trace.h

   1 #ifndef TRACE_H
   2 #define TRACE_H
   3
   4 #include "git-compat-util.h"
   5 #include "strbuf.h"
   6
   7 /**
   8  * The trace API can be used to print debug messages to stderr or a file. Trace
   9  * code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment
  10  * variables.
  11  *
  12  * The trace implementation automatically adds `timestamp file:line ... \n` to
  13  * all trace messages. E.g.:
  14  *
  15  * ------------
  16  * 23:59:59.123456 git.c:312               trace: built-in: git 'foo'
  17  * 00:00:00.000001 builtin/foo.c:99        foo: some message
  18  * ------------
  19  *
  20  * Bugs & Caveats
  21  * --------------
  22  *
  23  * GIT_TRACE_* environment variables can be used to tell Git to show
  24  * trace output to its standard error stream. Git can often spawn a pager
  25  * internally to run its subcommand and send its standard output and
  26  * standard error to it.
  27  *
  28  * Because GIT_TRACE_PERFORMANCE trace is generated only at the very end
  29  * of the program with atexit(), which happens after the pager exits, it
  30  * would not work well if you send its log to the standard error output
  31  * and let Git spawn the pager at the same time.
  32  *
  33  * As a work around, you can for example use '--no-pager', or set
  34  * GIT_TRACE_PERFORMANCE to another file descriptor which is redirected
  35  * to stderr, or set GIT_TRACE_PERFORMANCE to a file specified by its
  36  * absolute path.
  37  *
  38  * For example instead of the following command which by default may not
  39  * print any performance information:
  40  *
  41  * ------------
  42  * GIT_TRACE_PERFORMANCE=2 git log -1
  43  * ------------
  44  *
  45  * you may want to use:
  46  *
  47  * ------------
  48  * GIT_TRACE_PERFORMANCE=2 git --no-pager log -1
  49  * ------------
  50  *
  51  * or:
  52  *
  53  * ------------
  54  * GIT_TRACE_PERFORMANCE=3 3>&2 git log -1
  55  * ------------
  56  *
  57  * or:
  58  *
  59  * ------------
  60  * GIT_TRACE_PERFORMANCE=/path/to/log/file git log -1
  61  * ------------
  62  *
  63  */
  64
  65 /**
  66  * Defines a trace key (or category). The default (for API functions that
  67  * don't take a key) is `GIT_TRACE`.
  68  *
  69  * E.g. to define a trace key controlled by environment variable `GIT_TRACE_FOO`:
  70  *
  71  * ------------
  72  * static struct trace_key trace_foo = TRACE_KEY_INIT(FOO);
  73  *
  74  * static void trace_print_foo(const char *message)
  75  * {
  76  *      trace_printf_key(&trace_foo, "%s", message);
  77  * }
  78  * ------------
  79  *
  80  * Note: don't use `const` as the trace implementation stores internal state in
  81  * the `trace_key` structure.
  82  */
  83 struct trace_key {
  84         const char * const key;
  85         int fd;
  86         unsigned int initialized : 1;
  87         unsigned int  need_close : 1;
  88 };
  89
  90 extern struct trace_key trace_default_key;
  91
  92 #define TRACE_KEY_INIT(name) { .key = "GIT_TRACE_" #name }
  93 extern struct trace_key trace_perf_key;
  94 extern struct trace_key trace_setup_key;
  95
  96 void trace_repo_setup(const char *prefix);
  97
  98 /**
  99  * Checks whether the trace key is enabled. Used to prevent expensive
 100  * string formatting before calling one of the printing APIs.
 101  */
 102 int trace_want(struct trace_key *key);
 103
 104 /**
 105  * Enables or disables tracing for the specified key, as if the environment
 106  * variable was set to the given value.
 107  */
 108 void trace_override_envvar(struct trace_key *key, const char *value);
 109
 110 /**
 111  * Disables tracing for the specified key, even if the environment variable
 112  * was set.
 113  */
 114 void trace_disable(struct trace_key *key);
 115
 116 /**
 117  * Returns nanoseconds since the epoch (01/01/1970), typically used
 118  * for performance measurements.
 119  * Currently there are high precision timer implementations for Linux (using
 120  * `clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`).
 121  * Other platforms use `gettimeofday` as time source.
 122  */
 123 uint64_t getnanotime(void);
 124
 125 void trace_command_performance(const char **argv);
 126 void trace_verbatim(struct trace_key *key, const void *buf, unsigned len);
 127 uint64_t trace_performance_enter(void);
 128
 129 /*
 130  * TRACE_CONTEXT may be set to __FUNCTION__ if the compiler supports it. The
 131  * default is __FILE__, as it is consistent with assert(), and static function
 132  * names are not necessarily unique.
 133  *
 134  * __FILE__ ":" __FUNCTION__ doesn't work with GNUC, as __FILE__ is supplied
 135  * by the preprocessor as a string literal, and __FUNCTION__ is filled in by
 136  * the compiler as a string constant.
 137  */
 138 #ifndef TRACE_CONTEXT
 139 # define TRACE_CONTEXT __FILE__
 140 #endif
 141
 142 /**
 143  * Macros to add the file:line of the calling code, instead of that of
 144  * the trace function itself.
