mirror of
https://github.com/git/git.git
synced 2024-12-13 03:44:17 +08:00
4dda133385
Fix a typo in an example in the trace API documentation. * ep/trace-doc-sample-fix: api-trace.txt: fix typo
141 lines
3.8 KiB
Plaintext
141 lines
3.8 KiB
Plaintext
trace API
|
|
=========
|
|
|
|
The trace API can be used to print debug messages to stderr or a file. Trace
|
|
code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment
|
|
variables.
|
|
|
|
The trace implementation automatically adds `timestamp file:line ... \n` to
|
|
all trace messages. E.g.:
|
|
|
|
------------
|
|
23:59:59.123456 git.c:312 trace: built-in: git 'foo'
|
|
00:00:00.000001 builtin/foo.c:99 foo: some message
|
|
------------
|
|
|
|
Data Structures
|
|
---------------
|
|
|
|
`struct trace_key`::
|
|
|
|
Defines a trace key (or category). The default (for API functions that
|
|
don't take a key) is `GIT_TRACE`.
|
|
+
|
|
E.g. to define a trace key controlled by environment variable `GIT_TRACE_FOO`:
|
|
+
|
|
------------
|
|
static struct trace_key trace_foo = TRACE_KEY_INIT(FOO);
|
|
|
|
static void trace_print_foo(const char *message)
|
|
{
|
|
trace_printf_key(&trace_foo, "%s", message);
|
|
}
|
|
------------
|
|
+
|
|
Note: don't use `const` as the trace implementation stores internal state in
|
|
the `trace_key` structure.
|
|
|
|
Functions
|
|
---------
|
|
|
|
`int trace_want(struct trace_key *key)`::
|
|
|
|
Checks whether the trace key is enabled. Used to prevent expensive
|
|
string formatting before calling one of the printing APIs.
|
|
|
|
`void trace_disable(struct trace_key *key)`::
|
|
|
|
Disables tracing for the specified key, even if the environment
|
|
variable was set.
|
|
|
|
`void trace_printf(const char *format, ...)`::
|
|
`void trace_printf_key(struct trace_key *key, const char *format, ...)`::
|
|
|
|
Prints a formatted message, similar to printf.
|
|
|
|
`void trace_argv_printf(const char **argv, const char *format, ...)``::
|
|
|
|
Prints a formatted message, followed by a quoted list of arguments.
|
|
|
|
`void trace_strbuf(struct trace_key *key, const struct strbuf *data)`::
|
|
|
|
Prints the strbuf, without additional formatting (i.e. doesn't
|
|
choke on `%` or even `\0`).
|
|
|
|
`uint64_t getnanotime(void)`::
|
|
|
|
Returns nanoseconds since the epoch (01/01/1970), typically used
|
|
for performance measurements.
|
|
+
|
|
Currently there are high precision timer implementations for Linux (using
|
|
`clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`).
|
|
Other platforms use `gettimeofday` as time source.
|
|
|
|
`void trace_performance(uint64_t nanos, const char *format, ...)`::
|
|
`void trace_performance_since(uint64_t start, const char *format, ...)`::
|
|
|
|
Prints the elapsed time (in nanoseconds), or elapsed time since
|
|
`start`, followed by a formatted message. Enabled via environment
|
|
variable `GIT_TRACE_PERFORMANCE`. Used for manual profiling, e.g.:
|
|
+
|
|
------------
|
|
uint64_t start = getnanotime();
|
|
/* code section to measure */
|
|
trace_performance_since(start, "foobar");
|
|
------------
|
|
+
|
|
------------
|
|
uint64_t t = 0;
|
|
for (;;) {
|
|
/* ignore */
|
|
t -= getnanotime();
|
|
/* code section to measure */
|
|
t += getnanotime();
|
|
/* ignore */
|
|
}
|
|
trace_performance(t, "frotz");
|
|
------------
|
|
|
|
Bugs & Caveats
|
|
--------------
|
|
|
|
GIT_TRACE_* environment variables can be used to tell Git to show
|
|
trace output to its standard error stream. Git can often spawn a pager
|
|
internally to run its subcommand and send its standard output and
|
|
standard error to it.
|
|
|
|
Because GIT_TRACE_PERFORMANCE trace is generated only at the very end
|
|
of the program with atexit(), which happens after the pager exits, it
|
|
would not work well if you send its log to the standard error output
|
|
and let Git spawn the pager at the same time.
|
|
|
|
As a work around, you can for example use '--no-pager', or set
|
|
GIT_TRACE_PERFORMANCE to another file descriptor which is redirected
|
|
to stderr, or set GIT_TRACE_PERFORMANCE to a file specified by its
|
|
absolute path.
|
|
|
|
For example instead of the following command which by default may not
|
|
print any performance information:
|
|
|
|
------------
|
|
GIT_TRACE_PERFORMANCE=2 git log -1
|
|
------------
|
|
|
|
you may want to use:
|
|
|
|
------------
|
|
GIT_TRACE_PERFORMANCE=2 git --no-pager log -1
|
|
------------
|
|
|
|
or:
|
|
|
|
------------
|
|
GIT_TRACE_PERFORMANCE=3 3>&2 git log -1
|
|
------------
|
|
|
|
or:
|
|
|
|
------------
|
|
GIT_TRACE_PERFORMANCE=/path/to/log/file git log -1
|
|
------------
|