Update to 2.65.0
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Kalev Lember
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From e4a690f5dd959e74b2d6054826f61509892c8aa7 Mon Sep 17 00:00:00 2001
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From: Philip Withnall <withnall@endlessm.com>
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Date: Fri, 21 Feb 2020 14:44:44 +0000
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Subject: [PATCH] gcancellable: Fix minor race between GCancellable and
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GCancellableSource
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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There’s a minor race condition between cancellation of a `GCancellable`,
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and disposal/finalisation of a `GCancellableSource` in another thread.
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Thread A Thread B
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g_cancellable_cancel(C)
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→cancellable_source_cancelled(C, S)
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g_source_unref(S)
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cancellable_source_dispose(S)
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→→g_source_ref(S)
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→→# S is invalid at this point; crash
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Thankfully, the `GCancellable` sets `cancelled_running` while it’s
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emitting the `cancelled` signal, so if `cancellable_source_dispose()` is
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called while that’s high, we know that the thread which is doing the
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cancellation has already started (or is committed to starting) calling
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`cancellable_source_cancelled()`.
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Fix the race by resurrecting the `GCancellableSource` in
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`cancellable_source_dispose()`, and signalling this using
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`GCancellableSource.resurrected_during_cancellation`. Check for that
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flag in `cancellable_source_cancelled()` and ignore cancellation if it’s
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set.
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The modifications to `resurrected_during_cancellation` and the
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cancellable source’s refcount have to be done with `cancellable_mutex`
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held so that they are seen atomically by each thread. This should not
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affect performance too much, as it only happens during cancellation or
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disposal of a `GCancellableSource`.
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Signed-off-by: Philip Withnall <withnall@endlessm.com>
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Fixes: #1841
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---
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gio/gcancellable.c | 43 +++++++++++++++++++++++
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gio/tests/cancellable.c | 77 +++++++++++++++++++++++++++++++++++++++++
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2 files changed, 120 insertions(+)
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diff --git a/gio/gcancellable.c b/gio/gcancellable.c
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index d9e58b8e8..e687cca23 100644
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--- a/gio/gcancellable.c
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+++ b/gio/gcancellable.c
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@@ -643,6 +643,8 @@ typedef struct {
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GCancellable *cancellable;
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gulong cancelled_handler;
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+ /* Protected by cancellable_mutex: */
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+ gboolean resurrected_during_cancellation;
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} GCancellableSource;
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/*
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@@ -661,8 +663,24 @@ cancellable_source_cancelled (GCancellable *cancellable,
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gpointer user_data)
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{
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GSource *source = user_data;
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+ GCancellableSource *cancellable_source = (GCancellableSource *) source;
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+
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+ g_mutex_lock (&cancellable_mutex);
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+
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+ /* Drop the reference added in cancellable_source_dispose(); see the comment there.
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+ * The reference must be dropped after unlocking @cancellable_mutex since
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+ * it could be the final reference, and the dispose function takes
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+ * @cancellable_mutex. */
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+ if (cancellable_source->resurrected_during_cancellation)
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+ {
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+ cancellable_source->resurrected_during_cancellation = FALSE;
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+ g_mutex_unlock (&cancellable_mutex);
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+ g_source_unref (source);
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+ return;
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+ }
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g_source_ref (source);
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+ g_mutex_unlock (&cancellable_mutex);
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g_source_set_ready_time (source, 0);
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g_source_unref (source);
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}
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@@ -684,12 +702,37 @@ cancellable_source_dispose (GSource *source)
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{
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GCancellableSource *cancellable_source = (GCancellableSource *)source;
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+ g_mutex_lock (&cancellable_mutex);
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+
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if (cancellable_source->cancellable)
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{
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+ if (cancellable_source->cancellable->priv->cancelled_running)
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+ {
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+ /* There can be a race here: if thread A has called
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+ * g_cancellable_cancel() and has got as far as committing to call
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+ * cancellable_source_cancelled(), then thread B drops the final
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+ * ref on the GCancellableSource before g_source_ref() is called in
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+ * cancellable_source_cancelled(), then cancellable_source_dispose()
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+ * will run through and the GCancellableSource will be finalised
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+ * before cancellable_source_cancelled() gets to g_source_ref(). It
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+ * will then be left in a state where it’s committed to using a
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+ * dangling GCancellableSource pointer.
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+ *
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+ * Eliminate that race by resurrecting the #GSource temporarily, and
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+ * then dropping that reference in cancellable_source_cancelled(),
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+ * which should be guaranteed to fire because we’re inside a
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+ * @cancelled_running block.
