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authorBjörn Gustavsson <[email protected]>2015-04-14 23:21:36 +0200
committerBjörn Gustavsson <[email protected]>2016-03-31 14:24:12 +0200
commit3d70cee4034e4da37d125679345aa2a10c58cb34 (patch)
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Update Kernel documentation
Language cleaned up by technical writers from Combitech. Proofreading and corrections by Björn Gustavsson and Hans Bolinder.
Diffstat (limited to 'lib/kernel/doc/src/seq_trace.xml')
-rw-r--r--lib/kernel/doc/src/seq_trace.xml219
1 files changed, 111 insertions, 108 deletions
diff --git a/lib/kernel/doc/src/seq_trace.xml b/lib/kernel/doc/src/seq_trace.xml
index 857444e338..d29aceb564 100644
--- a/lib/kernel/doc/src/seq_trace.xml
+++ b/lib/kernel/doc/src/seq_trace.xml
@@ -29,24 +29,17 @@
<rev>A</rev>
</header>
<module>seq_trace</module>
- <modulesummary>Sequential Tracing of Messages</modulesummary>
+ <modulesummary>Sequential tracing of messages.</modulesummary>
<description>
<p>Sequential tracing makes it possible to trace all messages
resulting from one initial message. Sequential tracing is
- completely independent of the ordinary tracing in Erlang, which
- is controlled by the <c>erlang:trace/3</c> BIF. See the chapter
- <seealso marker="#whatis">What is Sequential Tracing</seealso>
- below for more information about what sequential tracing is and
- how it can be used.</p>
- <p><c>seq_trace</c> provides functions which control all aspects of
+ independent of the ordinary tracing in Erlang, which
+ is controlled by the <c>erlang:trace/3</c> BIF. For more information
+ about what sequential tracing is and how it can be used, see section
+ <seealso marker="#whatis">Sequential Tracing</seealso>.</p>
+ <p><c>seq_trace</c> provides functions that control all aspects of
sequential tracing. There are functions for activation,
- deactivation, inspection and for collection of the trace output.</p>
- <note>
- <p>The implementation of sequential tracing is in beta status.
- This means that the programming interface still might undergo
- minor adjustments (possibly incompatible) based on feedback
- from users.</p>
- </note>
+ deactivation, inspection, and for collection of the trace output.</p>
</description>
<datatypes>
<datatype>
@@ -239,20 +232,21 @@ seq_trace:set_token(OldToken), % activate the trace token again
</funcs>
<section>
- <title>Trace Messages Sent To the System Tracer</title>
- <p>The format of the messages are:</p>
+ <title>Trace Messages Sent to the System Tracer</title>
+ <p>The format of the messages is one of the following, depending on if
+ flag <c>timestamp</c> of the trace token is set to <c>true</c> or
+ <c>false</c>:</p>
<code type="none">
{seq_trace, Label, SeqTraceInfo, TimeStamp}</code>
<p>or</p>
<code type="none">
{seq_trace, Label, SeqTraceInfo}</code>
- <p>depending on whether the <c>timestamp</c> flag of the trace
- token is set to <c>true</c> or <c>false</c>. Where:</p>
+ <p>Where:</p>
<code type="none">
Label = int()
TimeStamp = {Seconds, Milliseconds, Microseconds}
Seconds = Milliseconds = Microseconds = int()</code>
- <p>The <c>SeqTraceInfo</c> can have the following formats:</p>
+ <p><c>SeqTraceInfo</c> can have the following formats:</p>
<taglist>
<tag><c>{send, Serial, From, To, Message}</c></tag>
<item>
@@ -262,141 +256,151 @@ TimeStamp = {Seconds, Milliseconds, Microseconds}
<tag><c>{'receive', Serial, From, To, Message}</c></tag>
<item>
<p>Used when a process <c>To</c> receives a message with a
- trace token that has the <c>'receive'</c> flag set to
- <c>true</c>.</p>
+ trace token that has flag <c>'receive'</c> set to <c>true</c>.</p>
</item>
<tag><c>{print, Serial, From, _, Info}</c></tag>
<item>
- <p>Used when a process <c>From</c> has called
+ <p>Used when a process <c>From</c> has called
<c>seq_trace:print(Label, TraceInfo)</c> and has a trace
- token with the <c>print</c> flag set to <c>true</c> and
+ token with flag <c>print</c> set to <c>true</c>, and
<c>label</c> set to <c>Label</c>.</p>
</item>
</taglist>
<p><c>Serial</c> is a tuple <c>{PreviousSerial, ThisSerial}</c>,
- where the first integer <c>PreviousSerial</c> denotes the serial
- counter passed in the last received message which carried a trace
- token. If the process is the first one in a new sequential trace,
- <c>PreviousSerial</c> is set to the value of the process internal
- "trace clock". The second integer <c>ThisSerial</c> is the serial
- counter that a process sets on outgoing messages and it is based
- on the process internal "trace clock" which is incremented by one
- before it is attached to the trace token in the message.</p>
+ where:</p>
+ <list type="bulleted">
+ <item><p>Integer <c>PreviousSerial</c> denotes the serial
+ counter passed in the last received message that carried a trace
+ token. If the process is the first in a new sequential trace,
