1 Overview of chrome://sync-internals 2 ----------------------------------- 3 4 This note explains how chrome://sync-internals (also known as 5 about:sync) interacts with the sync service/backend. 6 7 Basically, chrome://sync-internals sends messages to the sync backend 8 and the sync backend sends the reply asynchronously. The sync backend 9 also asynchronously raises events which chrome://sync-internals listen 10 to. 11 12 A message and its reply has a name and a list of arguments, which is 13 basically a wrapper around an immutable ListValue. 14 15 An event has a name and a details object, which is represented by a 16 JsEventDetails (js_event_details.h) object, which is basically a 17 wrapper around an immutable DictionaryValue. 18 19 Message/event flow 20 ------------------ 21 22 chrome://sync-internals is represented by SyncInternalsUI 23 (chrome/browser/ui/webui/sync_internals_ui.h). SyncInternalsUI 24 interacts with the sync service via a JsController (js_controller.h) 25 object, which has a ProcessJsMessage() method that just delegates to 26 an underlying JsBackend instance (js_backend.h). The SyncInternalsUI 27 object also registers itself (as a JsEventHandler 28 [js_event_handler.h]) to the JsController object, and any events 29 raised by the JsBackend are propagated to the JsController and then to 30 the registered JsEventHandlers. 31 32 The ProcessJsMessage() takes a WeakHandle (weak_handle.h) to a 33 JsReplyHandler (js_reply_handler.h), which the backend uses to send 34 replies safely across threads. SyncInternalsUI implements 35 JsReplyHandler, so it simply passes itself as the reply handler when 36 it calls ProcessJsMessage() on the JsController. 37 38 The following objects live on the UI thread: 39 40 - SyncInternalsUI (implements JsEventHandler, JsReplyHandler) 41 - SyncJsController (implements JsController, JsEventHandler) 42 43 The following objects live on the sync thread: 44 45 - SyncManager::SyncInternal (implements JsBackend) 46 47 Of course, none of these objects need to know where the other objects 48 live, since they interact via WeakHandles. 49
