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 /// \file ROOT/RLogger.hxx
 /// \ingroup Base ROOT7
 /// \author Axel Naumann <axel@cern.ch>
 /// \date 2015-03-29
 /// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
 /// is welcome!
 
 /*************************************************************************
  * Copyright (C) 1995-2020, Rene Brun and Fons Rademakers.               *
  * All rights reserved.                                                  *
  *                                                                       *
  * For the licensing terms see $ROOTSYS/LICENSE.                         *
  * For the list of contributors see $ROOTSYS/README/CREDITS.             *
  *************************************************************************/
 
 #ifndef ROOT7_RLogger
 #define ROOT7_RLogger
 
 #include <atomic>
 #include <list>
 #include <memory>
 #include <mutex>
 #include <sstream>
 #include <string>
 #include <utility>
 
 namespace ROOT {
 namespace Experimental {
 
 class RLogEntry;
 class RLogManager;
 
 /**
  Kinds of diagnostics.
  */
 enum class ELogLevel : unsigned char {
    kUnset,
    kFatal,   ///< An error which causes further processing to be unreliable
    kError,   ///< An error
    kWarning, ///< Warnings about likely unexpected behavior
    kInfo,    ///< Informational messages; used for instance for tracing
    kDebug    ///< Debug information; only useful for developers; can have added verbosity up to 255-kDebug.
 };
 
 inline ELogLevel operator+(ELogLevel severity, int offset)
 {
    return static_cast<ELogLevel>(static_cast<int>(severity) + offset);
 }
 
 /**
  Keep track of emitted errors and warnings.
  */
 class RLogDiagCount {
 protected:
    std::atomic<long long> fNumWarnings{0ll};    /// Number of warnings.
    std::atomic<long long> fNumErrors{0ll};      /// Number of errors.
    std::atomic<long long> fNumFatalErrors{0ll}; /// Number of fatal errors.
 
 public:
    /// Returns the current number of warnings.
    long long GetNumWarnings() const { return fNumWarnings; }
 
    /// Returns the current number of errors.
    long long GetNumErrors() const { return fNumErrors; }
 
    /// Returns the current number of fatal errors.
    long long GetNumFatalErrors() const { return fNumFatalErrors; }
 
    /// Increase warning or error count.
    void Increment(ELogLevel severity)
    {
       switch (severity) {
       case ELogLevel::kFatal: ++fNumFatalErrors; break;
       case ELogLevel::kError: ++fNumErrors; break;
       case ELogLevel::kWarning: ++fNumWarnings; break;
       default:;
       }
    }
 };
 
 /**
  Abstract RLogHandler base class. ROOT logs everything from info to error
  to entities of this class.
  */
 class RLogHandler {
 public:
    virtual ~RLogHandler();
    /// Emit a log entry.
    /// \param entry - the RLogEntry to be emitted.
    /// \returns false if further emission of this Log should be suppressed.
    ///
    /// \note This function is called concurrently; log emission must be locked
    /// if needed. (The default log handler using ROOT's DefaultErrorHandler is locked.)
    virtual bool Emit(const RLogEntry &entry) = 0;
 };
 
 /**
  A log configuration for a channel, e.g. "RHist".
  Each ROOT module has its own log, with potentially distinct verbosity.
  */
 class RLogChannel : public RLogDiagCount {
    /// Name as shown in diagnostics
    std::string fName;
 
    /// Verbosity of this channel. By default, use the global verbosity.
    ELogLevel fVerbosity = ELogLevel::kUnset;
 
 public:
    /// Construct an anonymous channel.
    RLogChannel() = default;
 
    /// Construct an anonymous channel with a default verbosity.
    explicit RLogChannel(ELogLevel verbosity) : fVerbosity(verbosity) {}
 
    /// Construct a log channel given its name, which is part of the diagnostics.
    RLogChannel(const std::string &name) : fName(name) {}
 
    ELogLevel SetVerbosity(ELogLevel verbosity)
    {
       std::swap(fVerbosity, verbosity);
       return verbosity;
    }
    ELogLevel GetVerbosity() const { return fVerbosity; }
    ELogLevel GetEffectiveVerbosity(const RLogManager &mgr) const;
 
    const std::string &GetName() const { return fName; }
 };
 
 /**
  A RLogHandler that multiplexes diagnostics to different client `RLogHandler`s
  and keeps track of the sum of `RLogDiagCount`s for all channels.
 
