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