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Logging Discussion

This issue is to collect discussion on goals for logging. This issue will be broken apart into workable issues/tasks as needs are pinned down.

ParaView is considering a move to loguru, so we should see if that meets our needs. It sounds promising -- lightweight and feature-rich: https://github.com/emilk/loguru/

Suggested log levels:

// namespace vtkm::log:
enum Level : loguru::Verbosity
{
  // Standard loguru levels:

  // Unhandled exceptions
  Fatal = loguru::Verbosity_FATAL,
  
  // Handled but worrysome exceptions, e.g. device fail-over
  Error = loguru::Verbosity_ERROR,

  // Good-to-know-but-not-urgent bad news, 
  // e.g. out-of-bounds parameters clamped to valid range.
  Warn  = loguru::Verbosity_WARNING,

  // General debugging information 
  // (detected hardware, temp use during development/debugging, etc)
  Info  = loguru::Verbosity_INFO,

  // 1-255: Available for application use:
  UserFirst = 1,
  UserLast = 255,

  // VTK-m specific levels

  // Timing data, first since it's most likely to be wanted by people mucking with loggers.
  // Filter/worklet execution times, DeviceAdapterAlgorithm calls
  Perf,

  // Host-side resource allocations/frees (e.g. ArrayHandle control buffers)
  MemCont,

  // Device-side resource allocations/frees (e.g ArrayHandle device buffers)
  MemExec,

  // host->device / device->host data copies
  MemTransfer,

  // Communcation info, e.g. MPI interaction
  Comm,

  // When a dynamic object is (or isn't) resolved, log the result
  CastAndCall,

  // 1024-2047 more verbose application levels
  UserVerboseFirst = 1024,
  UserVerboseLast = 2047
}

Desired loguru modifications:

  • Fix scope RAII move ctor
  • Add export macros
  • Increase scope timer precision.
  • Print log level names in output (instead of integers)
    • Runtime registration (Can be exposed to applications)
    • Truncate if needed to keep preamble fixed size / easily parsable
    • Allow -v verbosity option parsing to take a string.
    • Merge upstream.
  • Template class to get readable classnames (loguru::demangle(typeid(T).name()) should do it)
  • More readable array sizes (2.5 GB instead of XXXXXXXX bytes)
  • Compile time option to strip out all logging statements (strip by default)
Edited by Allison Vacanti