[evolution-data-server] I#130 - [CamelOfflineFolder] Multiple downsync operations can run simultaneously

[Milan Crha <mcrha src gnome org>]

commit 36ad8622a8be62d2d1647f22fb6b3597902c2d68
Author: Milan Crha <mcrha redhat com>
Date:   Fri Jun 21 18:35:14 2019 +0200

    I#130 - [CamelOfflineFolder] Multiple downsync operations can run simultaneously
    
    Closes https://gitlab.gnome.org/GNOME/evolution-data-server/issues/130

 src/camel/camel-offline-folder.c | 71 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 65 insertions(+), 6 deletions(-)
---
diff --git a/src/camel/camel-offline-folder.c b/src/camel/camel-offline-folder.c
index 5d0d809b2..b0c95c6a6 100644
--- a/src/camel/camel-offline-folder.c
+++ b/src/camel/camel-offline-folder.c
@@ -28,6 +28,7 @@
 #include "camel-offline-store.h"
 #include "camel-operation.h"
 #include "camel-session.h"
+#include "camel-string-utils.h"
 #include "camel-utils.h"
 
 #define CAMEL_OFFLINE_FOLDER_GET_PRIVATE(obj) \
@@ -43,6 +44,9 @@ struct _CamelOfflineFolderPrivate {
        GMutex store_changes_lock;
        guint store_changes_id;
        gboolean store_changes_after_frozen;
+
+       GMutex ongoing_downloads_lock;
+       GHashTable *ongoing_downloads; /* gchar * UID ~> g_thread_self() */
 };
 
 struct _AsyncContext {
@@ -71,6 +75,60 @@ async_context_free (AsyncContext *async_context)
        g_slice_free (AsyncContext, async_context);
 }
 
+static gboolean
+offline_folder_synchronize_message_wrapper_sync (CamelFolder *folder,
+                                                const gchar *uid,
+                                                GCancellable *cancellable,
+                                                GError **error)
+{
+       CamelOfflineFolder *offline_folder;
+       gboolean success;
+
+       g_return_val_if_fail (CAMEL_IS_OFFLINE_FOLDER (folder), FALSE);
+       g_return_val_if_fail (uid != NULL, FALSE);
+
+       offline_folder = CAMEL_OFFLINE_FOLDER (folder);
+
+       g_mutex_lock (&offline_folder->priv->ongoing_downloads_lock);
+       /* Another thread is downloading this message already, do not wait for it,
+          just move on to the next one. In case the previous/ongoing download
+          fails the message won't be downloaded. */
+       if (g_hash_table_contains (offline_folder->priv->ongoing_downloads, uid)) {
+               if (camel_debug ("downsync")) {
+                       printf ("[downsync]          %p: (%s : %s): skipping uid '%s', because it is already 
downloading by thread %p (this thread is %p)\n", camel_folder_get_parent_store (folder),
+                               camel_service_get_display_name (CAMEL_SERVICE (camel_folder_get_parent_store 
(folder))), camel_folder_get_full_name (folder),
+                               uid, g_hash_table_lookup (offline_folder->priv->ongoing_downloads, uid), 
g_thread_self ());
+               }
+               g_mutex_unlock (&offline_folder->priv->ongoing_downloads_lock);
+               return TRUE;
+       } else {
+               g_hash_table_insert (offline_folder->priv->ongoing_downloads, (gpointer) camel_pstring_strdup 
(uid), g_thread_self ());
+       }
+
+       if (camel_debug ("downsync")) {
+               printf ("[downsync]          %p: (%s : %s): going to download uid '%s' in thread %p\n", 
camel_folder_get_parent_store (folder),
+                       camel_service_get_display_name (CAMEL_SERVICE (camel_folder_get_parent_store 
(folder))), camel_folder_get_full_name (folder),
+                       uid, g_thread_self ());
+       }
+
+       g_mutex_unlock (&offline_folder->priv->ongoing_downloads_lock);
+
+       success = camel_folder_synchronize_message_sync (folder, uid, cancellable, error);
+
+       g_mutex_lock (&offline_folder->priv->ongoing_downloads_lock);
+       g_warn_if_fail (g_hash_table_remove (offline_folder->priv->ongoing_downloads, uid));
+
+       if (camel_debug ("downsync")) {
+               printf ("[downsync]          %p: (%s : %s): finished download of uid '%s' in thread %p, 
%s\n", camel_folder_get_parent_store (folder),
+                       camel_service_get_display_name (CAMEL_SERVICE (camel_folder_get_parent_store 
(folder))), camel_folder_get_full_name (folder),
+                       uid, g_thread_self (), success ? "success" : "failure");
+       }
+
+       g_mutex_unlock (&offline_folder->priv->ongoing_downloads_lock);
+
+       return success;
+}
+
 static void
 offline_downsync_data_free (OfflineDownsyncData *data)
 {
@@ -160,7 +218,7 @@ offline_folder_downsync_background (CamelSession *session,
                                        continue;
                        }
 
