<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2002</year><year>2013</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
</legalnotice>
<title>Description</title>
<prepared>Håkan Mattsson</prepared>
<responsible>Håkan Mattsson</responsible>
<docno></docno>
<approved>Håkan Mattsson</approved>
<checked></checked>
<date></date>
<rev>%VSN%</rev>
<file>et_desc.xml</file>
</header>
<section>
<title>Overview</title>
<p>The two major components of the <c>Event Tracer (ET)</c> tool
is a graphical sequence chart viewer (<c>et_viewer</c>) and its
backing storage (<c>et_collector</c>). One <c>Collector</c> may be
used as backing storage for several simultaneous <c>Viewers</c>
where each one may display a different view of the same trace
data.</p>
<p>The interface between the <c>Collector</c> and its
<c>Viewers</c> is public in order to enable other types of
<c>Viewers</c>. However in the following text we will focus on
usage of the <c>et_viewer</c>.</p>
<p>The main start function is <c>et_viewer:start/1</c>. By
default it will start both an <c>et_collector</c> and an
<c>et_viewer</c>:</p>
<p></p>
<code type="none"><![CDATA[
% erl -pa et/examples
Erlang R13B03 (erts-5.7.4) [64-bit] [smp:4:4] [rq:4]
[async-threads:0] [kernel-poll:false]
Eshell V5.7.4 (abort with ^G)
1> {ok, Viewer} = et_viewer:start([]).
{ok,<0.40.0>}]]></code>
<p>A <c>Viewer</c> gets trace <c>Events</c> from its
<c>Collector</c> by polling it regularly for more <c>Events</c> to
display. <c>Events</c> are for example reported to the
<c>Collector</c> with <c>et_collector:report_event/6</c>:</p>
<code type="none"><![CDATA[
2> Collector = et_viewer:get_collector_pid(Viewer).
<0.39.0>
3> et_collector:report_event(Collector, 60, my_shell, mnesia_tm, start_outer,
3> "Start outer transaction"),
3> et_collector:report_event(Collector, 40, mnesia_tm, my_shell, new_tid,
3> "New transaction id is 4711"),
3> et_collector:report_event(Collector, 20, my_shell, mnesia_locker, try_write_lock,
3> "Acquire write lock for {my_tab, key}"),
3> et_collector:report_event(Collector, 10, mnesia_locker, my_shell, granted,
3> "You got the write lock for {my_tab, key}"),
3> et_collector:report_event(Collector, 60, my_shell, do_commit,
3> "Perform transaction commit"),
3> et_collector:report_event(Collector, 40, my_shell, mnesia_locker, release_tid,
3> "Release all locks for transaction 4711"),
3> et_collector:report_event(Collector, 60, my_shell, mnesia_tm, delete_transaction,
3> "End of outer transaction"),
3> et_collector:report_event(Collector, 20, my_shell, end_outer,
3> "Transaction returned {atomic, ok}").
{ok,{table_handle,<0.39.0>,16402,trace_ts,
#Fun<et_collector.0.62831470>}}]]></code>
<p>This actually is a simulation of the process <c>Events</c>
caused by a <c>Mnesia</c> transaction that writes a record in a local
table:</p>
<code type="none"><![CDATA[
mnesia:transaction(fun() -> mnesia:write({my_tab, key, val}) end).]]></code>
<p>At this stage when we have a couple of <c>Events</c>, it is time to
show how it looks like in the graphical interface of
<c>et_viewer</c>:</p>
<p></p>
<image file="sim_trans.png">
<icaption>A simulated Mnesia transaction which writes one record</icaption>
</image>
<p>In the sequence chart, the actors (which symbolically has
performed the <c>Event</c>) are shown as named vertical bars. The
order of the actors may be altered by dragging (hold mouse button
1 pressed during the operation) the name tag of an actor and drop
it elsewhere:</p>
<image file="sim_trans_move_actor.png">
<icaption>Two actors has switched places</icaption>
</image>
<p>An <c>Event</c> may be an action performed by one single actor
(blue text label) or it may involve two actors and is then
depicted as an arrow directed from one actor to another (red text
label). Details of an <c>Event</c> can be shown by clicking (press
and release the mouse button 1) on the event label text or on the
arrow. When doing that a <c>Contents Viewer</c> window pops up. It
may look like this:</p>
<p></p>
<image file="sim_trans_write_lock.png">
<icaption>Details of a write lock message</icaption>
</image>
</section>
<section>
<title>Filters and dictionary</title>
<p>The <c>Event Tracer (ET)</c> uses named filters in various
contexts. An Event Trace filter is an <c>Erlang fun</c> that takes
some trace data as input and returns a possibly modified version
of it:
</p>
<p></p>
<code type="none"><![CDATA[
filter(TraceData) -> false | true | {true, NewEvent}
TraceData = Event | erlang_trace_data()
Event = #event{}
NewEvent = #event{}]]></code>
<p>The interface of the filter function is the same as the the
filter functions for the good old <c>lists:filtermap/2</c>. If the filter
returns <c>false</c> it means that the trace data should silently
be dropped. <c>true</c> means that the trace data data already is
an <c>Event Record</c> and that it should be kept as it is.
