From 9b83dc9f0d3309ebe79f2c26bb3b71563bc28922 Mon Sep 17 00:00:00 2001 From: Derek Mauro Date: Wed, 6 Dec 2023 06:25:05 -0800 Subject: Move vlog_config to the internal directory and change the namespace of VLogSite PiperOrigin-RevId: 588403935 Change-Id: I6a3af3c044b887ec65b19390d316cfb3ccdcc853 --- absl/log/internal/vlog_config.h | 163 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 163 insertions(+) create mode 100644 absl/log/internal/vlog_config.h (limited to 'absl/log/internal/vlog_config.h') diff --git a/absl/log/internal/vlog_config.h b/absl/log/internal/vlog_config.h new file mode 100644 index 00000000..b6e322c4 --- /dev/null +++ b/absl/log/internal/vlog_config.h @@ -0,0 +1,163 @@ +// Copyright 2022 The Abseil Authors +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// ----------------------------------------------------------------------------- +// vlog_config.h +// ----------------------------------------------------------------------------- +// +// This header file defines `VLogSite`, a public primitive that represents +// a callsite for the `VLOG` family of macros and related libraries. +// It also declares and defines multiple internal utilities used to implement +// `VLOG`, such as `VLogSiteManager`. + +#ifndef ABSL_LOG_INTERNAL_VLOG_CONFIG_H_ +#define ABSL_LOG_INTERNAL_VLOG_CONFIG_H_ + +// IWYU pragma: private, include "absl/log/log.h" + +#include +#include +#include +#include +#include + +#include "absl/base/attributes.h" +#include "absl/base/config.h" +#include "absl/base/optimization.h" +#include "absl/base/thread_annotations.h" +#include "absl/strings/string_view.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace log_internal { + +class SyntheticBinary; +class VLogSite; + +int RegisterAndInitialize(VLogSite* v); +void UpdateVLogSites(); +constexpr int kUseFlag = (std::numeric_limits::min)(); + +// Represents a unique callsite for a `VLOG()` or `VLOG_IS_ON()` call. +// +// Libraries that provide `VLOG`-like functionality should use this to +// efficiently handle --vmodule. +// +// VLogSite objects must not be destroyed until the program exits. Doing so will +// probably yield nasty segfaults in VLogSiteManager::UpdateLogSites(). The +// recommendation is to make all such objects function-local statics. +class VLogSite final { + public: + // `f` must not be destroyed until the program exits. + explicit constexpr VLogSite(const char* f) + : file_(f), v_(kUninitialized), next_(nullptr) {} + VLogSite(const VLogSite&) = delete; + VLogSite& operator=(const VLogSite&) = delete; + + // Inlining the function yields a ~3x performance improvement at the cost of a + // 1.5x code size increase at the call site. + // Takes locks but does not allocate memory. + ABSL_ATTRIBUTE_ALWAYS_INLINE + bool IsEnabled(int level) { + int stale_v = v_.load(std::memory_order_relaxed); + if (ABSL_PREDICT_TRUE(level > stale_v)) { + return false; + } + + // We put everything other than the fast path, i.e. vlogging is initialized + // but not on, behind an out-of-line function to reduce code size. + // "level" is almost always a call-site constant, so we can save a bit + // of code space by special-casing for a few common levels. +#if ABSL_HAVE_BUILTIN(__builtin_constant_p) || defined(__GNUC__) + if (__builtin_constant_p(level)) { + if (level == 0) return SlowIsEnabled0(stale_v); + if (level == 1) return SlowIsEnabled1(stale_v); + if (level == 2) return SlowIsEnabled2(stale_v); + if (level == 3) return SlowIsEnabled3(stale_v); + if (level == 4) return SlowIsEnabled4(stale_v); + if (level == 5) return SlowIsEnabled5(stale_v); + } +#endif + return SlowIsEnabled(stale_v, level); + } + + private: + friend int log_internal::RegisterAndInitialize(VLogSite* v); + friend void log_internal::UpdateVLogSites(); + friend class log_internal::SyntheticBinary; + static constexpr int kUninitialized = (std::numeric_limits::max)(); + + // SlowIsEnabled performs slower checks to determine whether a log site is + // enabled. Because it is expected to be called somewhat rarely + // (comparatively), it is not inlined to save on code size. + // + // Prerequisites to calling SlowIsEnabled: + // 1) stale_v is uninitialized OR + // 2) stale_v is initialized and >= level (meaning we must log). + // Takes locks but does not allocate memory. + ABSL_ATTRIBUTE_NOINLINE + bool SlowIsEnabled(int stale_v, int level); + ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled0(int stale_v); + ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled1(int stale_v); + ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled2(int stale_v); + ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled3(int stale_v); + ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled4(int stale_v); + ABSL_ATTRIBUTE_NOINLINE bool SlowIsEnabled5(int stale_v); + + // This object is too size-sensitive to use absl::string_view. + const char* const file_; + std::atomic v_; + std::atomic next_; +}; +static_assert(std::is_trivially_destructible::value, + "VLogSite must be trivially destructible"); + +// Returns the current verbose log level of `file`. +// Does not allocate memory. +int VLogLevel(absl::string_view file); + +// Registers a site `v` to get updated as `vmodule` and `v` change. Also +// initializes the site based on their current values, and returns that result. +// Does not allocate memory. +int RegisterAndInitialize(VLogSite* v); + +// Allocates memory. +void UpdateVLogSites(); + +// Completely overwrites the saved value of `vmodule`. +// Allocates memory. +void UpdateVModule(absl::string_view vmodule); + +// Updates the global verbosity level to `v` and returns the prior value. +// Allocates memory. +int UpdateGlobalVLogLevel(int v); + +// Atomically prepends `module_pattern=log_level` to the start of vmodule. +// Returns the prior value for `module_pattern` if there was an exact match and +// `global_v` otherwise. +// Allocates memory. +int PrependVModule(absl::string_view module_pattern, int log_level); + +// Registers `on_update` to be called whenever `v` or `vmodule` change. +// Allocates memory. +void OnVLogVerbosityUpdate(std::function cb); + +// Does not allocate memory. +VLogSite* SetVModuleListHeadForTestOnly(VLogSite* v); + +} // namespace log_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_LOG_INTERNAL_VLOG_CONFIG_H_ -- cgit v1.2.3