text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef BASE_LOGGING_H_
  #define BASE_LOGGING_H_
  
  #include <cassert>
  #include <string>
  #include <cstring>
  #include <sstream>
  
  #include "base/base_export.h"
  #include "base/basictypes.h"
  #include "base/debug/debugger.h"
  #include "build/build_config.h"
  
  //
  // Optional message capabilities
  // -----------------------------
  // Assertion failed messages and fatal errors are displayed in a dialog box
  // before the application exits. However, running this UI creates a message
  // loop, which causes application messages to be processed and potentially
  // dispatched to existing application windows. Since the application is in a
  // bad state when this assertion dialog is displayed, these messages may not
  // get processed and hang the dialog, or the application might go crazy.
  //
  // Therefore, it can be beneficial to display the error dialog in a separate
  // process from the main application. When the logging system needs to display
  // a fatal error dialog box, it will look for a program called
  // "DebugMessage.exe" in the same directory as the application executable. It
  // will run this application with the message as the command line, and will
  // not include the name of the application as is traditional for easier
  // parsing.
  //
  // The code for DebugMessage.exe is only one line. In WinMain, do:
  //   MessageBox(NULL, GetCommandLineW(), L"Fatal Error", 0);
  //
  // If DebugMessage.exe is not found, the logging code will use a normal
  // MessageBox, potentially causing the problems discussed above.
  
  
  // Instructions
  // ------------
  //
  // Make a bunch of macros for logging.  The way to log things is to stream
  // things to LOG(<a particular severity level>).  E.g.,
  //
  //   LOG(INFO) << "Found " << num_cookies << " cookies";
  //
  // You can also do conditional logging:
  //
  //   LOG_IF(INFO, num_cookies > 10) << "Got lots of cookies";
  //
  // The above will cause log messages to be output on the 1st, 11th, 21st, ...
  // times it is executed.  Note that the special COUNTER value is used to
  // identify which repetition is happening.
  //
  // The CHECK(condition) macro is active in both debug and release builds and
  // effectively performs a LOG(FATAL) which terminates the process and
  // generates a crashdump unless a debugger is attached.
  //
  // There are also "debug mode" logging macros like the ones above:
  //
  //   DLOG(INFO) << "Found cookies";
  //
  //   DLOG_IF(INFO, num_cookies > 10) << "Got lots of cookies";
  //
  // All "debug mode" logging is compiled away to nothing for non-debug mode
  // compiles.  LOG_IF and development flags also work well together
  // because the code can be compiled away sometimes.
  //
  // We also have
  //
  //   LOG_ASSERT(assertion);
  //   DLOG_ASSERT(assertion);
  //
  // which is syntactic sugar for {,D}LOG_IF(FATAL, assert fails) << assertion;
  //
  // There are "verbose level" logging macros.  They look like
  //
  //   VLOG(1) << "I'm printed when you run the program with --v=1 or more";
  //   VLOG(2) << "I'm printed when you run the program with --v=2 or more";
  //
  // These always log at the INFO log level (when they log at all).
  // The verbose logging can also be turned on module-by-module.  For instance,
  //    --vmodule=profile=2,icon_loader=1,browser_*=3,*/chromeos/*=4 --v=0
  // will cause:
  //   a. VLOG(2) and lower messages to be printed from profile.{h,cc}
  //   b. VLOG(1) and lower messages to be printed from icon_loader.{h,cc}
  //   c. VLOG(3) and lower messages to be printed from files prefixed with
  //      "browser"
  //   d. VLOG(4) and lower messages to be printed from files under a
  //     "chromeos" directory.
  //   e. VLOG(0) and lower messages to be printed from elsewhere
  //
  // The wildcarding functionality shown by (c) supports both '*' (match
  // 0 or more characters) and '?' (match any single character)
  // wildcards.  Any pattern containing a forward or backward slash will
  // be tested against the whole pathname and not just the module.
  // E.g., "*/foo/bar/*=2" would change the logging level for all code
  // in source files under a "foo/bar" directory.
  //
  // There's also VLOG_IS_ON(n) "verbose level" condition macro. To be used as
  //
  //   if (VLOG_IS_ON(2)) {
  //     // do some logging preparation and logging
  //     // that can't be accomplished with just VLOG(2) << ...;
  //   }
  //
  // There is also a VLOG_IF "verbose level" condition macro for sample
  // cases, when some extra computation and preparation for logs is not
  // needed.
  //
  //   VLOG_IF(1, (size > 1024))
  //      << "I'm printed when size is more than 1024 and when you run the "
  //         "program with --v=1 or more";
  //
  // We also override the standard 'assert' to use 'DLOG_ASSERT'.
  //
  // Lastly, there is:
  //
  //   PLOG(ERROR) << "Couldn't do foo";
  //   DPLOG(ERROR) << "Couldn't do foo";
  //   PLOG_IF(ERROR, cond) << "Couldn't do foo";
  //   DPLOG_IF(ERROR, cond) << "Couldn't do foo";
  //   PCHECK(condition) << "Couldn't do foo";
  //   DPCHECK(condition) << "Couldn't do foo";
  //
  // which append the last system error to the message in string form (taken from
  // GetLastError() on Windows and errno on POSIX).
  //
  // The supported severity levels for macros that allow you to specify one
  // are (in increasing order of severity) INFO, WARNING, ERROR, ERROR_REPORT,
  // and FATAL.
  //
  // Very important: logging a message at the FATAL severity level causes
  // the program to terminate (after the message is logged).
  //
  // Note the special severity of ERROR_REPORT only available/relevant in normal
  // mode, which displays error dialog without terminating the program. There is
  // no error dialog for severity ERROR or below in normal mode.
  //
  // There is also the special severity of DFATAL, which logs FATAL in
  // debug mode, ERROR in normal mode.
  
