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>Chapter 3. Linux Trace Toolkit Viewer Graphical Module Tutorial</TD
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><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="AEN84"
>3.5. How to handle events and use the graphical trace reading service</A
></H1
><P
>&#13;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.
</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN87"
>3.5.1. Module Related API</A
></H2
><P
>&#13;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.
</P
><P
>&#13;The contructor registration to the main windows adds button and menu
entry to each main window, thus allowing instanciation of viewers.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN91"
>3.5.2. Main Window</A
></H2
><P
>&#13;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.
</P
><P
>&#13;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.
</P
><P
>&#13;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.
</P
><P
>&#13;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.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN97"
>3.5.3. Viewer Instance Related API</A
></H2
><P
>&#13;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.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN100"
>3.5.4. Notices from Main Window</A
></H2
><P
></P
><DIV
CLASS="variablelist"
><DL
><DT
>time_window</DT
><DD
><P
>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.</P
></DD
><DT
>traceset</DT
><DD
><P
>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.</P
></DD
><DT
>filter</DT
><DD
><P
>This feature has not been implemented yet.</P
></DD
><DT
>current_time</DT
><DD
><P
>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.</P
></DD
><DT
>dividor</DT
><DD
><P
>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, ...</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN123"
>3.5.5. Reporting Changes to the Main Window</A
></H2
><P
>&#13;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.
</P
><P
>&#13;Available report methods are :
<P
></P
><UL
><LI
><P
>&#13;lttvwindow_report_time_window : reports the new time window.
</P
></LI
><LI
><P
>&#13;lttvwindow_report_current_time : reports the new current time.
</P
></LI
><LI
><P
>&#13;lttvwindow_report_dividor : reports the new horizontal dividor's position.
</P
></LI
></UL
>
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN134"
>3.5.6. Requesting Events to Main Window</A
></H2
><P
>&#13;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.
</P
><P
>&#13;EventsRequest consists in 
<P
></P
><UL
><LI
><P
>&#13;a pointer to the viewer specific data structure
</P
></LI
><LI
><P
>&#13;a start timestamp or position
</P
></LI
><LI
><P
>&#13;a stop_flag, ending the read process when set to TRUE
</P
></LI
><LI
><P
>&#13;a end timestamp and/or position and/or number of events to read
</P
></LI
><LI
><P
>&#13;hook lists to call for traceset/trace/tracefile begin and end, and for each
  event (event hooks and event_by_id hooks).
</P
></LI
></UL
>
</P
><P
>&#13;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.
</P
><P
>&#13;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).
</P
><P
>&#13;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.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="AEN152"
>3.5.7. GTK Events</A
></H2
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN154"
>3.5.7.1. Events and Signals</A
></H3
><P
>&#13;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.
</P
><P
>&#13;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.
</P
><P
>&#13;Signal emission and propagation is described there : 

<P
></P
><UL
><LI
><P
>&#13;http://www.gtk.org/tutorial/sec-signalemissionandpropagation.html
</P
></LI
></UL
>
</P
><P
>&#13;For further information on the GTK main loop (now a wrapper over glib main loop)
see :

<P
></P
><UL
><LI
><P
>&#13;http://developer.gnome.org/doc/API/2.0/gtk/gtk-General.html
</P
></LI
><LI
><P
>&#13;http://developer.gnome.org/doc/API/2.0/glib/glib-The-Main-Event-Loop.html
</P
></LI
></UL
>
</P
><P
>&#13;For documentation on event handling in GTK/GDK, see :

<P
></P
><UL
><LI
><P
>&#13;http://developer.gnome.org/doc/API/2.0/gdk/gdk-Events.html
</P
></LI
><LI
><P
>&#13;http://developer.gnome.org/doc/API/2.0/gdk/gdk-Event-Structures.html
</P
></LI
></UL
>
</P
><P
>&#13;Signals can be connected to handlers, emitted, propagated, blocked, 
stopped. See :

<P
></P
><UL
><LI
><P
>&#13;http://developer.gnome.org/doc/API/2.0/gobject/gobject-Signals.html
</P
></LI
></UL
>
</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="AEN178"
>3.5.7.2. The "expose_event"</A
></H3
><P
>&#13;Provides the exposed region in the GdkEventExpose structure. 
</P
><P
>&#13;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.
</P
><P
>&#13;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.
</P
><P
>&#13;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.
</P
><P
>&#13;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.
</P
><P
>&#13;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).
</P
><P
>&#13;It can add dotted lines and such visual effects to enhance the user's
experience.
</P
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