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Diffstat (limited to 'third_party/abseil_cpp/absl/base/internal/atomic_hook.h')
| -rw-r--r-- | third_party/abseil_cpp/absl/base/internal/atomic_hook.h | 200 |
1 files changed, 0 insertions, 200 deletions
diff --git a/third_party/abseil_cpp/absl/base/internal/atomic_hook.h b/third_party/abseil_cpp/absl/base/internal/atomic_hook.h deleted file mode 100644 index ae21cd7fe50a..000000000000 --- a/third_party/abseil_cpp/absl/base/internal/atomic_hook.h +++ /dev/null @@ -1,200 +0,0 @@ -// Copyright 2017 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. - -#ifndef ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_ -#define ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_ - -#include <atomic> -#include <cassert> -#include <cstdint> -#include <utility> - -#include "absl/base/attributes.h" -#include "absl/base/config.h" - -#if defined(_MSC_VER) && !defined(__clang__) -#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 0 -#else -#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 1 -#endif - -#if defined(_MSC_VER) -#define ABSL_HAVE_WORKING_ATOMIC_POINTER 0 -#else -#define ABSL_HAVE_WORKING_ATOMIC_POINTER 1 -#endif - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace base_internal { - -template <typename T> -class AtomicHook; - -// To workaround AtomicHook not being constant-initializable on some platforms, -// prefer to annotate instances with `ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES` -// instead of `ABSL_CONST_INIT`. -#if ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT -#define ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_CONST_INIT -#else -#define ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES -#endif - -// `AtomicHook` is a helper class, templatized on a raw function pointer type, -// for implementing Abseil customization hooks. It is a callable object that -// dispatches to the registered hook. Objects of type `AtomicHook` must have -// static or thread storage duration. -// -// A default constructed object performs a no-op (and returns a default -// constructed object) if no hook has been registered. -// -// Hooks can be pre-registered via constant initialization, for example: -// -// ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES static AtomicHook<void(*)()> -// my_hook(DefaultAction); -// -// and then changed at runtime via a call to `Store()`. -// -// Reads and writes guarantee memory_order_acquire/memory_order_release -// semantics. -template <typename ReturnType, typename... Args> -class AtomicHook<ReturnType (*)(Args...)> { - public: - using FnPtr = ReturnType (*)(Args...); - - // Constructs an object that by default performs a no-op (and - // returns a default constructed object) when no hook as been registered. - constexpr AtomicHook() : AtomicHook(DummyFunction) {} - - // Constructs an object that by default dispatches to/returns the - // pre-registered default_fn when no hook has been registered at runtime. -#if ABSL_HAVE_WORKING_ATOMIC_POINTER && ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT - explicit constexpr AtomicHook(FnPtr default_fn) - : hook_(default_fn), default_fn_(default_fn) {} -#elif ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT - explicit constexpr AtomicHook(FnPtr default_fn) - : hook_(kUninitialized), default_fn_(default_fn) {} -#else - // As of January 2020, on all known versions of MSVC this constructor runs in - // the global constructor sequence. If `Store()` is called by a dynamic - // initializer, we want to preserve the value, even if this constructor runs - // after the call to `Store()`. If not, `hook_` will be - // zero-initialized by the linker and we have no need to set it. - // https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html - explicit constexpr AtomicHook(FnPtr default_fn) - : /* hook_(deliberately omitted), */ default_fn_(default_fn) { - static_assert(kUninitialized == 0, "here we rely on zero-initialization"); - } -#endif - - // Stores the provided function pointer as the value for this hook. - // - // This is intended to be called once. Multiple calls are legal only if the - // same function pointer is provided for each call. The store is implemented - // as a memory_order_release operation, and read accesses are implemented as - // memory_order_acquire. - void Store(FnPtr fn) { - bool success = DoStore(fn); - static_cast<void>(success); - assert(success); - } - - // Invokes the registered callback. If no callback has yet been registered, a - // default-constructed object of the appropriate type is returned instead. - template <typename... CallArgs> - ReturnType operator()(CallArgs&&... args) const { - return DoLoad()(std::forward<CallArgs>(args)...); - } - - // Returns the registered callback, or nullptr if none has been registered. - // Useful if client code needs to conditionalize behavior based on whether a - // callback was registered. - // - // Note that atomic_hook.Load()() and atomic_hook() have different semantics: - // operator()() will perform a no-op if no callback was registered, while - // Load()() will dereference a null function pointer. Prefer operator()() to - // Load()() unless you must conditionalize behavior on whether a hook was - // registered. - FnPtr Load() const { - FnPtr ptr = DoLoad(); - return (ptr == DummyFunction) ? nullptr : ptr; - } - - private: - static ReturnType DummyFunction(Args...) { - return ReturnType(); - } - - // Current versions of MSVC (as of September 2017) have a broken - // implementation of std::atomic<T*>: Its constructor attempts to do the - // equivalent of a reinterpret_cast in a constexpr context, which is not - // allowed. - // - // This causes an issue when building with LLVM under Windows. To avoid this, - // we use a less-efficient, intptr_t-based implementation on Windows. -#if ABSL_HAVE_WORKING_ATOMIC_POINTER - // Return the stored value, or DummyFunction if no value has been stored. - FnPtr DoLoad() const { return hook_.load(std::memory_order_acquire); } - - // Store the given value. Returns false if a different value was already - // stored to this object. - bool DoStore(FnPtr fn) { - assert(fn); - FnPtr expected = default_fn_; - const bool store_succeeded = hook_.compare_exchange_strong( - expected, fn, std::memory_order_acq_rel, std::memory_order_acquire); - const bool same_value_already_stored = (expected == fn); - return store_succeeded || same_value_already_stored; - } - - std::atomic<FnPtr> hook_; -#else // !ABSL_HAVE_WORKING_ATOMIC_POINTER - // Use a sentinel value unlikely to be the address of an actual function. - static constexpr intptr_t kUninitialized = 0; - - static_assert(sizeof(intptr_t) >= sizeof(FnPtr), - "intptr_t can't contain a function pointer"); - - FnPtr DoLoad() const { - const intptr_t value = hook_.load(std::memory_order_acquire); - if (value == kUninitialized) { - return default_fn_; - } - return reinterpret_cast<FnPtr>(value); - } - - bool DoStore(FnPtr fn) { - assert(fn); - const auto value = reinterpret_cast<intptr_t>(fn); - intptr_t expected = kUninitialized; - const bool store_succeeded = hook_.compare_exchange_strong( - expected, value, std::memory_order_acq_rel, std::memory_order_acquire); - const bool same_value_already_stored = (expected == value); - return store_succeeded || same_value_already_stored; - } - - std::atomic<intptr_t> hook_; -#endif - - const FnPtr default_fn_; -}; - -#undef ABSL_HAVE_WORKING_ATOMIC_POINTER -#undef ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT - -} // namespace base_internal -ABSL_NAMESPACE_END -} // namespace absl - -#endif // ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_ |