technical/api-trace.html - external/gitster/git-htmldocs - Git at Google

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 <body class="article">
 <div id="header">
 <h1>trace API</h1>
 </div>
 <div id="content">
 <div id="preamble">
 <div class="sectionbody">
 <div class="paragraph"><p>The trace API can be used to print debug messages to stderr or a file. Trace
 code is inactive unless explicitly enabled by setting <code>GIT_TRACE*</code> environment
 variables.</p></div>
 <div class="paragraph"><p>The trace implementation automatically adds <code>timestamp file:line ... \n</code> to
 all trace messages. E.g.:</p></div>
 <div class="listingblock">
 <div class="content">
 <pre><code>23:59:59.123456 git.c:312 trace: built-in: git 'foo'
 00:00:00.000001 builtin/foo.c:99 foo: some message</code></pre>
 </div></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_data_structures">Data Structures</h2>
 <div class="sectionbody">
 <div class="dlist"><dl>
 <dt class="hdlist1">
 <code>struct trace_key</code>
 </dt>
 <dd>
 <p>
  Defines a trace key (or category). The default (for API functions that
  don&#8217;t take a key) is <code>GIT_TRACE</code>.
 </p>
 <div class="paragraph"><p>E.g. to define a trace key controlled by environment variable <code>GIT_TRACE_FOO</code>:</p></div>
 <div class="listingblock">
 <div class="content">
 <pre><code>static struct trace_key trace_foo = TRACE_KEY_INIT(FOO);

 static void trace_print_foo(const char *message)
 {
  trace_print_key(&amp;trace_foo, message);
 }</code></pre>
 </div></div>
 <div class="paragraph"><p>Note: don&#8217;t use <code>const</code> as the trace implementation stores internal state in
 the <code>trace_key</code> structure.</p></div>
 </dd>
 </dl></div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_functions">Functions</h2>
 <div class="sectionbody">
 <div class="dlist"><dl>
 <dt class="hdlist1">
 <code>int trace_want(struct trace_key *key)</code>
 </dt>
 <dd>
 <p>
  Checks whether the trace key is enabled. Used to prevent expensive
  string formatting before calling one of the printing APIs.
 </p>
 </dd>
 <dt class="hdlist1">
 <code>void trace_disable(struct trace_key *key)</code>
 </dt>
 <dd>
 <p>
  Disables tracing for the specified key, even if the environment
  variable was set.
 </p>
 </dd>
 <dt class="hdlist1">
 <code>void trace_printf(const char *format, ...)</code>
 </dt>
 <dt class="hdlist1">
 <code>void trace_printf_key(struct trace_key *key, const char *format, ...)</code>
 </dt>
 <dd>
 <p>
  Prints a formatted message, similar to printf.
 </p>
 </dd>
 <dt class="hdlist1">
 <code>void trace_argv_printf(const char **argv, const char *format, ...)`</code>
 </dt>
 <dd>
 <p>
  Prints a formatted message, followed by a quoted list of arguments.
 </p>
 </dd>
 <dt class="hdlist1">
 <code>void trace_strbuf(struct trace_key *key, const struct strbuf *data)</code>
 </dt>
 <dd>
 <p>
  Prints the strbuf, without additional formatting (i.e. doesn&#8217;t
  choke on <code>%</code> or even <code>\0</code>).
 </p>
 </dd>
 <dt class="hdlist1">
 <code>uint64_t getnanotime(void)</code>
 </dt>
 <dd>
 <p>
  Returns nanoseconds since the epoch (01/01/1970), typically used
  for performance measurements.
 </p>
 <div class="paragraph"><p>Currently there are high precision timer implementations for Linux (using
 <code>clock_gettime(CLOCK_MONOTONIC)</code>) and Windows (<code>QueryPerformanceCounter</code>).
 Other platforms use <code>gettimeofday</code> as time source.</p></div>
 </dd>
 <dt class="hdlist1">
 <code>void trace_performance(uint64_t nanos, const char *format, ...)</code>
 </dt>
 <dt class="hdlist1">
 <code>void trace_performance_since(uint64_t start, const char *format, ...)</code>
 </dt>
 <dd>
 <p>
  Prints the elapsed time (in nanoseconds), or elapsed time since
  <code>start</code>, followed by a formatted message. Enabled via environment
  variable <code>GIT_TRACE_PERFORMANCE</code>. Used for manual profiling, e.g.:
 </p>
 <div class="listingblock">
 <div class="content">
 <pre><code>uint64_t start = getnanotime();
 /* code section to measure */
 trace_performance_since(start, "foobar");</code></pre>
 </div></div>
 <div class="listingblock">
 <div class="content">
 <pre><code>uint64_t t = 0;
 for (;;) {
  /* ignore */
  t -= getnanotime();
  /* code section to measure */
  t += getnanotime();
  /* ignore */
 }
 trace_performance(t, "frotz");</code></pre>
 </div></div>
 </dd>
 </dl></div>
 </div>
 </div>
 </div>
 <div id="footnotes"><hr /></div>
 <div id="footer">
 <div id="footer-text">
 Last updated 2014-07-22 12:39:19 PDT
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	<body class="article">
	<div id="header">
	<h1>trace API</h1>
	</div>
	<div id="content">
	<div id="preamble">
	<div class="sectionbody">
	<div class="paragraph"><p>The trace API can be used to print debug messages to stderr or a file. Trace
	code is inactive unless explicitly enabled by setting <code>GIT_TRACE*</code> environment
	variables.</p></div>
	<div class="paragraph"><p>The trace implementation automatically adds <code>timestamp file:line ... \n</code> to
	all trace messages. E.g.:</p></div>
	<div class="listingblock">
	<div class="content">
	<pre><code>23:59:59.123456 git.c:312 trace: built-in: git 'foo'
	00:00:00.000001 builtin/foo.c:99 foo: some message</code></pre>
	</div></div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_data_structures">Data Structures</h2>
	<div class="sectionbody">
	<div class="dlist"><dl>
	<dt class="hdlist1">
	<code>struct trace_key</code>
	</dt>
	<dd>
	<p>
	Defines a trace key (or category). The default (for API functions that
	don’t take a key) is <code>GIT_TRACE</code>.
	</p>
	<div class="paragraph"><p>E.g. to define a trace key controlled by environment variable <code>GIT_TRACE_FOO</code>:</p></div>
	<div class="listingblock">
	<div class="content">
	<pre><code>static struct trace_key trace_foo = TRACE_KEY_INIT(FOO);

