From 4b2fbb4adba905eede6c61b4494acfdb660a3bb7 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Mon, 12 Oct 2020 10:33:47 -0700 Subject: Export of internal Abseil changes -- a5af5874c1c5cc02bd2a748d455321f82b6f2a93 by Andy Getzendanner : fix compile fails with asan and -Wredundant-decls Import of https://github.com/abseil/abseil-cpp/pull/801 PiperOrigin-RevId: 336693223 -- ed9df42ab2b742386c6692c2bed015374c919d9c by Derek Mauro : Fix integer conversion warning Fixes #814 PiperOrigin-RevId: 336651814 -- 0ab4c23884e72dce17b67c1eb520f9dbb802565d by Derek Mauro : Internal change PiperOrigin-RevId: 336585378 -- eba0e3dccd52a6e91bcff84075bef0affc650b74 by Matt Kulukundis : Add bitset operations to Futex helper. PiperOrigin-RevId: 336409368 -- 8b0709a8b4500bf5f0af4b602d76a298d81645e8 by Abseil Team : Fix code indentation in a comment. PiperOrigin-RevId: 336368167 -- bc3961c87a7e7760c10319a5b0349c279f7ae3ad by Samuel Benzaquen : Improve performance of the registry: - Reduce contention - Reduce memory usage for each flag by `6*sizeof(void*)`. - Replace one immortal allocation per-flag with a single one for all the flags - Slightly improve single-threaded performance by avoiding the std::map indirections. PiperOrigin-RevId: 336365904 -- 264ad9f28f935aad8b6b1437f8bf804fa9104346 by Abseil Team : Fix typo in comment on absl::Condition. PiperOrigin-RevId: 336311680 -- b5b808a8c75ca0df7b09eff9a423ec171d80f771 by Derek Mauro : Add missing Apache license headers PiperOrigin-RevId: 336294980 -- 89446c3a4793df8b95060385cf3e219357c3db1d by Andy Soffer : Internal changes PiperOrigin-RevId: 336287465 -- 57c8be4e294881bc79a6a44b8e4bf7ecbb19b9b9 by Matt Kulukundis : Extract Futex from an implementation detail of Wait to a private interface. PiperOrigin-RevId: 336123209 GitOrigin-RevId: a5af5874c1c5cc02bd2a748d455321f82b6f2a93 Change-Id: Ie5a0ebe28e571814e3e11d4c05ca308523ccf311 --- absl/flags/reflection.cc | 68 +++++++++++++++++++++++++++++++----------------- 1 file changed, 44 insertions(+), 24 deletions(-) (limited to 'absl/flags/reflection.cc') diff --git a/absl/flags/reflection.cc b/absl/flags/reflection.cc index d7060221..c6bf8aab 100644 --- a/absl/flags/reflection.cc +++ b/absl/flags/reflection.cc @@ -17,6 +17,7 @@ #include +#include #include #include @@ -56,21 +57,23 @@ class FlagRegistry { // Returns the flag object for the specified name, or nullptr if not found. // Will emit a warning if a 'retired' flag is specified. - CommandLineFlag* FindFlagLocked(absl::string_view name); + CommandLineFlag* FindFlag(absl::string_view name); static FlagRegistry& GlobalRegistry(); // returns a singleton registry private: friend class flags_internal::FlagSaverImpl; // reads all the flags in order // to copy them - friend void ForEachFlagUnlocked( - std::function visitor); + friend void ForEachFlag(std::function visitor); + friend void FinalizeRegistry(); - // The map from name to flag, for FindFlagLocked(). + // The map from name to flag, for FindFlag(). using FlagMap = std::map; using FlagIterator = FlagMap::iterator; using FlagConstIterator = FlagMap::const_iterator; FlagMap flags_; + std::vector flat_flags_; + std::atomic finalized_flags_{false}; absl::Mutex lock_; @@ -79,15 +82,6 @@ class FlagRegistry { FlagRegistry& operator=(const FlagRegistry&); }; -CommandLineFlag* FlagRegistry::FindFlagLocked(absl::string_view name) { - FlagConstIterator i = flags_.find(name); - if (i == flags_.end()) { - return nullptr; - } - - return i->second; -} - namespace { class FlagRegistryLock { @@ -101,8 +95,24 @@ class FlagRegistryLock { } // namespace +CommandLineFlag* FlagRegistry::FindFlag(absl::string_view name) { + if (finalized_flags_.load(std::memory_order_acquire)) { + // We could save some gcus here if we make `Name()` be non-virtual. + // We could move the `const char*` name to the base class. + auto it = std::partition_point( + flat_flags_.begin(), flat_flags_.end(), + [=](CommandLineFlag* f) { return f->Name() < name; }); + if (it != flat_flags_.end() && (*it)->Name() == name) return *it; + } + + FlagRegistryLock frl(*this); + auto it = flags_.find(name); + return it != flags_.end() ? it->second : nullptr; +} + void FlagRegistry::RegisterFlag(CommandLineFlag& flag) { FlagRegistryLock registry_lock(*this); + std::pair ins = flags_.insert(FlagMap::value_type(flag.Name(), &flag)); if (ins.second == false) { // means the name was already in the map @@ -152,18 +162,15 @@ FlagRegistry& FlagRegistry::GlobalRegistry() { // -------------------------------------------------------------------- -void ForEachFlagUnlocked(std::function visitor) { +void ForEachFlag(std::function visitor) { FlagRegistry& registry = FlagRegistry::GlobalRegistry(); - for (FlagRegistry::FlagConstIterator i = registry.flags_.begin(); - i != registry.flags_.end(); ++i) { - visitor(*i->second); + + if (registry.finalized_flags_.load(std::memory_order_acquire)) { + for (const auto& i : registry.flat_flags_) visitor(*i); } -} -void ForEachFlag(std::function visitor) { - FlagRegistry& registry = FlagRegistry::GlobalRegistry(); FlagRegistryLock frl(registry); - ForEachFlagUnlocked(visitor); + for (const auto& i : registry.flags_) visitor(*i.second); } // -------------------------------------------------------------------- @@ -173,6 +180,21 @@ bool RegisterCommandLineFlag(CommandLineFlag& flag) { return true; } +void FinalizeRegistry() { + auto& registry = FlagRegistry::GlobalRegistry(); + FlagRegistryLock frl(registry); + if (registry.finalized_flags_.load(std::memory_order_relaxed)) { + // Was already finalized. Ignore the second time. + return; + } + registry.flat_flags_.reserve(registry.flags_.size()); + for (const auto& f : registry.flags_) { + registry.flat_flags_.push_back(f.second); + } + registry.flags_.clear(); + registry.finalized_flags_.store(true, std::memory_order_release); +} + // -------------------------------------------------------------------- namespace { @@ -298,9 +320,7 @@ CommandLineFlag* FindCommandLineFlag(absl::string_view name) { if (name.empty()) return nullptr; flags_internal::FlagRegistry& registry = flags_internal::FlagRegistry::GlobalRegistry(); - flags_internal::FlagRegistryLock frl(registry); - - return registry.FindFlagLocked(name); + return registry.FindFlag(name); } // -------------------------------------------------------------------- -- cgit v1.2.3