<c>true</c> means that the <c>TraceData</c> already is an <c>Event
Record</c> and that it should be kept as it is. <c>{true,
NewEvent}</c> means that the original trace data should be
replaced with <c>Event</c>. This provides means to get rid of
unwanted <c>Events</c> as well as enabling alternate views of an
<c>Event</c>.</p>
<p>The first filter that the trace data is exposed for is the
<c>Collector Filter</c>. When a trace <c>Event</c> is reported with
<c>et_collector:report/2</c> (or
<c>et_collector:report_event/5,6</c>) the first thing that
happens, is that a message is sent to the <c>Collector</c> process
to fetch a handle that contains some useful stuff, such as the
<c>Collector Filter Fun</c> and an Ets table identifier. Then the
<c>Collector Filter Fun</c> is applied and if it returns
<c>true</c> (or <c>{true, NewEvent}</c>), the <c>Event</c> will be stored
in an Ets table. As an optimization, subsequent calls to
<c>et_collector:report</c>-functions can use the handle directly
instead of the <c>Collector Pid</c>.</p>
<p>All filters (registered in a <c>Collector</c> or in a
<c>Viewer</c>) must be able to handle an <c>Event record</c> as
input. The <c>Collector Filter</c> (that is the filter named
<c>all</c>) is a little bit special, as its input also may be raw
<c>Erlang Trace Data</c></p>
<p>The <c>Collector</c> manages a key/value based dictionary,
where the filters are stored. Updates of the dictionary is
propagated to all subscribing processes. When a <c>Viewer</c> is
started it is registered as a subscriber of dictionary
updates.</p>
<p>In each <c>Viewer</c> there is only one filter that is active
and all trace <c>Events</c> that the <c>Viewer</c> gets from the
<c>Collector</c> will pass thru that filter. By writing clever
filters it is possible to customize how the <c>Events</c> looks
like in the viewer. The following filter in
<c>et/examples/et_demo.erl</c> replaces the actor names
<c>mnesia_tm</c> and <c>mnesia_locker</c> and leaves everything
else in the record as it was:</p>
<p></p>
<codeinclude file="../../examples/et_demo.erl" tag="%mgr_actors" type="erl"></codeinclude>
<p>If we now add the filter to the running <c>Collector</c>:</p>
<p></p>
<code type="none"><![CDATA[
4> Fun = fun(E) -> et_demo:mgr_actors(E) end.
#Fun<erl_eval.6.13229925>
5> et_collector:dict_insert(Collector, {filter, mgr_actors}, Fun).
ok]]></code>
<p>you will see that the <c>Filter</c> menu in all viewers have
got a new entry called <c>mgr_actors</c>. Select it, and a new
<c>Viewer</c> window will pop up:</p>
<p></p>
<image file="sim_trans_mgr_actors.png">
<icaption>The same trace data in a different view</icaption>
</image>
<p>In order to see the nitty gritty details of an <c>Event</c> you
may click on the <c>Event</c> in order to start a <c>Contents
Viewer</c> for that <c>Event</c>. In the <c>Contents Viewer</c>
there also is a filter menu that enables inspection of the
<c>Event</c> from other views than the one selected in the
viewer. A click on the <c>new_tid</c> <c>Event</c> will cause a
<c>Contents Viewer</c> window to pop up, showing the <c>Event</c>
in the <c>mgr_actors</c> view:</p>
<p></p>
<image file="sim_trans_contents_viewer_mgr_actors.png">
<icaption>The trace <c>Event</c> in the mgr_actors view</icaption>
</image>
<p>Select the <c>all</c> entry in the <c>Filters</c> menu
and a new <c>Contents Viewer window</c> will pop up showing the
same trace <c>Event</c> in the collectors view:</p>
<p></p>
<image file="sim_trans_contents_viewer_collector.png">
<icaption>The same trace <c>Event</c> in the collectors
view</icaption>
</image>
</section>
<section>
<title>Trace clients</title>
<p>As you have seen, it is possible to use the
<c>et_collector:report_event/5,6</c> functions explicitly. By
using those functions you can write your own trace client that
reads trace data from any source stored in any format and just
feed the <c>Collector</c> with it. You may replace the default
<c>Collector Filter</c> with a filter that converts new exciting
trace data formats to <c>Event Records</c> or you may convert it
to an <c>Event Record</c> before you invoke
<c>et_collector:report/2</c> and then rely on the default
<c>Collector Filter</c> to handle the new format.</p>
<p>There are also existing functions in the API that reads from
various sources and calls <c>et_collector:report/2</c>:</p>
<list type="bulleted">
<item>
<p>The trace <c>Events</c> that are hosted by the <c>Collector</c> may be
stored to file and later be loaded by selecting <c>save</c>
and <c>load</c> entries in the <c>Viewers</c> <c>File</c> menu
or via the <c>et_collector</c> API.</p>
</item>
<item>
<p>It is also possible to perform live tracing of a running
system by making use of the built-in trace support in the
Erlang emulator. These Erlang traces can be directed to files
or to ports. See the reference manual for
<c>erlang:trace/4</c>, <c>erlang:trace_pattern/3</c>,
<c>dbg</c> and <c>ttb</c> for more info.</p>
<p>There are also corresponding trace client types that can
read the Erlang trace data format from such files or ports.
