From 12bc53e0318d80569270a5b26ccbc62b52022b89 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Thu, 12 Dec 2019 10:36:03 -0800 Subject: Export of internal Abseil changes -- c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro : Remove a floating point division by zero test. This isn't testing behavior related to the library, and MSVC warns about it in opt mode. PiperOrigin-RevId: 285220804 -- 68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental : This CL introduces following changes to the class FlagImpl: * We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately. * CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now. * Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call. * We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced. PiperOrigin-RevId: 285132636 -- ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck : Change null-term* (and nul-term*) to NUL-term* in comments PiperOrigin-RevId: 285036610 -- 729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro : Use the Posix implementation of thread identity on MinGW. Some versions of MinGW suffer from thread_local bugs. PiperOrigin-RevId: 285022920 -- 39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon : Implementation detail change. Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil. PiperOrigin-RevId: 285012012 GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1 --- absl/flags/internal/flag.h | 54 +++++++++++++++++++++++++--------------------- 1 file changed, 29 insertions(+), 25 deletions(-) (limited to 'absl/flags/internal/flag.h') diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h index 947a8ca..20de406 100644 --- a/absl/flags/internal/flag.h +++ b/absl/flags/internal/flag.h @@ -27,6 +27,7 @@ #include "absl/synchronization/mutex.h" namespace absl { +ABSL_NAMESPACE_BEGIN namespace flags_internal { constexpr int64_t AtomicInit() { return 0xababababababababll; } @@ -156,10 +157,11 @@ class FlagImpl { help_(help.source), help_source_kind_(help.kind), def_kind_(flags_internal::FlagDefaultSrcKind::kGenFunc), - default_src_(default_value_gen) {} + default_src_(default_value_gen), + data_guard_{} {} // Forces destruction of the Flag's data. - void Destroy() const; + void Destroy(); // Constant access methods std::string Help() const; @@ -170,9 +172,10 @@ class FlagImpl { void Read(const CommandLineFlag& flag, void* dst, const flags_internal::FlagOpFn dst_op) const ABSL_LOCKS_EXCLUDED(*DataGuard()); - // Attempts to parse supplied `value` std::string. - bool TryParse(const CommandLineFlag& flag, void* dst, absl::string_view value, - std::string* err) const + // Attempts to parse supplied `value` std::string. If parsing is successful, then + // it replaces `dst` with the new value. + bool TryParse(const CommandLineFlag& flag, void** dst, + absl::string_view value, std::string* err) const ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); template bool AtomicGet(T* v) const { @@ -226,8 +229,7 @@ class FlagImpl { void Init(); // Ensures that the lazily initialized data is initialized, // and returns pointer to the mutex guarding flags data. - absl::Mutex* DataGuard() const ABSL_LOCK_RETURNED(locks_->primary_mu); - + absl::Mutex* DataGuard() const ABSL_LOCK_RETURNED((absl::Mutex*)&data_guard_); // Returns heap allocated value of type T initialized with default value. std::unique_ptr MakeInitValue() const ABSL_EXCLUSIVE_LOCKS_REQUIRED(*DataGuard()); @@ -239,9 +241,12 @@ class FlagImpl { // Indicates if help message was supplied as literal or generator func. const FlagHelpSrcKind help_source_kind_; - // Mutable Flag's data. (guarded by DataGuard()). - // Indicates that locks_ and cur_ fields have been lazily initialized. + // Indicates that the Flag state is initialized. std::atomic inited_{false}; + // Mutable Flag state (guarded by data_guard_). + // Additional bool to protect against multiple concurrent constructions + // of `data_guard_`. + bool is_data_guard_inited_ = false; // Has flag value been modified? bool modified_ ABSL_GUARDED_BY(*DataGuard()) = false; // Specified on command line. @@ -261,22 +266,20 @@ class FlagImpl { // For some types, a copy of the current value is kept in an atomically // accessible field. std::atomic atomic_{flags_internal::AtomicInit()}; - // Mutation callback - FlagCallback callback_ = nullptr; - - // Lazily initialized mutexes for this flag value. We cannot inline a - // SpinLock or Mutex here because those have non-constexpr constructors and - // so would prevent constant initialization of this type. - // TODO(rogeeff): fix it once Mutex has constexpr constructor - // The following struct contains the locks in a CommandLineFlag struct. - // They are in a separate struct that is lazily allocated to avoid problems - // with static initialization and to avoid multiple allocations. - struct CommandLineFlagLocks { - absl::Mutex primary_mu; // protects several fields in CommandLineFlag - absl::Mutex callback_mu; // used to serialize callbacks - }; - CommandLineFlagLocks* locks_ = nullptr; // locks, laziliy allocated. + struct CallbackData { + FlagCallback func; + absl::Mutex guard; // Guard for concurrent callback invocations. + }; + CallbackData* callback_data_ ABSL_GUARDED_BY(*DataGuard()) = nullptr; + // This is reserved space for an absl::Mutex to guard flag data. It will be + // initialized in FlagImpl::Init via placement new. + // We can't use "absl::Mutex data_guard_", since this class is not literal. + // We do not want to use "absl::Mutex* data_guard_", since this would require + // heap allocation during initialization, which is both slows program startup + // and can fail. Using reserved space + placement new allows us to avoid both + // problems. + alignas(absl::Mutex) mutable char data_guard_[sizeof(absl::Mutex)]; }; // This is "unspecified" implementation of absl::Flag type. @@ -354,7 +357,7 @@ class Flag final : public flags_internal::CommandLineFlag { private: friend class FlagState; - void Destroy() const override { impl_.Destroy(); } + void Destroy() override { impl_.Destroy(); } void Read(void* dst) const override { impl_.Read(*this, dst, &flags_internal::FlagOps); @@ -414,6 +417,7 @@ T* MakeFromDefaultValue(EmptyBraces) { } } // namespace flags_internal +ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_FLAGS_INTERNAL_FLAG_H_ -- cgit v1.2.3