+ <c>PreviousSerial</c> is set to the value of the process internal
+ "trace clock".</p></item>
+ <item><p>Integer <c>ThisSerial</c> is the serial
+ counter that a process sets on outgoing messages. It is based
+ on the process internal "trace clock", which is incremented by one
+ before it is attached to the trace token in the message.</p></item>
+ </list>
</section>
<section>
<marker id="whatis"></marker>
- <title>What is Sequential Tracing</title>
+ <title>Sequential Tracing</title>
<p>Sequential tracing is a way to trace a sequence of messages sent
between different local or remote processes, where the sequence
- is initiated by one single message. In short it works like this:</p>
+ is initiated by a single message. In short, it works as follows:</p>
<p>Each process has a <em>trace token</em>, which can be empty or
- not empty. When not empty the trace token can be seen as
+ not empty. When not empty, the trace token can be seen as
the tuple <c>{Label, Flags, Serial, From}</c>. The trace token is
passed invisibly with each message.</p>
- <p>In order to start a sequential trace the user must explicitly set
+ <p>To start a sequential trace, the user must explicitly set
the trace token in the process that will send the first message
in a sequence.</p>
<p>The trace token of a process is set each time the process
matches a message in a receive statement, according to the trace
token carried by the received message, empty or not.</p>
- <p>On each Erlang node a process can be set as the <em>system tracer</em>. This process will receive trace messages each time
+ <p>On each Erlang node, a process can be set as the <em>system tracer</em>.
+ This process receives trace messages each time
a message with a trace token is sent or received (if the trace
token flag <c>send</c> or <c>'receive'</c> is set). The system
- tracer can then print each trace event, write it to a file or
+ tracer can then print each trace event, write it to a file, or
whatever suitable.</p>
<note>
- <p>The system tracer will only receive those trace events that
+ <p>The system tracer only receives those trace events that
occur locally within the Erlang node. To get the whole picture
- of a sequential trace that involves processes on several Erlang
+ of a sequential trace, involving processes on many Erlang
nodes, the output from the system tracer on each involved node
- must be merged (off line).</p>
+ must be merged (offline).</p>
</note>
- <p>In the following sections Sequential Tracing and its most
- fundamental concepts are described.</p>
+ <p>The following sections describe sequential tracing and its most
+ fundamental concepts.</p>
</section>
<section>
<title>Trace Token</title>
- <p>Each process has a current trace token. Initially the token is
+ <p>Each process has a current trace token. Initially, the token is
empty. When the process sends a message to another process, a
- copy of the current token will be sent "invisibly" along with
+ copy of the current token is sent "invisibly" along with
the message.</p>
- <p>The current token of a process is set in two ways, either</p>
- <list type="ordered">
+ <p>The current token of a process is set in one of the following two
+ ways:</p>
+ <list type="bulleted">
<item>
- <p>explicitly by the process itself, through a call to
- <c>seq_trace:set_token</c>, or</p>
+ <p>Explicitly by the process itself, through a call to
+ <c>seq_trace:set_token/1,2</c></p>
</item>
<item>
- <p>when a message is received.</p>
+ <p>When a message is received</p>
</item>
</list>
- <p>In both cases the current token will be set. In particular, if
- the token of a message received is empty, the current token of
+ <p>In both cases, the current token is set. In particular, if
+ the token of a received message is empty, the current token of
the process is set to empty.</p>
- <p>A trace token contains a label, and a set of flags. Both
- the label and the flags are set in 1 and 2 above.</p>
+ <p>A trace token contains a label and a set of flags. Both
+ the label and the flags are set in both alternatives above.</p>
</section>
<section>
<title>Serial</title>
- <p>The trace token contains a component which is called
- <c>serial</c>. It consists of two integers <c>Previous</c> and
+ <p>The trace token contains a component called
+ <c>serial</c>. It consists of two integers, <c>Previous</c> and
<c>Current</c>. The purpose is to uniquely identify each traced
- event within a trace sequence and to order the messages
- chronologically and in the different branches if any.</p>
+ event within a trace sequence, as well as to order the messages
+ chronologically and in the different branches, if any.</p>
<p>The algorithm for updating <c>Serial</c> can be described as
follows:</p>
- <p>Let each process have two counters <c>prev_cnt</c> and
- <c>curr_cnt</c> which both are set to 0 when a process is created.