The <c>et_collector:start_trace_client/3</c> function makes
use of these Erlang trace clients and redirects the trace data
to the <c>Collector</c>.</p>
<p>The default <c>Collector Filter</c> converts the raw Erlang
trace data format into <c>Event Records</c>. If you want to
perform this differently you can of course write your own
<c>Collector Filter</c> from scratch. But it may probably save
you some efforts if you first apply the default filter in
<c>et_selector:parse_event/2</c> before you apply your own
conversions of its output.</p>
</item>
</list>
</section>
<section>
<title>Global tracing</title>
<p>Setting up an Erlang tracer on a set of nodes and connecting
trace clients to the ports of these tracers is not intuitive. In
order to make this it easier the <c>Event Tracer</c> has a notion
of global tracing. When used, the <c>et_collector</c> process will
monitor Erlang nodes and when one connects, an Erlang tracer will
automatically be started on the newly connected node. A
corresponding trace client will also be started on the
<c>Collector</c> node in order to automatically forward the trace
<c>Events</c> to the <c>Collector</c>. Set the boolean parameter
<c>trace_global</c> to <c>true</c> for either the
<c>et_collector</c> or <c>et_viewer</c> in order to activate the
global tracing. There is no restriction on how many concurrent
(anonymous) collectors you can have, but you can only have one
<b>global</b> <c>Collector</c> as its name is registered in
<c>global</c>.</p>
<p>In order to further simplify the tracing, you can make use of
the <c>et:trace_me/4,5</c> functions. These functions are intended
to be invoked from other applications when there are interesting
<c>Events</c>, in your application that needs to be
highlighted. The functions are extremely light weight as they do
nothing besides returning an atom. These functions are
specifically designed to be traced for. As the caller explicitly
provides the values for the <c>Event Record</c> fields, the
default <c>Collector Filter</c> is able to automatically provide a
customized <c>Event Record</c> without any user defined filter
functions.</p>
<p>In normal operation, the <c>et:trace_me/4,5</c> calls are almost
for free. When tracing is needed, you can either activate tracing
on these functions explicitly. Or you can combine the usage of
<c>trace_global</c> with the usage of <c>trace_pattern</c>. When
set, the <c>trace_pattern</c> will automatically be activated on
all connected nodes. </p>
<p>One nice thing with the <c>trace_pattern</c> is that it
provides a very simple way of minimizing the amount of generated
trace data by allowing you to explicitly control the detail level
of the tracing. As you may have seen the <c>et_viewer</c> have a
slider called <c>"Detail Level"</c> that allows you to control the
detail level of the trace <c>Events</c> displayed in the
<c>Viewer</c>. On the other hand if you set a low detail level in
the <c>trace_pattern</c>, lots of the trace data will never be
generated and thus not sent over the socket to the trace client
and stored in the <c>Collector</c>.</p>
</section>
<section>
<title>Viewer window</title>
<p>Almost all functionality available in the <c>et_viewer</c> is
also available via shortcuts. Which key that has the same effect
as selecting a menu entry is shown enclosed in parentheses. For
example pressing the key <c>r</c> is equivalent to selecting the
menu entry <c>Viewer->Refresh</c>.</p>
<p>File menu:</p>
<list type="bulleted">
<item>
<p><c>Clear all events in the Collector</c> - Deletes all
<c>Events</c> stored in the <c>Collector</c> and notifies all
connected <c>Viewers</c> about this.</p>
</item>
<item>
<p><c>Load events to the Collector from file</c> - Loads the
<c>Collector</c> with <c>Events</c> from a file and notifies
all connected <c>Viewers</c> about this.</p>
</item>
<item>
<p><c>Save all events in the Collector to file</c> - Saves all
<c>Events</c> stored in the <c>Collector</c> to file.</p>
</item>
<item>
