/*****************************************************************************

Copyright (c) 2020, 2022, MariaDB Corporation.

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA

*****************************************************************************/

#pragma once
#include "univ.i"
#include "rw_lock.h"

#if defined __linux__
/* futex(2): FUTEX_WAIT_PRIVATE, FUTEX_WAKE_PRIVATE */
#elif defined __OpenBSD__ || defined __FreeBSD__ || defined __DragonFly__
/* system calls similar to Linux futex(2) */
#elif defined _WIN32
/* SRWLOCK as well as WaitOnAddress(), WakeByAddressSingle() */
#else
# define SUX_LOCK_GENERIC /* fall back to generic synchronization primitives */
#endif

#if !defined SUX_LOCK_GENERIC && 0 /* defined SAFE_MUTEX */
# define SUX_LOCK_GENERIC /* Use dummy implementation for debugging purposes */
#endif

#ifndef UNIV_PFS_RWLOCK
# define SRW_LOCK_INIT(key) init()
# define SRW_LOCK_ARGS(file, line) /* nothing */
# define SRW_LOCK_CALL /* nothing */
#else
# define SRW_LOCK_INIT(key) init(key)
# define SRW_LOCK_ARGS(file, line) file, line
# define SRW_LOCK_CALL __FILE__, __LINE__
#endif

/** An exclusive-only variant of srw_lock */
template<bool spinloop>
class pthread_mutex_wrapper final
{
  pthread_mutex_t lock;
#ifdef UNIV_DEBUG
  /** whether the mutex is usable; set by init(); cleared by destroy() */
  bool initialized{false};
public:
  ~pthread_mutex_wrapper() noexcept { ut_ad(!initialized); }
#endif
public:
  void init() noexcept
  {
    ut_ad(!initialized);
    ut_d(initialized= true);
    if (spinloop)
      pthread_mutex_init(&lock, MY_MUTEX_INIT_FAST);
    else
      pthread_mutex_init(&lock, nullptr);
  }
  void destroy() noexcept
  {
    ut_ad(initialized); ut_d(initialized=false);
    pthread_mutex_destroy(&lock);
  }
# ifdef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
  void wr_lock() noexcept { ut_ad(initialized); pthread_mutex_lock(&lock); }
# else
private:
  void wr_wait() noexcept;
public:
  inline void wr_lock() noexcept;
# endif
  void wr_unlock() noexcept { ut_ad(initialized); pthread_mutex_unlock(&lock); }
  bool wr_lock_try() noexcept
  { ut_ad(initialized); return !pthread_mutex_trylock(&lock); }
};

# ifndef PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP
template<> void pthread_mutex_wrapper<true>::wr_wait() noexcept;
template<>
inline void pthread_mutex_wrapper<false>::wr_lock() noexcept
{ ut_ad(initialized); pthread_mutex_lock(&lock); }
template<>
inline void pthread_mutex_wrapper<true>::wr_lock() noexcept
{ if (!wr_lock_try()) wr_wait(); }
# endif

template<bool spinloop> class ssux_lock_impl;

/** Futex-based mutex */
template<bool spinloop>
class srw_mutex_impl final
{
  friend ssux_lock_impl<spinloop>;
  /** The lock word, containing HOLDER + WAITER if the lock is being held,
  plus WAITER times the number of waiters */
  std::atomic<uint32_t> lock;
  /** Identifies that the lock is being held */
  static constexpr uint32_t HOLDER= 1;
  /** Identifies a lock waiter */
  static constexpr uint32_t WAITER= 2;

#ifdef SUX_LOCK_GENERIC
public:
  /** The mutex for the condition variables. */
  pthread_mutex_t mutex;
private:
  /** Condition variable for the lock word. Used with mutex. */
  pthread_cond_t cond;
#endif