  namespace logging {
  
  // Where to record logging output? A flat file and/or system debug log via
  // OutputDebugString. Defaults on Windows to LOG_ONLY_TO_FILE, and on
  // POSIX to LOG_ONLY_TO_SYSTEM_DEBUG_LOG (aka stderr).
  enum LoggingDestination { LOG_NONE,
                            LOG_ONLY_TO_FILE,
                            LOG_ONLY_TO_SYSTEM_DEBUG_LOG,
                            LOG_TO_BOTH_FILE_AND_SYSTEM_DEBUG_LOG };
  
  // Indicates that the log file should be locked when being written to.
  // Often, there is no locking, which is fine for a single threaded program.
  // If logging is being done from multiple threads or there can be more than
  // one process doing the logging, the file should be locked during writes to
  // make each log outut atomic. Other writers will block.
  //
  // All processes writing to the log file must have their locking set for it to
  // work properly. Defaults to DONT_LOCK_LOG_FILE.
  enum LogLockingState { LOCK_LOG_FILE, DONT_LOCK_LOG_FILE };
  
  // On startup, should we delete or append to an existing log file (if any)?
  // Defaults to APPEND_TO_OLD_LOG_FILE.
  enum OldFileDeletionState { DELETE_OLD_LOG_FILE, APPEND_TO_OLD_LOG_FILE };
  
  enum DcheckState {
    DISABLE_DCHECK_FOR_NON_OFFICIAL_RELEASE_BUILDS,
    ENABLE_DCHECK_FOR_NON_OFFICIAL_RELEASE_BUILDS
  };
  
  // TODO(avi): do we want to do a unification of character types here?
  #if defined(OS_WIN)
  typedef wchar_t PathChar;
  #else
  typedef char PathChar;
  #endif
  
  // Define different names for the BaseInitLoggingImpl() function depending on
  // whether NDEBUG is defined or not so that we'll fail to link if someone tries
  // to compile logging.cc with NDEBUG but includes logging.h without defining it,
  // or vice versa.
  #if NDEBUG
  #define BaseInitLoggingImpl BaseInitLoggingImpl_built_with_NDEBUG
  #else
  #define BaseInitLoggingImpl BaseInitLoggingImpl_built_without_NDEBUG
  #endif
  
  // Implementation of the InitLogging() method declared below.  We use a
  // more-specific name so we can #define it above without affecting other code
  // that has named stuff "InitLogging".
  BASE_EXPORT bool BaseInitLoggingImpl(const PathChar* log_file,
                                       LoggingDestination logging_dest,
                                       LogLockingState lock_log,
                                       OldFileDeletionState delete_old,
                                       DcheckState dcheck_state);
  
  // Sets the log file name and other global logging state. Calling this function
  // is recommended, and is normally done at the beginning of application init.
  // If you don't call it, all the flags will be initialized to their default
  // values, and there is a race condition that may leak a critical section
  // object if two threads try to do the first log at the same time.
  // See the definition of the enums above for descriptions and default values.
  //
  // The default log file is initialized to "debug.log" in the application
  // directory. You probably don't want this, especially since the program
  // directory may not be writable on an enduser's system.
  //
  // This function may be called a second time to re-direct logging (e.g after
  // loging in to a user partition), however it should never be called more than
  // twice.
  inline bool InitLogging(const PathChar* log_file,
                          LoggingDestination logging_dest,
                          LogLockingState lock_log,
                          OldFileDeletionState delete_old,
                          DcheckState dcheck_state) {
    return BaseInitLoggingImpl(log_file, logging_dest, lock_log,
                               delete_old, dcheck_state);
  }
  
  // Sets the log level. Anything at or above this level will be written to the
  // log file/displayed to the user (if applicable). Anything below this level
  // will be silently ignored. The log level defaults to 0 (everything is logged
  // up to level INFO) if this function is not called.
  // Note that log messages for VLOG(x) are logged at level -x, so setting
  // the min log level to negative values enables verbose logging.
  BASE_EXPORT void SetMinLogLevel(int level);
  
  // Gets the current log level.
  BASE_EXPORT int GetMinLogLevel();
  
  // Gets the VLOG default verbosity level.
  BASE_EXPORT int GetVlogVerbosity();
  
  // Gets the current vlog level for the given file (usually taken from
  // __FILE__).
  
  // Note that |N| is the size *with* the null terminator.
  BASE_EXPORT int GetVlogLevelHelper(const char* file_start, size_t N);
  
  template <size_t N>
  int GetVlogLevel(const char (&file)[N]) {
    return GetVlogLevelHelper(file, N);
  }
  
  // Sets the common items you want to be prepended to each log message.
  // process and thread IDs default to off, the timestamp defaults to on.
  // If this function is not called, logging defaults to writing the timestamp
  // only.
  BASE_EXPORT void SetLogItems(bool enable_process_id, bool enable_thread_id,
                               bool enable_timestamp, bool enable_tickcount);
  
  // Sets whether or not you'd like to see fatal debug messages popped up in
  // a dialog box or not.
  // Dialogs are not shown by default.
  BASE_EXPORT void SetShowErrorDialogs(bool enable_dialogs);
  
  // Sets the Log Assert Handler that will be used to notify of check failures.
  // The default handler shows a dialog box and then terminate the process,
  // however clients can use this function to override with their own handling
  // (e.g. a silent one for Unit Tests)
  typedef void (*LogAssertHandlerFunction)(const std::string& str);
  BASE_EXPORT void SetLogAssertHandler(LogAssertHandlerFunction handler);
  
