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chromium / external / gitster / git-htmldocs / 77f65806c33ea8493158d64561e03fa54dd15d0f / . / technical / api-trace.html
blob: 311969285652dab5f54fabf116157c3b165e13f8 [file] [log] [blame]
Junio C Hamano944ce252018-05-30 22:25:26[diff] [blame]1<?xml version="1.0" encoding="UTF-8"?>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
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Junio C Hamano944ce252018-05-30 22:25:26[diff] [blame]7<meta name="generator" content="AsciiDoc 8.6.10" />
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]8<title>trace API</title>
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]91.monospaced, code, pre {
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Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]95 padding: 0;
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Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]101
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]229span.image img { border-style: none; vertical-align: text-bottom; }
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]230a.image:visited { color: white; }
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]359div.toclevel0, div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]360 margin-top: 0;
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]417div.unbreakable { page-break-inside: avoid; }
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Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]419
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Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]425div.tableblock {
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Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]458table.tableblock {
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]537
538
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]539</style>
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544/////////////////////////////////////////////////////////////////////
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546/////////////////////////////////////////////////////////////////////
547
548/* Author: Mihai Bazon, September 2002
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]583 var re = new RegExp('[hH]([1-'+(toclevels+1)+'])');
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]584 // Function that scans the DOM tree for header elements (the DOM2
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]612 if (entry.nodeName.toLowerCase() == 'div'
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]613 && entry.getAttribute("class")
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637},
638
639
640/////////////////////////////////////////////////////////////////////
641// Footnotes generator
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643
644/* Based on footnote generation code from:
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646 */
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Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]658 if (entry.nodeName.toLowerCase() == 'div' && entry.getAttribute("class") == "footnote")
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]659 entriesToRemove.push(entry);
660 }
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664
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707
708install: function(toclevels) {
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710
711 function reinstall() {
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715 }
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720 reinstall();
721 }
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723 timerId = setInterval(reinstall, 500);
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726 else
727 window.onload = reinstallAndRemoveTimer;
728}
729
730}
731asciidoc.install();
732/*]]>*/
733</script>
734</head>
735<body class="article">
736<div id="header">
737<h1>trace API</h1>
738</div>
739<div id="content">
740<div id="preamble">
741<div class="sectionbody">
742<div class="paragraph"><p>The trace API can be used to print debug messages to stderr or a file. Trace
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]743code is inactive unless explicitly enabled by setting <code>GIT_TRACE*</code> environment
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]744variables.</p></div>
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]745<div class="paragraph"><p>The trace implementation automatically adds <code>timestamp file:line ... \n</code> to
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]746all trace messages. E.g.:</p></div>
747<div class="listingblock">
748<div class="content">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]749<pre><code>23:59:59.123456 git.c:312 trace: built-in: git 'foo'
75000:00:00.000001 builtin/foo.c:99 foo: some message</code></pre>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]751</div></div>
752</div>
753</div>
754<div class="sect1">
755<h2 id="_data_structures">Data Structures</h2>
756<div class="sectionbody">
757<div class="dlist"><dl>
758<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]759<code>struct trace_key</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]760</dt>
761<dd>
762<p>
763 Defines a trace key (or category). The default (for API functions that
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]764 don&#8217;t take a key) is <code>GIT_TRACE</code>.
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]765</p>
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]766<div class="paragraph"><p>E.g. to define a trace key controlled by environment variable <code>GIT_TRACE_FOO</code>:</p></div>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]767<div class="listingblock">
768<div class="content">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]769<pre><code>static struct trace_key trace_foo = TRACE_KEY_INIT(FOO);
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]770
771static void trace_print_foo(const char *message)
772{
Junio C Hamano5996b672016-04-13 22:01:41[diff] [blame]773 trace_printf_key(&amp;trace_foo, "%s", message);
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]774}</code></pre>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]775</div></div>
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]776<div class="paragraph"><p>Note: don&#8217;t use <code>const</code> as the trace implementation stores internal state in
777the <code>trace_key</code> structure.</p></div>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]778</dd>
779</dl></div>
780</div>
781</div>
782<div class="sect1">
783<h2 id="_functions">Functions</h2>
784<div class="sectionbody">
785<div class="dlist"><dl>
786<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]787<code>int trace_want(struct trace_key *key)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]788</dt>
789<dd>
790<p>
791 Checks whether the trace key is enabled. Used to prevent expensive
792 string formatting before calling one of the printing APIs.
793</p>
794</dd>
795<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]796<code>void trace_disable(struct trace_key *key)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]797</dt>
798<dd>
799<p>
800 Disables tracing for the specified key, even if the environment
801 variable was set.