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+ */
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+ g_source_ref (source);
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+ cancellable_source->resurrected_during_cancellation = TRUE;
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+ }
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+
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g_clear_signal_handler (&cancellable_source->cancelled_handler,
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cancellable_source->cancellable);
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g_clear_object (&cancellable_source->cancellable);
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}
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+
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+ g_mutex_unlock (&cancellable_mutex);
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}
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static gboolean
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diff --git a/gio/tests/cancellable.c b/gio/tests/cancellable.c
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index 4ba9f6326..002bdccca 100644
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--- a/gio/tests/cancellable.c
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+++ b/gio/tests/cancellable.c
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@@ -228,6 +228,82 @@ test_cancel_null (void)
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g_cancellable_cancel (NULL);
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}
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+typedef struct
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+{
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+ GCond cond;
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+ GMutex mutex;
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+ GSource *cancellable_source; /* (owned) */
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+} ThreadedDisposeData;
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+
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+static gboolean
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+cancelled_cb (GCancellable *cancellable,
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+ gpointer user_data)
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+{
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+ /* Nothing needs to be done here. */
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+ return G_SOURCE_CONTINUE;
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+}
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+
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+static gpointer
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+threaded_dispose_thread_cb (gpointer user_data)
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+{
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+ ThreadedDisposeData *data = user_data;
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+
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+ /* Synchronise with the main thread before trying to reproduce the race. */
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+ g_mutex_lock (&data->mutex);
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+ g_cond_broadcast (&data->cond);
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+ g_mutex_unlock (&data->mutex);
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+
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+ /* Race with cancellation of the cancellable. */
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+ g_source_unref (data->cancellable_source);
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+
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+ return NULL;
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+}
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+
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+static void
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+test_cancellable_source_threaded_dispose (void)
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+{
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+ guint i;
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+
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+ g_test_summary ("Test a thread race between disposing of a GCancellableSource "
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+ "(in one thread) and cancelling the GCancellable it refers "
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+ "to (in another thread)");
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+ g_test_bug ("https://gitlab.gnome.org/GNOME/glib/issues/1841");
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+
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+ for (i = 0; i < 100000; i++)
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+ {
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+ GCancellable *cancellable = NULL;
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+ GSource *cancellable_source = NULL;
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+ ThreadedDisposeData data;
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+ GThread *thread = NULL;
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+
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+ /* Create a cancellable and a cancellable source for it. For this test,
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+ * there’s no need to attach the source to a #GMainContext. */
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+ cancellable = g_cancellable_new ();
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+ cancellable_source = g_cancellable_source_new (cancellable);
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+ g_source_set_callback (cancellable_source, G_SOURCE_FUNC (cancelled_cb), NULL, NULL);
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+
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+ /* Create a new thread and wait until it’s ready to execute before
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+ * cancelling our cancellable. */
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+ g_cond_init (&data.cond);
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+ g_mutex_init (&data.mutex);
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+ data.cancellable_source = g_steal_pointer (&cancellable_source);
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+
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+ g_mutex_lock (&data.mutex);
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+ thread = g_thread_new ("/cancellable-source/threaded-dispose",
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+ threaded_dispose_thread_cb, &data);
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+ g_cond_wait (&data.cond, &data.mutex);
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+ g_mutex_unlock (&data.mutex);
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+
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+ /* Race with disposal of the cancellable source. */
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+ g_cancellable_cancel (cancellable);
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+
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+ g_thread_join (g_steal_pointer (&thread));
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+ g_mutex_clear (&data.mutex);
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+ g_cond_clear (&data.cond);
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+ g_object_unref (cancellable);
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+ }
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+}
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+
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int
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main (int argc, char *argv[])
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{
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@@ -235,6 +311,7 @@ main (int argc, char *argv[])
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g_test_add_func ("/cancellable/multiple-concurrent", test_cancel_multiple_concurrent);
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g_test_add_func ("/cancellable/null", test_cancel_null);
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+ g_test_add_func ("/cancellable-source/threaded-dispose", test_cancellable_source_threaded_dispose);
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return g_test_run ();
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}
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--
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2.24.1
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11
glib2.spec
11
glib2.spec
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%global _changelog_trimtime %(date +%s -d "1 year ago")
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Name: glib2
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Version: 2.64.3
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Version: 2.65.0
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Release: 1%{?dist}
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Summary: A library of handy utility functions
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License: LGPLv2+
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URL: http://www.gtk.org
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Source0: http://download.gnome.org/sources/glib/2.64/glib-%{version}.tar.xz
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# https://bugzilla.redhat.com/show_bug.cgi?id=1825230
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# https://gitlab.gnome.org/GNOME/glib/-/commit/e4a690f5dd959e74b2d6054826f61509892c8aa7
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Patch0: gcancellable-race-fix.patch
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Source0: http://download.gnome.org/sources/glib/2.65/glib-%{version}.tar.xz
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BuildRequires: chrpath
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BuildRequires: gcc
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@ -219,6 +215,9 @@ glib-compile-schemas %{_datadir}/glib-2.0/schemas &> /dev/null || :
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%{_datadir}/installed-tests
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%changelog
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* Mon Jun 22 2020 Kalev Lember <klember@redhat.com> - 2.65.0-1
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- Update to 2.65.0
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* Wed May 20 2020 Kalev Lember <klember@redhat.com> - 2.64.3-1
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- Update to 2.64.3
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2
sources
2
sources
@ -1 +1 @@
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SHA512 (glib-2.64.3.tar.xz) = a3828c37a50e86eb8791be53bd8af848d144e4580841ffab28f3b6eae5144f5cdf4a5d4b43130615b97488e700b274c2468fc7d561b3701a1fc686349501a1db
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SHA512 (glib-2.65.0.tar.xz) = 0bad09a41c7860d31522729e18a20d208de60935b081407cc9307cfc865b58e751ed3978b864081d4b59744c584d37e77cf0b055e9daae91cb73b4b93a6d9ee1
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