  // Sets the Log Report Handler that will be used to notify of check failures
  // in non-debug mode. The default handler shows a dialog box and continues
  // the execution, however clients can use this function to override with their
  // own handling.
  typedef void (*LogReportHandlerFunction)(const std::string& str);
  BASE_EXPORT void SetLogReportHandler(LogReportHandlerFunction handler);
  
  // Sets the Log Message Handler that gets passed every log message before
  // it's sent to other log destinations (if any).
  // Returns true to signal that it handled the message and the message
  // should not be sent to other log destinations.
  typedef bool (*LogMessageHandlerFunction)(int severity,
      const char* file, int line, size_t message_start, const std::string& str);
  BASE_EXPORT void SetLogMessageHandler(LogMessageHandlerFunction handler);
  BASE_EXPORT LogMessageHandlerFunction GetLogMessageHandler();
  
  typedef int LogSeverity;
  const LogSeverity LOG_VERBOSE = -1;  // This is level 1 verbosity
  // Note: the log severities are used to index into the array of names,
  // see log_severity_names.
  #ifndef DISABLE_ANDROID_BASE_LOGGING
  const LogSeverity LOG_INFO = 0;
  const LogSeverity LOG_WARNING = 1;
  #endif
  const LogSeverity LOG_ERROR = 2;
  const LogSeverity LOG_ERROR_REPORT = 3;
  const LogSeverity LOG_FATAL = 4;
  const LogSeverity LOG_NUM_SEVERITIES = 5;
  
  // LOG_DFATAL is LOG_FATAL in debug mode, ERROR in normal mode
  #ifdef NDEBUG
  const LogSeverity LOG_DFATAL = LOG_ERROR;
  #else
  const LogSeverity LOG_DFATAL = LOG_FATAL;
  #endif
  
  // A few definitions of macros that don't generate much code. These are used
  // by LOG() and LOG_IF, etc. Since these are used all over our code, it's
  // better to have compact code for these operations.
  #define COMPACT_GOOGLE_LOG_EX_INFO(ClassName, ...) \
    logging::ClassName(__FILE__, __LINE__, logging::LOG_INFO , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_EX_WARNING(ClassName, ...) \
    logging::ClassName(__FILE__, __LINE__, logging::LOG_WARNING , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_EX_ERROR(ClassName, ...) \
    logging::ClassName(__FILE__, __LINE__, logging::LOG_ERROR , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_EX_ERROR_REPORT(ClassName, ...) \
    logging::ClassName(__FILE__, __LINE__, \
                       logging::LOG_ERROR_REPORT , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_EX_FATAL(ClassName, ...) \
    logging::ClassName(__FILE__, __LINE__, logging::LOG_FATAL , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_EX_DFATAL(ClassName, ...) \
    logging::ClassName(__FILE__, __LINE__, logging::LOG_DFATAL , ##__VA_ARGS__)
  
  #define COMPACT_GOOGLE_LOG_INFO \
    COMPACT_GOOGLE_LOG_EX_INFO(LogMessage)
  #define COMPACT_GOOGLE_LOG_WARNING \
    COMPACT_GOOGLE_LOG_EX_WARNING(LogMessage)
  #define COMPACT_GOOGLE_LOG_ERROR \
    COMPACT_GOOGLE_LOG_EX_ERROR(LogMessage)
  #define COMPACT_GOOGLE_LOG_ERROR_REPORT \
    COMPACT_GOOGLE_LOG_EX_ERROR_REPORT(LogMessage)
  #define COMPACT_GOOGLE_LOG_FATAL \
    COMPACT_GOOGLE_LOG_EX_FATAL(LogMessage)
  #define COMPACT_GOOGLE_LOG_DFATAL \
    COMPACT_GOOGLE_LOG_EX_DFATAL(LogMessage)
  
  #if defined(OS_WIN)
  // wingdi.h defines ERROR to be 0. When we call LOG(ERROR), it gets
  // substituted with 0, and it expands to COMPACT_GOOGLE_LOG_0. To allow us
  // to keep using this syntax, we define this macro to do the same thing
  // as COMPACT_GOOGLE_LOG_ERROR, and also define ERROR the same way that
  // the Windows SDK does for consistency.
  #define ERROR 0
  #define COMPACT_GOOGLE_LOG_EX_0(ClassName, ...) \
    COMPACT_GOOGLE_LOG_EX_ERROR(ClassName , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_0 COMPACT_GOOGLE_LOG_ERROR
  // Needed for LOG_IS_ON(ERROR).
  const LogSeverity LOG_0 = LOG_ERROR;
  #endif
  
  // As special cases, we can assume that LOG_IS_ON(ERROR_REPORT) and
  // LOG_IS_ON(FATAL) always hold.  Also, LOG_IS_ON(DFATAL) always holds
  // in debug mode.  In particular, CHECK()s will always fire if they
  // fail.
  #define LOG_IS_ON(severity) \
    ((::logging::LOG_ ## severity) >= ::logging::GetMinLogLevel())
  
  // We can't do any caching tricks with VLOG_IS_ON() like the
  // google-glog version since it requires GCC extensions.  This means
  // that using the v-logging functions in conjunction with --vmodule
  // may be slow.
  #define VLOG_IS_ON(verboselevel) \
    ((verboselevel) <= ::logging::GetVlogLevel(__FILE__))
  
  // Helper macro which avoids evaluating the arguments to a stream if
  // the condition doesn't hold.
  #define LAZY_STREAM(stream, condition)                                  \
    !(condition) ? (void) 0 : ::logging::LogMessageVoidify() & (stream)
  