+ <p>Let each process have two counters, <c>prev_cnt</c> and
+ <c>curr_cnt</c>, both are set to <c>0</c> when a process is created.
The counters are updated at the following occasions:</p>
<list type="bulleted">
<item>
- <p><em>When the process is about to send a message and the trace token is not empty.</em></p>
+ <p><em>When the process is about to send a message and the trace token
+ is not empty.</em></p>
<p>Let the serial of the trace token be <c>tprev</c> and
- <c>tcurr</c>. <br></br>
-<c>curr_cnt := curr_cnt + 1</c> <br></br>
-<c>tprev := prev_cnt</c> <br></br>
-<c>tcurr := curr_cnt</c></p>
+ <c>tcurr</c>.</p>
+ <pre>
+curr_cnt := curr_cnt + 1
+tprev := prev_cnt
+tcurr := curr_cnt</pre>
<p>The trace token with <c>tprev</c> and <c>tcurr</c> is then
passed along with the message.</p>
</item>
<item>
- <p><em>When the process calls</em><c>seq_trace:print(Label, Info)</c>, <em>Label matches the label part of the trace token and the trace token print flag is true.</em></p>
- <p>The same algorithm as for send above.</p>
+ <p><em>When the process calls</em> <c>seq_trace:print(Label, Info)</c>,
+ <c>Label</c> <em>matches the label part of the trace token and the
+ trace token print flag is <c>true</c>.</em></p>
+ <p>The algorithm is the same as for send above.</p>
</item>
<item>
- <p><em>When a message is received and contains a nonempty trace token.</em></p>
+ <p><em>When a message is received and contains a non-empty trace
+ token.</em></p>
<p>The process trace token is set to the trace token from
the message.</p>
<p>Let the serial of the trace token be <c>tprev</c> and
- <c>tcurr</c>. <br></br>
-<c><![CDATA[if (curr_cnt < tcurr )]]></c> <br></br>
-
- &nbsp; &nbsp; &nbsp; &nbsp;<c>curr_cnt := tcurr</c> <br></br>
-<c>prev_cnt := tcurr</c></p>
+ <c>tcurr</c>.</p>
+ <code>
+<![CDATA[if (curr_cnt < tcurr )]]>
+ curr_cnt := tcurr
+prev_cnt := tcurr</code>
</item>
</list>
- <p>The <c>curr_cnt</c> of a process is incremented each time
+ <p><c>curr_cnt</c> of a process is incremented each time
the process is involved in a sequential trace. The counter can
reach its limit (27 bits) if a process is very long-lived and is
- involved in much sequential tracing. If the counter overflows it
- will not be possible to use the serial for ordering of the trace
- events. To prevent the counter from overflowing in the middle of
- a sequential trace the function <c>seq_trace:reset_trace/0</c>
- can be called to reset the <c>prev_cnt</c> and <c>curr_cnt</c> of
- all processes in the Erlang node. This function will also set all
- trace tokens in processes and their message queues to empty and
- will thus stop all ongoing sequential tracing.</p>
+ involved in much sequential tracing. If the counter overflows, the
+ serial for ordering of the trace events cannot be used. To prevent
+ the counter from overflowing in the middle of
+ a sequential trace, function <c>seq_trace:reset_trace/0</c>
+ can be called to reset <c>prev_cnt</c> and <c>curr_cnt</c> of
+ all processes in the Erlang node. This function also sets all
+ trace tokens in processes and their message queues to empty, and
+ thus stops all ongoing sequential tracing.</p>
</section>
<section>
- <title>Performance considerations</title>
- <p>The performance degradation for a system which is enabled for
- Sequential Tracing is negligible as long as no tracing is
- activated. When tracing is activated there will of course be an
- extra cost for each traced message but all other messages will be
+ <title>Performance Considerations</title>
+ <p>The performance degradation for a system that is enabled for
+ sequential tracing is negligible as long as no tracing is
+ activated. When tracing is activated, there is an
+ extra cost for each traced message, but all other messages are
unaffected.</p>
</section>
@@ -404,13 +408,13 @@ TimeStamp = {Seconds, Milliseconds, Microseconds}
<title>Ports</title>
<p>Sequential tracing is not performed across ports.</p>
