[tracker] TrackerMonitor: Workaround design flaw in libinotify.

[Carlos Garnacho <carlosg src gnome org>]

commit 049e81f878da80a8564192a21cc5991aa29bc341
Author: Carlos Garnacho <carlos lanedo com>
Date:   Thu Feb 4 16:29:13 2010 +0100

    TrackerMonitor: Workaround design flaw in libinotify.
    
    libinotify keeps a hashtable of watch descriptor/handle, and does
    removing in an asyncrhonous manner. So when inotify_add_watch()
    reuses a watch descriptor, removing/adding whithout having
    libinotify process the events coming from the fd may cause the
    wrong handle (the just added one) to be removed.
    
    TrackerMonitor now adds, and then removes old monitors, when a
    directory is moved, so there's no opportunity to remove the wrong
    handle.

 src/libtracker-miner/tracker-monitor.c |   29 +++++++++++++----------------
 1 files changed, 13 insertions(+), 16 deletions(-)
---
diff --git a/src/libtracker-miner/tracker-monitor.c b/src/libtracker-miner/tracker-monitor.c
index 4905a91..efd7843 100644
--- a/src/libtracker-miner/tracker-monitor.c
+++ b/src/libtracker-miner/tracker-monitor.c
@@ -1271,9 +1271,15 @@ monitor_move (TrackerMonitor *monitor,
 	gpointer iter_file, iter_file_monitor;
 	guint items_moved = 0;
 
-	/* So this is tricky. What we have to do is, remove all
-	 * monitors recursively for the OLD directory and add new
-	 * monitors recursively for the NEW directory.
+	/* So this is tricky. What we have to do is:
+	 *
+	 * 1) Add all monitors for the new_file directory hierarchy
+	 * 2) Then remove the monitors for old_file
+	 *
+	 * This order is necessary because inotify can reuse watch
+	 * descriptors, and libinotify will remove handles
+	 * asynchronously on IN_IGNORE, so the opposite sequence
+	 * may possibly remove valid, just added, monitors.
 	 */
 	new_monitors = g_hash_table_new_full (g_file_hash,
 	                                      (GEqualFunc) g_file_equal,
@@ -1281,10 +1287,7 @@ monitor_move (TrackerMonitor *monitor,
 	                                      NULL);
 	old_prefix = g_file_get_path (old_file);
 
-	/* Remove the monitor for the top level directory */
-	tracker_monitor_remove (monitor, old_file);
-
-	/* Remove the monitor for the subdirectories */
+	/* Find out which subdirectories should have a file monitor added */
 	g_hash_table_iter_init (&iter, monitor->private->monitors);
 	while (g_hash_table_iter_next (&iter, &iter_file, &iter_file_monitor)) {
 		GFile *f;
@@ -1327,16 +1330,7 @@ monitor_move (TrackerMonitor *monitor,
 			g_object_unref (f);
 		}
 
-		g_hash_table_iter_remove (&iter);
-
-		g_debug ("Removed monitor for path:'%s', total monitors:%d",
-		         old_path,
-		         g_hash_table_size (monitor->private->monitors));
-
 		g_free (old_path);
-
-		/* We reset this because now it is possible we have limit - 1 */
-		monitor->private->monitor_limit_warned = FALSE;
 		items_moved++;
 	}
 
@@ -1350,6 +1344,9 @@ monitor_move (TrackerMonitor *monitor,
 		g_hash_table_iter_remove (&iter);
 	}
 
+	/* Remove the monitor for the old top level directory hierarchy */
+	tracker_monitor_remove_recursively (monitor, old_file);
+
 	g_hash_table_unref (new_monitors);
 	g_free (old_prefix);