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<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>2002</year><year>2021</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>H&aring;kan Mattsson</prepared>
    <responsible>H&aring;kan Mattsson</responsible>
    <docno></docno>
    <approved>H&aring;kan 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>

    <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>

    <image file="sim_trans_contents_viewer_mgr_actors.png">
      <icaption>The trace Event 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>

    <image file="sim_trans_contents_viewer_collector.png">
      <icaption>The same trace Event 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
    <em>global</em> <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 in the
        <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>

