diff options
Diffstat (limited to 'absl/flags/internal/flag.cc')
-rw-r--r-- | absl/flags/internal/flag.cc | 382 |
1 files changed, 382 insertions, 0 deletions
diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc new file mode 100644 index 00000000..5a921e28 --- /dev/null +++ b/absl/flags/internal/flag.cc @@ -0,0 +1,382 @@ +// +// 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/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(FlagStaticTypeId flag_type_id) { +#define DONT_VALIDATE(T) \ + if (flag_type_id == &FlagStaticTypeIdGen<T>) return false; + ABSL_FLAGS_INTERNAL_BUILTIN_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 + +void FlagImpl::Init() { + new (&data_guard_) absl::Mutex; + + absl::MutexLock lock(reinterpret_cast<absl::Mutex*>(&data_guard_)); + + value_.dynamic = MakeInitValue().release(); + StoreAtomic(); +} + +// Ensures that the lazily initialized data is initialized, +// and returns pointer to the mutex guarding flags data. +absl::Mutex* FlagImpl::DataGuard() const { + absl::call_once(const_cast<FlagImpl*>(this)->init_control_, &FlagImpl::Init, + const_cast<FlagImpl*>(this)); + + // data_guard_ is initialized. + return reinterpret_cast<absl::Mutex*>(&data_guard_); +} + +void FlagImpl::AssertValidType(FlagStaticTypeId type_id) const { + FlagStaticTypeId this_type_id = flags_internal::StaticTypeId(op_); + + // `type_id` is the type id corresponding to the declaration visibile at the + // call site. `this_type_id` is the type id corresponding to the type stored + // during flag definition. They must match for this operation to be + // well-defined. + if (ABSL_PREDICT_TRUE(type_id == this_type_id)) return; + + void* lhs_runtime_type_id = type_id(); + void* rhs_runtime_type_id = this_type_id(); + + if (lhs_runtime_type_id == rhs_runtime_type_id) return; + +#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI) + if (*reinterpret_cast<std::type_info*>(lhs_runtime_type_id) == + *reinterpret_cast<std::type_info*>(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; + if (DefaultKind() == FlagDefaultKind::kDynamicValue) { + res = flags_internal::Clone(op_, default_value_.dynamic_value); + } else { + res = (*default_value_.gen_func)(); + } + return {res, DynValueDeleter{op_}}; +} + +void FlagImpl::StoreValue(const void* src) { + flags_internal::Copy(op_, src, value_.dynamic); + StoreAtomic(); + 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(); +} + +bool FlagImpl::IsModified() const { + absl::MutexLock l(DataGuard()); + return modified_; +} + +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 { + absl::MutexLock l(DataGuard()); + + return flags_internal::Unparse(op_, value_.dynamic); +} + +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(); +} + +bool FlagImpl::RestoreState(const void* value, bool modified, + bool on_command_line, int64_t counter) { + { + absl::MutexLock l(DataGuard()); + + if (counter_ == counter) return false; + } + + Write(value); + + { + absl::MutexLock l(DataGuard()); + + modified_ = modified; + on_command_line_ = on_command_line; + } + + return true; +} + +// 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 { + absl::ReaderMutexLock l(DataGuard()); + + flags_internal::CopyConstruct(op_, value_.dynamic, dst); +} + +void FlagImpl::StoreAtomic() { + size_t data_size = flags_internal::Sizeof(op_); + + if (data_size <= sizeof(int64_t)) { + int64_t t = 0; + std::memcpy(&t, value_.dynamic, data_size); + value_.atomics.small_atomic.store(t, std::memory_order_release); + } +#if defined(ABSL_FLAGS_INTERNAL_ATOMIC_DOUBLE_WORD) + else if (data_size <= sizeof(FlagsInternalTwoWordsType)) { + FlagsInternalTwoWordsType t{0, 0}; + std::memcpy(&t, value_.dynamic, data_size); + value_.atomics.big_atomic.store(t, std::memory_order_release); + } +#endif +} + +void FlagImpl::Write(const void* src) { + absl::MutexLock l(DataGuard()); + + if (ShouldValidateFlagValue(flags_internal::StaticTypeId(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::SetFromString(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(), + "): std::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 |