<p><c>Print setup</c> - Enables editing of printer setting,
such as paper and layout.</p>
</item>
<item>
<p><c>Print current page</c> - Prints the events on the
current page. The page size is dependent of the selected paper
type.</p>
</item>
<item>
<p><c>Print all pages</c> - Prints all events. The page size
is dependent of the selected paper type.</p>
</item>
<item>
<p><c>Close this Viewer</c> - Closes this <c>Viewer</c>
window, but keeps all other <c>Viewers</c> windows and the
<c>Collector</c> process.</p>
</item>
<item>
<p><c>Close other Viewers, but this</c> - Keeps this
<c>Viewer</c> window and its <c>Collector</c> process, but
closes all other <c>Viewers</c> windowsconnected to the same
<c>Collector</c>.</p>
</item>
<item>
<p><c>Close all Viewers and the Collector</c> - Closes the
<c>Collector</c> and all <c>Viewers</c> connected to it.</p>
</item>
</list>
<p>Viewer menu:</p>
<list type="bulleted">
<item>
<p><c>First</c> - Scrolls <c>this</c> viewer to the first
<c>Event</c> in the <c>Collector</c>.</p>
</item>
<item>
<p><c>Last</c> - Scrolls <c>this</c> viewer to the last
<c>Event</c> in the <c>Collector</c>.</p>
</item>
<item>
<p><c>Prev</c> - Scrolls <c>this</c> viewer one page
backwards.</p>
</item>
<item>
<p><c>Next</c> - Scrolls <c>this</c> viewer one page
forward.</p>
</item>
<item>
<p><c>Refresh</c> - Clears <c>this</c> viewer and re-read its
<c>Events</c> from the <c>Collector</c>.</p>
</item>
<item>
<p><c>Up</c> - Scrolls a few <c>Events</c> backwards.</p>
</item>
<item>
<p><c>Down</c> - Scrolls a few <c>Events</c> forward.</p>
</item>
<item>
<p><c>Display all actors.</c> - Reset the settings for hidden
and/or highlighted actors.</p>
</item>
</list>
<p>Collector menu:</p>
<list type="bulleted">
<item>
<p><c>First</c> - Scrolls<c>all</c> viewers to the first
<c>Event</c> in the <c>Collector</c>.</p>
</item>
<item>
<p><c>Last</c> - Scrolls <c>all</c> viewers to the last
<c>Event</c> in the <c>Collector</c>.</p>
</item>
<item>
<p><c>Prev</c> - Scrolls <c>all</c> viewers one page
backwards.</p>
</item>
<item>
<p><c>Next</c> - Scrolls <c>all</c> viewers one page
forward.</p>
</item>
<item>
<p><c>Refresh</c> - Clears <c>all</c> viewers and re-read
their <c>Events</c> from the <c>Collector</c>.</p>
</item>
</list>
<p>Filters and scaling menu:</p>
<list type="bulleted">
<item>
<p><c>ActiveFilter (=)</c> - Starts a new <c>Viewer</c> window
with the same active filter and scale as the current one.</p>
</item>
<item>
<p><c>ActiveFilter (+)</c> - Starts a new <c>Viewer</c> window
with the same active filter but a larger scale than the
current one.</p>
</item>
<item>
<p><c>ActiveFilter (-)</c> - Starts a new <c>Viewer </c>window
with the same active filter but a smaller scale than the
current one.</p>
</item>
<item>
<p><c>all (0)</c> - Starts a new <c>Viewer</c> with the
<c>Collector Filter</c> as active filter. It will cause all
events in the collector to be viewed.</p>
</item>
<item>
<p><c>AnotherFilter (2)</c> - If more filters are inserted
into the dictionary, these will turn up here as entries in the
<c>Filters</c> menu. The second filter will get the shortcut
number 2, the next one number 3 etc. The names are sorted.</p>
</item>
</list>
<p>Slider and radio buttons:</p>
<list type="bulleted">
<item>
<p><c>Hide From=To</c> - When true, this means that the
<c>Viewer</c> will hide all <c>Events</c> where the from-actor
equals to its to-actor. These events are sometimes called
actions.</p>
</item>
<item>
<p><c>Hide (excluded actors)</c> - When true, this means that
the <c>Viewer</c> will hide all <c>Events</c> whose actors are
marked as excluded. Excluded actors are normally enclosed in
round brackets when they are displayed inthe
<c>Viewer</c>.</p>
</item>
<item>
<p><c>Detail level</c> - This slider controls the resolution
of the <c>Viewer</c>. Only <c>Events</c> with a detail level
<c>smaller</c> than the selected one (default=100=max) are
displayed.</p>
</item>
</list>
<p>Other features:</p>
<list type="bulleted">
<item>
<p><c>Vertical scroll</c> - Use mouse wheel and up/down arrows