802</p>
803</dd>
804<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]805<code>void trace_printf(const char *format, ...)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]806</dt>
807<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]808<code>void trace_printf_key(struct trace_key *key, const char *format, ...)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]809</dt>
810<dd>
811<p>
812 Prints a formatted message, similar to printf.
813</p>
814</dd>
815<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]816<code>void trace_argv_printf(const char **argv, const char *format, ...)`</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]817</dt>
818<dd>
819<p>
820 Prints a formatted message, followed by a quoted list of arguments.
821</p>
822</dd>
823<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]824<code>void trace_strbuf(struct trace_key *key, const struct strbuf *data)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]825</dt>
826<dd>
827<p>
828 Prints the strbuf, without additional formatting (i.e. doesn&#8217;t
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]829 choke on <code>%</code> or even <code>\0</code>).
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]830</p>
831</dd>
832<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]833<code>uint64_t getnanotime(void)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]834</dt>
835<dd>
836<p>
837 Returns nanoseconds since the epoch (01/01/1970), typically used
838 for performance measurements.
839</p>
840<div class="paragraph"><p>Currently there are high precision timer implementations for Linux (using
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]841<code>clock_gettime(CLOCK_MONOTONIC)</code>) and Windows (<code>QueryPerformanceCounter</code>).
842Other platforms use <code>gettimeofday</code> as time source.</p></div>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]843</dd>
844<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]845<code>void trace_performance(uint64_t nanos, const char *format, ...)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]846</dt>
847<dt class="hdlist1">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]848<code>void trace_performance_since(uint64_t start, const char *format, ...)</code>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]849</dt>
850<dd>
851<p>
852 Prints the elapsed time (in nanoseconds), or elapsed time since
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]853 <code>start</code>, followed by a formatted message. Enabled via environment
854 variable <code>GIT_TRACE_PERFORMANCE</code>. Used for manual profiling, e.g.:
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]855</p>
856<div class="listingblock">
857<div class="content">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]858<pre><code>uint64_t start = getnanotime();
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]859/* code section to measure */
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]860trace_performance_since(start, "foobar");</code></pre>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]861</div></div>
862<div class="listingblock">
863<div class="content">
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]864<pre><code>uint64_t t = 0;
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]865for (;;) {
866 /* ignore */
867 t -= getnanotime();
868 /* code section to measure */
869 t += getnanotime();
870 /* ignore */
871}
Junio C Hamanoc14e6ad2014-10-31 20:25:53[diff] [blame]872trace_performance(t, "frotz");</code></pre>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]873</div></div>
874</dd>
875</dl></div>
876</div>
877</div>
Junio C Hamanobec5da42016-04-06 22:58:21[diff] [blame]878<div class="sect1">
879<h2 id="_bugs_amp_caveats">Bugs &amp; Caveats</h2>
880<div class="sectionbody">
881<div class="paragraph"><p>GIT_TRACE_* environment variables can be used to tell Git to show
882trace output to its standard error stream. Git can often spawn a pager
883internally to run its subcommand and send its standard output and
884standard error to it.</p></div>
885<div class="paragraph"><p>Because GIT_TRACE_PERFORMANCE trace is generated only at the very end
886of the program with atexit(), which happens after the pager exits, it
887would not work well if you send its log to the standard error output
888and let Git spawn the pager at the same time.</p></div>
889<div class="paragraph"><p>As a work around, you can for example use <em>--no-pager</em>, or set
890GIT_TRACE_PERFORMANCE to another file descriptor which is redirected
891to stderr, or set GIT_TRACE_PERFORMANCE to a file specified by its
892absolute path.</p></div>
893<div class="paragraph"><p>For example instead of the following command which by default may not
894print any performance information:</p></div>
895<div class="listingblock">
896<div class="content">
897<pre><code>GIT_TRACE_PERFORMANCE=2 git log -1</code></pre>
898</div></div>
899<div class="paragraph"><p>you may want to use:</p></div>
900<div class="listingblock">
901<div class="content">
902<pre><code>GIT_TRACE_PERFORMANCE=2 git --no-pager log -1</code></pre>
903</div></div>
904<div class="paragraph"><p>or:</p></div>
905<div class="listingblock">
906<div class="content">
907<pre><code>GIT_TRACE_PERFORMANCE=3 3&gt;&amp;2 git log -1</code></pre>
908</div></div>
909<div class="paragraph"><p>or:</p></div>
910<div class="listingblock">
911<div class="content">
912<pre><code>GIT_TRACE_PERFORMANCE=/path/to/log/file git log -1</code></pre>
913</div></div>
914</div>
915</div>
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]916</div>
917<div id="footnotes"><hr /></div>
918<div id="footer">
919<div id="footer-text">
Junio C Hamano2ef0ba32018-01-26 23:13:53[diff] [blame]920Last updated
Junio C Hamano49bcf742018-06-13 22:04:15[diff] [blame]921 2018-01-26 15:11:04 PST
Junio C Hamanodbe51052014-07-22 19:39:51[diff] [blame]922</div>
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