 145  *
 146  * Note: with C99 variadic macros, __VA_ARGS__ must include the last fixed
 147  * parameter ('format' in this case). Otherwise, a call without variable
 148  * arguments will have a surplus ','. E.g.:
 149  *
 150  *  #define foo(format, ...) bar(format, __VA_ARGS__)
 151  *  foo("test");
 152  *
 153  * will expand to
 154  *
 155  *  bar("test",);
 156  *
 157  * which is invalid (note the ',)'). With GNUC, '##__VA_ARGS__' drops the
 158  * comma, but this is non-standard.
 159  */
 160
 161 /**
 162  * trace_printf(), accepts "const char *format, ...".
 163  *
 164  * Prints a formatted message, similar to printf.
 165  */
 166 #define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
 167
 168 /**
 169  * trace_printf_key(), accepts "struct trace_key *key, const char *format, ...".
 170  */
 171 #define trace_printf_key(key, ...)                                          \
 172         do {                                                                \
 173                 if (trace_pass_fl(key))                                     \
 174                         trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
 175                                             __VA_ARGS__);                   \
 176         } while (0)
 177
 178 /**
 179  * trace_argv_printf(), accepts "struct trace_key *key, const char *format, ...)".
 180  *
 181  * Prints a formatted message, followed by a quoted list of arguments.
 182  */
 183 #define trace_argv_printf(argv, ...)                                        \
 184         do {                                                                \
 185                 if (trace_pass_fl(&trace_default_key))                      \
 186                         trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,       \
 187                                             argv, __VA_ARGS__);             \
 188         } while (0)
 189
 190 /**
 191  * trace_strbuf(), accepts "struct trace_key *key, const struct strbuf *data".
 192  *
 193  * Prints the strbuf, without additional formatting (i.e. doesn't
 194  * choke on `%` or even `\0`).
 195  */
 196 #define trace_strbuf(key, data)                                             \
 197         do {                                                                \
 198                 if (trace_pass_fl(key))                                     \
 199                         trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
 200         } while (0)
 201
 202 /**
 203  * trace_performance(), accepts "uint64_t nanos, const char *format, ...".
 204  *
 205  * Prints elapsed time (in nanoseconds) if GIT_TRACE_PERFORMANCE is enabled.
 206  *
 207  * Example:
 208  * ------------
 209  * uint64_t t = 0;
 210  * for (;;) {
 211  *      // ignore
 212  * t -= getnanotime();
 213  * // code section to measure
 214  * t += getnanotime();
 215  * // ignore
 216  * }
 217  * trace_performance(t, "frotz");
 218  * ------------
 219  */
 220 #define trace_performance(nanos, ...)                                       \
 221         do {                                                                \
 222                 if (trace_pass_fl(&trace_perf_key))                         \
 223                         trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
 224                                              __VA_ARGS__);                  \
 225         } while (0)
 226
 227 /**
 228  * trace_performance_since(), accepts "uint64_t start, const char *format, ...".
 229  *
 230  * Prints elapsed time since 'start' if GIT_TRACE_PERFORMANCE is enabled.
 231  *
 232  * Example:
 233  * ------------
 234  * uint64_t start = getnanotime();
 235  * // code section to measure
 236  * trace_performance_since(start, "foobar");
 237  * ------------
 238  */
 239 #define trace_performance_since(start, ...)                                 \
 240         do {                                                                \
 241                 if (trace_pass_fl(&trace_perf_key))                         \
 242                         trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
 243                                              getnanotime() - (start),       \
 244                                              __VA_ARGS__);                  \
 245         } while (0)
 246
 247 /**
 248  * trace_performance_leave(), accepts "const char *format, ...".
 249  */
 250 #define trace_performance_leave(...)                                        \
 251         do {                                                                \
 252                 if (trace_pass_fl(&trace_perf_key))                         \
 253                         trace_performance_leave_fl(TRACE_CONTEXT, __LINE__, \
 254                                                    getnanotime(),           \
 255                                                    __VA_ARGS__);            \
 256         } while (0)
 257
 258 /* backend functions, use non-*fl macros instead */
 259 __attribute__((format (printf, 4, 5)))
 260 void trace_printf_key_fl(const char *file, int line, struct trace_key *key,
 261                          const char *format, ...);
 262 __attribute__((format (printf, 4, 5)))
 263 void trace_argv_printf_fl(const char *file, int line, const char **argv,
 264                           const char *format, ...);
 265 void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 266                      const struct strbuf *data);
 267 __attribute__((format (printf, 4, 5)))
 268 void trace_performance_fl(const char *file, int line,
 269                           uint64_t nanos, const char *fmt, ...);
 270 __attribute__((format (printf, 4, 5)))
 271 void trace_performance_leave_fl(const char *file, int line,
 272                                 uint64_t nanos, const char *fmt, ...);
 273 static inline int trace_pass_fl(struct trace_key *key)
 274 {
 275         return key->fd || !key->initialized;
 276 }
 277
 278 #endif /* TRACE_H */