diff options
Diffstat (limited to 'third_party/abseil_cpp/absl/flags/internal/flag.cc')
| -rw-r--r-- | third_party/abseil_cpp/absl/flags/internal/flag.cc | 564 |
1 files changed, 564 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/flags/internal/flag.cc b/third_party/abseil_cpp/absl/flags/internal/flag.cc new file mode 100644 index 000000000000..96c026dcb5d2 --- /dev/null +++ b/third_party/abseil_cpp/absl/flags/internal/flag.cc @@ -0,0 +1,564 @@ +// +// 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. + +#include "absl/flags/internal/flag.h" + +#include <stddef.h> +#include <stdint.h> +#include <string.h> + +#include <atomic> +#include <memory> +#include <string> +#include <vector> + +#include "absl/base/attributes.h" +#include "absl/base/casts.h" +#include "absl/base/config.h" +#include "absl/base/const_init.h" +#include "absl/base/optimization.h" +#include "absl/flags/internal/commandlineflag.h" +#include "absl/flags/usage_config.h" +#include "absl/strings/str_cat.h" +#include "absl/strings/string_view.h" +#include "absl/synchronization/mutex.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace flags_internal { + +// The help message indicating that the commandline flag has been +// 'stripped'. It will not show up when doing "-help" and its +// variants. The flag is stripped if ABSL_FLAGS_STRIP_HELP is set to 1 +// before including absl/flags/flag.h +const char kStrippedFlagHelp[] = "\001\002\003\004 (unknown) \004\003\002\001"; + +namespace { + +// Currently we only validate flag values for user-defined flag types. +bool ShouldValidateFlagValue(FlagFastTypeId flag_type_id) { +#define DONT_VALIDATE(T, _) \ + if (flag_type_id == base_internal::FastTypeId<T>()) return false; + ABSL_FLAGS_INTERNAL_SUPPORTED_TYPES(DONT_VALIDATE) +#undef DONT_VALIDATE + + return true; +} + +// RAII helper used to temporarily unlock and relock `absl::Mutex`. +// This is used when we need to ensure that locks are released while +// invoking user supplied callbacks and then reacquired, since callbacks may +// need to acquire these locks themselves. +class MutexRelock { + public: + explicit MutexRelock(absl::Mutex* mu) : mu_(mu) { mu_->Unlock(); } + ~MutexRelock() { mu_->Lock(); } + + MutexRelock(const MutexRelock&) = delete; + MutexRelock& operator=(const MutexRelock&) = delete; + + private: + absl::Mutex* mu_; +}; + +} // namespace + +/////////////////////////////////////////////////////////////////////////////// +// Persistent state of the flag data. + +class FlagImpl; + +class FlagState : public flags_internal::FlagStateInterface { + public: + template <typename V> + FlagState(FlagImpl* flag_impl, const V& v, bool modified, + bool on_command_line, int64_t counter) + : flag_impl_(flag_impl), + value_(v), + modified_(modified), + on_command_line_(on_command_line), + counter_(counter) {} + + ~FlagState() override { + if (flag_impl_->ValueStorageKind() != FlagValueStorageKind::kAlignedBuffer) + return; + flags_internal::Delete(flag_impl_->op_, value_.heap_allocated); + } + + private: + friend class FlagImpl; + + // Restores the flag to the saved state. + void Restore() const override { + if (!flag_impl_->RestoreState(*this)) return; + + ABSL_INTERNAL_LOG( + INFO, absl::StrCat("Restore saved value of ", flag_impl_->Name(), + " to: ", flag_impl_->CurrentValue())); + } + + // Flag and saved flag data. + FlagImpl* flag_impl_; + union SavedValue { + explicit SavedValue(void* v) : heap_allocated(v) {} + explicit SavedValue(int64_t v) : one_word(v) {} + explicit SavedValue(flags_internal::AlignedTwoWords