  // We use the preprocessor's merging operator, "##", so that, e.g.,
  // LOG(INFO) becomes the token COMPACT_GOOGLE_LOG_INFO.  There's some funny
  // subtle difference between ostream member streaming functions (e.g.,
  // ostream::operator<<(int) and ostream non-member streaming functions
  // (e.g., ::operator<<(ostream&, string&): it turns out that it's
  // impossible to stream something like a string directly to an unnamed
  // ostream. We employ a neat hack by calling the stream() member
  // function of LogMessage which seems to avoid the problem.
  #define LOG_STREAM(severity) COMPACT_GOOGLE_LOG_ ## severity.stream()
  
  #define LOG(severity) LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity))
  #define LOG_IF(severity, condition) \
    LAZY_STREAM(LOG_STREAM(severity), LOG_IS_ON(severity) && (condition))
  
  #define SYSLOG(severity) LOG(severity)
  #define SYSLOG_IF(severity, condition) LOG_IF(severity, condition)
  
  // The VLOG macros log with negative verbosities.
  #define VLOG_STREAM(verbose_level) \
    logging::LogMessage(__FILE__, __LINE__, -verbose_level).stream()
  
  #define VLOG(verbose_level) \
    LAZY_STREAM(VLOG_STREAM(verbose_level), VLOG_IS_ON(verbose_level))
  
  #define VLOG_IF(verbose_level, condition) \
    LAZY_STREAM(VLOG_STREAM(verbose_level), \
        VLOG_IS_ON(verbose_level) && (condition))
  
  #if defined (OS_WIN)
  #define VPLOG_STREAM(verbose_level) \
    logging::Win32ErrorLogMessage(__FILE__, __LINE__, -verbose_level, \
      ::logging::GetLastSystemErrorCode()).stream()
  #elif defined(OS_POSIX)
  #define VPLOG_STREAM(verbose_level) \
    logging::ErrnoLogMessage(__FILE__, __LINE__, -verbose_level, \
      ::logging::GetLastSystemErrorCode()).stream()
  #endif
  
  #define VPLOG(verbose_level) \
    LAZY_STREAM(VPLOG_STREAM(verbose_level), VLOG_IS_ON(verbose_level))
  
  #define VPLOG_IF(verbose_level, condition) \
    LAZY_STREAM(VPLOG_STREAM(verbose_level), \
      VLOG_IS_ON(verbose_level) && (condition))
  
  // TODO(akalin): Add more VLOG variants, e.g. VPLOG.
  
  #define LOG_ASSERT(condition)  \
    LOG_IF(FATAL, !(condition)) << "Assert failed: " #condition ". "
  #define SYSLOG_ASSERT(condition) \
    SYSLOG_IF(FATAL, !(condition)) << "Assert failed: " #condition ". "
  
  #if defined(OS_WIN)
  #define LOG_GETLASTERROR_STREAM(severity) \
    COMPACT_GOOGLE_LOG_EX_ ## severity(Win32ErrorLogMessage, \
        ::logging::GetLastSystemErrorCode()).stream()
  #define LOG_GETLASTERROR(severity) \
    LAZY_STREAM(LOG_GETLASTERROR_STREAM(severity), LOG_IS_ON(severity))
  #define LOG_GETLASTERROR_MODULE_STREAM(severity, module) \
    COMPACT_GOOGLE_LOG_EX_ ## severity(Win32ErrorLogMessage, \
        ::logging::GetLastSystemErrorCode(), module).stream()
  #define LOG_GETLASTERROR_MODULE(severity, module)                       \
    LAZY_STREAM(LOG_GETLASTERROR_STREAM(severity, module),                \
                LOG_IS_ON(severity))
  // PLOG_STREAM is used by PLOG, which is the usual error logging macro
  // for each platform.
  #define PLOG_STREAM(severity) LOG_GETLASTERROR_STREAM(severity)
  #elif defined(OS_POSIX)
  #define LOG_ERRNO_STREAM(severity) \
    COMPACT_GOOGLE_LOG_EX_ ## severity(ErrnoLogMessage, \
        ::logging::GetLastSystemErrorCode()).stream()
  #define LOG_ERRNO(severity) \
    LAZY_STREAM(LOG_ERRNO_STREAM(severity), LOG_IS_ON(severity))
  // PLOG_STREAM is used by PLOG, which is the usual error logging macro
  // for each platform.
  #define PLOG_STREAM(severity) LOG_ERRNO_STREAM(severity)
  #endif
  
  #define PLOG(severity)                                          \
    LAZY_STREAM(PLOG_STREAM(severity), LOG_IS_ON(severity))
  
  #define PLOG_IF(severity, condition) \
    LAZY_STREAM(PLOG_STREAM(severity), LOG_IS_ON(severity) && (condition))
  
  // http://crbug.com/16512 is open for a real fix for this.  For now, Windows
  // uses OFFICIAL_BUILD and other platforms use the branding flag when NDEBUG is
  // defined.
  #if ( defined(OS_WIN) && defined(OFFICIAL_BUILD)) || \
      (!defined(OS_WIN) && defined(NDEBUG) && defined(GOOGLE_CHROME_BUILD))
  #define LOGGING_IS_OFFICIAL_BUILD 1
  #else
  #define LOGGING_IS_OFFICIAL_BUILD 0
  #endif
  
  // The actual stream used isn't important.
  #define EAT_STREAM_PARAMETERS                                           \
    true ? (void) 0 : ::logging::LogMessageVoidify() & LOG_STREAM(FATAL)
  
  // CHECK dies with a fatal error if condition is not true.  It is *not*
  // controlled by NDEBUG, so the check will be executed regardless of
  // compilation mode.
  //
  // We make sure CHECK et al. always evaluates their arguments, as
  // doing CHECK(FunctionWithSideEffect()) is a common idiom.
  
