webrtc/system_wrappers/interface/logging.h

/*
 *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

// This is a highly stripped-down version of libjingle's talk/base/logging.h.
// It is a thin wrapper around WEBRTC_TRACE, maintaining the libjingle log
// semantics to ease a transition to that format.

// NOTE: LS_INFO maps to a new trace level which should be reserved for
// infrequent, non-verbose logs. The other levels below kTraceWarning have been
// rendered essentially useless due to their verbosity. Carefully consider the
// impact of adding a new LS_INFO log. If it will be logged at anything
// approaching a frame or packet frequency, use LS_VERBOSE if necessary, or
// preferably, do not log at all.

//   LOG(...) an ostream target that can be used to send formatted
// output to a variety of logging targets, such as debugger console, stderr,
// file, or any StreamInterface.
//   The severity level passed as the first argument to the LOGging
// functions is used as a filter, to limit the verbosity of the logging.
//   Static members of LogMessage documented below are used to control the
// verbosity and target of the output.
//   There are several variations on the LOG macro which facilitate logging
// of common error conditions, detailed below.

// LOG(sev) logs the given stream at severity "sev", which must be a
//     compile-time constant of the LoggingSeverity type, without the namespace
//     prefix.
// LOG_V(sev) Like LOG(), but sev is a run-time variable of the LoggingSeverity
//     type (basically, it just doesn't prepend the namespace).
// LOG_F(sev) Like LOG(), but includes the name of the current function.

// Additional helper macros added by WebRTC:
// LOG_API is a shortcut for API call logging. Pass in the input parameters of
// the method. For example:
//   Foo(int bar, int baz) {
//     LOG_API2(bar, baz);
//   }
//
// LOG_FERR is a shortcut for logging a failed function call. For example:
//   if (!Foo(bar)) {
//     LOG_FERR1(LS_WARNING, Foo, bar);
//   }

#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_LOGGING_H_
#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_LOGGING_H_

#include <sstream>

namespace webrtc {

//////////////////////////////////////////////////////////////////////

// Note that the non-standard LoggingSeverity aliases exist because they are
// still in broad use.  The meanings of the levels are:
//  LS_SENSITIVE: Information which should only be logged with the consent
//   of the user, due to privacy concerns.
//  LS_VERBOSE: This level is for data which we do not want to appear in the
//   normal debug log, but should appear in diagnostic logs.
//  LS_INFO: Chatty level used in debugging for all sorts of things, the default
//   in debug builds.
//  LS_WARNING: Something that may warrant investigation.
//  LS_ERROR: Something that should not have occurred.
enum LoggingSeverity {
  LS_SENSITIVE, LS_VERBOSE, LS_INFO, LS_WARNING, LS_ERROR
};

class LogMessage {
 public:
  LogMessage(const char* file, int line, LoggingSeverity sev);
  ~LogMessage();

  static bool Loggable(LoggingSeverity sev);
  std::ostream& stream() { return print_stream_; }

 private:
  // The ostream that buffers the formatted message before output
  std::ostringstream print_stream_;

  // The severity level of this message
  LoggingSeverity severity_;
};

//////////////////////////////////////////////////////////////////////
// Macros which automatically disable logging when WEBRTC_LOGGING == 0
//////////////////////////////////////////////////////////////////////

#ifndef LOG
#if defined(WEBRTC_LOGGING)

// The following non-obvious technique for implementation of a
// conditional log stream was stolen from google3/base/logging.h.

// 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&) { }
};

#define LOG_SEVERITY_PRECONDITION(sev) \
  !(webrtc::LogMessage::Loggable(sev)) \
    ? (void) 0 \
    : webrtc::LogMessageVoidify() &

#define LOG(sev) \
  LOG_SEVERITY_PRECONDITION(webrtc::sev) \
    webrtc::LogMessage(__FILE__, __LINE__, webrtc::sev).stream()

// The _V version is for when a variable is passed in.  It doesn't do the
// namespace concatination.
#define LOG_V(sev) \
  LOG_SEVERITY_PRECONDITION(sev) \
    webrtc::LogMessage(__FILE__, __LINE__, sev).stream()

// The _F version prefixes the message with the current function name.
#if (defined(__GNUC__) && defined(_DEBUG)) || defined(WANT_PRETTY_LOG_F)
#define LOG_F(sev) LOG(sev) << __PRETTY_FUNCTION__ << ": "
#else
#define LOG_F(sev) LOG(sev) << __FUNCTION__ << ": "
#endif

#else  // !defined(WEBRTC_LOGGING)

// Hopefully, the compiler will optimize away some of this code.
// Note: syntax of "1 ? (void)0 : LogMessage" was causing errors in g++,
//   converted to "while (false)"
#define LOG(sev) \
  while (false)webrtc::LogMessage(NULL, 0, webrtc::sev).stream()
#define LOG_V(sev) \
  while (false) webrtc::LogMessage(NULL, 0, sev).stream()
#define LOG_F(sev) LOG(sev) << __FUNCTION__ << ": "

#endif  // !defined(WEBRTC_LOGGING)

#define LOG_API0() LOG_F(LS_VERBOSE)
#define LOG_API1(v1) LOG_API0() << #v1 << "=" << v1
#define LOG_API2(v1, v2) LOG_API1(v1) \
    << ", " << #v2 << "=" << v2
#define LOG_API3(v1, v2, v3) LOG_API2(v1, v2) \
    << ", " << #v3 << "=" << v3

#define LOG_FERR0(sev, func) LOG(sev) << #func << " failed"
#define LOG_FERR1(sev, func, v1) LOG_FERR0(sev, func) \
    << ": " << #v1 << "=" << v1
#define LOG_FERR2(sev, func, v1, v2) LOG_FERR1(sev, func, v1) \
    << ", " << #v2 << "=" << v2
#define LOG_FERR3(sev, func, v1, v2, v3) LOG_FERR2(sev, func, v1, v2) \
    << ", " << #v3 << "=" << v3
#define LOG_FERR4(sev, func, v1, v2, v3, v4) LOG_FERR3(sev, func, v1, v2, v3) \
    << ", " << #v4 << "=" << v4

#endif  // LOG

}  // namespace webrtc

#endif  // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_LOGGING_H_