diff options
Diffstat (limited to 'absl/flags/internal/flag.h')
| -rw-r--r-- | absl/flags/internal/flag.h | 237 |
1 files changed, 160 insertions, 77 deletions
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h index 2b21c440..ce0ccf2d 100644 --- a/absl/flags/internal/flag.h +++ b/absl/flags/internal/flag.h @@ -16,12 +16,15 @@ #ifndef ABSL_FLAGS_INTERNAL_FLAG_H_ #define ABSL_FLAGS_INTERNAL_FLAG_H_ +#include <atomic> #include <cstring> +#include "absl/base/thread_annotations.h" #include "absl/flags/internal/commandlineflag.h" #include "absl/flags/internal/registry.h" #include "absl/memory/memory.h" #include "absl/strings/str_cat.h" +#include "absl/synchronization/mutex.h" namespace absl { namespace flags_internal { @@ -66,6 +69,124 @@ using FlagCallback = void (*)(); void InvokeCallback(absl::Mutex* primary_mu, absl::Mutex* callback_mu, FlagCallback cb) ABSL_EXCLUSIVE_LOCKS_REQUIRED(primary_mu); +// The class encapsulates the Flag's data and safe access to it. +class FlagImpl { + public: + constexpr FlagImpl(const flags_internal::FlagOpFn op, + const flags_internal::FlagMarshallingOpFn marshalling_op, + const flags_internal::InitialValGenFunc initial_value_gen) + : op_(op), + marshalling_op_(marshalling_op), + initial_value_gen_(initial_value_gen) {} + + // Forces destruction of the Flag's data. + void Destroy() const; + + // Constant access methods + bool IsModified() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + bool IsSpecifiedOnCommandLine() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + std::string DefaultValue() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + std::string CurrentValue() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + void Read(const CommandLineFlag& flag, void* dst, + const flags_internal::FlagOpFn dst_op) const + ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + // Attempts to parse supplied `value` std::string. + bool TryParse(const CommandLineFlag& flag, void* dst, absl::string_view value, + std::string* err) const + ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu); + template <typename T> + bool AtomicGet(T* v) const { + const int64_t r = atomic_.load(std::memory_order_acquire); + if (r != flags_internal::AtomicInit()) { + std::memcpy(v, &r, sizeof(T)); + return true; + } + + return false; + } + + // Mutating access methods + void Write(const CommandLineFlag& flag, const void* src, + const flags_internal::FlagOpFn src_op) + ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + bool SetFromString(const CommandLineFlag& flag, absl::string_view value, + FlagSettingMode set_mode, ValueSource source, + std::string* err) ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + // If possible, updates copy of the Flag's value that is stored in an + // atomic word. + void StoreAtomic() ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu); + + // Interfaces to operate on callbacks. + void SetCallback(const flags_internal::FlagCallback mutation_callback) + ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + void InvokeCallback() const ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu); + + // Interfaces to save/restore mutable flag data + template <typename T> + std::unique_ptr<flags_internal::FlagStateInterface> SaveState( + Flag<T>* flag) const ABSL_LOCKS_EXCLUDED(locks_->primary_mu) { + T&& cur_value = flag->Get(); + absl::MutexLock l(DataGuard()); + + return absl::make_unique<flags_internal::FlagState<T>>( + flag, std::move(cur_value), modified_, on_command_line_, counter_); + } + bool RestoreState(const CommandLineFlag& flag, const void* value, + bool modified, bool on_command_line, int64_t counter) + ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + + // Value validation interfaces. + void CheckDefaultValueParsingRoundtrip(const CommandLineFlag& flag) const + ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + bool ValidateInputValue(absl::string_view value) const + ABSL_LOCKS_EXCLUDED(locks_->primary_mu); + + private: + // Lazy initialization of the Flag's data. + 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); + + // Immutable Flag's data. + const FlagOpFn op_; // Type-specific handler + const FlagMarshallingOpFn marshalling_op_; // Marshalling ops handler + const InitialValGenFunc initial_value_gen_; // Makes flag's initial value + + // Mutable Flag's data. (guarded by locks_->primary_mu). + // Indicates that locks_, cur_ and def_ fields have been lazily initialized. + std::atomic<bool> inited_{false}; + // Has flag value been modified? + bool modified_ ABSL_GUARDED_BY(locks_->primary_mu) = false; + // Specified on command line. + bool on_command_line_ ABSL_GUARDED_BY(locks_->primary_mu) = false; + // Lazily initialized pointer to default value + void* def_ ABSL_GUARDED_BY(locks_->primary_mu) = nullptr; + // Lazily initialized pointer to current value + void* cur_ ABSL_GUARDED_BY(locks_->primary_mu) = nullptr; + // Mutation counter + int64_t counter_ ABSL_GUARDED_BY(locks_->primary_mu) = 0; + // For some types, a copy of the current value is kept in an atomically + // accessible field. + std::atomic<int64_t> 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. +}; + // This is "unspecified" implementation of absl::Flag<T> type. template <typename T> class Flag final : public flags_internal::CommandLineFlag { @@ -76,30 +197,11 @@ class Flag final : public flags_internal::CommandLineFlag { const flags_internal::InitialValGenFunc initial_value_gen) : flags_internal::CommandLineFlag( name, flags_internal::HelpText::FromFunctionPointer(help_gen), - filename, &flags_internal::FlagOps<T>, marshalling_op, - initial_value_gen, - /*def=*/nullptr, - /*cur=*/nullptr), - atomic_(flags_internal::AtomicInit()), - callback_(nullptr) {} + filename), + impl_(&flags_internal::FlagOps<T>, marshalling_op, initial_value_gen) {} T Get() const { - // Implementation notes: - // - // We are wrapping a union around the value of `T` to serve three purposes: - // - // 1. `U.value` has correct size and alignment for a value of type `T` - // 2. The `U.value` constructor is not invoked since U's constructor does - // not - // do it explicitly. - // 3. The `U.value` destructor is invoked since U's destructor does it - // explicitly. This makes `U` a kind of RAII wrapper around non default - // constructible value of T, which is destructed when we leave the - // scope. We do need to destroy U.value, which is constructed by - // CommandLineFlag::Read even though we left it in a moved-from state - // after std::move. - // - // All of this serves to avoid requiring `T` being default constructible. + // See implementation notes in CommandLineFlag::Get(). union U { T value; U() {} @@ -107,89 +209,70 @@ class Flag final : public flags_internal::CommandLineFlag { }; U u; - Read(&u.value, &flags_internal::FlagOps<T>); + impl_.Read(*this, &u.value, &flags_internal::FlagOps<T>); return std::move(u.value); } - bool AtomicGet(T* v) const { - const int64_t r = atomic_.load(std::memory_order_acquire); - if (r != flags_internal::AtomicInit()) { - std::memcpy(v, &r, sizeof(T)); - return true; - } - - return false; - } + bool AtomicGet(T* v) const { return impl_.AtomicGet(v); } - void Set(const T& v) { Write(&v, &flags_internal::FlagOps<T>); } + void Set(const T& v) { impl_.Write(*this, &v, &flags_internal::FlagOps<T>); } void SetCallback(const flags_internal::FlagCallback mutation_callback) { - absl::MutexLock l(InitFlagIfNecessary()); - - callback_ = mutation_callback; - - InvokeCallback(); + impl_.SetCallback(mutation_callback); } - private: - friend class FlagState<T>; - - void Destroy() const override { - // Values are heap allocated for Abseil Flags. - if (cur_) Delete(op_, cur_); - if (def_) Delete(op_, def_); - - delete locks_; + // CommandLineFlag interface + bool IsModified() const override { return impl_.IsModified(); } + bool IsSpecifiedOnCommandLine() const override { + return impl_.IsSpecifiedOnCommandLine(); } + std::string DefaultValue() const override { return impl_.DefaultValue(); } + std::string CurrentValue() const override { return impl_.CurrentValue(); } - void StoreAtomic() override { - if (sizeof(T) <= sizeof(int64_t)) { - int64_t t = 0; - std::memcpy(&t, cur_, (std::min)(sizeof(T), sizeof(int64_t))); - atomic_.store(t, std::memory_order_release); - } + bool ValidateInputValue(absl::string_view value) const override { + return impl_.ValidateInputValue(value); } // Interfaces to save and restore flags to/from persistent state. // Returns current flag state or nullptr if flag does not support // saving and restoring a state. std::unique_ptr<flags_internal::FlagStateInterface> SaveState() override { - T curr_value = Get(); - - absl::MutexLock l(InitFlagIfNecessary()); - - return absl::make_unique<flags_internal::FlagState<T>>( - this, std::move(curr_value), modified_, on_command_line_, counter_); + return impl_.SaveState(this); } // Restores the flag state to the supplied state object. If there is // nothing to restore returns false. Otherwise returns true. bool RestoreState(const flags_internal::FlagState<T>& flag_state) { - if (MutationCounter() == flag_state.counter_) return false; - - Set(flag_state.cur_value_); + return impl_.RestoreState(*this, &flag_state.cur_value_, + flag_state.modified_, flag_state.on_command_line_, + flag_state.counter_); + } - // Race condition here? This should disappear once we move the rest of the - // flag's data into Flag's internals. + bool SetFromString(absl::string_view value, + flags_internal::FlagSettingMode set_mode, + flags_internal::ValueSource source, + std::string* error) override { + return impl_.SetFromString(*this, value, set_mode, source, error); + } - absl::MutexLock l(InitFlagIfNecessary()); - modified_ = flag_state.modified_; - on_command_line_ = flag_state.on_command_line_; - return true; + void CheckDefaultValueParsingRoundtrip() const override { + impl_.CheckDefaultValueParsingRoundtrip(*this); } - // Interfaces to overate on callbacks. - void InvokeCallback() override - ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) { - flags_internal::InvokeCallback(&locks_->primary_mu, &locks_->callback_mu, - callback_); + private: + friend class FlagState<T>; + + void Destroy() const override { impl_.Destroy(); } + + void Read(void* dst) const override { + impl_.Read(*this, dst, &flags_internal::FlagOps<T>); + } + flags_internal::FlagOpFn TypeId() const override { + return &flags_internal::FlagOps<T>; } // Flag's data - // For some types, a copy of the current value is kept in an atomically - // accessible field. - std::atomic<int64_t> atomic_; - FlagCallback callback_; // Mutation callback + FlagImpl impl_; }; template <typename T> |