From 535033a4f01f772e696ad2201b34403203b98bea Mon Sep 17 00:00:00 2001 From: Colin Walters Date: Thu, 16 Jun 2016 22:16:27 -0400 Subject: [PATCH] pull: Ensure we always process queue only from main thread I was easily reproducing a hang on pulls with thousands of requests on current git master. The initial symptom seemed to be that there are multiple code paths where we don't invoke `session_thread_process_pending_queue()`. We really need to do that any time we remove something from the outstanding queue, to ensure it gets filled again. A further issue is that we were tying the lifecycle of the pending object to the `GTask`, but the task could be unref'd from the main thread (via a `GSource` on the main thread), and that introduced threadsafety issues, because the hash table and other data suddenly could be concurrently modified. Both of these need to be fixed together. First, we introduce `Arc`, and ensure that both the main and worker threads hold references. Second, we ensure that we re-process the queue *immediately* whenever a task is done, inside the worker thread, rather than doing it incidentally via an unref. This architecture is quite similar to what the outside pull code is doing. Closes: #350 Approved by: jlebon --- src/libostree/ostree-fetcher.c | 55 +++++++++++++++++++++++++++++----- 1 file changed, 47 insertions(+), 8 deletions(-) diff --git a/src/libostree/ostree-fetcher.c b/src/libostree/ostree-fetcher.c index d956d95952..313df6a8dc 100644 --- a/src/libostree/ostree-fetcher.c +++ b/src/libostree/ostree-fetcher.c @@ -67,7 +67,12 @@ typedef struct { guint64 total_downloaded; } ThreadClosure; +static void +session_thread_process_pending_queue (ThreadClosure *thread_closure); + typedef struct { + volatile int ref_count; + ThreadClosure *thread_closure; SoupURI *uri; @@ -186,10 +191,22 @@ pending_task_compare (gconstpointer a, (priority_a < priority_b) ? -1 : 1; } +static OstreeFetcherPendingURI * +pending_uri_ref (OstreeFetcherPendingURI *pending) +{ + g_return_val_if_fail (pending != NULL, NULL); + g_return_val_if_fail (pending->ref_count > 0, NULL); + + g_atomic_int_inc (&pending->ref_count); + + return pending; +} + static void -pending_uri_free (OstreeFetcherPendingURI *pending) +pending_uri_unref (OstreeFetcherPendingURI *pending) { - g_hash_table_remove (pending->thread_closure->outstanding, pending); + if (!g_atomic_int_dec_and_test (&pending->ref_count)) + return; g_clear_pointer (&pending->thread_closure, thread_closure_unref); @@ -331,8 +348,7 @@ session_thread_process_pending_queue (ThreadClosure *thread_closure) pending = g_task_get_task_data (task); cancellable = g_task_get_cancellable (task); - /* pending_uri_free() removes this. */ - g_hash_table_add (thread_closure->outstanding, pending); + g_hash_table_add (thread_closure->outstanding, pending_uri_ref (pending)); soup_request_send_async (pending->request, cancellable, @@ -540,7 +556,7 @@ _ostree_fetcher_constructed (GObject *object) self->thread_closure->tmpdir_dfd = -1; self->thread_closure->tmpdir_lock = empty_lockfile; - self->thread_closure->outstanding = g_hash_table_new (NULL, NULL); + self->thread_closure->outstanding = g_hash_table_new_full (NULL, NULL, NULL, (GDestroyNotify)pending_uri_unref); self->thread_closure->output_stream_set = g_hash_table_new_full (NULL, NULL, (GDestroyNotify) NULL, (GDestroyNotify) g_object_unref); @@ -742,6 +758,18 @@ on_stream_read (GObject *object, GAsyncResult *result, gpointer user_data); +static void +remove_pending_rerun_queue (OstreeFetcherPendingURI *pending) +{ + /* Hold a temporary ref to ensure the reference to + * pending->thread_closure is valid. + */ + pending_uri_ref (pending); + g_hash_table_remove (pending->thread_closure->outstanding, pending); + session_thread_process_pending_queue (pending->thread_closure); + pending_uri_unref (pending); +} + static void on_out_splice_complete (GObject *object, GAsyncResult *result, @@ -770,7 +798,10 @@ on_out_splice_complete (GObject *object, out: if (local_error) - g_task_return_error (task, local_error); + { + g_task_return_error (task, local_error); + remove_pending_rerun_queue (pending); + } g_object_unref (task); } @@ -802,6 +833,7 @@ on_stream_read (GObject *object, g_task_return_pointer (task, g_strdup (pending->out_tmpfile), (GDestroyNotify) g_free); + remove_pending_rerun_queue (pending); } else { @@ -837,7 +869,10 @@ on_stream_read (GObject *object, out: if (local_error) - g_task_return_error (task, local_error); + { + g_task_return_error (task, local_error); + remove_pending_rerun_queue (pending); + } g_object_unref (task); } @@ -883,6 +918,7 @@ on_request_sent (GObject *object, g_strdup (pending->out_tmpfile), (GDestroyNotify) g_free); } + remove_pending_rerun_queue (pending); goto out; } else if (!SOUP_STATUS_IS_SUCCESSFUL (msg->status_code)) @@ -947,6 +983,7 @@ on_request_sent (GObject *object, g_task_return_pointer (task, g_object_ref (pending->request_body), (GDestroyNotify) g_object_unref); + remove_pending_rerun_queue (pending); } out: @@ -955,6 +992,7 @@ on_request_sent (GObject *object, if (pending->request_body) (void) g_input_stream_close (pending->request_body, NULL, NULL); g_task_return_error (task, local_error); + remove_pending_rerun_queue (pending); } g_object_unref (task); @@ -979,6 +1017,7 @@ ostree_fetcher_request_uri_internal (OstreeFetcher *self, /* SoupRequest is created in session thread. */ pending = g_new0 (OstreeFetcherPendingURI, 1); + pending->ref_count = 1; pending->thread_closure = thread_closure_ref (self->thread_closure); pending->uri = soup_uri_copy (uri); pending->max_size = max_size; @@ -986,7 +1025,7 @@ ostree_fetcher_request_uri_internal (OstreeFetcher *self, task = g_task_new (self, cancellable, callback, user_data); g_task_set_source_tag (task, source_tag); - g_task_set_task_data (task, pending, (GDestroyNotify) pending_uri_free); + g_task_set_task_data (task, pending, (GDestroyNotify) pending_uri_unref); /* We'll use the GTask priority for our own priority queue. */ g_task_set_priority (task, priority);