[california] Notify of EDS property changes from within main loop: BUg #734895

[Jim Nelson <jnelson src gnome org>]

commit c7bb7e3a5dd01f31ec075522589e983710cc0f25
Author: Jim Nelson <jim yorba org>
Date:   Thu Aug 21 17:05:37 2014 -0700

    Notify of EDS property changes from within main loop: BUg #734895
    
    EDS sometimes make ESource and ECalendarSource property changes from
    background thread.  California's code expects all property changes to
    occur in the foreground thread.  This change ensures these property
    notifications always happen in the default main loop.

 src/backing/eds/backing-eds-calendar-source.vala |   69 ++++++++++++++++++++--
 1 files changed, 64 insertions(+), 5 deletions(-)
---
diff --git a/src/backing/eds/backing-eds-calendar-source.vala 
b/src/backing/eds/backing-eds-calendar-source.vala
index 3533c8d..ad587a1 100644
--- a/src/backing/eds/backing-eds-calendar-source.vala
+++ b/src/backing/eds/backing-eds-calendar-source.vala
@@ -17,6 +17,8 @@ internal class EdsCalendarSource : CalendarSource {
     private E.SourceCalendar eds_calendar;
     private E.CalClient? client = null;
     private Scheduled? scheduled_source_write = null;
+    private Scheduled? scheduled_source_read = null;
+    private Gee.HashSet<string> dirty_read_properties = new Gee.HashSet<string>();
     private Cancellable? source_write_cancellable = null;
     
     public EdsCalendarSource(E.Source eds_source, E.SourceCalendar eds_calendar) {
@@ -28,11 +30,17 @@ internal class EdsCalendarSource : CalendarSource {
         // read-only until opened, when state can be determined from client
         read_only = true;
         
-        // use unidirectional bindings so source updates (writing) only occurs when changed from
-        // within the app
-        eds_source.bind_property("display-name", this, PROP_TITLE, BindingFlags.SYNC_CREATE);
-        eds_calendar.bind_property("selected", this, PROP_VISIBLE, BindingFlags.SYNC_CREATE);
-        eds_calendar.bind_property("color", this, PROP_COLOR, BindingFlags.SYNC_CREATE);
+        // can't bind directly because EDS sometimes updates its properties in background threads
+        // and our code expects change notifications to only occur in main thread, so schedule
+        // those notifications in the main loop
+        eds_source.notify["display-name"].connect(on_schedule_source_property_read);
+        eds_calendar.notify["selected"].connect(on_schedule_source_property_read);
+        eds_calendar.notify["color"].connect(on_schedule_source_property_read);
+        
+        // ...and initialize
+        title = eds_source.display_name;
+        visible = eds_calendar.selected;
+        color = eds_calendar.color;
         
         // when changed within the app, need to write it back out
         notify[PROP_TITLE].connect(on_title_changed);
@@ -41,8 +49,59 @@ internal class EdsCalendarSource : CalendarSource {
     }
     
     ~EdsCalendarSource() {
+        // wait for writes to be flushed out, but don't bother doing the same for reads
         if (scheduled_source_write != null)
             scheduled_source_write.wait();
+        
+        // TODO: May need to have these connections happen under open/close to protect against
+        // race conditions, i.e. disconnecting while the property notification is occurring,
+        // meaning the scheduled callback may still occur after dtor exits
+        eds_source.notify["display-name"].disconnect(on_schedule_source_property_read);
+        eds_calendar.notify["selected"].disconnect(on_schedule_source_property_read);
+        eds_calendar.notify["color"].disconnect(on_schedule_source_property_read);
+        
+        // although disconnected, for safety cancel under lock
+        lock (dirty_read_properties) {
+            scheduled_source_read = null;
+        }
+    }
+    
+    private void on_schedule_source_property_read(Object object, ParamSpec pspec) {
+        // schedule the property read in the main (UI) loop so notifications of this object's
+        // properties happen there and not in a background thread ... note that lock for
+        // dirty_read_properties is used for both hash set and Scheduled
+        lock (dirty_read_properties) {
+            dirty_read_properties.add(pspec.name);
+            scheduled_source_read = new Scheduled.once_at_idle(on_read_properties);
+        }
+    }
+    
+    private void on_read_properties() {
+        // make copy under lock and key
+        Gee.HashSet<string> copy = new Gee.HashSet<string>();
+        lock (dirty_read_properties) {
+            copy.add_all(dirty_read_properties);
+            dirty_read_properties.clear();
+        }
+        
+        // update locally outside of lock
+        foreach (string name in copy) {
+            debug("EDS updated %s property %s", to_string(), name);
+            
+            switch (name) {
+                case "display-name":
+                    title = eds_source.display_name;
+                break;
+                
+                case "selected":
+                    visible = eds_calendar.selected;
+                break;
+                
+                case "color":
+                    color = eds_calendar.color;
+                break;
+            }
+        }
     }
     
     private void on_title_changed() {