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// Copyright 2023 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/synchronization/internal/win32_waiter.h"
#ifdef ABSL_INTERNAL_HAVE_WIN32_WAITER
#include <windows.h>
#include "absl/base/config.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/thread_identity.h"
#include "absl/base/optimization.h"
#include "absl/synchronization/internal/kernel_timeout.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace synchronization_internal {
#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
constexpr char Win32Waiter::kName[];
#endif
class Win32Waiter::WinHelper {
public:
static SRWLOCK *GetLock(Win32Waiter *w) {
return reinterpret_cast<SRWLOCK *>(&w->mu_storage_);
}
static CONDITION_VARIABLE *GetCond(Win32Waiter *w) {
return reinterpret_cast<CONDITION_VARIABLE *>(&w->cv_storage_);
}
static_assert(sizeof(SRWLOCK) == sizeof(void *),
"`mu_storage_` does not have the same size as SRWLOCK");
static_assert(alignof(SRWLOCK) == alignof(void *),
"`mu_storage_` does not have the same alignment as SRWLOCK");
static_assert(sizeof(CONDITION_VARIABLE) == sizeof(void *),
"`ABSL_CONDITION_VARIABLE_STORAGE` does not have the same size "
"as `CONDITION_VARIABLE`");
static_assert(
alignof(CONDITION_VARIABLE) == alignof(void *),
"`cv_storage_` does not have the same alignment as `CONDITION_VARIABLE`");
// The SRWLOCK and CONDITION_VARIABLE types must be trivially constructible
// and destructible because we never call their constructors or destructors.
static_assert(std::is_trivially_constructible<SRWLOCK>::value,
"The `SRWLOCK` type must be trivially constructible");
static_assert(
std::is_trivially_constructible<CONDITION_VARIABLE>::value,
"The `CONDITION_VARIABLE` type must be trivially constructible");
static_assert(std::is_trivially_destructible<SRWLOCK>::value,
"The `SRWLOCK` type must be trivially destructible");
static_assert(std::is_trivially_destructible<CONDITION_VARIABLE>::value,
"The `CONDITION_VARIABLE` type must be trivially destructible");
};
class LockHolder {
public:
explicit LockHolder(SRWLOCK* mu) : mu_(mu) {
AcquireSRWLockExclusive(mu_);
}
LockHolder(const LockHolder&) = delete;
LockHolder& operator=(const LockHolder&) = delete;
~LockHolder() {
ReleaseSRWLockExclusive(mu_);
}
private:
SRWLOCK* mu_;
};
Win32Waiter::Win32Waiter() {
auto *mu = ::new (static_cast<void *>(&mu_storage_)) SRWLOCK;
auto *cv = ::new (static_cast<void *>(&cv_storage_)) CONDITION_VARIABLE;
InitializeSRWLock(mu);
InitializeConditionVariable(cv);
waiter_count_ = 0;
wakeup_count_ = 0;
}
bool Win32Waiter::Wait(KernelTimeout t) {
SRWLOCK *mu = WinHelper::GetLock(this);
CONDITION_VARIABLE *cv = WinHelper::GetCond(this);
LockHolder h(mu);
++waiter_count_;
// Loop until we find a wakeup to consume or timeout.
// Note that, since the thread ticker is just reset, we don't need to check
// whether the thread is idle on the very first pass of the loop.
bool first_pass = true;
while (wakeup_count_ == 0) {
if (!first_pass) MaybeBecomeIdle();
// No wakeups available, time to wait.
if (!SleepConditionVariableSRW(cv, mu, t.InMillisecondsFromNow(), 0)) {
// GetLastError() returns a Win32 DWORD, but we assign to
// unsigned long to simplify the ABSL_RAW_LOG case below. The uniform
// initialization guarantees this is not a narrowing conversion.
const unsigned long err{GetLastError()}; // NOLINT(runtime/int)
if (err == ERROR_TIMEOUT) {
--waiter_count_;
return false;
} else {
ABSL_RAW_LOG(FATAL, "SleepConditionVariableSRW failed: %lu", err);
}
}
first_pass = false;
}
// Consume a wakeup and we're done.
--wakeup_count_;
--waiter_count_;
return true;
}
void Win32Waiter::Post() {
LockHolder h(WinHelper::GetLock(this));
++wakeup_count_;
InternalCondVarPoke();
}
void Win32Waiter::Poke() {
LockHolder h(WinHelper::GetLock(this));
InternalCondVarPoke();
}
void Win32Waiter::InternalCondVarPoke() {
if (waiter_count_ != 0) {
WakeConditionVariable(WinHelper::GetCond(this));
}
}
} // namespace synchronization_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_INTERNAL_HAVE_WIN32_WAITER
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