  #if LOGGING_IS_OFFICIAL_BUILD
  
  // Make all CHECK functions discard their log strings to reduce code
  // bloat for official builds.
  
  // TODO(akalin): This would be more valuable if there were some way to
  // remove BreakDebugger() from the backtrace, perhaps by turning it
  // into a macro (like __debugbreak() on Windows).
  #define CHECK(condition)                                                \
    !(condition) ? ::base::debug::BreakDebugger() : EAT_STREAM_PARAMETERS
  
  #define PCHECK(condition) CHECK(condition)
  
  #define CHECK_OP(name, op, val1, val2) CHECK((val1) op (val2))
  
  #else
  
  #define CHECK(condition)                       \
    LAZY_STREAM(LOG_STREAM(FATAL), !(condition)) \
    << "Check failed: " #condition ". "
  
  #define PCHECK(condition) \
    LAZY_STREAM(PLOG_STREAM(FATAL), !(condition)) \
    << "Check failed: " #condition ". "
  
  // Helper macro for binary operators.
  // Don't use this macro directly in your code, use CHECK_EQ et al below.
  //
  // TODO(akalin): Rewrite this so that constructs like if (...)
  // CHECK_EQ(...) else { ... } work properly.
  #define CHECK_OP(name, op, val1, val2)                          \
    if (std::string* _result =                                    \
        logging::Check##name##Impl((val1), (val2),                \
                                   #val1 " " #op " " #val2))      \
      logging::LogMessage(__FILE__, __LINE__, _result).stream()
  
  #endif
  
  // Build the error message string.  This is separate from the "Impl"
  // function template because it is not performance critical and so can
  // be out of line, while the "Impl" code should be inline.  Caller
  // takes ownership of the returned string.
  template<class t1, class t2>
  std::string* MakeCheckOpString(const t1& v1, const t2& v2, const char* names) {
    std::ostringstream ss;
    ss << names << " (" << v1 << " vs. " << v2 << ")";
    std::string* msg = new std::string(ss.str());
    return msg;
  }
  
  // MSVC doesn't like complex extern templates and DLLs.
  #if !defined(COMPILER_MSVC)
  // Commonly used instantiations of MakeCheckOpString<>. Explicitly instantiated
  // in logging.cc.
  extern template BASE_EXPORT std::string* MakeCheckOpString<int, int>(
      const int&, const int&, const char* names);
  extern template BASE_EXPORT
  std::string* MakeCheckOpString<unsigned long, unsigned long>(
      const unsigned long&, const unsigned long&, const char* names);
  extern template BASE_EXPORT
  std::string* MakeCheckOpString<unsigned long, unsigned int>(
      const unsigned long&, const unsigned int&, const char* names);
  extern template BASE_EXPORT
  std::string* MakeCheckOpString<unsigned int, unsigned long>(
      const unsigned int&, const unsigned long&, const char* names);
  extern template BASE_EXPORT
  std::string* MakeCheckOpString<std::string, std::string>(
      const std::string&, const std::string&, const char* name);
  #endif
  
  // Helper functions for CHECK_OP macro.
  // The (int, int) specialization works around the issue that the compiler
  // will not instantiate the template version of the function on values of
  // unnamed enum type - see comment below.
  #define DEFINE_CHECK_OP_IMPL(name, op) \
    template <class t1, class t2> \
    inline std::string* Check##name##Impl(const t1& v1, const t2& v2, \
                                          const char* names) { \
      if (v1 op v2) return NULL; \
      else return MakeCheckOpString(v1, v2, names); \
    } \
    inline std::string* Check##name##Impl(int v1, int v2, const char* names) { \
      if (v1 op v2) return NULL; \
      else return MakeCheckOpString(v1, v2, names); \
    }
  DEFINE_CHECK_OP_IMPL(EQ, ==)
  DEFINE_CHECK_OP_IMPL(NE, !=)
  DEFINE_CHECK_OP_IMPL(LE, <=)
  DEFINE_CHECK_OP_IMPL(LT, < )
  DEFINE_CHECK_OP_IMPL(GE, >=)
  DEFINE_CHECK_OP_IMPL(GT, > )
  #undef DEFINE_CHECK_OP_IMPL
  
  #define CHECK_EQ(val1, val2) CHECK_OP(EQ, ==, val1, val2)
  #define CHECK_NE(val1, val2) CHECK_OP(NE, !=, val1, val2)
  #define CHECK_LE(val1, val2) CHECK_OP(LE, <=, val1, val2)
  #define CHECK_LT(val1, val2) CHECK_OP(LT, < , val1, val2)
  #define CHECK_GE(val1, val2) CHECK_OP(GE, >=, val1, val2)
  #define CHECK_GT(val1, val2) CHECK_OP(GT, > , val1, val2)
  
  #if LOGGING_IS_OFFICIAL_BUILD
  // In order to have optimized code for official builds, remove DLOGs and
  // DCHECKs.
  #define ENABLE_DLOG 0
  #define ENABLE_DCHECK 0
  
  #elif defined(NDEBUG)
  // Otherwise, if we're a release build, remove DLOGs but not DCHECKs
  // (since those can still be turned on via a command-line flag).
  #define ENABLE_DLOG 0
  #define ENABLE_DCHECK 1
  
  #else
  // Otherwise, we're a debug build so enable DLOGs and DCHECKs.
  #define ENABLE_DLOG 1
  #define ENABLE_DCHECK 1
  #endif
  
  // Definitions for DLOG et al.
  