  `RLogHandler::Get()` returns the process's (static) log manager.
  */
 
 class RLogManager : public RLogChannel, public RLogHandler {
    std::mutex fMutex;
    std::list<std::unique_ptr<RLogHandler>> fHandlers;
 
 public:
    /// Initialize taking a RLogHandler.
    RLogManager(std::unique_ptr<RLogHandler> lh) : RLogChannel(ELogLevel::kWarning)
    {
       fHandlers.emplace_back(std::move(lh));
    }
 
    static RLogManager &Get();
 
    /// Add a RLogHandler in the front - to be called before all others.
    void PushFront(std::unique_ptr<RLogHandler> handler) { fHandlers.emplace_front(std::move(handler)); }
 
    /// Add a RLogHandler in the back - to be called after all others.
    void PushBack(std::unique_ptr<RLogHandler> handler) { fHandlers.emplace_back(std::move(handler)); }
 
    /// Remove and return the given log handler. Returns `nullptr` if not found.
    std::unique_ptr<RLogHandler> Remove(RLogHandler *handler);
 
    // Emit a `RLogEntry` to the RLogHandlers.
    // Returns false if further emission of this Log should be suppressed.
    bool Emit(const RLogEntry &entry) override;
 };
 
 /**
  A diagnostic location, part of an RLogEntry.
  */
 struct RLogLocation {
    std::string fFile;
    std::string fFuncName;
    int fLine; // C++11 forbids "= 0" for braced-init-list initialization.
 };
 
 /**
  A diagnostic that can be emitted by the RLogManager.
  One can construct a RLogEntry through RLogBuilder, including streaming into
  the diagnostic message and automatic emission.
  */
 
 class RLogEntry {
 public:
    RLogLocation fLocation;
    std::string fMessage;
    RLogChannel *fChannel = nullptr;
    ELogLevel fLevel = ELogLevel::kFatal;
 
    RLogEntry(ELogLevel level, RLogChannel &channel) : fChannel(&channel), fLevel(level) {}
    RLogEntry(ELogLevel level, RLogChannel &channel, const RLogLocation &loc)
       : fLocation(loc), fChannel(&channel), fLevel(level)
    {
    }
 
    bool IsDebug() const { return fLevel >= ELogLevel::kDebug; }
    bool IsInfo() const { return fLevel == ELogLevel::kInfo; }
    bool IsWarning() const { return fLevel == ELogLevel::kWarning; }
    bool IsError() const { return fLevel == ELogLevel::kError; }
    bool IsFatal() const { return fLevel == ELogLevel::kFatal; }
 };
 
 namespace Detail {
 /**
  Builds a diagnostic entry, emitted by the static RLogManager upon destruction of this builder,
  where - by definition - the RLogEntry has been completely built.
 
  This builder can be used through the utility preprocessor macros R__LOG_ERROR,
  R__LOG_WARNING etc like this:
 ~~~ {.cpp}
      R__LOG_INFO(ROOT::Experimental::HistLog()) << "all we know is " << 42;
      const int decreasedInfoLevel = 5;
      R__LOG_XDEBUG(ROOT::WebGUILog(), decreasedInfoLevel) << "nitty-gritty details";
 ~~~
  This will automatically capture the current class and function name, the file and line number.
  */
 
 class RLogBuilder : public std::ostringstream {
    /// The log entry to be built.
    RLogEntry fEntry;
 
 public:
    RLogBuilder(ELogLevel level, RLogChannel &channel) : fEntry(level, channel) {}
    RLogBuilder(ELogLevel level, RLogChannel &channel, const std::string &filename, int line,
                const std::string &funcname)
       : fEntry(level, channel, {filename, funcname, line})
    {
    }
 
    /// Emit the log entry through the static log manager.
    ~RLogBuilder()
    {
       fEntry.fMessage = str();
       RLogManager::Get().Emit(fEntry);
    }
 };
 } // namespace Detail
 
 /**
  Change the verbosity level (global or specific to the RLogChannel passed to the
  constructor) for the lifetime of this object.
  Example:
 ~~~ {.cpp}
  RLogScopedVerbosity debugThis(gFooLog, ELogLevel::kDebug);
  Foo::SomethingToDebug();
 ~~~
  */
 class RLogScopedVerbosity {
    RLogChannel *fChannel;
    ELogLevel fPrevLevel;
 
 public:
    RLogScopedVerbosity(RLogChannel &channel, ELogLevel verbosity)
       : fChannel(&channel), fPrevLevel(channel.SetVerbosity(verbosity))
    {
    }
    explicit RLogScopedVerbosity(ELogLevel verbosity) : RLogScopedVerbosity(RLogManager::Get(), verbosity) {}
    ~RLogScopedVerbosity() { fChannel->SetVerbosity(fPrevLevel); }
 };
 
 /**
  Object to count the number of warnings and errors emitted by a section of code,
  after construction of this type.
  */
 class RLogScopedDiagCount {
    RLogDiagCount *fCounter = nullptr;
    /// The number of the RLogDiagCount's emitted warnings at construction time of *this.
    long long fInitialWarnings = 0;
    /// The number of the RLogDiagCount's emitted errors at construction time.
    long long fInitialErrors = 0;
    /// The number of the RLogDiagCount's emitted fatal errors at construction time.
    long long fInitialFatalErrors = 0;
 
 public:
    /// Construct the scoped count given a counter (e.g. a channel or RLogManager).
    /// The counter's lifetime must exceed the lifetime of this object!
    explicit RLogScopedDiagCount(RLogDiagCount &cnt)
       : fCounter(&cnt), fInitialWarnings(cnt.GetNumWarnings()), fInitialErrors(cnt.GetNumErrors()),
         fInitialFatalErrors(cnt.GetNumFatalErrors())
    {
    }
 
