107 lines
3.6 KiB
Diff
107 lines
3.6 KiB
Diff
From 5d74233476d61771b4d67d50bec5420f551ef922 Mon Sep 17 00:00:00 2001
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Tue, 4 Apr 2017 09:56:47 +0200
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Subject: [PATCH] gmain: only signal GWakeup right before or during a blocking
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poll
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Since commit e4ee307 ("Do not wake up main loop if change is from same
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thread", bug 761102), GMainContext uses context->owner to decide if the
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event loop is being run in the current thread. However, what really
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matters is the phase in the prepare/query/poll/check/dispatch sequence.
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Wakeups are only needed between the end of prepare and the end of poll,
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and then only if prepare found that no sources were ready.
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There is no need to take threads into account, because prepare, check
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and all callers of conditional_wakeup all look at the new need_wakeup
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flag inside LOCK_CONTEXT/UNLOCK_CONTEXT.
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With this change, g_main_context_is_owner and g_main_context_wait are
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the only functions for which acquire/release matters, just like before
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commit e4ee307.
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Signed-off-by: Paolo Bonzini <bonzini@gnu.org>
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---
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glib/gmain.c | 30 +++++++++++++++++++-----------
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1 file changed, 19 insertions(+), 11 deletions(-)
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diff --git a/glib/gmain.c b/glib/gmain.c
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index ab2908e52..af0a29ae5 100644
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--- a/glib/gmain.c
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+++ b/glib/gmain.c
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@@ -277,7 +277,8 @@ struct _GMainContext
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guint next_id;
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GList *source_lists;
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- gint in_check_or_prepare;
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+ gboolean in_check_or_prepare;
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+ gboolean need_wakeup;
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GPollRec *poll_records;
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guint n_poll_records;
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@@ -651,6 +652,7 @@ g_main_context_new (void)
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context->pending_dispatches = g_ptr_array_new ();
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+ context->need_wakeup = FALSE;
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context->time_is_fresh = FALSE;
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context->wakeup = g_wakeup_new ();
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@@ -1127,17 +1129,11 @@ source_remove_from_context (GSource *source,
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static void
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conditional_wakeup (GMainContext *context)
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{
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- /* We want to signal wakeups in two cases:
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- * 1 When the context is owned by another thread
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- * 2 When the context owner is NULL (two subcases)
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- * 2a Possible if the context has never been acquired
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- * 2b Or if the context has no current owner
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- *
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- * At least case 2a) is necessary to ensure backwards compatibility with
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- * qemu's use of GMainContext.
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- * https://bugzilla.gnome.org/show_bug.cgi?id=761102#c14
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+ /* This flag is set if at the start of prepare() we have no other ready
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+ * sources, and hence would wait in poll(). In that case, any other threads
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+ * attaching sources will need to signal a wakeup.
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*/
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- if (context->owner != G_THREAD_SELF)
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+ if (context->need_wakeup)
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g_wakeup_signal (context->wakeup);
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}
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@@ -3469,6 +3465,10 @@ g_main_context_prepare (GMainContext *context,
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LOCK_CONTEXT (context);
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+ /* context->need_wakeup is protected by LOCK_CONTEXT/UNLOCK_CONTEXT,
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+ * so need not set it yet.
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+ */
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+
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context->time_is_fresh = FALSE;
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if (context->in_check_or_prepare)
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@@ -3594,6 +3594,8 @@ g_main_context_prepare (GMainContext *context,
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}
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}
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g_source_iter_clear (&iter);
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+ /* See conditional_wakeup() where this is used */
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+ context->need_wakeup = (n_ready == 0);
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TRACE (GLIB_MAIN_CONTEXT_AFTER_PREPARE (context, current_priority, n_ready));
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@@ -3728,6 +3730,12 @@ g_main_context_check (GMainContext *context,
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TRACE (GLIB_MAIN_CONTEXT_BEFORE_CHECK (context, max_priority, fds, n_fds));
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+ /* We don't need to wakeup during check or dispatch, because
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+ * all sources will be re-evaluated during prepare/query.
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+ */
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+ context->need_wakeup = FALSE;
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+
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+ /* And if we have a wakeup pending, acknowledge it */
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for (i = 0; i < n_fds; i++)
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{
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if (fds[i].fd == context->wake_up_rec.fd)
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--
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2.12.2
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