  #if ENABLE_DLOG
  
  #define DLOG_IS_ON(severity) LOG_IS_ON(severity)
  #define DLOG_IF(severity, condition) LOG_IF(severity, condition)
  #define DLOG_ASSERT(condition) LOG_ASSERT(condition)
  #define DPLOG_IF(severity, condition) PLOG_IF(severity, condition)
  #define DVLOG_IF(verboselevel, condition) VLOG_IF(verboselevel, condition)
  #define DVPLOG_IF(verboselevel, condition) VPLOG_IF(verboselevel, condition)
  
  #else  // ENABLE_DLOG
  
  // If ENABLE_DLOG is off, we want to avoid emitting any references to
  // |condition| (which may reference a variable defined only if NDEBUG
  // is not defined).  Contrast this with DCHECK et al., which has
  // different behavior.
  
  #define DLOG_IS_ON(severity) false
  #define DLOG_IF(severity, condition) EAT_STREAM_PARAMETERS
  #define DLOG_ASSERT(condition) EAT_STREAM_PARAMETERS
  #define DPLOG_IF(severity, condition) EAT_STREAM_PARAMETERS
  #define DVLOG_IF(verboselevel, condition) EAT_STREAM_PARAMETERS
  #define DVPLOG_IF(verboselevel, condition) EAT_STREAM_PARAMETERS
  
  #endif  // ENABLE_DLOG
  
  // DEBUG_MODE is for uses like
  //   if (DEBUG_MODE) foo.CheckThatFoo();
  // instead of
  //   #ifndef NDEBUG
  //     foo.CheckThatFoo();
  //   #endif
  //
  // We tie its state to ENABLE_DLOG.
  enum { DEBUG_MODE = ENABLE_DLOG };
  
  #undef ENABLE_DLOG
  
  #define DLOG(severity)                                          \
    LAZY_STREAM(LOG_STREAM(severity), DLOG_IS_ON(severity))
  
  #if defined(OS_WIN)
  #define DLOG_GETLASTERROR(severity) \
    LAZY_STREAM(LOG_GETLASTERROR_STREAM(severity), DLOG_IS_ON(severity))
  #define DLOG_GETLASTERROR_MODULE(severity, module)                      \
    LAZY_STREAM(LOG_GETLASTERROR_STREAM(severity, module),                \
                DLOG_IS_ON(severity))
  #elif defined(OS_POSIX)
  #define DLOG_ERRNO(severity)                                    \
    LAZY_STREAM(LOG_ERRNO_STREAM(severity), DLOG_IS_ON(severity))
  #endif
  
  #define DPLOG(severity)                                         \
    LAZY_STREAM(PLOG_STREAM(severity), DLOG_IS_ON(severity))
  
  #define DVLOG(verboselevel) DVLOG_IF(verboselevel, VLOG_IS_ON(verboselevel))
  
  #define DVPLOG(verboselevel) DVPLOG_IF(verboselevel, VLOG_IS_ON(verboselevel))
  
  // Definitions for DCHECK et al.
  
  #if ENABLE_DCHECK
  
  #if defined(NDEBUG)
  
  BASE_EXPORT extern DcheckState g_dcheck_state;
  
  #if defined(DCHECK_ALWAYS_ON)
  
  #define DCHECK_IS_ON() true
  #define COMPACT_GOOGLE_LOG_EX_DCHECK(ClassName, ...) \
    COMPACT_GOOGLE_LOG_EX_FATAL(ClassName , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_FATAL
  const LogSeverity LOG_DCHECK = LOG_FATAL;
  
  #else
  
  #define COMPACT_GOOGLE_LOG_EX_DCHECK(ClassName, ...) \
    COMPACT_GOOGLE_LOG_EX_ERROR_REPORT(ClassName , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_ERROR_REPORT
  const LogSeverity LOG_DCHECK = LOG_ERROR_REPORT;
  #define DCHECK_IS_ON()                                                  \
    ((::logging::g_dcheck_state ==                                        \
      ::logging::ENABLE_DCHECK_FOR_NON_OFFICIAL_RELEASE_BUILDS) &&        \
     LOG_IS_ON(DCHECK))
  
  #endif  // defined(DCHECK_ALWAYS_ON)
  
  #else  // defined(NDEBUG)
  
  // On a regular debug build, we want to have DCHECKs enabled.
  #define COMPACT_GOOGLE_LOG_EX_DCHECK(ClassName, ...) \
    COMPACT_GOOGLE_LOG_EX_FATAL(ClassName , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_FATAL
  const LogSeverity LOG_DCHECK = LOG_FATAL;
  #define DCHECK_IS_ON() true
  
  #endif  // defined(NDEBUG)
  
  #else  // ENABLE_DCHECK
  
  // These are just dummy values since DCHECK_IS_ON() is always false in
  // this case.
  #define COMPACT_GOOGLE_LOG_EX_DCHECK(ClassName, ...) \
    COMPACT_GOOGLE_LOG_EX_INFO(ClassName , ##__VA_ARGS__)
  #define COMPACT_GOOGLE_LOG_DCHECK COMPACT_GOOGLE_LOG_INFO
  const LogSeverity LOG_DCHECK = LOG_INFO;
  #define DCHECK_IS_ON() false
  
  #endif  // ENABLE_DCHECK
  #undef ENABLE_DCHECK
  
  // DCHECK et al. make sure to reference |condition| regardless of
  // whether DCHECKs are enabled; this is so that we don't get unused
  // variable warnings if the only use of a variable is in a DCHECK.
  // This behavior is different from DLOG_IF et al.
  
