src/gromacs/utility/logger.h

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  35 /*! \libinternal \file
  36  * \brief
  37  * Declares functionality for logging.
  38  *
  39  * See \ref page_logging for an overview of the functionality.
  40  *
  41  * \inlibraryapi
  42  * \ingroup module_utility
  43  */
  44 #ifndef GMX_UTILITY_LOGGER_H
  45 #define GMX_UTILITY_LOGGER_H
  46
  47 #include <string>
  48
  49 namespace gmx
  50 {
  51
  52 struct LogEntry
  53 {
  54     LogEntry() : asParagraph(false) {}
  55
  56     std::string text;
  57     bool        asParagraph;
  58 };
  59
  60 /*! \libinternal \brief
  61  * Target where log output can be written.
  62  *
  63  * \ingroup module_utility
  64  */
  65 class ILogTarget
  66 {
  67     public:
  68         virtual ~ILogTarget();
  69
  70         //! Writes a log entry to this target.
  71         virtual void writeEntry(const LogEntry &entry) = 0;
  72 };
  73
  74 /*! \libinternal \brief
  75  * Helper class for creating log entries with ::GMX_LOG.
  76  *
  77  * \ingroup module_utility
  78  */
  79 class LogEntryWriter
  80 {
  81     public:
  82         //! Appends given text to the log entry.
  83         LogEntryWriter &appendText(const char *text)
  84         {
  85             entry_.text.append(text);
  86             return *this;
  87         }
  88         //! Appends given text to the log entry.
  89         LogEntryWriter &appendText(const std::string &text)
  90         {
  91             entry_.text.append(text);
  92             return *this;
  93         }
  94         //! Appends given text to the log entry, with printf-style formatting.
  95         LogEntryWriter &appendTextFormatted(const char *fmt, ...);
  96         //! Writes the log entry with empty lines before and after.
  97         LogEntryWriter &asParagraph()
  98         {
  99             entry_.asParagraph = true;
 100             return *this;
 101         }
 102
 103     private:
 104         LogEntry    entry_;
 105
 106         friend class LogWriteHelper;
 107 };
 108
 109 /*! \internal \brief
 110  * Helper class for implementing ::GMX_LOG.
 111  *
 112  * \ingroup module_utility
 113  */
 114 class LogWriteHelper
 115 {
 116     public:
 117         //! Initializes a helper for writing to the given target.
 118         explicit LogWriteHelper(ILogTarget *target) : target_(target) {}
 119
 120         // Should be explicit, once that works in CUDA.
 121         /*! \brief
 122          * Returns whether anything needs to be written.
 123          *
 124          * Note that the return value is unintuitively `false` when the target
 125          * is active, to allow implementing ::GMX_LOG like it is now.
 126          */
 127         operator bool() const { return target_ == nullptr; }
 128
 129         /*! \brief
 130          * Writes the entry from the given writer to the log target.
 131          *
 132          * This is implemented as an assignment operator to get proper
 133          * precedence for operations for the ::GMX_LOG macro; this is a common
 134          * technique for implementing macros that allow streming information to
 135          * them (see, e.g., Google Test).
 136          */
 137         LogWriteHelper &operator=(const LogEntryWriter &entryWriter)
 138         {
 139             target_->writeEntry(entryWriter.entry_);
 140             return *this;
 141         }
 142
 143     private:
 144         ILogTarget *target_;
 145 };
 146
 147 /*! \libinternal \brief
 148  * Represents a single logging level.
 149  *
 150  * Typically this type is not used directly, but instances in MDLogger are
 151  * simply accessed through ::GMX_LOG in code that writes to the log.
 152  *
 153  * \ingroup module_utility
 154  */
 155 class LogLevelHelper
 156 {
 157     public:
 158         //! Initializes a helper for writing to the given target.
 159         explicit LogLevelHelper(ILogTarget *target) : target_(target) {}
 160
 161         // Both of the below should be explicit, once that works in CUDA.
 162         //! Returns whether the output for this log level goes anywhere.
 163         operator bool() const { return target_ != nullptr; }
 164
 165         //! Creates a helper for ::GMX_LOG.
 166         operator LogWriteHelper() const { return LogWriteHelper(target_); }
 167
 168     private:
 169         ILogTarget *target_;
 170 };
 171
 172 /*! \libinternal \brief
 173  * Declares a logging interface.
 174  *
 175  * Typically, this object is not created directly, but instead through
 176  * LoggerBuilder.
 177  *
 178  * For now, this is named MDLogger, since it is used only there, and it is not
 179  * clear whether the logging levels can be the same throughout the code.  It
 180  * should be relatively straightforward to split this into multiple classes
 181  * with different supported logging levels without changing calling code, or to
 182  * rename it to Logger if we do not need any specialization.
 183  *
 184  * \ingroup module_utility
 185  */
 186 class MDLogger
 187 {
 188     public:
 189         //! Supported logging levels.
 190         enum LogLevel
 191         {
 192             Warning,
 193             Info
 194         };
 195         //! Number of logging levels.
 196         static const int LogLevelCount = static_cast<int>(Info) + 1;
 197
 198         MDLogger();
 199         //! Creates a logger with the given targets.
 200         explicit MDLogger(ILogTarget *targets[LogLevelCount]);
 201
 202         //! For writing at LogLevel::Warning level.
 203         LogLevelHelper warning;
 204         //! For writing at LogLevel::Info level.
 205         LogLevelHelper info;
 206 };
 207
 208 /*! \brief
 209  * Helper to log information using gmx::MDLogger.
 210  *
 211  * \param  logger  LogLevelHelper instance to use for logging.
 212  *
 213  * Used as
 214  * \code
 215    GMX_LOG(logger.warning).appendText(...);
 216    \endcode
 217  * and ensures that the code to format the output is only executed when the
 218  * output goes somewhere.
 219  *
 220  * See LogEntryWriter for functions that can be used with the macro (such as
 221  * the appendText() in the example).
 222  *
 223  * \ingroup module_utility
 224  */
 225 #define GMX_LOG(logger) \
 226     if (::gmx::LogWriteHelper helper = ::gmx::LogWriteHelper(logger)) { } else \
 227         helper = ::gmx::LogEntryWriter()
 228
 229 } // namespace gmx
 230
 231 #endif