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-rw-r--r--absl/synchronization/internal/waiter.cc57
1 files changed, 50 insertions, 7 deletions
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index 74b09650..f17ea56f 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -40,6 +40,8 @@
#include <atomic>
#include <cassert>
#include <cstdint>
+#include <new>
+#include <type_traits>
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/thread_identity.h"
@@ -328,6 +330,43 @@ void Waiter::Poke() {
#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_WIN32
+class Waiter::WinHelper {
+ public:
+ static SRWLOCK *GetLock(Waiter *w) {
+ return reinterpret_cast<SRWLOCK *>(&w->mu_storage_);
+ }
+
+ static CONDITION_VARIABLE *GetCond(Waiter *w) {
+ return reinterpret_cast<CONDITION_VARIABLE *>(&w->cv_storage_);
+ }
+
+ static_assert(sizeof(SRWLOCK) == sizeof(Waiter::SRWLockStorage),
+ "SRWLockStorage does not have the same size as SRWLOCK");
+ static_assert(
+ alignof(SRWLOCK) == alignof(Waiter::SRWLockStorage),
+ "SRWLockStorage does not have the same alignment as SRWLOCK");
+
+ static_assert(sizeof(CONDITION_VARIABLE) ==
+ sizeof(Waiter::ConditionVariableStorage),
+ "ABSL_CONDITION_VARIABLE_STORAGE does not have the same size "
+ "as CONDITION_VARIABLE");
+ static_assert(alignof(CONDITION_VARIABLE) ==
+ alignof(Waiter::ConditionVariableStorage),
+ "ConditionVariableStorage does not have the same "
+ "alignment as CONDITION_VARIABLE");
+
+ // The SRWLOCK and CONDITION_VARIABLE types must be trivially constuctible
+ // 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) {
@@ -346,14 +385,19 @@ class LockHolder {
};
void Waiter::Init() {
- InitializeSRWLock(&mu_);
- InitializeConditionVariable(&cv_);
+ 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_.store(0, std::memory_order_relaxed);
wakeup_count_.store(0, std::memory_order_relaxed);
}
bool Waiter::Wait(KernelTimeout t) {
- LockHolder h(&mu_);
+ SRWLOCK *mu = WinHelper::GetLock(this);
+ CONDITION_VARIABLE *cv = WinHelper::GetCond(this);
+
+ LockHolder h(mu);
waiter_count_.fetch_add(1, std::memory_order_relaxed);
// Loop until we find a wakeup to consume or timeout.
@@ -371,8 +415,7 @@ bool Waiter::Wait(KernelTimeout t) {
}
// No wakeups available, time to wait.
- if (!SleepConditionVariableSRW(
- &cv_, &mu_, t.InMillisecondsFromNow(), 0)) {
+ 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.
@@ -399,11 +442,11 @@ void Waiter::Poke() {
return;
}
// Potentially a waker. Take the lock and check again.
- LockHolder h(&mu_);
+ LockHolder h(WinHelper::GetLock(this));
if (waiter_count_.load(std::memory_order_relaxed) == 0) {
return;
}
- WakeConditionVariable(&cv_);
+ WakeConditionVariable(WinHelper::GetCond(this));
}
#else