	static void trace_print_foo(const char *message)
	{
	trace_print_key(&trace_foo, message);
	}</code></pre>
	</div></div>
	<div class="paragraph"><p>Note: don’t use <code>const</code> as the trace implementation stores internal state in
	the <code>trace_key</code> structure.</p></div>
	</dd>
	</dl></div>
	</div>
	</div>
	<div class="sect1">
	<h2 id="_functions">Functions</h2>
	<div class="sectionbody">
	<div class="dlist"><dl>
	<dt class="hdlist1">
	<code>int trace_want(struct trace_key *key)</code>
	</dt>
	<dd>
	<p>
	Checks whether the trace key is enabled. Used to prevent expensive
	string formatting before calling one of the printing APIs.
	</p>
	</dd>
	<dt class="hdlist1">
	<code>void trace_disable(struct trace_key *key)</code>
	</dt>
	<dd>
	<p>
	Disables tracing for the specified key, even if the environment
	variable was set.
	</p>
	</dd>
	<dt class="hdlist1">
	<code>void trace_printf(const char *format, ...)</code>
	</dt>
	<dt class="hdlist1">
	<code>void trace_printf_key(struct trace_key key, const char format, ...)</code>
	</dt>
	<dd>
	<p>
	Prints a formatted message, similar to printf.
	</p>
	</dd>
	<dt class="hdlist1">
	<code>void trace_argv_printf(const char *argv, const char format, ...)`</code>
	</dt>
	<dd>
	<p>
	Prints a formatted message, followed by a quoted list of arguments.
	</p>
	</dd>
	<dt class="hdlist1">
	<code>void trace_strbuf(struct trace_key key, const struct strbuf data)</code>
	</dt>
	<dd>
	<p>
	Prints the strbuf, without additional formatting (i.e. doesn’t
	choke on <code>%</code> or even <code>\0</code>).
	</p>
	</dd>
	<dt class="hdlist1">
	<code>uint64_t getnanotime(void)</code>
	</dt>
	<dd>
	<p>
	Returns nanoseconds since the epoch (01/01/1970), typically used
	for performance measurements.
	</p>
	<div class="paragraph"><p>Currently there are high precision timer implementations for Linux (using
	<code>clock_gettime(CLOCK_MONOTONIC)</code>) and Windows (<code>QueryPerformanceCounter</code>).
	Other platforms use <code>gettimeofday</code> as time source.</p></div>
	</dd>
	<dt class="hdlist1">
	<code>void trace_performance(uint64_t nanos, const char *format, ...)</code>
	</dt>
	<dt class="hdlist1">
	<code>void trace_performance_since(uint64_t start, const char *format, ...)</code>
	</dt>
	<dd>
	<p>
	Prints the elapsed time (in nanoseconds), or elapsed time since
	<code>start</code>, followed by a formatted message. Enabled via environment
	variable <code>GIT_TRACE_PERFORMANCE</code>. Used for manual profiling, e.g.:
	</p>
	<div class="listingblock">
	<div class="content">
	<pre><code>uint64_t start = getnanotime();
	/* code section to measure */
	trace_performance_since(start, "foobar");</code></pre>
	</div></div>
	<div class="listingblock">
	<div class="content">
	<pre><code>uint64_t t = 0;
	for (;;) {
	/* ignore */
	t -= getnanotime();
	/* code section to measure */
	t += getnanotime();
	/* ignore */
	}
	trace_performance(t, "frotz");</code></pre>
	</div></div>
	</dd>
	</dl></div>
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	Last updated 2014-07-22 12:39:19 PDT
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