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Changes imported from Abseil "staging" branch:

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- b527a3e4b36b644ac424e3c525b1cd393f6f6c40 Fix some typos in the usage examples by Jorg Brown <jorg@google.com>
  - 82be4a9adf3bb0ddafc0d46274969c99afffe870 Fix typo in optional.h comment. by Abseil Team <absl-team@google.com>
  - d6ee63bf8fc51fba074c23b33cebc28c808d7f07 Remove internal-only identifiers from code. by Daniel Katz <katzdm@google.com>
  - f9c3ad2f0d73f53b21603638af8b4bed636e79f4 Use easier understandable names for absl::StartsWith and ... by Abseil Team <absl-team@google.com>
  - 7c16c14fefee89c927b8789d6043c4691bcffc9b Add -Wno-missing-prototypes back to the LLVM copts. by Derek Mauro <dmauro@google.com>
  - 2f4b7d2e50c7023240242f1e15db60ccd7e8768d IWYU | absl/strings by Juemin Yang <jueminyang@google.com>
  - a99cbcc1daa34a2d6a2bb26de275e05173cc77e9 IWYU | absl/type by Juemin Yang <jueminyang@google.com>
  - 12e1146d0fc76c071d7e0ebaabb62f0a984fae66 Use LLVM_FLAGS and LLVM_TEST_FLAGS when --compiler=llvm. by Derek Mauro <dmauro@google.com>
  - cd6bea616abda558d0bace5bd77455662a233688 IWYU | absl/debugging by Juemin Yang <jueminyang@google.com>
  - d9a7382e59d46a8581b6b7a31cd5a48bb89326e9 IWYU | absl/synchronization by Juemin Yang <jueminyang@google.com>
  - 07ec7d6d5a4a666f4183c5d0ed9c342baa7b24bc IWYU | absl/numeric by Juemin Yang <jueminyang@google.com>
  - 12bfe40051f4270f8707e191af5652f83f2f750c Remove the RoundTrip{Float,Double}ToBuffer routines from ... by Jorg Brown <jorg@google.com>
  - eeb4fd67c9d97f66cb9475c3c5e51ab132f1c810 Adds conversion functions for converting between absl/tim... by Greg Miller <jgm@google.com>
  - 59a2108d05d4ea85dc5cc11e49b2cd2335d4295a Change Substitute to use %.6g formatting rather than 15/1... by Jorg Brown <jorg@google.com>
  - 394becb48e0fcd161642cdaac5120d32567e0ef8 IWYU | absl/meta by Juemin Yang <jueminyang@google.com>
  - 1e5da6e8da336699b2469dcf6dda025b9b0ec4c9 Rewrite atomic_hook.h to not use std::atomic<T*> under Wi... by Greg Falcon <gfalcon@google.com>

GitOrigin-RevId: b527a3e4b36b644ac424e3c525b1cd393f6f6c40
Change-Id: I14e331d91c956ef045ac7927091a9f179716de0c
This commit is contained in:
Abseil Team 2017-09-24 08:20:48 -07:00 • committed by Derek Mauro
parent 53c239d1fc
commit cf6ab6bb2b
68 changed files with 629 additions and 831 deletions
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104
absl/base/internal/atomic_hook.h
View file

@ -18,28 +18,12 @@
#include <atomic>
#include <cassert>
#include <cstdint>
#include <utility>
namespace absl {
namespace base_internal {
// In current versions of MSVC (as of July 2017), a std::atomic<T> where T is a
// pointer to function cannot be constant-initialized with an address constant
// expression. That is, the following code does not compile:
// void NoOp() {}
// constexpr std::atomic<void(*)()> ptr(NoOp);
//
// This is the only compiler we support that seems to have this issue. We
// conditionalize on MSVC here to use a fallback implementation. But we
// should revisit this occasionally. If MSVC fixes this compiler bug, we
// can then change this to be conditionalized on the value on _MSC_FULL_VER
// instead.
#ifdef _MSC_FULL_VER
#define ABSL_HAVE_FUNCTION_ADDRESS_CONSTANT_EXPRESSION 0
#else
#define ABSL_HAVE_FUNCTION_ADDRESS_CONSTANT_EXPRESSION 1
#endif
template <typename T>
class AtomicHook;
@ -55,7 +39,7 @@ class AtomicHook<ReturnType (*)(Args...)> {
public:
using FnPtr = ReturnType (*)(Args...);
constexpr AtomicHook() : hook_(DummyFunction) {}
constexpr AtomicHook() : hook_(kInitialValue) {}
// Stores the provided function pointer as the value for this hook.
//
@ -64,28 +48,16 @@ class AtomicHook<ReturnType (*)(Args...)> {
// as a memory_order_release operation, and read accesses are implemented as
// memory_order_acquire.
void Store(FnPtr fn) {
assert(fn);
FnPtr expected = DummyFunction;
hook_.compare_exchange_strong(expected, fn, std::memory_order_acq_rel,
std::memory_order_acquire);
// If the compare and exchange failed, make sure that's because hook_ was
// already set to `fn` by an earlier call. Any other state reflects an API
// violation (calling Store() multiple times with different values).
//
// Avoid ABSL_RAW_CHECK, since raw logging depends on AtomicHook.
assert(expected == DummyFunction || expected == 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 {
FnPtr hook = hook_.load(std::memory_order_acquire);
if (ABSL_HAVE_FUNCTION_ADDRESS_CONSTANT_EXPRESSION || hook) {
return hook(std::forward<CallArgs>(args)...);
} else {
return ReturnType();
}
return DoLoad()(std::forward<CallArgs>(args)...);
}
// Returns the registered callback, or nullptr if none has been registered.
@ -98,23 +70,79 @@ class AtomicHook<ReturnType (*)(Args...)> {
// Load()() unless you must conditionalize behavior on whether a hook was
// registered.
FnPtr Load() const {
FnPtr ptr = hook_.load(std::memory_order_acquire);
FnPtr ptr = DoLoad();
return (ptr == DummyFunction) ? nullptr : ptr;
}
private:
#if ABSL_HAVE_FUNCTION_ADDRESS_CONSTANT_EXPRESSION
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.
#ifdef _MSC_FULL_VER
#define ABSL_HAVE_WORKING_ATOMIC_POINTER 0
#else
static constexpr FnPtr DummyFunction = nullptr;
#define ABSL_HAVE_WORKING_ATOMIC_POINTER 1
#endif
#if ABSL_HAVE_WORKING_ATOMIC_POINTER
static constexpr FnPtr kInitialValue = &DummyFunction;
// 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 = DummyFunction;
hook_.compare_exchange_strong(expected, fn, std::memory_order_acq_rel,
std::memory_order_acquire);
const bool store_succeeded = (expected == DummyFunction);
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 kInitialValue = 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 == 0) {
return DummyFunction;
}
return reinterpret_cast<FnPtr>(value);
}
bool DoStore(FnPtr fn) {
assert(fn);
const auto value = reinterpret_cast<intptr_t>(fn);
intptr_t expected = 0;
hook_.compare_exchange_strong(expected, value, std::memory_order_acq_rel,
std::memory_order_acquire);
const bool store_succeeded = (expected == 0);
const bool same_value_already_stored = (expected == value);
return store_succeeded || same_value_already_stored;
}
std::atomic<intptr_t> hook_;
#endif
};
#undef ABSL_HAVE_FUNCTION_ADDRESS_CONSTANT_EXPRESSION
#undef ABSL_HAVE_WORKING_ATOMIC_POINTER
} // namespace base_internal
} // namespace absl