Differential D355 Diff 749 files/gmain-only-signal-GWakeup-right-before-or-during-a-blocking-poll.patch

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files/gmain-only-signal-GWakeup-right-before-or-during-a-blocking-poll.patch

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				From 5d74233476d61771b4d67d50bec5420f551ef922 Mon Sep 17 00:00:00 2001
				From: Paolo Bonzini <pbonzini@redhat.com>
				Date: Tue, 4 Apr 2017 09:56:47 +0200
				Subject: [PATCH] gmain: only signal GWakeup right before or during a blocking
				poll

				Since commit e4ee307 ("Do not wake up main loop if change is from same
				thread", bug 761102), GMainContext uses context->owner to decide if the
				event loop is being run in the current thread. However, what really
				matters is the phase in the prepare/query/poll/check/dispatch sequence.
				Wakeups are only needed between the end of prepare and the end of poll,
				and then only if prepare found that no sources were ready.

				There is no need to take threads into account, because prepare, check
				and all callers of conditional_wakeup all look at the new need_wakeup
				flag inside LOCK_CONTEXT/UNLOCK_CONTEXT.

				With this change, g_main_context_is_owner and g_main_context_wait are
				the only functions for which acquire/release matters, just like before
				commit e4ee307.

				Signed-off-by: Paolo Bonzini <bonzini@gnu.org>
				---
				glib/gmain.c \| 30 +++++++++++++++++++-----------
				1 file changed, 19 insertions(+), 11 deletions(-)

				diff --git a/glib/gmain.c b/glib/gmain.c
				index ab2908e52..af0a29ae5 100644
				--- a/glib/gmain.c
				+++ b/glib/gmain.c
				@@ -277,7 +277,8 @@ struct _GMainContext

				guint next_id;
				GList *source_lists;
				- gint in_check_or_prepare;
				+ gboolean in_check_or_prepare;
				+ gboolean need_wakeup;

				GPollRec *poll_records;
				guint n_poll_records;
				@@ -651,6 +652,7 @@ g_main_context_new (void)

				context->pending_dispatches = g_ptr_array_new ();

				+ context->need_wakeup = FALSE;
				context->time_is_fresh = FALSE;

				context->wakeup = g_wakeup_new ();
				@@ -1127,17 +1129,11 @@ source_remove_from_context (GSource *source,
				static void
				conditional_wakeup (GMainContext *context)
				{
				- /* We want to signal wakeups in two cases:
				- * 1 When the context is owned by another thread
				- * 2 When the context owner is NULL (two subcases)
				- * 2a Possible if the context has never been acquired
				- * 2b Or if the context has no current owner
				- *
				- * At least case 2a) is necessary to ensure backwards compatibility with
				- * qemu's use of GMainContext.
				- * https://bugzilla.gnome.org/show_bug.cgi?id=761102#c14
				+ /* This flag is set if at the start of prepare() we have no other ready
				+ * sources, and hence would wait in poll(). In that case, any other threads
				+ * attaching sources will need to signal a wakeup.
				*/
				- if (context->owner != G_THREAD_SELF)
				+ if (context->need_wakeup)
				g_wakeup_signal (context->wakeup);
				}

				@@ -3469,6 +3465,10 @@ g_main_context_prepare (GMainContext *context,

				LOCK_CONTEXT (context);

				+ /* context->need_wakeup is protected by LOCK_CONTEXT/UNLOCK_CONTEXT,
				+ * so need not set it yet.
				+ */
				+
				context->time_is_fresh = FALSE;

				if (context->in_check_or_prepare)
				@@ -3594,6 +3594,8 @@ g_main_context_prepare (GMainContext *context,
				}
				}
				g_source_iter_clear (&iter);
				+ /* See conditional_wakeup() where this is used */
				+ context->need_wakeup = (n_ready == 0);

				TRACE (GLIB_MAIN_CONTEXT_AFTER_PREPARE (context, current_priority, n_ready));

				@@ -3728,6 +3730,12 @@ g_main_context_check (GMainContext *context,

				TRACE (GLIB_MAIN_CONTEXT_BEFORE_CHECK (context, max_priority, fds, n_fds));

				+ /* We don't need to wakeup during check or dispatch, because
				+ * all sources will be re-evaluated during prepare/query.
				+ */
				+ context->need_wakeup = FALSE;
				+
				+ /* And if we have a wakeup pending, acknowledge it */
				for (i = 0; i < n_fds; i++)
				{
				if (fds[i].fd == context->wake_up_rec.fd)
				--
				2.12.2