// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. // Defines the VLOG_IS_ON macro that controls the variable-verbosity // conditional logging. // // It's used by VLOG and VLOG_IF in logging.h // and by RAW_VLOG in raw_logging.h to trigger the logging. // // It can also be used directly e.g. like this: // if (VLOG_IS_ON(2)) { // // do some logging preparation and logging // // that can't be accomplished e.g. via just VLOG(2) << ...; // } // // The truth value that VLOG_IS_ON(level) returns is determined by // the three verbosity level flags: // --v=<n> Gives the default maximal active V-logging level; // 0 is the default. // Normally positive values are used for V-logging levels. // --vmodule=<str> Gives the per-module maximal V-logging levels to override // the value given by --v. // E.g. "my_module=2,foo*=3" would change the logging level // for all code in source files "my_module.*" and "foo*.*" // ("-inl" suffixes are also disregarded for this matching). // --silent_init When true has the effect of increasing // the argument of VLOG_IS_ON by 1, // thus suppressing one more level of verbose logging. // // SetVLOGLevel helper function is provided to do limited dynamic control over // V-logging by overriding the per-module settings given via --vmodule flag. // // CAVEAT: --vmodule functionality is not available in non gcc compilers. // #ifndef BASE_VLOG_IS_ON_H_ #define BASE_VLOG_IS_ON_H_ #include "base/atomicops.h" #include "base/basictypes.h" #include "base/port.h" #include "base/commandlineflags.h" #include "base/log_severity.h" DECLARE_int32(v); // in vlog_is_on.cc DECLARE_bool(silent_init); // in google.cc #if defined(__GNUC__) // We pack an int16 verbosity level and an int16 epoch into an // Atomic32 at every VLOG_IS_ON() call site. The level determines // whether the site should log, and the epoch determines whether the // site is stale and should be reinitialized. A verbosity level of // kUseFlag (-1) indicates that the value of FLAGS_v should be used as // the verbosity level. When the site is (re)initialized, a verbosity // level for the current source file is retrieved from an internal // list. This list is mutated through calls to SetVLOGLevel() and // mutations to the --vmodule flag. New log sites are initialized // with a stale epoch and a verbosity level of kUseFlag. // // TODO(llansing): Investigate using GCC's __builtin_constant_p() to // generate less code at call sites where verbositylevel is known to // be a compile-time constant. #define VLOG_IS_ON(verboselevel) \ ({ static Atomic32 site__ = ::base::internal::kDefaultSite; \ ::base::internal::VLogEnabled(&site__, (verboselevel), __FILE__); }) #else // GNU extensions not available, so we do not support --vmodule. // Dynamic value of FLAGS_v always controls the logging level. // // TODO(llansing): Investigate supporting --vmodule on other platforms. #define VLOG_IS_ON(verboselevel) \ (FLAGS_v >= (verboselevel) + FLAGS_silent_init) #endif // Set VLOG(_IS_ON) level for module_pattern to log_level. // This lets us dynamically control what is normally set by the --vmodule flag. // Returns the level that previously applied to module_pattern. // NOTE: To change the log level for VLOG(_IS_ON) sites // that have already executed after/during InitGoogle, // one needs to supply the exact --vmodule pattern that applied to them. // (If no --vmodule pattern applied to them // the value of FLAGS_v will continue to control them.) int SetVLOGLevel(const char* module_pattern, int log_level); // Private implementation details. No user-serviceable parts inside. namespace base { namespace internal { // Each log site determines whether its log level is up to date by // comparing its epoch to this global epoch. Whenever the program's // vmodule configuration changes (ex: SetVLOGLevel is called), the // global epoch is advanced, invalidating all site epochs. extern Atomic32 vlog_epoch; // A log level of kUseFlag means "read the logging level from FLAGS_v." const int kUseFlag = -1; // Log sites use FLAGS_v by default, and have an initial epoch of 0. const Atomic32 kDefaultSite = kUseFlag << 16; // The global epoch is the least significant half of an Atomic32, and // may only be accessed through atomic operations. inline Atomic32 GlobalEpoch() { return Acquire_Load(&vlog_epoch) & 0x0000FFFF; } // The least significant half of a site is the epoch. inline int SiteEpoch(Atomic32 site) { return site & 0x0000FFFF; } // The most significant half of a site is the logging level. inline int SiteLevel(Atomic32 site) { return site >> 16; } // Construct a logging site from a logging level and epoch. inline Atomic32 Site(int level, int epoch) { return ((level & 0x0000FFFF) << 16) | (epoch & 0x0000FFFF); } // Attempt to initialize or reinitialize a VLOG site. Returns the // level of the log site, regardless of whether the attempt succeeds // or fails. // site: The address of the log site's state. // fname: The filename of the current source file. int InitVLOG(Atomic32* site, const char* fname); // Determine whether verbose logging should occur at a given log site. // // TODO(llansing): Find a way to eliminate FLAGS_silent_init from this // function while preserving the silent initialization behavior. The // common-case code path shouldn't pay for silent initialization. inline bool VLogEnabled(Atomic32* site, int32 level, const char* const file) { const Atomic32 site_copy = Acquire_Load(site); const int32 site_level = PREDICT_TRUE(SiteEpoch(site_copy) == GlobalEpoch()) ? SiteLevel(site_copy) : InitVLOG(site, file); return (site_level == kUseFlag ? FLAGS_v : site_level) >= (level + FLAGS_silent_init); } } // namespace internal } // namespace base #endif // BASE_VLOG_IS_ON_H_