-                       success = camel_folder_synchronize_message_sync (
+                       success = offline_folder_synchronize_message_wrapper_sync (
                                data->folder, uid, cancellable, error);
                }
        } else {
@@ -386,6 +444,9 @@ offline_folder_finalize (GObject *object)
        CamelOfflineFolder *offline_folder = CAMEL_OFFLINE_FOLDER (object);
 
        g_mutex_clear (&offline_folder->priv->store_changes_lock);
+       g_mutex_clear (&offline_folder->priv->ongoing_downloads_lock);
+
+       g_hash_table_destroy (offline_folder->priv->ongoing_downloads);
 
        /* Chain up to parent's method. */
        G_OBJECT_CLASS (camel_offline_folder_parent_class)->finalize (object);
@@ -530,7 +591,7 @@ offline_folder_downsync_sync (CamelOfflineFolder *offline,
                                camel_folder_get_full_name (folder));
 
                        /* Stop on failure */
-                       if (!camel_folder_synchronize_message_sync (folder, uid, cancellable, &local_error)) {
+                       if (!offline_folder_synchronize_message_wrapper_sync (folder, uid, cancellable, 
&local_error)) {
                                if (camel_debug ("downsync")) {
                                        printf ("[downsync]          %p: (%s : %s): aborting, failed to 
download uid:%s error:%s\n", camel_folder_get_parent_store (folder),
                                                camel_service_get_display_name (CAMEL_SERVICE 
(camel_folder_get_parent_store (folder))), camel_folder_get_full_name (folder),
@@ -539,10 +600,6 @@ offline_folder_downsync_sync (CamelOfflineFolder *offline,
                                g_clear_error (&local_error);
                                camel_operation_pop_message (cancellable);
                                break;
-                       } else if (camel_debug ("downsync")) {
-                               printf ("[downsync]          %p: (%s : %s): uid '%s' downloaded\n", 
camel_folder_get_parent_store (folder),
-                                       camel_service_get_display_name (CAMEL_SERVICE 
(camel_folder_get_parent_store (folder))), camel_folder_get_full_name (folder),
-                                       uid);
                        }
 
                        camel_operation_pop_message (cancellable);
@@ -603,8 +660,10 @@ camel_offline_folder_init (CamelOfflineFolder *folder)
        folder->priv = CAMEL_OFFLINE_FOLDER_GET_PRIVATE (folder);
 
        g_mutex_init (&folder->priv->store_changes_lock);
+       g_mutex_init (&folder->priv->ongoing_downloads_lock);
        folder->priv->store_changes_after_frozen = FALSE;
        folder->priv->offline_sync = CAMEL_THREE_STATE_INCONSISTENT;
+       folder->priv->ongoing_downloads = g_hash_table_new_full (g_str_hash, g_str_equal, (GDestroyNotify) 
camel_pstring_free, NULL);
 
        g_signal_connect (
                folder, "changed",