media/cdm/ppapi/cdm_logging.h

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // This file defines useful logging macros/methods for CDM adapter.
   6
   7 #ifndef MEDIA_CDM_PPAPI_CDM_LOGGING_H_
   8 #define MEDIA_CDM_PPAPI_CDM_LOGGING_H_
   9
  10 #include <ostream>
  11 #include <sstream>
  12 #include <string>
  13
  14 namespace media {
  15
  16 namespace {
  17
  18 // The following classes/macros are adapted from base/logging.h.
  19
  20 // This class is used to explicitly ignore values in the conditional
  21 // logging macros.  This avoids compiler warnings like "value computed
  22 // is not used" and "statement has no effect".
  23 class LogMessageVoidify {
  24  public:
  25   LogMessageVoidify() {}
  26   // This has to be an operator with a precedence lower than << but
  27   // higher than ?:
  28   void operator&(std::ostream&) {}
  29 };
  30
  31 }  // namespace
  32
  33 // This class is used to avoid having to include <iostream> in this file.
  34 class CdmLogStream {
  35  public:
  36   CdmLogStream() {}
  37
  38   // Retrieves the stream that we write to. This header cannot depend on
  39   // <iostream> because that will add static initializers to all files that
  40   // include this header. See crbug.com/94794.
  41   std::ostream& stream();
  42 };
  43
  44 // This class serves two purposes:
  45 // (1) It adds common headers to the log message, e.g. timestamp, process ID.
  46 // (2) It adds a line break at the end of the log message.
  47 // This class is copied and modified from base/logging.* but is quite different
  48 // in terms of how things work. This class is designed to work only with the
  49 // CDM_DLOG() defined below and should not be used for other purposes.
  50 class CdmLogMessage {
  51  public:
  52   CdmLogMessage(const char* file, int line);
  53   ~CdmLogMessage();
  54
  55   std::string message() { return stream_.str(); }
  56
  57  private:
  58   std::ostringstream stream_;
  59 };
  60
  61 // Helper macro which avoids evaluating the arguments to a stream if
  62 // the condition doesn't hold.
  63 #define CDM_LAZY_STREAM(stream, condition) \
  64   !(condition) ? (void) 0 : LogMessageVoidify() & (stream)
  65
  66 #if defined(NDEBUG)
  67 // Logging is disabled for the release builds, theoretically the compiler should
  68 // take care of removing the references to CdmLogMessage but it's not always the
  69 // case when some specific optimizations are turned on (like PGO). Update the
  70 // macro to make sure that we don't try to do any logging or to refer to
  71 // CdmLogMessage in release.
  72 #define CDM_DLOG_IS_ON() false
  73 #define CDM_DLOG() CDM_LAZY_STREAM(CdmLogStream().stream(), CDM_DLOG_IS_ON())
  74 #else
  75 #define CDM_DLOG_IS_ON() true
  76 #define CDM_DLOG() CDM_LAZY_STREAM(CdmLogStream().stream(), CDM_DLOG_IS_ON()) \
  77     << CdmLogMessage(__FILE__, __LINE__).message()
  78 #endif
  79
  80 }  // namespace media
  81
  82 #endif  // MEDIA_CDM_PPAPI_CDM_LOGGING_H_