xpcom/base/Logging.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_logging_h
   8 #define mozilla_logging_h
   9
  10 #include <stdint.h>
  11 #include <stdlib.h>
  12 #include <string.h>
  13 #include <stdarg.h>
  14
  15 #include "mozilla/Assertions.h"
  16 #include "mozilla/Atomics.h"
  17 #include "mozilla/Attributes.h"
  18 #include "mozilla/Likely.h"
  19
  20 // We normally have logging enabled everywhere, but measurements showed that
  21 // having logging enabled on Android is quite expensive (hundreds of kilobytes
  22 // for both the format strings for logging and the code to perform all the
  23 // logging calls).  Because retrieving logs from a mobile device is
  24 // comparatively more difficult for Android than it is for desktop and because
  25 // desktop machines tend to be less space/bandwidth-constrained than Android
  26 // devices, we've chosen to leave logging enabled on desktop, but disabled on
  27 // Android.  Given that logging can still be useful for development purposes,
  28 // however, we leave logging enabled on Android developer builds.
  29 #if !defined(ANDROID) || !defined(RELEASE_OR_BETA)
  30 #  define MOZ_LOGGING_ENABLED 1
  31 #else
  32 #  define MOZ_LOGGING_ENABLED 0
  33 #endif
  34
  35 // The mandatory extension we add to log files.  Note that rotate will append
  36 // the file piece number still at the end.
  37 #define MOZ_LOG_FILE_EXTENSION ".moz_log"
  38
  39 // Token for Process ID substitution.
  40 #define MOZ_LOG_PID_TOKEN "%PID"
  41
  42 namespace mozilla {
  43
  44 class TimeStamp;
  45
  46 // While not a 100% mapping to PR_LOG's numeric values, mozilla::LogLevel does
  47 // maintain a direct mapping for the Disabled, Debug and Verbose levels.
  48 //
  49 // Mappings of LogLevel to PR_LOG's numeric values:
  50 //
  51 //   +---------+------------------+-----------------+
  52 //   | Numeric | NSPR Logging     | Mozilla Logging |
  53 //   +---------+------------------+-----------------+
  54 //   |       0 | PR_LOG_NONE      | Disabled        |
  55 //   |       1 | PR_LOG_ALWAYS    | Error           |
  56 //   |       2 | PR_LOG_ERROR     | Warning         |
  57 //   |       3 | PR_LOG_WARNING   | Info            |
  58 //   |       4 | PR_LOG_DEBUG     | Debug           |
  59 //   |       5 | PR_LOG_DEBUG + 1 | Verbose         |
  60 //   +---------+------------------+-----------------+
  61 //
  62 enum class LogLevel {
  63   Disabled = 0,
  64   Error,
  65   Warning,
  66   Info,
  67   Debug,
  68   Verbose,
  69 };
  70
  71 /**
  72  * Safely converts an integer into a valid LogLevel.
  73  */
  74 LogLevel ToLogLevel(int32_t aLevel);
  75
  76 class LogModule {
  77  public:
  78   ~LogModule() { ::free(mName); }
  79
  80   /**
  81    * Retrieves the module with the given name. If it does not already exist
  82    * it will be created.
  83    *
  84    * @param aName The name of the module.
  85    * @return A log module for the given name. This may be shared.
  86    */
  87   static LogModule* Get(const char* aName);
  88
  89   /**
  90    * Logging processes -MOZ_LOG and -MOZ_LOG_FILE command line arguments
  91    * to override or set modules and the file as if passed through MOZ_LOG
  92    * and MOZ_LOG_FILE env vars.  It's fine to pass (0, nullptr) if args
  93    * are not accessible in the caller's context, it will just do nothing.
  94    * Note that the args take effect (are processed) only when this function
  95    * is called the first time.
  96    */
  97   static void Init(int argc, char* argv[]);
  98
  99   /**
 100    * Sets the log file to the given filename.
 101    */
 102   static void SetLogFile(const char* aFilename);
 103
 104   /**
 105    * @param aBuffer - pointer to a buffer
 106    * @param aLength - the length of the buffer
 107    *
 108    * @return the actual length of the filepath.
 109    */
 110   static uint32_t GetLogFile(char* aBuffer, size_t aLength);
 111
 112   /**
 113    * @param aAddTimestamp If we should log a time stamp with every message.
