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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_print_key(&trace_foo, 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");
------------
|