v) : two_words(v) {} + + void* heap_allocated; + int64_t one_word; + flags_internal::AlignedTwoWords two_words; + } value_; + bool modified_; + bool on_command_line_; + int64_t counter_; +}; + +/////////////////////////////////////////////////////////////////////////////// +// Flag implementation, which does not depend on flag value type. + +DynValueDeleter::DynValueDeleter(FlagOpFn op_arg) : op(op_arg) {} + +void DynValueDeleter::operator()(void* ptr) const { + if (op == nullptr) return; + + Delete(op, ptr); +} + +void FlagImpl::Init() { + new (&data_guard_) absl::Mutex; + + auto def_kind = static_cast<FlagDefaultKind>(def_kind_); + + switch (ValueStorageKind()) { + case FlagValueStorageKind::kAlignedBuffer: + // For this storage kind the default_value_ always points to gen_func + // during initialization. + assert(def_kind == FlagDefaultKind::kGenFunc); + (*default_value_.gen_func)(AlignedBufferValue()); + break; + case FlagValueStorageKind::kOneWordAtomic: { + alignas(int64_t) std::array<char, sizeof(int64_t)> buf{}; + if (def_kind == FlagDefaultKind::kGenFunc) { + (*default_value_.gen_func)(buf.data()); + } else { + assert(def_kind != FlagDefaultKind::kDynamicValue); + std::memcpy(buf.data(), &default_value_, Sizeof(op_)); + } + OneWordValue().store(absl::bit_cast<int64_t>(buf), + std::memory_order_release); + break; + } + case FlagValueStorageKind::kTwoWordsAtomic: { + // For this storage kind the default_value_ always points to gen_func + // during initialization. + assert(def_kind == FlagDefaultKind::kGenFunc); + alignas(AlignedTwoWords) std::array<char, sizeof(AlignedTwoWords)> buf{}; + (*default_value_.gen_func)(buf.data()); + auto atomic_value = absl::bit_cast<AlignedTwoWords>(buf); + TwoWordsValue().store(atomic_value, std::memory_order_release); + break; + } + } +} + +absl::Mutex* FlagImpl::DataGuard() const { + absl::call_once(const_cast<FlagImpl*>(this)->init_control_, &FlagImpl::Init, + const_cast<FlagImpl*>(this)); + + // data_guard_ is initialized inside Init. + return reinterpret_cast<absl::Mutex*>(&data_guard_); +} + +void FlagImpl::AssertValidType(FlagFastTypeId rhs_type_id, + const std::type_info* (*gen_rtti)()) const { + FlagFastTypeId lhs_type_id = flags_internal::FastTypeId(op_); + + // `rhs_type_id` is the fast type id corresponding to the declaration + // visibile at the call site. `lhs_type_id` is the fast type id + // corresponding to the type specified in flag definition. They must match + // for this operation to be well-defined. + if (ABSL_PREDICT_TRUE(lhs_type_id == rhs_type_id)) return; + + const std::type_info* lhs_runtime_type_id = + flags_internal::RuntimeTypeId(op_); + const std::type_info* rhs_runtime_type_id = (*gen_rtti)(); + + if (lhs_runtime_type_id == rhs_runtime_type_id) return; + +#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI) + if (*lhs_runtime_type_id == *rhs_runtime_type_id) return; +#endif + + ABSL_INTERNAL_LOG( + FATAL, absl::StrCat("Flag '", Name(), + "' is defined as one type and declared as another")); +} + +std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const { + void* res = nullptr; + switch (DefaultKind()) { + case FlagDefaultKind::kDynamicValue: + res = flags_internal::Clone(op_, default_value_.dynamic_value); + break; + case FlagDefaultKind::kGenFunc: + res = flags_internal::Alloc(op_); + (*default_value_.gen_func)(res); + break; + default: + res = flags_internal::Clone(op_, &default_value_); + break; + } + return {res, DynValueDeleter{op_}}; +} + +void FlagImpl::StoreValue(const void* src) { + switch (ValueStorageKind()) { + case