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    * @param aCaptureStacks If we should capture stacks for the Firefox
 124    * Profiler markers that are recorded for for each log entry.
 125    */
 126   static void SetCaptureStacks(bool aCaptureStacks);
 127
 128   /**
 129    * Indicates whether or not the given log level is enabled.
 130    */
 131   bool ShouldLog(LogLevel aLevel) const { return mLevel >= aLevel; }
 132
 133   /**
 134    * Retrieves the log module's current level.
 135    */
 136   LogLevel Level() const { return mLevel; }
 137
 138   /**
 139    * Sets the log module's level.
 140    */
 141   void SetLevel(LogLevel level);
 142
 143   /**
 144    * Print a log message for this module.
 145    */
 146   void Printv(LogLevel aLevel, const char* aFmt, va_list aArgs) const
 147       MOZ_FORMAT_PRINTF(3, 0);
 148
 149   void Printv(LogLevel aLevel, const TimeStamp* aStart, const char* aFmt,
 150               va_list aArgs) const MOZ_FORMAT_PRINTF(4, 0);
 151
 152   /**
 153    * Retrieves the module name.
 154    */
 155   const char* Name() const { return mName; }
 156
 157  private:
 158   friend class LogModuleManager;
 159
 160   explicit LogModule(const char* aName, LogLevel aLevel)
 161       : mName(strdup(aName)), mLevel(aLevel) {}
 162
 163   LogModule(LogModule&) = delete;
 164   LogModule& operator=(const LogModule&) = delete;
 165
 166   char* mName;
 167
 168   Atomic<LogLevel, Relaxed> mLevel;
 169 };
 170
 171 /**
 172  * Helper class that lazy loads the given log module. This is safe to use for
 173  * declaring static references to log modules and can be used as a replacement
 174  * for accessing a LogModule directly.
 175  *
 176  * Example usage:
 177  *   static LazyLogModule sLayoutLog("layout");
 178  *
 179  *   void Foo() {
 180  *     MOZ_LOG(sLayoutLog, LogLevel::Verbose, ("Entering foo"));
 181  *   }
 182  */
 183 class LazyLogModule final {
 184  public:
 185   explicit constexpr LazyLogModule(const char* aLogName)
 186       : mLogName(aLogName), mLog(nullptr) {}
 187
 188   MOZ_NEVER_INLINE_DEBUG operator LogModule*() {
 189     // NB: The use of an atomic makes the reading and assignment of mLog
 190     //     thread-safe. There is a small chance that mLog will be set more
 191     //     than once, but that's okay as it will be set to the same LogModule
 192     //     instance each time. Also note LogModule::Get is thread-safe.
 193     LogModule* tmp = mLog;
 194     if (MOZ_UNLIKELY(!tmp)) {
 195       tmp = LogModule::Get(mLogName);
 196       mLog = tmp;
 197     }
 198
 199     return tmp;
 200   }
 201
 202  private:
 203   const char* const mLogName;
 204
 205   Atomic<LogModule*, ReleaseAcquire> mLog;
 206 };
 207
 208 namespace detail {
 209
 210 inline bool log_test(const LogModule* module, LogLevel level) {
 211   MOZ_ASSERT(level != LogLevel::Disabled);
 212   return module && module->ShouldLog(level);
 213 }
 214
 215 void log_print(const LogModule* aModule, LogLevel aLevel, const char* aFmt, ...)
 216     MOZ_FORMAT_PRINTF(3, 4);
 217
 218 void log_print(const LogModule* aModule, LogLevel aLevel, TimeStamp* aStart,
 219                const char* aFmt, ...) MOZ_FORMAT_PRINTF(4, 5);
 220 }  // namespace detail
 221
 222 }  // namespace mozilla
 223
 224 // Helper macro used convert MOZ_LOG's third parameter, |_args|, from a
 225 // parenthesized form to a varargs form. For example:
 226 //   ("%s", "a message") => "%s", "a message"
 227 #define MOZ_LOG_EXPAND_ARGS(...) __VA_ARGS__
 228
 229 #if MOZ_LOGGING_ENABLED
 230 #  define MOZ_LOG_TEST(_module, _level) \
 231     MOZ_UNLIKELY(mozilla::detail::log_test(_module, _level))
 232 #else
 233 // Define away MOZ_LOG_TEST here so the compiler will fold away entire
 234 // logging blocks via dead code elimination, e.g.:
 235 //
 236 //   if (MOZ_LOG_TEST(...)) {
 237 //     ...compute things to log and log them...