 114    */
 115   static void SetAddTimestamp(bool aAddTimestamp);
 116
 117   /**
 118    * @param aIsSync If we should flush the file after every logged message.
 119    */
 120   static void SetIsSync(bool aIsSync);
 121
 122   /**
 123    * Indicates whether or not the given log level is enabled.
 124    */
 125   bool ShouldLog(LogLevel aLevel) const { return mLevel >= aLevel; }
 126
 127   /**
 128    * Retrieves the log module's current level.
 129    */
 130   LogLevel Level() const { return mLevel; }
 131
 132   /**
 133    * Sets the log module's level.
 134    */
 135   void SetLevel(LogLevel level);
 136
 137   /**
 138    * Print a log message for this module.
 139    */
 140   void Printv(LogLevel aLevel, const char* aFmt, va_list aArgs) const
 141       MOZ_FORMAT_PRINTF(3, 0);
 142
 143   void Printv(LogLevel aLevel, const TimeStamp* aStart, const char* aFmt,
 144               va_list aArgs) const MOZ_FORMAT_PRINTF(4, 0);
 145
 146   /**
 147    * Retrieves the module name.
 148    */
 149   const char* Name() const { return mName; }
 150
 151  private:
 152   friend class LogModuleManager;
 153
 154   explicit LogModule(const char* aName, LogLevel aLevel)
 155       : mName(strdup(aName)), mLevel(aLevel) {}
 156
 157   LogModule(LogModule&) = delete;
 158   LogModule& operator=(const LogModule&) = delete;
 159
 160   char* mName;
 161
 162   Atomic<LogLevel, Relaxed> mLevel;
 163 };
 164
 165 /**
 166  * Helper class that lazy loads the given log module. This is safe to use for
 167  * declaring static references to log modules and can be used as a replacement
 168  * for accessing a LogModule directly.
 169  *
 170  * Example usage:
 171  *   static LazyLogModule sLayoutLog("layout");
 172  *
 173  *   void Foo() {
 174  *     MOZ_LOG(sLayoutLog, LogLevel::Verbose, ("Entering foo"));
 175  *   }
 176  */
 177 class LazyLogModule final {
 178  public:
 179   explicit constexpr LazyLogModule(const char* aLogName)
 180       : mLogName(aLogName), mLog(nullptr) {}
 181
 182   MOZ_NEVER_INLINE_DEBUG operator LogModule*() {
 183     // NB: The use of an atomic makes the reading and assignment of mLog
 184     //     thread-safe. There is a small chance that mLog will be set more
 185     //     than once, but that's okay as it will be set to the same LogModule
 186     //     instance each time. Also note LogModule::Get is thread-safe.
 187     LogModule* tmp = mLog;
 188     if (MOZ_UNLIKELY(!tmp)) {
 189       tmp = LogModule::Get(mLogName);
 190       mLog = tmp;
 191     }
 192
 193     return tmp;
 194   }
 195
 196  private:
 197   const char* const mLogName;
 198
 199   Atomic<LogModule*, ReleaseAcquire> mLog;
 200 };
 201
 202 namespace detail {
 203
 204 inline bool log_test(const LogModule* module, LogLevel level) {
 205   MOZ_ASSERT(level != LogLevel::Disabled);
 206   return module && module->ShouldLog(level);
 207 }
 208
 209 void log_print(const LogModule* aModule, LogLevel aLevel, const char* aFmt, ...)
 210     MOZ_FORMAT_PRINTF(3, 4);
 211
 212 void log_print(const LogModule* aModule, LogLevel aLevel, TimeStamp* aStart,
 213                const char* aFmt, ...) MOZ_FORMAT_PRINTF(4, 5);
 214 }  // namespace detail
 215
 216 }  // namespace mozilla
 217
 218 // Helper macro used convert MOZ_LOG's third parameter, |_args|, from a
 219 // parenthesized form to a varargs form. For example:
 220 //   ("%s", "a message") => "%s", "a message"
 221 #define MOZ_LOG_EXPAND_ARGS(...) __VA_ARGS__
 222
 223 #if MOZ_LOGGING_ENABLED
 224 #  define MOZ_LOG_TEST(_module, _level) \
 225     MOZ_UNLIKELY(mozilla::detail::log_test(_module, _level))
 226 #else
 227 // Define away MOZ_LOG_TEST here so the compiler will fold away entire
 228 // logging blocks via dead code elimination, e.g.:
 229 //
 230 //   if (MOZ_LOG_TEST(...)) {
 231 //     ...compute things to log and log them...
