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Diffstat (limited to 'third_party/abseil-cpp/absl/strings/internal/cordz_info.h')
| -rw-r--r-- | third_party/abseil-cpp/absl/strings/internal/cordz_info.h | 298 |
1 files changed, 298 insertions, 0 deletions
diff --git a/third_party/abseil-cpp/absl/strings/internal/cordz_info.h b/third_party/abseil-cpp/absl/strings/internal/cordz_info.h new file mode 100644 index 0000000000..026d5b9981 --- /dev/null +++ b/third_party/abseil-cpp/absl/strings/internal/cordz_info.h @@ -0,0 +1,298 @@ +// Copyright 2019 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. + +#ifndef ABSL_STRINGS_CORDZ_INFO_H_ +#define ABSL_STRINGS_CORDZ_INFO_H_ + +#include <atomic> +#include <cstdint> +#include <functional> + +#include "absl/base/config.h" +#include "absl/base/internal/raw_logging.h" +#include "absl/base/internal/spinlock.h" +#include "absl/base/thread_annotations.h" +#include "absl/strings/internal/cord_internal.h" +#include "absl/strings/internal/cordz_functions.h" +#include "absl/strings/internal/cordz_handle.h" +#include "absl/strings/internal/cordz_statistics.h" +#include "absl/strings/internal/cordz_update_tracker.h" +#include "absl/synchronization/mutex.h" +#include "absl/types/span.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace cord_internal { + +// CordzInfo tracks a profiled Cord. Each of these objects can be in two places. +// If a Cord is alive, the CordzInfo will be in the global_cordz_infos map, and +// can also be retrieved via the linked list starting with +// global_cordz_infos_head and continued via the cordz_info_next() method. When +// a Cord has reached the end of its lifespan, the CordzInfo object will be +// migrated out of the global_cordz_infos list and the global_cordz_infos_map, +// and will either be deleted or appended to the global_delete_queue. If it is +// placed on the global_delete_queue, the CordzInfo object will be cleaned in +// the destructor of a CordzSampleToken object. +class ABSL_LOCKABLE CordzInfo : public CordzHandle { + public: + using MethodIdentifier = CordzUpdateTracker::MethodIdentifier; + + // TrackCord creates a CordzInfo instance which tracks important metrics of + // a sampled cord, and stores the created CordzInfo instance into `cord'. All + // CordzInfo instances are placed in a global list which is used to discover + // and snapshot all actively tracked cords. Callers are responsible for + // calling UntrackCord() before the tracked Cord instance is deleted, or to + // stop tracking the sampled Cord. Callers are also responsible for guarding + // changes to the 'tree' value of a Cord (InlineData.tree) through the Lock() + // and Unlock() calls. Any change resulting in a new tree value for the cord + // requires a call to SetCordRep() before the old tree has been unreffed + // and/or deleted. `method` identifies the Cord public API method initiating + // the cord to be sampled. + // Requires `cord` to hold a tree, and `cord.cordz_info()` to be null. + static void TrackCord(InlineData& cord, MethodIdentifier method); + + // Identical to TrackCord(), except that this function fills the + // `parent_stack` and `parent_method` properties of the returned CordzInfo + // instance from the provided `src` instance if `src` is sampled. + // This function should be used for sampling 'copy constructed' and 'copy + // assigned' cords. This function allows 'cord` to be already sampled, in + // which case the CordzInfo will be newly created from `src`. + static void TrackCord(InlineData& cord, const InlineData& src, + MethodIdentifier method); + + // Maybe sample the cord identified by 'cord' for method 'method'. + // Uses `cordz_should_profile` to randomly pick cords to be sampled, and if + // so, invokes `TrackCord` to start sampling `cord`. + static void MaybeTrackCord(InlineData& cord, MethodIdentifier method); + + // Maybe sample the cord identified by 'cord' for method 'method'. + // `src` identifies a 'parent' cord which is assigned to `cord`, typically the + // input cord for a copy constructor, or an assign method such as `operator=` + // `cord` will be sampled if (and only if) `src` is sampled. + // If `cord` is currently being sampled and `src` is not being sampled, then + // this function will stop sampling the cord and reset the cord's cordz_info. + // + // Previously this function defined that `cord` will be sampled if either + // `src` is sampled, or if `cord` is randomly picked for sampling. However, + // this can cause issues, as there may be paths where some cord is assigned an + // indirect copy of it's own value. As such a 'string of copies' would then + // remain sampled (`src.is_profiled`), then assigning such a cord back to + // 'itself' creates a cycle where the cord will converge to 'always sampled`. + // + // For example: + // + // Cord x; + // for (...) { + // // Copy ctor --> y.is_profiled := x.is_profiled | random(...) + // Cord y = x; + // ... + // // Assign x = y --> x.is_profiled = y.is_profiled | random(...) + // // ==> x.is_profiled |= random(...) + // // ==> x converges to 'always profiled' + // x = y; + // } + static void MaybeTrackCord(InlineData& cord, const InlineData& src, + MethodIdentifier method); + + // Stops tracking changes for a sampled cord, and deletes the provided info. + // This function must be called before the sampled cord instance is deleted, + // and before the root cordrep of the sampled cord is unreffed. + // This function may extend the lifetime of the cordrep in cases where the + // CordInfo instance is being held by a concurrent collection thread. + void Untrack(); + + // Invokes UntrackCord() on `info` if `info` is not null. + static void MaybeUntrackCord(CordzInfo* info); + + CordzInfo() = delete; + CordzInfo(const CordzInfo&) = delete; + CordzInfo& operator=(const CordzInfo&) = delete; + + // Retrieves the oldest existing CordzInfo. + static CordzInfo* Head(const CordzSnapshot& snapshot) + ABSL_NO_THREAD_SAFETY_ANALYSIS; + + // Retrieves the next oldest existing CordzInfo older than 'this' instance. + CordzInfo* Next(const CordzSnapshot& snapshot) const + ABSL_NO_THREAD_SAFETY_ANALYSIS; + + // Locks this instance for the update identified by `method`. + // Increases the count for `method` in `update_tracker`. + void Lock(MethodIdentifier method) ABSL_EXCLUSIVE_LOCK_FUNCTION(mutex_); + + // Unlocks this instance. If the contained `rep` has been set to null + // indicating the Cord has been cleared or is otherwise no longer sampled, + // then this method will delete this CordzInfo instance. + void Unlock() ABSL_UNLOCK_FUNCTION(mutex_); + + // Asserts that this CordzInfo instance is locked. + void AssertHeld() ABSL_ASSERT_EXCLUSIVE_LOCK(mutex_); + + // Updates the `rep` property of this instance. This methods is invoked by + // Cord logic each time the root node of a sampled Cord changes, and before + // the old root reference count is deleted. This guarantees that collection + // code can always safely take a reference on the tracked cord. + // Requires a lock to be held through the `Lock()` method. + // TODO(b/117940323): annotate with ABSL_EXCLUSIVE_LOCKS_REQUIRED once all + // Cord code is in a state where this can be proven true by the compiler. + void SetCordRep(CordRep* rep); + + // Returns the current `rep` property of this instance with a reference + // added, or null if this instance represents a cord that has since been + // deleted or untracked. + CordRep* RefCordRep() const ABSL_LOCKS_EXCLUDED(mutex_); + + // Returns the current value of `rep_` for testing purposes only. + CordRep* GetCordRepForTesting() const ABSL_NO_THREAD_SAFETY_ANALYSIS { + return rep_; + } + + // Sets the current value of `rep_` for testing purposes only. + void SetCordRepForTesting(CordRep* rep) ABSL_NO_THREAD_SAFETY_ANALYSIS { + rep_ = rep; + } + + // Returns the stack trace for where the cord was first sampled. Cords are + // potentially sampled when they promote from an inlined cord to a tree or + // ring representation, which is not necessarily the location where the cord + // was first created. Some cords are created as inlined cords, and only as + // data is added do they become a non-inlined cord. However, typically the + // location represents reasonably well where the cord is 'created'. + absl::Span<void* const> GetStack() const; + + // Returns