 238 //   }
 239 #  define MOZ_LOG_TEST(_module, _level) false
 240 #endif
 241
 242 // The natural definition of the MOZ_LOG macro would expand to:
 243 //
 244 //   do {
 245 //     if (MOZ_LOG_TEST(_module, _level)) {
 246 //       mozilla::detail::log_print(_module, ...);
 247 //     }
 248 //   } while (0)
 249 //
 250 // However, since _module is a LazyLogModule, and we need to call
 251 // LazyLogModule::operator() to get a LogModule* for the MOZ_LOG_TEST
 252 // macro and for the logging call, we'll wind up doing *two* calls, one
 253 // for each, rather than a single call.  The compiler is not able to
 254 // fold the two calls into one, and the extra call can have a
 255 // significant effect on code size.  (Making LazyLogModule::operator() a
 256 // `const` function does not have any effect.)
 257 //
 258 // Therefore, we will have to make a single call ourselves.  But again,
 259 // the natural definition:
 260 //
 261 //   do {
 262 //     ::mozilla::LogModule* real_module = _module;
 263 //     if (MOZ_LOG_TEST(real_module, _level)) {
 264 //       mozilla::detail::log_print(real_module, ...);
 265 //     }
 266 //   } while (0)
 267 //
 268 // also has a problem: if logging is disabled, then we will call
 269 // LazyLogModule::operator() unnecessarily, and the compiler will not be
 270 // able to optimize away the call as dead code.  We would like to avoid
 271 // such a scenario, as the whole point of disabling logging is for the
 272 // logging statements to not generate any code.
 273 //
 274 // Therefore, we need different definitions of MOZ_LOG, depending on
 275 // whether logging is enabled or not.  (We need an actual definition of
 276 // MOZ_LOG even when logging is disabled to ensure the compiler sees that
 277 // variables only used during logging code are actually used, even if the
 278 // code will never be executed.)  Hence, the following code.
 279 //
 280 // MOZ_LOG_DURATION takes a start time, and will generate a time range
 281 // in the logs.  Also, if the Firefox Profiler is running,
 282 // MOZ_LOG_DURATION will generate a marker with a time duration
 283 // instead of a single point in time.
 284 #if MOZ_LOGGING_ENABLED
 285 #  define MOZ_LOG(_module, _level, _args)                      \
 286     do {                                                       \
 287       const ::mozilla::LogModule* moz_real_module = _module;   \
 288       if (MOZ_LOG_TEST(moz_real_module, _level)) {             \
 289         mozilla::detail::log_print(moz_real_module, _level,    \
 290                                    MOZ_LOG_EXPAND_ARGS _args); \
 291       }                                                        \
 292     } while (0)
 293 #  define MOZ_LOG_DURATION(_module, _level, start, _args)          \
 294     do {                                                           \
 295       const ::mozilla::LogModule* moz_real_module = _module;       \
 296       if (MOZ_LOG_TEST(moz_real_module, _level)) {                 \
 297         mozilla::detail::log_print(moz_real_module, _level, start, \
 298                                    MOZ_LOG_EXPAND_ARGS _args);     \
 299       }                                                            \
 300     } while (0)
 301 #else
 302 #  define MOZ_LOG(_module, _level, _args)                      \
 303     do {                                                       \
 304       if (MOZ_LOG_TEST(_module, _level)) {                     \
 305         mozilla::detail::log_print(_module, _level,            \
 306                                    MOZ_LOG_EXPAND_ARGS _args); \
 307       }                                                        \
 308     } while (0)
 309 #  define MOZ_LOG_DURATION(_module, _level, start, _args)      \
 310     do {                                                       \
 311       if (MOZ_LOG_TEST(_module, _level)) {                     \
 312         mozilla::detail::log_print(_module, _level, start,     \
 313                                    MOZ_LOG_EXPAND_ARGS _args); \
 314       }                                                        \
 315     } while (0)
 316 #endif
 317
 318 // This #define is a Logging.h-only knob!  Don't encourage people to get fancy
 319 // with their log definitions by exporting it outside of Logging.h.
 320 #undef MOZ_LOGGING_ENABLED
 321
 322 #endif  // mozilla_logging_h