FlagValueStorageKind::kAlignedBuffer: + Copy(op_, src, AlignedBufferValue()); + break; + case FlagValueStorageKind::kOneWordAtomic: { + int64_t one_word_val = 0; + std::memcpy(&one_word_val, src, Sizeof(op_)); + OneWordValue().store(one_word_val, std::memory_order_release); + break; + } + case FlagValueStorageKind::kTwoWordsAtomic: { + AlignedTwoWords two_words_val{0, 0}; + std::memcpy(&two_words_val, src, Sizeof(op_)); + TwoWordsValue().store(two_words_val, std::memory_order_release); + break; + } + } + + modified_ = true; + ++counter_; + InvokeCallback(); +} + +absl::string_view FlagImpl::Name() const { return name_; } + +std::string FlagImpl::Filename() const { + return flags_internal::GetUsageConfig().normalize_filename(filename_); +} + +std::string FlagImpl::Help() const { + return HelpSourceKind() == FlagHelpKind::kLiteral ? help_.literal + : help_.gen_func(); +} + +FlagFastTypeId FlagImpl::TypeId() const { + return flags_internal::FastTypeId(op_); +} + +bool FlagImpl::IsSpecifiedOnCommandLine() const { + absl::MutexLock l(DataGuard()); + return on_command_line_; +} + +std::string FlagImpl::DefaultValue() const { + absl::MutexLock l(DataGuard()); + + auto obj = MakeInitValue(); + return flags_internal::Unparse(op_, obj.get()); +} + +std::string FlagImpl::CurrentValue() const { + auto* guard = DataGuard(); // Make sure flag initialized + switch (ValueStorageKind()) { + case FlagValueStorageKind::kAlignedBuffer: { + absl::MutexLock l(guard); + return flags_internal::Unparse(op_, AlignedBufferValue()); + } + case FlagValueStorageKind::kOneWordAtomic: { + const auto one_word_val = + absl::bit_cast<std::array<char, sizeof(int64_t)>>( + OneWordValue().load(std::memory_order_acquire)); + return flags_internal::Unparse(op_, one_word_val.data()); + } + case FlagValueStorageKind::kTwoWordsAtomic: { + const auto two_words_val = + absl::bit_cast<std::array<char, sizeof(AlignedTwoWords)>>( + TwoWordsValue().load(std::memory_order_acquire)); + return flags_internal::Unparse(op_, two_words_val.data()); + } + } + + return ""; +} + +void FlagImpl::SetCallback(const FlagCallbackFunc mutation_callback) { + absl::MutexLock l(DataGuard()); + + if (callback_ == nullptr) { + callback_ = new FlagCallback; + } + callback_->func = mutation_callback; + + InvokeCallback(); +} + +void FlagImpl::InvokeCallback() const { + if (!callback_) return; + + // Make a copy of the C-style function pointer that we are about to invoke + // before we release the lock guarding it. + FlagCallbackFunc cb = callback_->func; + + // If the flag has a mutation callback this function invokes it. While the + // callback is being invoked the primary flag's mutex is unlocked and it is + // re-locked back after call to callback is completed. Callback invocation is + // guarded by flag's secondary mutex instead which prevents concurrent + // callback invocation. Note that it is possible for other thread to grab the + // primary lock and update flag's value at any time during the callback + // invocation. This is by design. Callback can get a value of the flag if + // necessary, but it might be different from the value initiated the callback + // and it also can be different by the time the callback invocation is + // completed. Requires that *primary_lock be held in exclusive mode; it may be + // released and reacquired by the implementation. + MutexRelock relock(DataGuard()); + absl::MutexLock lock(&callback_->guard); + cb(); +} + +std::unique_ptr<FlagStateInterface> FlagImpl::SaveState() { + absl::MutexLock l(DataGuard()); + + bool modified = modified_; + bool on_command_line = on_command_line_; + switch (ValueStorageKind()) { + case FlagValueStorageKind::kAlignedBuffer: { + return absl::make_unique<FlagState>( + this, flags_internal::Clone(op_, AlignedBufferValue()), modified, + on_command_line, counter_); + } + case FlagValueStorageKind::kOneWordAtomic: { + return absl::make_unique<FlagState>( + this, OneWordValue().load(std::memory_order_acquire), modified, + on_command_line, counter_); + } + case FlagValueStorageKind::kTwoWordsAtomic: { + return absl::make_unique<FlagState>( + this, TwoWordsValue().load(std::memory_order_acquire), modified, + on_command_line, counter_); + } + } + return nullptr; +} + +bool FlagImpl::RestoreState(const FlagState& flag_state) { + absl::MutexLock l(DataGuard()); + + if (flag_state.counter_ == counter_) { + return false; + } + + switch (ValueStorageKind()) { + case FlagValueStorageKind::kAlignedBuffer: + StoreValue(flag_state.value_.heap_allocated); + break; + case FlagValueStorageKind::kOneWordAtomic: + StoreValue(&flag_state.value_.one_word); + break; + case FlagValueStorageKind::kTwoWordsAtomic: + StoreValue(&flag_state.value_.two_words); + break; + } + + modified_ = flag_state.modified_; + on_command_line_ = flag_state.on_command_line_; + + return true; +} + +template <typename StorageT> +StorageT* FlagImpl::OffsetValue() const { + char* p = reinterpret_cast<char*>(const_cast<FlagImpl*>(this)); + // The offset is deduced via Flag value type specific op_. + size_t offset = flags_internal::ValueOffset(op_); + + return reinterpret_cast<StorageT*>(p + offset); +} + +void* FlagImpl::AlignedBufferValue() const { + assert(ValueStorageKind() == FlagValueStorageKind::kAlignedBuffer); + return OffsetValue<void>(); +} + +std::atomic<int64_t>& FlagImpl::OneWordValue() const { + assert(ValueStorageKind() == FlagValueStorageKind::kOneWordAtomic); + return OffsetValue<FlagOneWordValue>()->value; +} + +std::atomic<AlignedTwoWords>& FlagImpl::TwoWordsValue() const { + assert(ValueStorageKind() == FlagValueStorageKind::kTwoWordsAtomic); + return OffsetValue<FlagTwoWordsValue>()->value; +} + +// Attempts to parse supplied `value` string using parsing routine in the `flag` +// argument. If parsing successful, this function replaces the dst with newly +// parsed value. In case if any error is encountered in either step, the error +// message is stored in 'err' +std::unique_ptr<void, DynValueDeleter> FlagImpl::TryParse( + absl::string_view value, std::string* err) const { + std::unique_ptr<void, DynValueDeleter> tentative_value = MakeInitValue(); + + std::string parse_err; + if (!flags_internal::Parse(op_, value, tentative_value.get(), &parse_err)) { + absl::string_view err_sep = parse_err.empty() ? "" : "; "; + *err = absl::StrCat("Illegal value '", value, "' specified for flag '", + Name(), "'", err_sep, parse_err); + return nullptr; + } + + return tentative_value; +} + +void FlagImpl::Read(void* dst) const { + auto* guard = DataGuard(); // Make sure flag initialized + switch (ValueStorageKind()) { + case FlagValueStorageKind::kAlignedBuffer: { + absl::MutexLock l(guard); + flags_internal::CopyConstruct(op_, AlignedBufferValue(), dst); + break; + } + case FlagValueStorageKind::kOneWordAtomic: { + const int64_t one_word_val = + OneWordValue().load(std::memory_order_acquire); + std::memcpy(dst, &one_word_val, Sizeof(op_)); + break; + } + case FlagValueStorageKind::kTwoWordsAtomic: { + const AlignedTwoWords two_words_val = + TwoWordsValue().load(std::memory_order_acquire); + std::memcpy(dst, &two_words_val, Sizeof(op_)); + break; + } + } +} + +void