to scroll little. Use page up/down and home/end buttons to
scroll more.</p>
</item>
<item>
<p><c>Display details of an event</c> - Left mouse click on
the event label or the arrowand a new <c>Contents Viewer</c>
window will pop up, displaying the contents of an
<c>Event</c>.</p>
</item>
<item>
<p><c>Highlight actor (toggle)</c> - Left mouse click on the
actor name tag. The actor name will be enclosed in square
brackets <c>[]</c>. When one or more actors are highlighted,
only events related to those actors are displayed. All others
are hidden.</p>
</item>
<item>
<p><c>Exclude actor (toggle)</c> - Right mouse click on the
actor name tag. The actor name will be enclosed in round
brackets <c>()</c>. When an actor is excluded, all events
related to this actor is hidden. If the checkbox <c>Hide
(excluded actors)</c> is checked, even the name tags and
corresponding vertical line of excluded actors will be
hidden.</p>
</item>
<item>
<p><c>Move actor</c> - Left mouse button drag and drop on
actor name tag. Move the actor by first clicking on the actor
name, keeping the button pressed while moving the cursor to a
new location and release the button where the actor should be
moved to.</p>
</item>
<item>
<p><c>Display all actors</c> - Press the 'a' button. Reset the
settings for hidden and/or highlighted actors.</p>
</item>
</list>
</section>
<section>
<title>Configuration</title>
<p>The <c>Event Records</c> in the Ets table are ordered by their
timestamp. Which timestamp that should be used is controlled via
the <c>event_order</c> parameter. Default is <c>trace_ts</c> which
means the time when the trace data was generated. <c>event_ts</c>
means the time when the trace data was parsed (transformed into an
<c>Event Record</c>).</p>
</section>
<section>
<title>Contents viewer window</title>
<p>File menu:</p>
<list type="bulleted">
<item>
<p><c>Close</c> - Close this window.</p>
</item>
<item>
<p><c>Save</c> - Save the contents of this window to file.</p>
</item>
</list>
<p>Filters menu:</p>
<list type="bulleted">
<item>
<p><c>ActiveFilter</c> - Start a new <c>Contents Viewer
window</c> with the same active filter.</p>
</item>
<item>
<p><c>AnotherFilter (2)</c> - If more filters are inserted
into the dictionary, these will turn up here as entries in the
<c>Filters</c> menu. The second filter will be number 2, the
next one number 3 etc. The names are sorted.</p>
</item>
</list>
<p>Hide menu:</p>
<list type="bulleted">
<item>
<p><c>Hide actor in viewer</c> - Known actors are shown as a
named vertical bars in the <c>Viewer</c> window. By hiding the
actor, its vertical bar will be removed and the <c>Viewer</c>
will be refreshed.</p>
<p><c>Hiding the actor</c> is only useful if the
<c>max_actors</c> threshold has been reached, as it then will
imply that the "hidden" actor will be displayed as if it were
<c>"UNKNOWN"</c>. If the <c>max_actors</c> threshold not have
been reached, the actor will re-appear as a vertical bar in
the <c>Viewer</c>.</p>
</item>
<item>
<p><c>Show actor in viewer</c> - This implies that the actor
will be added as a known actor in the <c>Viewer</c> with its
own vertical bar.</p>
</item>
</list>
<p>Search menu:</p>
<list type="bulleted">
<item>
<p><c>Forward from this event</c> - Set this event to be the first
event in the viewer and change its display mode to be enter
forward search mode. The actor of this event (from, to or
both) will be added to the list of selected actors.</p>
</item>
<item>
<p><c>Reverse from this event</c> - Set this event to be the
first <c>Event</c> in the <c>Viewer</c> and change its display
mode to be enter reverse search mode. The actor of this
<c>Event</c> (from, to or both) will be added to the list of
selected actors. Observe, that the <c>Events</c> will be shown
in reverse order.</p>
</item>
<item>
<p><c>Abort search. Display all</c> - Switch the display mode
of the <c>Viewer</c> to show all <c>Events</c> regardless of
any ongoing searches. Abort the searches.</p>
</item>
</list>
</section>
</chapter>