  #define DCHECK(condition)                                           \
    LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON() && !(condition))   \
    << "Check failed: " #condition ". "
  
  #define DPCHECK(condition)                                          \
    LAZY_STREAM(PLOG_STREAM(DCHECK), DCHECK_IS_ON() && !(condition))  \
    << "Check failed: " #condition ". "
  
  // Helper macro for binary operators.
  // Don't use this macro directly in your code, use DCHECK_EQ et al below.
  #define DCHECK_OP(name, op, val1, val2)                         \
    if (DCHECK_IS_ON())                                           \
      if (std::string* _result =                                  \
          logging::Check##name##Impl((val1), (val2),              \
                                     #val1 " " #op " " #val2))    \
        logging::LogMessage(                                      \
            __FILE__, __LINE__, ::logging::LOG_DCHECK,            \
            _result).stream()
  
  // Equality/Inequality checks - compare two values, and log a
  // LOG_DCHECK message including the two values when the result is not
  // as expected.  The values must have operator<<(ostream, ...)
  // defined.
  //
  // You may append to the error message like so:
  //   DCHECK_NE(1, 2) << ": The world must be ending!";
  //
  // We are very careful to ensure that each argument is evaluated exactly
  // once, and that anything which is legal to pass as a function argument is
  // legal here.  In particular, the arguments may be temporary expressions
  // which will end up being destroyed at the end of the apparent statement,
  // for example:
  //   DCHECK_EQ(string("abc")[1], 'b');
  //
  // WARNING: These may not compile correctly if one of the arguments is a pointer
  // and the other is NULL. To work around this, simply static_cast NULL to the
  // type of the desired pointer.
  
  #define DCHECK_EQ(val1, val2) DCHECK_OP(EQ, ==, val1, val2)
  #define DCHECK_NE(val1, val2) DCHECK_OP(NE, !=, val1, val2)
  #define DCHECK_LE(val1, val2) DCHECK_OP(LE, <=, val1, val2)
  #define DCHECK_LT(val1, val2) DCHECK_OP(LT, < , val1, val2)
  #define DCHECK_GE(val1, val2) DCHECK_OP(GE, >=, val1, val2)
  #define DCHECK_GT(val1, val2) DCHECK_OP(GT, > , val1, val2)
  
  #define NOTREACHED() DCHECK(false)
  
  // Redefine the standard assert to use our nice log files
  #undef assert
  #define assert(x) DLOG_ASSERT(x)
  
  // This class more or less represents a particular log message.  You
  // create an instance of LogMessage and then stream stuff to it.
  // When you finish streaming to it, ~LogMessage is called and the
  // full message gets streamed to the appropriate destination.
  //
  // You shouldn't actually use LogMessage's constructor to log things,
  // though.  You should use the LOG() macro (and variants thereof)
  // above.
  class BASE_EXPORT LogMessage {
   public:
    LogMessage(const char* file, int line, LogSeverity severity, int ctr);
  
    // Two special constructors that generate reduced amounts of code at
    // LOG call sites for common cases.
    //
    // Used for LOG(INFO): Implied are:
    // severity = LOG_INFO, ctr = 0
    //
    // Using this constructor instead of the more complex constructor above
    // saves a couple of bytes per call site.
    LogMessage(const char* file, int line);
  
    // Used for LOG(severity) where severity != INFO.  Implied
    // are: ctr = 0
    //
    // Using this constructor instead of the more complex constructor above
    // saves a couple of bytes per call site.
    LogMessage(const char* file, int line, LogSeverity severity);
  
    // A special constructor used for check failures.  Takes ownership
    // of the given string.
    // Implied severity = LOG_FATAL
    LogMessage(const char* file, int line, std::string* result);
  
    // A special constructor used for check failures, with the option to
    // specify severity.  Takes ownership of the given string.
    LogMessage(const char* file, int line, LogSeverity severity,
               std::string* result);
  
    ~LogMessage();
  
    std::ostream& stream() { return stream_; }
  
   private:
    void Init(const char* file, int line);
  
    LogSeverity severity_;
    std::ostringstream stream_;
    size_t message_start_;  // Offset of the start of the message (past prefix
                            // info).
    // The file and line information passed in to the constructor.
    const char* file_;
    const int line_;
  
  #if defined(OS_WIN)
    // Stores the current value of GetLastError in the constructor and restores
    // it in the destructor by calling SetLastError.
    // This is useful since the LogMessage class uses a lot of Win32 calls
    // that will lose the value of GLE and the code that called the log function
    // will have lost the thread error value when the log call returns.
    class SaveLastError {
     public:
      SaveLastError();
      ~SaveLastError();
  
      unsigned long get_error() const { return last_error_; }
  
     protected:
      unsigned long last_error_;
    };
  
    SaveLastError last_error_;
  #endif
  
    DISALLOW_COPY_AND_ASSIGN(LogMessage);
  };
  
  // A non-macro interface to the log facility; (useful
  // when the logging level is not a compile-time constant).
  inline void LogAtLevel(int const log_level, std::string const &msg) {
    LogMessage(__FILE__, __LINE__, log_level).stream() << msg;
  }
  
  // This class is used to explicitly ignore values in the conditional
  // logging macros.  This avoids compiler warnings like "value computed
  // is not used" and "statement has no effect".
  class LogMessageVoidify {
   public:
    LogMessageVoidify() { }
    // This has to be an operator with a precedence lower than << but
    // higher than ?:
    void operator&(std::ostream&) { }
  };
  
  #if defined(OS_WIN)
  typedef unsigned long SystemErrorCode;
  #elif defined(OS_POSIX)
  typedef int SystemErrorCode;
  #endif
  