FlagImpl::Write(const void* src) { + absl::MutexLock l(DataGuard()); + + if (ShouldValidateFlagValue(flags_internal::FastTypeId(op_))) { + std::unique_ptr<void, DynValueDeleter> obj{flags_internal::Clone(op_, src), + DynValueDeleter{op_}}; + std::string ignored_error; + std::string src_as_str = flags_internal::Unparse(op_, src); + if (!flags_internal::Parse(op_, src_as_str, obj.get(), &ignored_error)) { + ABSL_INTERNAL_LOG(ERROR, absl::StrCat("Attempt to set flag '", Name(), + "' to invalid value ", src_as_str)); + } + } + + StoreValue(src); +} + +// Sets the value of the flag based on specified string `value`. If the flag +// was successfully set to new value, it returns true. Otherwise, sets `err` +// to indicate the error, leaves the flag unchanged, and returns false. There +// are three ways to set the flag's value: +// * Update the current flag value +// * Update the flag's default value +// * Update the current flag value if it was never set before +// The mode is selected based on 'set_mode' parameter. +bool FlagImpl::ParseFrom(absl::string_view value, FlagSettingMode set_mode, + ValueSource source, std::string* err) { + absl::MutexLock l(DataGuard()); + + switch (set_mode) { + case SET_FLAGS_VALUE: { + // set or modify the flag's value + auto tentative_value = TryParse(value, err); + if (!tentative_value) return false; + + StoreValue(tentative_value.get()); + + if (source == kCommandLine) { + on_command_line_ = true; + } + break; + } + case SET_FLAG_IF_DEFAULT: { + // set the flag's value, but only if it hasn't been set by someone else + if (modified_) { + // TODO(rogeeff): review and fix this semantic. Currently we do not fail + // in this case if flag is modified. This is misleading since the flag's + // value is not updated even though we return true. + // *err = absl::StrCat(Name(), " is already set to ", + // CurrentValue(), "\n"); + // return false; + return true; + } + auto tentative_value = TryParse(value, err); + if (!tentative_value) return false; + + StoreValue(tentative_value.get()); + break; + } + case SET_FLAGS_DEFAULT: { + auto tentative_value = TryParse(value, err); + if (!tentative_value) return false; + + if (DefaultKind() == FlagDefaultKind::kDynamicValue) { + void* old_value = default_value_.dynamic_value; + default_value_.dynamic_value = tentative_value.release(); + tentative_value.reset(old_value); + } else { + default_value_.dynamic_value = tentative_value.release(); + def_kind_ = static_cast<uint8_t>(FlagDefaultKind::kDynamicValue); + } + + if (!modified_) { + // Need to set both default value *and* current, in this case. + StoreValue(default_value_.dynamic_value); + modified_ = false; + } + break; + } + } + + return true; +} + +void FlagImpl::CheckDefaultValueParsingRoundtrip() const { + std::string v = DefaultValue(); + + absl::MutexLock lock(DataGuard()); + + auto dst = MakeInitValue(); + std::string error; + if (!flags_internal::Parse(op_, v, dst.get(), &error)) { + ABSL_INTERNAL_LOG( + FATAL, + absl::StrCat("Flag ", Name(), " (from ", Filename(), + "): string form of default value '", v, + "' could not be parsed; error=", error)); + } + + // We do not compare dst to def since parsing/unparsing may make + // small changes, e.g., precision loss for floating point types. +} + +bool FlagImpl::ValidateInputValue(absl::string_view value) const { + absl::MutexLock l(DataGuard()); + + auto obj = MakeInitValue(); + std::string ignored_error; + return flags_internal::Parse(op_, value, obj.get(), &ignored_error); +} + +} // namespace flags_internal +ABSL_NAMESPACE_END +} // namespace absl |