 232 //   }
 233 #  define MOZ_LOG_TEST(_module, _level) false
 234 #endif
 235
 236 // The natural definition of the MOZ_LOG macro would expand to:
 237 //
 238 //   do {
 239 //     if (MOZ_LOG_TEST(_module, _level)) {
 240 //       mozilla::detail::log_print(_module, ...);
 241 //     }
 242 //   } while (0)
 243 //
 244 // However, since _module is a LazyLogModule, and we need to call
 245 // LazyLogModule::operator() to get a LogModule* for the MOZ_LOG_TEST
 246 // macro and for the logging call, we'll wind up doing *two* calls, one
 247 // for each, rather than a single call.  The compiler is not able to
 248 // fold the two calls into one, and the extra call can have a
 249 // significant effect on code size.  (Making LazyLogModule::operator() a
 250 // `const` function does not have any effect.)
 251 //
 252 // Therefore, we will have to make a single call ourselves.  But again,
 253 // the natural definition:
 254 //
 255 //   do {
 256 //     ::mozilla::LogModule* real_module = _module;
 257 //     if (MOZ_LOG_TEST(real_module, _level)) {
 258 //       mozilla::detail::log_print(real_module, ...);
 259 //     }
 260 //   } while (0)
 261 //
 262 // also has a problem: if logging is disabled, then we will call
 263 // LazyLogModule::operator() unnecessarily, and the compiler will not be
 264 // able to optimize away the call as dead code.  We would like to avoid
 265 // such a scenario, as the whole point of disabling logging is for the
 266 // logging statements to not generate any code.
 267 //
 268 // Therefore, we need different definitions of MOZ_LOG, depending on
 269 // whether logging is enabled or not.  (We need an actual definition of
 270 // MOZ_LOG even when logging is disabled to ensure the compiler sees that
 271 // variables only used during logging code are actually used, even if the
 272 // code will never be executed.)  Hence, the following code.
 273 //
 274 // MOZ_LOG_DURATION takes a start time, and will generate a time range
 275 // in the logs.  Also, if 'profilermarkers' is used in the env var
 276 // MOZ_LOG, MOZ_LOG_DURATION will generate a marker with a time
 277 // duration instead of a single point in time.
 278 #if MOZ_LOGGING_ENABLED
 279 #  define MOZ_LOG(_module, _level, _args)                      \
 280     do {                                                       \
 281       const ::mozilla::LogModule* moz_real_module = _module;   \
 282       if (MOZ_LOG_TEST(moz_real_module, _level)) {             \
 283         mozilla::detail::log_print(moz_real_module, _level,    \
 284                                    MOZ_LOG_EXPAND_ARGS _args); \
 285       }                                                        \
 286     } while (0)
 287 #  define MOZ_LOG_DURATION(_module, _level, start, _args)          \
 288     do {                                                           \
 289       const ::mozilla::LogModule* moz_real_module = _module;       \
 290       if (MOZ_LOG_TEST(moz_real_module, _level)) {                 \
 291         mozilla::detail::log_print(moz_real_module, _level, start, \
 292                                    MOZ_LOG_EXPAND_ARGS _args);     \
 293       }                                                            \
 294     } while (0)
 295 #else
 296 #  define MOZ_LOG(_module, _level, _args)                      \
 297     do {                                                       \
 298       if (MOZ_LOG_TEST(_module, _level)) {                     \
 299         mozilla::detail::log_print(_module, _level,            \
 300                                    MOZ_LOG_EXPAND_ARGS _args); \
 301       }                                                        \
 302     } while (0)
 303 #  define MOZ_LOG_DURATION(_module, _level, start, _args)      \
 304     do {                                                       \
 305       if (MOZ_LOG_TEST(_module, _level)) {                     \
 306         mozilla::detail::log_print(_module, _level, start,     \
 307                                    MOZ_LOG_EXPAND_ARGS _args); \
 308       }                                                        \
 309     } while (0)
 310 #endif
 311
 312 // This #define is a Logging.h-only knob!  Don't encourage people to get fancy
 313 // with their log definitions by exporting it outside of Logging.h.
 314 #undef MOZ_LOGGING_ENABLED
 315
 316 #endif  // mozilla_logging_h