  // Alias for ::GetLastError() on Windows and errno on POSIX. Avoids having to
  // pull in windows.h just for GetLastError() and DWORD.
  BASE_EXPORT SystemErrorCode GetLastSystemErrorCode();
  
  #if defined(OS_WIN)
  // Appends a formatted system message of the GetLastError() type.
  class BASE_EXPORT Win32ErrorLogMessage {
   public:
    Win32ErrorLogMessage(const char* file,
                         int line,
                         LogSeverity severity,
                         SystemErrorCode err,
                         const char* module);
  
    Win32ErrorLogMessage(const char* file,
                         int line,
                         LogSeverity severity,
                         SystemErrorCode err);
  
    // Appends the error message before destructing the encapsulated class.
    ~Win32ErrorLogMessage();
  
    std::ostream& stream() { return log_message_.stream(); }
  
   private:
    SystemErrorCode err_;
    // Optional name of the module defining the error.
    const char* module_;
    LogMessage log_message_;
  
    DISALLOW_COPY_AND_ASSIGN(Win32ErrorLogMessage);
  };
  #elif defined(OS_POSIX)
  // Appends a formatted system message of the errno type
  class BASE_EXPORT ErrnoLogMessage {
   public:
    ErrnoLogMessage(const char* file,
                    int line,
                    LogSeverity severity,
                    SystemErrorCode err);
  
    // Appends the error message before destructing the encapsulated class.
    ~ErrnoLogMessage();
  
    std::ostream& stream() { return log_message_.stream(); }
  
   private:
    SystemErrorCode err_;
    LogMessage log_message_;
  
    DISALLOW_COPY_AND_ASSIGN(ErrnoLogMessage);
  };
  #endif  // OS_WIN
  
  // Closes the log file explicitly if open.
  // NOTE: Since the log file is opened as necessary by the action of logging
  //       statements, there's no guarantee that it will stay closed
  //       after this call.
  BASE_EXPORT void CloseLogFile();
  
  // Async signal safe logging mechanism.
  BASE_EXPORT void RawLog(int level, const char* message);
  
  #define RAW_LOG(level, message) logging::RawLog(logging::LOG_ ## level, message)
  
  #define RAW_CHECK(condition)                                                   \
    do {                                                                         \
      if (!(condition))                                                          \
        logging::RawLog(logging::LOG_FATAL, "Check failed: " #condition "\n");   \
    } while (0)
  
  #if defined(OS_WIN)
  // Returns the default log file path.
  BASE_EXPORT std::wstring GetLogFileFullPath();
  #endif
  
  }  // namespace logging
  
  // These functions are provided as a convenience for logging, which is where we
  // use streams (it is against Google style to use streams in other places). It
  // is designed to allow you to emit non-ASCII Unicode strings to the log file,
  // which is normally ASCII. It is relatively slow, so try not to use it for
  // common cases. Non-ASCII characters will be converted to UTF-8 by these
  // operators.
  BASE_EXPORT std::ostream& operator<<(std::ostream& out, const wchar_t* wstr);
  inline std::ostream& operator<<(std::ostream& out, const std::wstring& wstr) {
    return out << wstr.c_str();
  }
  
  // The NOTIMPLEMENTED() macro annotates codepaths which have
  // not been implemented yet.
  //
  // The implementation of this macro is controlled by NOTIMPLEMENTED_POLICY:
  //   0 -- Do nothing (stripped by compiler)
  //   1 -- Warn at compile time
  //   2 -- Fail at compile time
  //   3 -- Fail at runtime (DCHECK)
  //   4 -- [default] LOG(ERROR) at runtime
  //   5 -- LOG(ERROR) at runtime, only once per call-site
  
  #ifndef NOTIMPLEMENTED_POLICY
  #if defined(OS_ANDROID) && defined(OFFICIAL_BUILD)
  #define NOTIMPLEMENTED_POLICY 0
  #else
  // Select default policy: LOG(ERROR)
  #define NOTIMPLEMENTED_POLICY 4
  #endif
  #endif
  
  #if defined(COMPILER_GCC)
  // On Linux, with GCC, we can use __PRETTY_FUNCTION__ to get the demangled name
  // of the current function in the NOTIMPLEMENTED message.
  #define NOTIMPLEMENTED_MSG "Not implemented reached in " << __PRETTY_FUNCTION__
  #else
  #define NOTIMPLEMENTED_MSG "NOT IMPLEMENTED"
  #endif
  
  #if NOTIMPLEMENTED_POLICY == 0
  #define NOTIMPLEMENTED() EAT_STREAM_PARAMETERS
  #elif NOTIMPLEMENTED_POLICY == 1
  // TODO, figure out how to generate a warning
  #define NOTIMPLEMENTED() COMPILE_ASSERT(false, NOT_IMPLEMENTED)
  #elif NOTIMPLEMENTED_POLICY == 2
  #define NOTIMPLEMENTED() COMPILE_ASSERT(false, NOT_IMPLEMENTED)
  #elif NOTIMPLEMENTED_POLICY == 3
  #define NOTIMPLEMENTED() NOTREACHED()
  #elif NOTIMPLEMENTED_POLICY == 4
  #define NOTIMPLEMENTED() LOG(ERROR) << NOTIMPLEMENTED_MSG
  #elif NOTIMPLEMENTED_POLICY == 5
  #define NOTIMPLEMENTED() do {\
    static bool logged_once = false;\
    LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG;\
    logged_once = true;\
  } while(0);\
  EAT_STREAM_PARAMETERS
  #endif
  
  #endif  // BASE_LOGGING_H_
  