
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gint64 timeout_usec;
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gint n_poll;
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if (context == NULL)
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@ -3818,17 +3847,32 @@ g_main_context_query (GMainContext *context,
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LOCK_CONTEXT (context);
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n_poll = g_main_context_query_unlocked (context, max_priority, timeout, fds, n_fds);
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n_poll = g_main_context_query_unlocked (context, max_priority, &timeout_usec, fds, n_fds);
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UNLOCK_CONTEXT (context);
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if (timeout != NULL)
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{
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/* Propagate timeout to caller but reduce resolution to milliseconds for
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* a typical poll() cycle. Avoid returning 0 to reduce chances of
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* spinning CPU by callers.
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*
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* When on Linux with timerfd(), we may get lower resolution internally
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* from this by using our internal timerfd.
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*/
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if (timeout_usec >= 0)
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*timeout = ((timeout_usec + 999) / 1000);
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else
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*timeout = -1;
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}
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return n_poll;
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}
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static gint
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g_main_context_query_unlocked (GMainContext *context,
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gint max_priority,
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gint *timeout,
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gint64 *timeout,
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GPollFD *fds,
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gint n_fds)
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{
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@ -4163,7 +4207,7 @@ g_main_context_iterate_unlocked (GMainContext *context,
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GThread *self)
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{
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gint max_priority = 0;
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gint timeout;
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gint64 timeout;
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gboolean some_ready;
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gint nfds, allocated_nfds;
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GPollFD *fds = NULL;
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@ -4489,7 +4533,7 @@ g_main_loop_get_context (GMainLoop *loop)
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/* HOLDS: context's lock */
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static void
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g_main_context_poll_unlocked (GMainContext *context,
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int timeout,
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gint64 timeout_usec,
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int priority,
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GPollFD *fds,
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int n_fds)
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@ -4501,8 +4545,50 @@ g_main_context_poll_unlocked (GMainContext *context,
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#endif
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GPollFunc poll_func;
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int timeout_msec;
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#ifdef HAVE_TIMERFD
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struct itimerspec timeout_ts;
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#endif
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if (n_fds || timeout != 0)
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/* Always round up for poll() to avoid spinning. When timerfd
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* is available, that will allow for lower latency by awaking
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* from poll() naturally.
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*/
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if (timeout_usec == 0)
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timeout_msec = 0;
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else if (timeout_usec > 0)
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timeout_msec = (timeout_usec + 999) / 1000;
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else
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timeout_msec = -1;
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#ifdef HAVE_TIMERFD
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if (context->timerfd_rec.fd > -1)
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{
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timeout_ts.it_interval.tv_sec = 0;
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timeout_ts.it_interval.tv_nsec = 0;
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if (timeout_usec > 0)
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{
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gint64 abs = context->time + timeout_usec;
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timeout_ts.it_value.tv_sec = abs / G_USEC_PER_SEC;
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timeout_ts.it_value.tv_nsec = (abs % G_USEC_PER_SEC) * 1000;
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}
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else
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{
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timeout_ts.it_value.tv_sec = 0;
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timeout_ts.it_value.tv_nsec = 0;
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}
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if (memcmp (&timeout_ts, &context->timerfd_spec, sizeof timeout_ts) != 0)
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{
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context->timerfd_spec = timeout_ts;
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timerfd_settime (context->timerfd_rec.fd, TFD_TIMER_ABSTIME, &timeout_ts, NULL);
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}
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}
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#endif
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if (n_fds || timeout_usec != 0)
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{
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int ret, errsv;
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@ -4511,14 +4597,14 @@ g_main_context_poll_unlocked (GMainContext *context,
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if (_g_main_poll_debug)
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{
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g_print ("polling context=%p n=%d timeout=%d\n",
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context, n_fds, timeout);
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context, n_fds, timeout_msec);
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poll_timer = g_timer_new ();
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}
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#endif
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poll_func = context->poll_func;
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UNLOCK_CONTEXT (context);
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ret = (*poll_func) (fds, n_fds, timeout);
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ret = (*poll_func) (fds, n_fds, timeout_msec);
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LOCK_CONTEXT (context);
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errsv = errno;
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@ -4537,7 +4623,7 @@ g_main_context_poll_unlocked (GMainContext *context,
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{
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g_print ("g_main_poll(%d) timeout: %d - elapsed %12.10f seconds",
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n_fds,
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timeout,
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timeout_msec,
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g_timer_elapsed (poll_timer, NULL));
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g_timer_destroy (poll_timer);
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pollrec = context->poll_records;
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@ -4573,7 +4659,7 @@ g_main_context_poll_unlocked (GMainContext *context,
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g_print ("\n");
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}
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#endif
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} /* if (n_fds || timeout != 0) */
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} /* if (n_fds || timeout_usec != 0) */
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}
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/**
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10
meson.build
10
meson.build
@ -1007,6 +1007,16 @@ if cc.links('''#include <sys/eventfd.h>
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glib_conf.set('HAVE_EVENTFD', 1)
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endif
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# Check for timerfd_create(2)
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if cc.links('''#include <sys/timerfd.h>
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#include <unistd.h>
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int main (int argc, char ** argv) {
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timerfd_create (CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
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return 0;
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}''', name : 'timerfd_create(2) system call')
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glib_conf.set('HAVE_TIMERFD', 1)
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endif
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# Check for pidfd_open(2)
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if cc.links('''#include <sys/syscall.h>
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#include <sys/wait.h>
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