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Diffstat (limited to 'trace.h')
| -rw-r--r-- | trace.h | 278 |
1 files changed, 278 insertions, 0 deletions
@@ -0,0 +1,278 @@ +#ifndef TRACE_H +#define TRACE_H + +#include "git-compat-util.h" +#include "strbuf.h" + +/** + * 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 + * ------------ + * + * 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 + * ------------ + * + */ + +/** + * 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. + */ +struct trace_key { + const char * const key; + int fd; + unsigned int initialized : 1; + unsigned int need_close : 1; +}; + +extern struct trace_key trace_default_key; + +#define TRACE_KEY_INIT(name) { .key = "GIT_TRACE_" #name } +extern struct trace_key trace_perf_key; +extern struct trace_key trace_setup_key; + +void trace_repo_setup(const char *prefix); + +/** + * Checks whether the trace key is enabled. Used to prevent expensive + * string formatting before calling one of the printing APIs. + */ +int trace_want(struct trace_key *key); + +/** + * Enables or disables tracing for the specified key, as if the environment + * variable was set to the given value. + */ +void trace_override_envvar(struct trace_key *key, const char *value); + +/** + * Disables tracing for the specified key, even if the environment variable + * was set. + */ +void trace_disable(struct trace_key *key); + +/** + * 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. + */ +uint64_t getnanotime(void); + +void trace_command_performance(const char **argv); +void trace_verbatim(struct trace_key *key, const void *buf, unsigned len); +uint64_t trace_performance_enter(void); + +/* + * TRACE_CONTEXT may be set to __FUNCTION__ if the compiler supports it. The + * default is __FILE__, as it is consistent with assert(), and static function + * names are not necessarily unique. + * + * __FILE__ ":" __FUNCTION__ doesn't work with GNUC, as __FILE__ is supplied + * by the preprocessor as a string literal, and __FUNCTION__ is filled in by + * the compiler as a string constant. + */ +#ifndef TRACE_CONTEXT +# define TRACE_CONTEXT __FILE__ +#endif + +/** + * Macros to add the file:line of the calling code, instead of that of + * the trace function itself. + * + * Note: with C99 variadic macros, __VA_ARGS__ must include the last fixed + * parameter ('format' in this case). Otherwise, a call without variable + * arguments will have a surplus ','. E.g.: + * + * #define foo(format, ...) bar(format, __VA_ARGS__) + * foo("test"); + * + * will expand to + * + * bar("test",); + * + * which is invalid (note the ',)'). With GNUC, '##__VA_ARGS__' drops the + * comma, but this is non-standard. + */ + +/** + * trace_printf(), accepts "const char *format, ...". + * + * Prints a formatted message, similar to printf. + */ +#define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__) + +/** + * trace_printf_key(), accepts "struct trace_key *key, const char *format, ...". + */ +#define trace_printf_key(key, ...) \ + do { \ + if (trace_pass_fl(key)) \ + trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key, \ + __VA_ARGS__); \ + } while (0) + +/** + * trace_argv_printf(), accepts "struct trace_key *key, const char *format, ...)". + * + * Prints a formatted message, followed by a quoted list of arguments. + */ +#define trace_argv_printf(argv, ...) \ + do { \ + if (trace_pass_fl(&trace_default_key)) \ + trace_argv_printf_fl(TRACE_CONTEXT, __LINE__, \ + argv, __VA_ARGS__); \ + } while (0) + +/** + * trace_strbuf(), accepts "struct trace_key *key, const struct strbuf *data". + * + * Prints the strbuf, without additional formatting (i.e. doesn't + * choke on `%` or even `\0`). + */ +#define trace_strbuf(key, data) \ + do { \ + if (trace_pass_fl(key)) \ + trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\ + } while (0) + +/** + * trace_performance(), accepts "uint64_t nanos, const char *format, ...". + * + * Prints elapsed time (in nanoseconds) if GIT_TRACE_PERFORMANCE is enabled. + * + * Example: + * ------------ + * uint64_t t = 0; + * for (;;) { + * // ignore + * t -= getnanotime(); + * // code section to measure + * t += getnanotime(); + * // ignore + * } + * trace_performance(t, "frotz"); + * ------------ + */ +#define trace_performance(nanos, ...) \ + do { \ + if (trace_pass_fl(&trace_perf_key)) \ + trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\ + __VA_ARGS__); \ + } while (0) + +/** + * trace_performance_since(), accepts "uint64_t start, const char *format, ...". + * + * Prints elapsed time since 'start' if GIT_TRACE_PERFORMANCE is enabled. + * + * Example: + * ------------ + * uint64_t start = getnanotime(); + * // code section to measure + * trace_performance_since(start, "foobar"); + * ------------ + */ +#define trace_performance_since(start, ...) \ + do { \ + if (trace_pass_fl(&trace_perf_key)) \ + trace_performance_fl(TRACE_CONTEXT, __LINE__, \ + getnanotime() - (start), \ + __VA_ARGS__); \ + } while (0) + +/** + * trace_performance_leave(), accepts "const char *format, ...". + */ +#define trace_performance_leave(...) \ + do { \ + if (trace_pass_fl(&trace_perf_key)) \ + trace_performance_leave_fl(TRACE_CONTEXT, __LINE__, \ + getnanotime(), \ + __VA_ARGS__); \ + } while (0) + +/* backend functions, use non-*fl macros instead */ +__attribute__((format (printf, 4, 5))) +void trace_printf_key_fl(const char *file, int line, struct trace_key *key, + const char *format, ...); +__attribute__((format (printf, 4, 5))) +void trace_argv_printf_fl(const char *file, int line, const char **argv, + const char *format, ...); +void trace_strbuf_fl(const char *file, int line, struct trace_key *key, + const struct strbuf *data); +__attribute__((format (printf, 4, 5))) +void trace_performance_fl(const char *file, int line, + uint64_t nanos, const char *fmt, ...); +__attribute__((format (printf, 4, 5))) +void trace_performance_leave_fl(const char *file, int line, + uint64_t nanos, const char *fmt, ...); +static inline int trace_pass_fl(struct trace_key *key) +{ + return key->fd || !key->initialized; +} + +#endif /* TRACE_H */ |