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Diffstat (limited to 'third_party/cld/base/vlog_is_on.h')
| -rw-r--r-- | third_party/cld/base/vlog_is_on.h | 141 |
1 files changed, 141 insertions, 0 deletions
diff --git a/third_party/cld/base/vlog_is_on.h b/third_party/cld/base/vlog_is_on.h new file mode 100644 index 0000000..57c11ff --- /dev/null +++ b/third_party/cld/base/vlog_is_on.h @@ -0,0 +1,141 @@ +// 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 "third_party/cld/base/commandlineflags.h" +#include "third_party/cld/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_ |