    /// Construct the scoped count for any diagnostic, whatever its channel.
    RLogScopedDiagCount() : RLogScopedDiagCount(RLogManager::Get()) {}
 
    /// Get the number of warnings that the RLogDiagCount has emitted since construction of *this.
    long long GetAccumulatedWarnings() const { return fCounter->GetNumWarnings() - fInitialWarnings; }
 
    /// Get the number of errors that the RLogDiagCount has emitted since construction of *this.
    long long GetAccumulatedErrors() const { return fCounter->GetNumErrors() - fInitialErrors; }
 
    /// Get the number of errors that the RLogDiagCount has emitted since construction of *this.
    long long GetAccumulatedFatalErrors() const { return fCounter->GetNumFatalErrors() - fInitialFatalErrors; }
 
    /// Whether the RLogDiagCount has emitted a warnings since construction time of *this.
    bool HasWarningOccurred() const { return GetAccumulatedWarnings(); }
 
    /// Whether the RLogDiagCount has emitted an error (fatal or not) since construction time of *this.
    bool HasErrorOccurred() const { return GetAccumulatedErrors() + GetAccumulatedFatalErrors(); }
 
    /// Whether the RLogDiagCount has emitted an error or a warning since construction time of *this.
    bool HasErrorOrWarningOccurred() const { return HasWarningOccurred() || HasErrorOccurred(); }
 };
 
 namespace Internal {
 
 inline RLogChannel &GetChannelOrManager()
 {
    return RLogManager::Get();
 }
 inline RLogChannel &GetChannelOrManager(RLogChannel &channel)
 {
    return channel;
 }
 
 } // namespace Internal
 
 inline ELogLevel RLogChannel::GetEffectiveVerbosity(const RLogManager &mgr) const
 {
    if (fVerbosity == ELogLevel::kUnset)
       return mgr.GetVerbosity();
    return fVerbosity;
 }
 
 } // namespace Experimental
 } // namespace ROOT
 
 #if defined(_MSC_VER)
 #define R__LOG_PRETTY_FUNCTION __FUNCSIG__
 #else
 #define R__LOG_PRETTY_FUNCTION __PRETTY_FUNCTION__
 #endif
 
 /*
  Some implementation details:
 
  - The conditional `RLogBuilder` use prevents stream operators from being called if
  verbosity is too low, i.e.:
  ~~~
  RLogScopedVerbosity silence(RLogLevel::kFatal);
  R__LOG_DEBUG(7) << WillNotBeCalled();
  ~~~
  - To update counts of warnings / errors / fatal errors, those RLogEntries must
  always be created, even if in the end their emission will be silenced. This
  should be fine, performance-wise, as they should not happen frequently.
  - Use `(condition) && RLogBuilder(...)` instead of `if (condition) RLogBuilder(...)`
  to prevent "ambiguous else" in invocations such as `if (something) R__LOG_DEBUG()...`.
  */
 #define R__LOG_TO_CHANNEL(SEVERITY, CHANNEL)                                                                        \
    ((SEVERITY < ROOT::Experimental::ELogLevel::kInfo + 0) ||                                                        \
      ROOT::Experimental::Internal::GetChannelOrManager(CHANNEL).GetEffectiveVerbosity(                              \
         ROOT::Experimental::RLogManager::Get()) >= SEVERITY) &&                                                     \
       ROOT::Experimental::Detail::RLogBuilder(SEVERITY, ROOT::Experimental::Internal::GetChannelOrManager(CHANNEL), \
                                               __FILE__, __LINE__, R__LOG_PRETTY_FUNCTION)
 
 /// \name LogMacros
 /// Macros to log diagnostics.
 /// ~~~ {.cpp}
 ///     R__LOG_INFO(ROOT::Experimental::HistLog()) << "all we know is " << 42;
 ///
 ///     RLogScopedVerbosity verbose(kDebug + 5);
 ///     const int decreasedInfoLevel = 5;
 ///     R__LOG_DEBUG(ROOT::WebGUILog(), decreasedInfoLevel) << "nitty-gritty details";
 /// ~~~
 ///\{
 #define R__LOG_FATAL(...) R__LOG_TO_CHANNEL(ROOT::Experimental::ELogLevel::kFatal, __VA_ARGS__)
 #define R__LOG_ERROR(...) R__LOG_TO_CHANNEL(ROOT::Experimental::ELogLevel::kError, __VA_ARGS__)
 #define R__LOG_WARNING(...) R__LOG_TO_CHANNEL(ROOT::Experimental::ELogLevel::kWarning, __VA_ARGS__)
 #define R__LOG_INFO(...) R__LOG_TO_CHANNEL(ROOT::Experimental::ELogLevel::kInfo, __VA_ARGS__)
 #define R__LOG_DEBUG(DEBUGLEVEL, ...) R__LOG_TO_CHANNEL(ROOT::Experimental::ELogLevel::kDebug + DEBUGLEVEL, __VA_ARGS__)
 ///\}
 
 #endif

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