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#pragma once
#include "public.h"
#include "spin_lock_base.h"
#include <library/cpp/yt/memory/public.h>
#include <util/system/rwlock.h>
#include <atomic>
namespace NYT::NThreading {
////////////////////////////////////////////////////////////////////////////////
//! Single-writer multiple-readers spin lock.
/*!
* Reader-side calls are pretty cheap.
* The lock is unfair.
*/
class TReaderWriterSpinLock
: public TSpinLockBase
{
public:
using TSpinLockBase::TSpinLockBase;
//! Acquires the reader lock.
/*!
* Optimized for the case of read-intensive workloads.
* Cheap (just one atomic increment and no spinning if no writers are present).
* Don't use this call if forks are possible: forking at some
* intermediate point inside #AcquireReader may corrupt the lock state and
* leave lock forever stuck for the child process.
*/
void AcquireReader() noexcept;
//! Acquires the reader lock.
/*!
* A more expensive version of #AcquireReader (includes at least
* one atomic load and CAS; also may spin even if just readers are present).
* In contrast to #AcquireReader, this method can be used in the presence of forks.
* Note that fork-friendliness alone does not provide fork-safety: additional
* actions must be performed to release the lock after a fork.
*/
void AcquireReaderForkFriendly() noexcept;
//! Tries acquiring the reader lock; see #AcquireReader.
//! Returns |true| on success.
bool TryAcquireReader() noexcept;
//! Tries acquiring the reader lock (and does this in a fork-friendly manner); see #AcquireReaderForkFriendly.
//! returns |true| on success.
bool TryAcquireReaderForkFriendly() noexcept;
//! Releases the reader lock.
/*!
* Cheap (just one atomic decrement).
*/
void ReleaseReader() noexcept;
//! Acquires the writer lock.
/*!
* Rather cheap (just one CAS).
*/
void AcquireWriter() noexcept;
//! Tries acquiring the writer lock; see #AcquireWriter.
//! Returns |true| on success.
bool TryAcquireWriter() noexcept;
//! Releases the writer lock.
/*!
* Cheap (just one atomic store).
*/
void ReleaseWriter() noexcept;
//! Returns true if the lock is taken (either by a reader or writer).
/*!
* This is inherently racy.
* Only use for debugging and diagnostic purposes.
*/
bool IsLocked() const noexcept;
//! Returns true if the lock is taken by reader.
/*!
* This is inherently racy.
* Only use for debugging and diagnostic purposes.
*/
bool IsLockedByReader() const noexcept;
//! Returns true if the lock is taken by writer.
/*!
* This is inherently racy.
* Only use for debugging and diagnostic purposes.
*/
bool IsLockedByWriter() const noexcept;
private:
using TValue = ui32;
static constexpr TValue UnlockedValue = 0;
static constexpr TValue WriterMask = 1;
static constexpr TValue ReaderDelta = 2;
std::atomic<TValue> Value_ = UnlockedValue;
bool TryAndTryAcquireReader() noexcept;
bool TryAndTryAcquireWriter() noexcept;
void AcquireReaderSlow() noexcept;
void AcquireReaderForkFriendlySlow() noexcept;
void AcquireWriterSlow() noexcept;
};
////////////////////////////////////////////////////////////////////////////////
//! A variant of TReaderWriterSpinLock occupyig the whole cache line.
class TPaddedReaderWriterSpinLock
: public TReaderWriterSpinLock
{
private:
[[maybe_unused]]
char Padding_[CacheLineSize - sizeof(TReaderWriterSpinLock)];
};
////////////////////////////////////////////////////////////////////////////////
template <class T>
struct TReaderSpinlockTraits
{
static void Acquire(T* spinlock);
static void Release(T* spinlock);
};
template <class T>
struct TForkFriendlyReaderSpinlockTraits
{
static void Acquire(T* spinlock);
static void Release(T* spinlock);
};
template <class T>
struct TWriterSpinlockTraits
{
static void Acquire(T* spinlock);
static void Release(T* spinlock);
};
template <class T>
using TReaderGuard = TGuard<T, TReaderSpinlockTraits<T>>;
template <class T>
using TWriterGuard = TGuard<T, TWriterSpinlockTraits<T>>;
template <class T>
auto ReaderGuard(const T& lock);
template <class T>
auto ReaderGuard(const T* lock);
template <class T>
auto ForkFriendlyReaderGuard(const T& lock);
template <class T>
auto ForkFriendlyReaderGuard(const T* lock);
template <class T>
auto WriterGuard(const T& lock);
template <class T>
auto WriterGuard(const T* lock);
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT::NThreading
#define RW_SPIN_LOCK_INL_H_
#include "rw_spin_lock-inl.h"
#undef RW_SPIN_LOCK_INL_H_
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