1// Copyright (c) 2006-2009 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// Defines the VLOG_IS_ON macro that controls the variable-verbosity 6// conditional logging. 7// 8// It's used by VLOG and VLOG_IF in logging.h 9// and by RAW_VLOG in raw_logging.h to trigger the logging. 10// 11// It can also be used directly e.g. like this: 12// if (VLOG_IS_ON(2)) { 13// // do some logging preparation and logging 14// // that can't be accomplished e.g. via just VLOG(2) << ...; 15// } 16// 17// The truth value that VLOG_IS_ON(level) returns is determined by 18// the three verbosity level flags: 19// --v=<n> Gives the default maximal active V-logging level; 20// 0 is the default. 21// Normally positive values are used for V-logging levels. 22// --vmodule=<str> Gives the per-module maximal V-logging levels to override 23// the value given by --v. 24// E.g. "my_module=2,foo*=3" would change the logging level 25// for all code in source files "my_module.*" and "foo*.*" 26// ("-inl" suffixes are also disregarded for this matching). 27// --silent_init When true has the effect of increasing 28// the argument of VLOG_IS_ON by 1, 29// thus suppressing one more level of verbose logging. 30// 31// SetVLOGLevel helper function is provided to do limited dynamic control over 32// V-logging by overriding the per-module settings given via --vmodule flag. 33// 34// CAVEAT: --vmodule functionality is not available in non gcc compilers. 35// 36 37#ifndef BASE_VLOG_IS_ON_H_ 38#define BASE_VLOG_IS_ON_H_ 39 40#include "base/atomicops.h" 41#include "base/basictypes.h" 42#include "base/port.h" 43#include "base/commandlineflags.h" 44#include "base/log_severity.h" 45 46DECLARE_int32(v); // in vlog_is_on.cc 47DECLARE_bool(silent_init); // in google.cc 48 49#if defined(__GNUC__) 50// We pack an int16 verbosity level and an int16 epoch into an 51// Atomic32 at every VLOG_IS_ON() call site. The level determines 52// whether the site should log, and the epoch determines whether the 53// site is stale and should be reinitialized. A verbosity level of 54// kUseFlag (-1) indicates that the value of FLAGS_v should be used as 55// the verbosity level. When the site is (re)initialized, a verbosity 56// level for the current source file is retrieved from an internal 57// list. This list is mutated through calls to SetVLOGLevel() and 58// mutations to the --vmodule flag. New log sites are initialized 59// with a stale epoch and a verbosity level of kUseFlag. 60// 61// TODO(llansing): Investigate using GCC's __builtin_constant_p() to 62// generate less code at call sites where verbositylevel is known to 63// be a compile-time constant. 64#define VLOG_IS_ON(verboselevel) \ 65 ({ static Atomic32 site__ = ::base::internal::kDefaultSite; \ 66 ::base::internal::VLogEnabled(&site__, (verboselevel), __FILE__); }) 67#else 68// GNU extensions not available, so we do not support --vmodule. 69// Dynamic value of FLAGS_v always controls the logging level. 70// 71// TODO(llansing): Investigate supporting --vmodule on other platforms. 72#define VLOG_IS_ON(verboselevel) \ 73 (FLAGS_v >= (verboselevel) + FLAGS_silent_init) 74#endif 75 76// Set VLOG(_IS_ON) level for module_pattern to log_level. 77// This lets us dynamically control what is normally set by the --vmodule flag. 78// Returns the level that previously applied to module_pattern. 79// NOTE: To change the log level for VLOG(_IS_ON) sites 80// that have already executed after/during InitGoogle, 81// one needs to supply the exact --vmodule pattern that applied to them. 82// (If no --vmodule pattern applied to them 83// the value of FLAGS_v will continue to control them.) 84int SetVLOGLevel(const char* module_pattern, int log_level); 85 86// Private implementation details. No user-serviceable parts inside. 87namespace base { 88namespace internal { 89 90// Each log site determines whether its log level is up to date by 91// comparing its epoch to this global epoch. Whenever the program's 92// vmodule configuration changes (ex: SetVLOGLevel is called), the 93// global epoch is advanced, invalidating all site epochs. 94extern Atomic32 vlog_epoch; 95 96// A log level of kUseFlag means "read the logging level from FLAGS_v." 97const int kUseFlag = -1; 98 99// Log sites use FLAGS_v by default, and have an initial epoch of 0. 100const Atomic32 kDefaultSite = kUseFlag << 16; 101 102// The global epoch is the least significant half of an Atomic32, and 103// may only be accessed through atomic operations. 104inline Atomic32 GlobalEpoch() { 105 return Acquire_Load(&vlog_epoch) & 0x0000FFFF; 106} 107 108// The least significant half of a site is the epoch. 109inline int SiteEpoch(Atomic32 site) { return site & 0x0000FFFF; } 110 111// The most significant half of a site is the logging level. 112inline int SiteLevel(Atomic32 site) { return site >> 16; } 113 114// Construct a logging site from a logging level and epoch. 115inline Atomic32 Site(int level, int epoch) { 116 return ((level & 0x0000FFFF) << 16) | (epoch & 0x0000FFFF); 117} 118 119// Attempt to initialize or reinitialize a VLOG site. Returns the 120// level of the log site, regardless of whether the attempt succeeds 121// or fails. 122// site: The address of the log site's state. 123// fname: The filename of the current source file. 124int InitVLOG(Atomic32* site, const char* fname); 125 126// Determine whether verbose logging should occur at a given log site. 127// 128// TODO(llansing): Find a way to eliminate FLAGS_silent_init from this 129// function while preserving the silent initialization behavior. The 130// common-case code path shouldn't pay for silent initialization. 131inline bool VLogEnabled(Atomic32* site, int32 level, const char* const file) { 132 const Atomic32 site_copy = Acquire_Load(site); 133 const int32 site_level = 134 PREDICT_TRUE(SiteEpoch(site_copy) == GlobalEpoch()) ? 135 SiteLevel(site_copy) : InitVLOG(site, file); 136 return (site_level == kUseFlag ? FLAGS_v : site_level) >= 137 (level + FLAGS_silent_init); 138} 139 140} // namespace internal 141} // namespace base 142 143#endif // BASE_VLOG_IS_ON_H_ 144