<p>If the user for some reason wants to pass the trace token to a
- port this has to be done manually in the code of the port
+ port, this must be done manually in the code of the port
controlling process. The port controlling processes have to check
the appropriate sequential trace settings (as obtained from
- <c>seq_trace:get_token/1</c> and include trace information in
+ <c>seq_trace:get_token/1</c>) and include trace information in
the message data sent to their respective ports.</p>
<p>Similarly, for messages received from a port, a port controller
- has to retrieve trace specific information, and set appropriate
+ has to retrieve trace-specific information, and set appropriate
sequential trace flags through calls to
<c>seq_trace:set_token/2</c>.</p>
</section>
@@ -418,23 +422,23 @@ TimeStamp = {Seconds, Milliseconds, Microseconds}
<section>
<title>Distribution</title>
<p>Sequential tracing between nodes is performed transparently.
- This applies to C-nodes built with Erl_Interface too. A C-node
- built with Erl_Interface only maintains one trace token, which
- means that the C-node will appear as one process from
+ This applies to C-nodes built with <c>Erl_Interface</c> too. A C-node
+ built with <c>Erl_Interface</c> only maintains one trace token, which
+ means that the C-node appears as one process from
the sequential tracing point of view.</p>
- <p>In order to be able to perform sequential tracing between
+ <p>To be able to perform sequential tracing between
distributed Erlang nodes, the distribution protocol has been
- extended (in a backward compatible way). An Erlang node which
- supports sequential tracing can communicate with an older
- (OTP R3B) node but messages passed within that node can of course
+ extended (in a backward compatible way). An Erlang node
+ supporting sequential tracing can communicate with an older
+ (Erlang/OTP R3B) node but messages passed within that node can
not be traced.</p>
</section>
<section>
- <title>Example of Usage</title>
- <p>The example shown here will give rough idea of how the new
- primitives can be used and what kind of output it will produce.</p>
- <p>Assume that we have an initiating process with
+ <title>Example of Use</title>
+ <p>This example gives a rough idea of how the new
+ primitives can be used and what kind of output it produces.</p>
+ <p>Assume that you have an initiating process with
<c><![CDATA[Pid == <0.30.0>]]></c> like this:</p>
<code type="none">
-module(seqex).
@@ -463,8 +467,8 @@ loop() ->
PortController ! {ack,Ack}
end,
loop().</code>
- <p>A possible output from the system's sequential_tracer (inspired
- by AXE-10 and MD-110) could look like:</p>
+ <p>A possible output from the system's <c>sequential_tracer</c> can be
+ like this:</p>
<pre>
17:&lt;0.30.0> Info {0,1} WITH
"**** Trace Started ****"
@@ -475,7 +479,7 @@ loop() ->
17:&lt;0.30.0> Received {2,4} FROM &lt;0.31.0> WITH
{ack,{received,the_message}}</pre>
<p>The implementation of a system tracer process that produces
- the printout above could look like this:</p>
+ this printout can look like this:</p>
<code type="none">
tracer() ->
receive
@@ -502,16 +506,15 @@ print_trace({'receive',Serial,From,To,Message}) ->
print_trace({send,Serial,From,To,Message}) ->
io:format("~p Sent ~p TO ~p WITH~n~p~n",
[From,Serial,To,Message]).</code>
- <p>The code that creates a process that runs the tracer function
- above and sets that process as the system tracer could look like
- this:</p>
+ <p>The code that creates a process that runs this tracer function
+ and sets that process as the system tracer can look like this:</p>
<code type="none">
start() ->
Pid = spawn(?MODULE,tracer,[]),
seq_trace:set_system_tracer(Pid), % set Pid as the system tracer
ok.</code>
- <p>With a function like <c>test/0</c> below the whole example can be
- started.</p>
+ <p>With a function like <c>test/0</c>, the whole example can be
+ started:</p>
<code type="none">
test() ->
P = spawn(?MODULE, loop, [port]),