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) { "GIT_TRACE_" #name, 0, 0, 0 }
  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  * Disables tracing for the specified key, even if the environment variable
 106  * was set.
 107  */
 108 void trace_disable(struct trace_key *key);
 109
 110 /**
 111  * Returns nanoseconds since the epoch (01/01/1970), typically used
 112  * for performance measurements.
 113  * Currently there are high precision timer implementations for Linux (using
 114  * `clock_gettime(CLOCK_MONOTONIC)`) and Windows (`QueryPerformanceCounter`).
 115  * Other platforms use `gettimeofday` as time source.
 116  */
 117 uint64_t getnanotime(void);
 118
 119 void trace_command_performance(const char **argv);
 120 void trace_verbatim(struct trace_key *key, const void *buf, unsigned len);
 121 uint64_t trace_performance_enter(void);
 122
 123 #ifndef HAVE_VARIADIC_MACROS
 124
 125 /**
 126  * Prints a formatted message, similar to printf.
 127  */
 128 __attribute__((format (printf, 1, 2)))
 129 void trace_printf(const char *format, ...);
 130
 131 __attribute__((format (printf, 2, 3)))
 132 void trace_printf_key(struct trace_key *key, const char *format, ...);
 133
 134 /**
 135  * Prints a formatted message, followed by a quoted list of arguments.
 136  */
 137 __attribute__((format (printf, 2, 3)))
 138 void trace_argv_printf(const char **argv, const char *format, ...);
 139
 140 /**
 141  * Prints the strbuf, without additional formatting (i.e. doesn't
 142  * choke on `%` or even `\0`).
 143  */
 144 void trace_strbuf(struct trace_key *key, const struct strbuf *data);
 145
 146 /**
 147  * Prints elapsed time (in nanoseconds) if GIT_TRACE_PERFORMANCE is enabled.
 148  *
 149  * Example:
 150  * ------------
 151  * uint64_t t = 0;
 152  * for (;;) {
 153  *      // ignore
 154  * t -= getnanotime();
 155  * // code section to measure
 156  * t += getnanotime();
 157  * // ignore
 158  * }
 159  * trace_performance(t, "frotz");
 160  * ------------
 161  */
 162 __attribute__((format (printf, 2, 3)))
 163 void trace_performance(uint64_t nanos, const char *format, ...);
 164
 165 /**
 166  * Prints elapsed time since 'start' if GIT_TRACE_PERFORMANCE is enabled.
 167  *
 168  * Example:
 169  * ------------
 170  * uint64_t start = getnanotime();
 171  * // code section to measure
 172  * trace_performance_since(start, "foobar");
 173  * ------------
 174  */
 175 __attribute__((format (printf, 2, 3)))
 176 void trace_performance_since(uint64_t start, const char *format, ...);
 177
 178 __attribute__((format (printf, 1, 2)))
 179 void trace_performance_leave(const char *format, ...);
 180
 181 #else
 182
 183 /*
 184  * Macros to add file:line - see above for C-style declarations of how these
 185  * should be used.
 186  */
 187
 188 /*
 189  * TRACE_CONTEXT may be set to __FUNCTION__ if the compiler supports it. The
 190  * default is __FILE__, as it is consistent with assert(), and static function
 191  * names are not necessarily unique.
 192  *
 193  * __FILE__ ":" __FUNCTION__ doesn't work with GNUC, as __FILE__ is supplied
 194  * by the preprocessor as a string literal, and __FUNCTION__ is filled in by
 195  * the compiler as a string constant.
 196  */
 197 #ifndef TRACE_CONTEXT
 198 # define TRACE_CONTEXT __FILE__
 199 #endif
 200
 201 /*
 202  * Note: with C99 variadic macros, __VA_ARGS__ must include the last fixed
 203  * parameter ('format' in this case). Otherwise, a call without variable
 204  * arguments will have a surplus ','. E.g.:
 205  *
 206  *  #define foo(format, ...) bar(format, __VA_ARGS__)
 207  *  foo("test");
 208  *
 209  * will expand to
 210  *
 211  *  bar("test",);
 212  *
 213  * which is invalid (note the ',)'). With GNUC, '##__VA_ARGS__' drops the
 214  * comma, but this is non-standard.
 215  */
 216
 217 #define trace_printf_key(key, ...)                                          \
 218         do {                                                                \
 219                 if (trace_pass_fl(key))                                     \
 220                         trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
 221                                             __VA_ARGS__);                   \
 222         } while (0)
 223
 224 #define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
 225
 226 #define trace_argv_printf(argv, ...)                                        \
 227         do {                                                                \
 228                 if (trace_pass_fl(&trace_default_key))                      \
 229                         trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,       \
 230                                             argv, __VA_ARGS__);             \
 231         } while (0)
 232
 233 #define trace_strbuf(key, data)                                             \
 234         do {                                                                \
 235                 if (trace_pass_fl(key))                                     \
 236                         trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
 237         } while (0)
 238
 239 #define trace_performance(nanos, ...)                                       \
 240         do {                                                                \
 241                 if (trace_pass_fl(&trace_perf_key))                         \
 242                         trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
 243                                              __VA_ARGS__);                  \
 244         } while (0)
 245
 246 #define trace_performance_since(start, ...)                                 \
 247         do {                                                                \
 248                 if (trace_pass_fl(&trace_perf_key))                         \
 249                         trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
 250                                              getnanotime() - (start),       \
 251                                              __VA_ARGS__);                  \
 252         } while (0)
 253
 254 #define trace_performance_leave(...)                                        \
 255         do {                                                                \
 256                 if (trace_pass_fl(&trace_perf_key))                         \
 257                         trace_performance_leave_fl(TRACE_CONTEXT, __LINE__, \
 258                                                    getnanotime(),           \
 259                                                    __VA_ARGS__);            \
 260         } while (0)
 261
 262 /* backend functions, use non-*fl macros instead */
 263 __attribute__((format (printf, 4, 5)))
 264 void trace_printf_key_fl(const char *file, int line, struct trace_key *key,
 265                          const char *format, ...);
 266 __attribute__((format (printf, 4, 5)))
 267 void trace_argv_printf_fl(const char *file, int line, const char **argv,
 268                           const char *format, ...);
 269 void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 270                      const struct strbuf *data);
 271 __attribute__((format (printf, 4, 5)))
 272 void trace_performance_fl(const char *file, int line,
 273                           uint64_t nanos, const char *fmt, ...);
 274 __attribute__((format (printf, 4, 5)))
 275 void trace_performance_leave_fl(const char *file, int line,
 276                                 uint64_t nanos, const char *fmt, ...);
 277 static inline int trace_pass_fl(struct trace_key *key)
 278 {
 279         return key->fd || !key->initialized;
 280 }
 281
 282 #endif /* HAVE_VARIADIC_MACROS */
 283
 284 #endif /* TRACE_H */