diff options
Diffstat (limited to 'absl/flags/flag.h')
| -rw-r--r-- | absl/flags/flag.h | 170 |
1 files changed, 145 insertions, 25 deletions
diff --git a/absl/flags/flag.h b/absl/flags/flag.h index 28925927..cff02c1f 100644 --- a/absl/flags/flag.h +++ b/absl/flags/flag.h @@ -29,16 +29,21 @@ #ifndef ABSL_FLAGS_FLAG_H_ #define ABSL_FLAGS_FLAG_H_ +#include <string> +#include <type_traits> + #include "absl/base/attributes.h" #include "absl/base/casts.h" +#include "absl/base/config.h" #include "absl/flags/config.h" #include "absl/flags/declare.h" #include "absl/flags/internal/commandlineflag.h" #include "absl/flags/internal/flag.h" +#include "absl/flags/internal/registry.h" #include "absl/flags/marshalling.h" namespace absl { -inline namespace lts_2019_08_08 { +ABSL_NAMESPACE_BEGIN // Flag // @@ -64,8 +69,103 @@ inline namespace lts_2019_08_08 { // ABSL_FLAG(int, count, 0, "Count of items to process"); // // No public methods of `absl::Flag<T>` are part of the Abseil Flags API. +#if !defined(_MSC_VER) || defined(__clang__) template <typename T> using Flag = flags_internal::Flag<T>; +#else +// MSVC debug builds do not implement initialization with constexpr constructors +// correctly. To work around this we add a level of indirection, so that the +// class `absl::Flag` contains an `internal::Flag*` (instead of being an alias +// to that class) and dynamically allocates an instance when necessary. We also +// forward all calls to internal::Flag methods via trampoline methods. In this +// setup the `absl::Flag` class does not have constructor and virtual methods, +// all the data members are public and thus MSVC is able to initialize it at +// link time. To deal with multiple threads accessing the flag for the first +// time concurrently we use an atomic boolean indicating if flag object is +// initialized. We also employ the double-checked locking pattern where the +// second level of protection is a global Mutex, so if two threads attempt to +// construct the flag concurrently only one wins. +// This solution is based on a recomendation here: +// https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html?childToView=648454#comment-648454 + +namespace flags_internal { +absl::Mutex* GetGlobalConstructionGuard(); +} // namespace flags_internal + +template <typename T> +class Flag { + public: + // No constructor and destructor to ensure this is an aggregate type. + // Visual Studio 2015 still requires the constructor for class to be + // constexpr initializable. +#if _MSC_VER <= 1900 + constexpr Flag(const char* name, const char* filename, + const flags_internal::HelpGenFunc help_gen, + const flags_internal::FlagDfltGenFunc default_value_gen) + : name_(name), + filename_(filename), + help_gen_(help_gen), + default_value_gen_(default_value_gen), + inited_(false), + impl_(nullptr) {} +#endif + + flags_internal::Flag<T>* GetImpl() const { + if (!inited_.load(std::memory_order_acquire)) { + absl::MutexLock l(flags_internal::GetGlobalConstructionGuard()); + + if (inited_.load(std::memory_order_acquire)) { + return impl_; + } + + impl_ = + new flags_internal::Flag<T>(name_, filename_, + {flags_internal::FlagHelpMsg(help_gen_), + flags_internal::FlagHelpKind::kGenFunc}, + default_value_gen_); + inited_.store(true, std::memory_order_release); + } + + return impl_; + } + + // Public methods of `absl::Flag<T>` are NOT part of the Abseil Flags API. + // See https://abseil.io/docs/cpp/guides/flags + bool IsRetired() const { return GetImpl()->IsRetired(); } + bool IsAbseilFlag() const { return GetImpl()->IsAbseilFlag(); } + absl::string_view Name() const { return GetImpl()->Name(); } + std::string Help() const { return GetImpl()->Help(); } + bool IsModified() const { return GetImpl()->IsModified(); } + bool IsSpecifiedOnCommandLine() const { + return GetImpl()->IsSpecifiedOnCommandLine(); + } + absl::string_view Typename() const { return GetImpl()->Typename(); } + std::string Filename() const { return GetImpl()->Filename(); } + std::string DefaultValue() const { return GetImpl()->DefaultValue(); } + std::string CurrentValue() const { return GetImpl()->CurrentValue(); } + template <typename U> + inline bool IsOfType() const { + return GetImpl()->template IsOfType<U>(); + } + T Get() const { return GetImpl()->Get(); } + bool AtomicGet(T* v) const { return GetImpl()->AtomicGet(v); } + void Set(const T& v) { GetImpl()->Set(v); } + void SetCallback(const flags_internal::FlagCallbackFunc mutation_callback) { + GetImpl()->SetCallback(mutation_callback); + } + void InvokeCallback() { GetImpl()->InvokeCallback(); } + + // The data members are logically private, but they need to be public for + // this to be an aggregate type. + const char* name_; + const char* filename_; + const flags_internal::HelpGenFunc help_gen_; + const flags_internal::FlagDfltGenFunc default_value_gen_; + + mutable std::atomic<bool> inited_; + mutable flags_internal::Flag<T>* impl_; +}; +#endif // GetFlag() // @@ -84,23 +184,10 @@ using Flag = flags_internal::Flag<T>; // // FLAGS_firstname is a Flag of type `std::string` // std::string first_name = absl::GetFlag(FLAGS_firstname); template <typename T> -T GetFlag(const absl::Flag<T>& flag) { -#define ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE(BIT) \ - static_assert( \ - !std::is_same<T, BIT>::value, \ - "Do not specify explicit template parameters to absl::GetFlag"); - ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE) -#undef ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE - +ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) { return flag.Get(); } -// Overload for `GetFlag()` for types that support lock-free reads. -#define ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT(T) \ - extern T GetFlag(const absl::Flag<T>& flag); -ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT) -#undef ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT - // SetFlag() // // Sets the value of an `absl::Flag` to the value `v`. Do not construct an @@ -122,7 +209,7 @@ void SetFlag(absl::Flag<T>* flag, const V& v) { flag->Set(value); } -} // inline namespace lts_2019_08_08 +ABSL_NAMESPACE_END } // namespace absl @@ -186,13 +273,23 @@ void SetFlag(absl::Flag<T>* flag, const V& v) { #if ABSL_FLAGS_STRIP_NAMES #define ABSL_FLAG_IMPL_FLAGNAME(txt) "" #define ABSL_FLAG_IMPL_FILENAME() "" +#if !defined(_MSC_VER) || defined(__clang__) #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \ absl::flags_internal::FlagRegistrar<T, false>(&flag) #else +#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \ + absl::flags_internal::FlagRegistrar<T, false>(flag.GetImpl()) +#endif +#else #define ABSL_FLAG_IMPL_FLAGNAME(txt) txt #define ABSL_FLAG_IMPL_FILENAME() __FILE__ +#if !defined(_MSC_VER) || defined(__clang__) #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \ absl::flags_internal::FlagRegistrar<T, true>(&flag) +#else +#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \ + absl::flags_internal::FlagRegistrar<T, true>(flag.GetImpl()) +#endif #endif // ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_HELP @@ -203,9 +300,19 @@ void SetFlag(absl::Flag<T>* flag, const V& v) { #define ABSL_FLAG_IMPL_FLAGHELP(txt) txt #endif -#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt) \ - static std::string AbslFlagsWrapHelp##name() { \ - return ABSL_FLAG_IMPL_FLAGHELP(txt); \ +// AbslFlagHelpGenFor##name is used to encapsulate both immediate (method Const) +// and lazy (method NonConst) evaluation of help message expression. We choose +// between the two via the call to HelpArg in absl::Flag instantiation below. +// If help message expression is constexpr evaluable compiler will optimize +// away this whole struct. +#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt) \ + struct AbslFlagHelpGenFor##name { \ + template <typename T = void> \ + static constexpr const char* Const() { \ + return absl::flags_internal::HelpConstexprWrap( \ + ABSL_FLAG_IMPL_FLAGHELP(txt)); \ + } \ + static std::string NonConst() { return ABSL_FLAG_IMPL_FLAGHELP(txt); } \ } #define ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value) \ @@ -218,17 +325,30 @@ void SetFlag(absl::Flag<T>* flag, const V& v) { // Note: Name of registrar object is not arbitrary. It is used to "grab" // global name for FLAGS_no<flag_name> symbol, thus preventing the possibility // of defining two flags with names foo and nofoo. +#if !defined(_MSC_VER) || defined(__clang__) #define ABSL_FLAG_IMPL(Type, name, default_value, help) \ namespace absl /* block flags in namespaces */ {} \ ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value) \ - ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, help) \ - ABSL_CONST_INIT absl::Flag<Type> FLAGS_##name( \ - ABSL_FLAG_IMPL_FLAGNAME(#name), &AbslFlagsWrapHelp##name, \ - ABSL_FLAG_IMPL_FILENAME(), \ - &absl::flags_internal::FlagMarshallingOps<Type>, \ - &AbslFlagsInitFlag##name); \ + ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, help); \ + ABSL_CONST_INIT absl::Flag<Type> FLAGS_##name{ \ + ABSL_FLAG_IMPL_FLAGNAME(#name), ABSL_FLAG_IMPL_FILENAME(), \ + absl::flags_internal::HelpArg<AbslFlagHelpGenFor##name>(0), \ + &AbslFlagsInitFlag##name}; \ extern bool FLAGS_no##name; \ bool FLAGS_no##name = ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name) +#else +// MSVC version uses aggregate initialization. We also do not try to +// optimize away help wrapper. +#define ABSL_FLAG_IMPL(Type, name, default_value, help) \ + namespace absl /* block flags in namespaces */ {} \ + ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value) \ + ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, help); \ + ABSL_CONST_INIT absl::Flag<Type> FLAGS_##name{ \ + ABSL_FLAG_IMPL_FLAGNAME(#name), ABSL_FLAG_IMPL_FILENAME(), \ + &AbslFlagHelpGenFor##name::NonConst, &AbslFlagsInitFlag##name}; \ + extern bool FLAGS_no##name; \ + bool FLAGS_no##name = ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name) +#endif // ABSL_RETIRED_FLAG // |