the stack trace for a sampled cord's 'parent stack trace'. This + // value may be set if the cord is sampled (promoted) after being created + // from, or being assigned the value of an existing (sampled) cord. + absl::Span<void* const> GetParentStack() const; + + // Retrieves the CordzStatistics associated with this Cord. The statistics + // are only updated when a Cord goes through a mutation, such as an Append + // or RemovePrefix. + CordzStatistics GetCordzStatistics() const; + + private: + using SpinLock = absl::base_internal::SpinLock; + using SpinLockHolder = ::absl::base_internal::SpinLockHolder; + + // Global cordz info list. CordzInfo stores a pointer to the global list + // instance to harden against ODR violations. + struct List { + constexpr explicit List(absl::ConstInitType) + : mutex(absl::kConstInit, + absl::base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL) {} + + SpinLock mutex; + std::atomic<CordzInfo*> head ABSL_GUARDED_BY(mutex){nullptr}; + }; + + static constexpr int kMaxStackDepth = 64; + + explicit CordzInfo(CordRep* rep, const CordzInfo* src, + MethodIdentifier method); + ~CordzInfo() override; + + // Sets `rep_` without holding a lock. + void UnsafeSetCordRep(CordRep* rep) ABSL_NO_THREAD_SAFETY_ANALYSIS; + + void Track(); + + // Returns the parent method from `src`, which is either `parent_method_` or + // `method_` depending on `parent_method_` being kUnknown. + // Returns kUnknown if `src` is null. + static MethodIdentifier GetParentMethod(const CordzInfo* src); + + // Fills the provided stack from `src`, copying either `parent_stack_` or + // `stack_` depending on `parent_stack_` being empty, returning the size of + // the parent stack. + // Returns 0 if `src` is null. + static int FillParentStack(const CordzInfo* src, void** stack); + + void ODRCheck() const { +#ifndef NDEBUG + ABSL_RAW_CHECK(list_ == &global_list_, "ODR violation in Cord"); +#endif + } + + // Non-inlined implementation of `MaybeTrackCord`, which is executed if + // either `src` is sampled or `cord` is sampled, and either untracks or + // tracks `cord` as documented per `MaybeTrackCord`. + static void MaybeTrackCordImpl(InlineData& cord, const InlineData& src, + MethodIdentifier method); + + ABSL_CONST_INIT static List global_list_; + List* const list_ = &global_list_; + + // ci_prev_ and ci_next_ require the global list mutex to be held. + // Unfortunately we can't use thread annotations such that the thread safety + // analysis understands that list_ and global_list_ are one and the same. + std::atomic<CordzInfo*> ci_prev_{nullptr}; + std::atomic<CordzInfo*> ci_next_{nullptr}; + + mutable absl::Mutex mutex_; + CordRep* rep_ ABSL_GUARDED_BY(mutex_); + + void* stack_[kMaxStackDepth]; + void* parent_stack_[kMaxStackDepth]; + const int stack_depth_; + const int parent_stack_depth_; + const MethodIdentifier method_; + const MethodIdentifier parent_method_; + CordzUpdateTracker update_tracker_; + const absl::Time create_time_; +}; + +inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeTrackCord( + InlineData& cord, MethodIdentifier method) { + if (ABSL_PREDICT_FALSE(cordz_should_profile())) { + TrackCord(cord, method); + } +} + +inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeTrackCord( + InlineData& cord, const InlineData& src, MethodIdentifier method) { + if (ABSL_PREDICT_FALSE(InlineData::is_either_profiled(cord, src))) { + MaybeTrackCordImpl(cord, src, method); + } +} + +inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CordzInfo::MaybeUntrackCord( + CordzInfo* info) { + if (ABSL_PREDICT_FALSE(info)) { + info->Untrack(); + } +} + +inline void CordzInfo::AssertHeld() ABSL_ASSERT_EXCLUSIVE_LOCK(mutex_) { +#ifndef NDEBUG + mutex_.AssertHeld(); +#endif +} + +inline void CordzInfo::SetCordRep(CordRep* rep) { + AssertHeld(); + rep_ = rep; +} + +inline void CordzInfo::UnsafeSetCordRep(CordRep* rep) { rep_ = rep; } + +inline CordRep* CordzInfo::RefCordRep() const ABSL_LOCKS_EXCLUDED(mutex_) { + MutexLock lock(&mutex_); + return rep_ ? CordRep::Ref(rep_) : nullptr; +} + +} // namespace cord_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_STRINGS_CORDZ_INFO_H_ |