| Linux Trace Toolkit Viewer Developer Guide | ||
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The events that are delivered by the main window are defined in lttvwindow/lttvwindow.h. Let's describe them and their use in details. Remember that you can refer to the control flow viewer module as an example.
A viewer plugin is, before anything, a plugin. As a dynamically loadable module, it thus has an init and a destroy function called whenever it is loaded/initialized and unloaded/destroyed. A graphical module depends on lttvwindow for construction of its viewer instances. In order to achieve this, it must register its constructor function to the main window along with button description or text menu entry description. A module keeps a list of every viewer that currently sits in memory so it can destroy them before the module gets unloaded/destroyed.
The contructor registration to the main windows adds button and menu entry to each main window, thus allowing instanciation of viewers.
The main window is a container that offers menus, buttons and a notebook. Some of those menus and buttons are part of the core of the main window, others are dynamically added and removed when modules are loaded/unloaded.
The notebook contains as much tabs as wanted. Each tab is linked with a set of traces (traceset). Each trace contains many tracefiles (one per cpu). A trace corresponds to a kernel being traced. A traceset corresponds to many traces read together. The time span of a traceset goes from the earliest start of all the traces to the latest end of all the traces.
Inside each tab are added the viewers. When they interact with the main window through the lttvwindow API, they affect the other viewers located in the same tab as they are.
The insertion of many viewers in a tab permits a quick look at all the information wanted in a glance. The main window does merge the read requests from all the viewers in the same tab in a way that every viewer will get exactly the events it asked for, while the event reading loop and state update are shared. It improves performance of events delivery to the viewers.
The lifetime of a viewer is as follows. The viewer constructor function is called each time an instance view is created (one subwindow of this viewer type is created by the user either by clicking on the menu item or the button corresponding to the viewer). Thereafter, the viewer gets hooks called for different purposes by the window containing it. These hooks are detailed below. It also has to deal with GTK Events. Finally, it can be destructed by having its top level widget unreferenced by the main window or by any GTK Event causing a "destroy-event" signal on the its top widget. Another possible way for it do be destroyed is if the module gets unloaded. The module unload function will have to emit a "destroy" signal on each top level widget of all instances of its viewers.
This is the time interval visible on the viewer's tab. Every viewer that cares about being synchronised by respect to the time with other viewers should register to this notification. They should redraw all or part of their display when this occurs.
This notification is called whenever a trace is added/removed from the traceset. As it affects all the data displayed by the viewer, it sould redraw itself totally.
This feature has not been implemented yet.
Being able to zoom nearer a specific time or highlight a specific time on every viewer in synchronicity implies that the viewer has to shown a visual sign over the drawing or select an event when it receives this notice. It should also inform the main window with the appropriate report API function when a user selects a specific time as being the current time.
This notice links the positions of the horizontal dividors between the graphic display zone of every viewer and their Y axis, typically showing processes, cpus, ...
In most cases, the enclosing window knows about updates such as described in the Notification section higher. There are a few cases, however, where updates are caused by actions known by a view instance. For example, clicking in a view may update the current time; all viewers within the same window must be told about the new current time to change the currently highlighted time point. A viewer reports such events by calling lttvwindow_report_current_time on its lttvwindow. The lttvwindow will consequently call current_time_notify for each of its contained viewers.
Available report methods are :
lttvwindow_report_time_window : reports the new time window.
lttvwindow_report_current_time : reports the new current time.
lttvwindow_report_dividor : reports the new horizontal dividor's position.
Events can be requested by passing a EventsRequest structure to the main window. They will be delivered later when the next g_idle functions will be called. Event delivery is done by calling the event hook for this event ID, or the main event hooks. A pointer to the EventsRequest structure is passed as hook_data to the event hooks of the viewers.
EventsRequest consists in
a pointer to the viewer specific data structure
a start timestamp or position
a stop_flag, ending the read process when set to TRUE
a end timestamp and/or position and/or number of events to read
hook lists to call for traceset/trace/tracefile begin and end, and for each event (event hooks and event_by_id hooks).
The main window will deliver events for every EventRequests it has pending through an algorithm that guarantee that all events requested, and only them, will be delivered to the viewer between the call of the tracefile_begin hooks and the call of the tracefile_end hooks.
If a viewer wants to stop the event request at a certain point inside the event hooks, it has to set the stop_flag to TRUE and return TRUE from the hook function. Then return value will stop the process traceset. Then, the main window will look for the stop_flag and remove the EventRequests from its lists, calling the process_traceset_end for this request (it removes hooks from the context and calls the after hooks).
It no stop_flag is risen, the end timestamp, end position or number of events to read has to be reached to determine the end of the request. Otherwise, the end of traceset does determine it.
GTK is quite different from the other graphical toolkits around there. The main difference resides in that there are many X Windows inside one GtkWindow, instead of just one. That means that X events are delivered by the glib main loop directly to the widget corresponding to the GdkWindow affected by the X event.
Event delivery to a widget emits a signal on that widget. Then, if a handler is connected to this widget's signal, it will be executed. There are default handlers for signals, connected at class instantiation time. There is also the possibility to connect other handlers to these signals, which is what should be done in most cases when a viewer needs to interact with X in any way.
Signal emission and propagation is described there :
http://www.gtk.org/tutorial/sec-signalemissionandpropagation.html
For further information on the GTK main loop (now a wrapper over glib main loop) see :
http://developer.gnome.org/doc/API/2.0/gtk/gtk-General.html
http://developer.gnome.org/doc/API/2.0/glib/glib-The-Main-Event-Loop.html
For documentation on event handling in GTK/GDK, see :
http://developer.gnome.org/doc/API/2.0/gdk/gdk-Events.html
http://developer.gnome.org/doc/API/2.0/gdk/gdk-Event-Structures.html
Signals can be connected to handlers, emitted, propagated, blocked, stopped. See :
http://developer.gnome.org/doc/API/2.0/gobject/gobject-Signals.html
Provides the exposed region in the GdkEventExpose structure.
There are two ways of dealing with exposures. The first one is to directly draw on the screen and the second one is to draw in a pixmap buffer, and then to update the screen when necessary.
In the first case, the expose event will be responsible for registering hooks to process_traceset and require time intervals to the main window. So, in this scenario, if a part of the screen is damaged, the trace has to be read to redraw the screen.
In the second case, with a pixmap buffer, the expose handler is only responsible of showing the pixmap buffer on the screen. If the pixmap buffer has never been filled with a drawing, the expose handler may ask for it to be filled.
The interest of using events request to the main window instead of reading the events directly from the trace comes from the fact that the main window does merge requests from the different viewers in the same tab so that the read loop and the state update is shared. As viewers will, in the common scenario, request the same events, only one pass through the trace that will call the right hooks for the right intervals will be done.
When the traceset read is over for a events request, the traceset_end hook is called. It has the responsibility of finishing the drawing if some parts still need to be drawn and to show it on the screen (if the viewer uses a pixmap buffer).
It can add dotted lines and such visual effects to enhance the user's experience.