  /** Wait until the mutex has been acquired */
  void wait_and_lock() noexcept;
  /** Wait for lock!=lk */
  inline void wait(uint32_t lk) noexcept;
  /** Wake up one wait() thread */
  void wake() noexcept;
  /** Wake up all wait() threads */
  inline void wake_all() noexcept;
public:
  /** @return whether the mutex is being held or waited for */
  bool is_locked_or_waiting() const noexcept
  { return lock.load(std::memory_order_acquire) != 0; }
  /** @return whether the mutex is being held by any thread */
  bool is_locked() const noexcept
  { return (lock.load(std::memory_order_acquire) & HOLDER) != 0; }

  void init() noexcept
  {
    DBUG_ASSERT(!is_locked_or_waiting());
#ifdef SUX_LOCK_GENERIC
    pthread_mutex_init(&mutex, nullptr);
    pthread_cond_init(&cond, nullptr);
#endif
  }
  void destroy() noexcept
  {
    DBUG_ASSERT(!is_locked_or_waiting());
#ifdef SUX_LOCK_GENERIC
    pthread_mutex_destroy(&mutex);
    pthread_cond_destroy(&cond);
#endif
  }

  /** @return whether the mutex was acquired */
  bool wr_lock_try() noexcept
  {
    uint32_t lk= 0;
    return lock.compare_exchange_strong(lk, HOLDER + WAITER,
                                        std::memory_order_acquire,
                                        std::memory_order_relaxed);
  }

  void wr_lock() noexcept { if (!wr_lock_try()) wait_and_lock(); }
  void wr_unlock() noexcept
  {
    const uint32_t lk=
      lock.fetch_sub(HOLDER + WAITER, std::memory_order_release);
    if (lk != HOLDER + WAITER)
    {
      DBUG_ASSERT(lk & HOLDER);
      wake();
    }
  }
};

#ifdef SUX_LOCK_GENERIC
typedef pthread_mutex_wrapper<true> srw_spin_mutex;
typedef pthread_mutex_wrapper<false> srw_mutex;
#else
typedef srw_mutex_impl<true> srw_spin_mutex;
typedef srw_mutex_impl<false> srw_mutex;
#endif

template<bool spinloop> class srw_lock_impl;

/** Slim shared-update-exclusive lock with no recursion */
template<bool spinloop>
class ssux_lock_impl
{
#ifdef UNIV_PFS_RWLOCK
  friend class ssux_lock;
# ifdef SUX_LOCK_GENERIC
# elif defined _WIN32
# else
  friend srw_lock_impl<spinloop>;
# endif
#endif
  /** mutex for synchronization; held by U or X lock holders */
  srw_mutex_impl<spinloop> writer;
#ifdef SUX_LOCK_GENERIC
  /** Condition variable for "readers"; used with writer.mutex. */
  pthread_cond_t readers_cond;
#endif
  /** S or U holders, and WRITER flag for X holder or waiter */
  std::atomic<uint32_t> readers;
  /** indicates an X request; readers=WRITER indicates granted X lock */
  static constexpr uint32_t WRITER= 1U << 31;

  /** Wait for readers!=lk */
  inline void wait(uint32_t lk) noexcept;

  /** Wait for readers!=lk|WRITER */
  void wr_wait(uint32_t lk) noexcept;
  /** Wake up wait() on the last rd_unlock() */
  void wake() noexcept;
public:
  /** Acquire a read lock, with a spin loop */
  void rd_lock_spin() noexcept;
  /** Acquire a read lock, without a spin loop */
  void rd_lock_nospin() noexcept;

  void init() noexcept
  {
    writer.init();
    DBUG_ASSERT(is_vacant());
#ifdef SUX_LOCK_GENERIC
    pthread_cond_init(&readers_cond, nullptr);
#endif
  }
  void destroy() noexcept
  {
    DBUG_ASSERT(is_vacant());
    writer.destroy();
#ifdef SUX_LOCK_GENERIC
    pthread_cond_destroy(&readers_cond);
#endif
  }
  /** @return whether any writer is waiting */
  bool is_waiting() const noexcept
  { return (readers.load(std::memory_order_relaxed) & WRITER) != 0; }
#ifndef DBUG_OFF
  /** @return whether the lock is being held or waited for */
  bool is_vacant() const noexcept { return !is_locked_or_waiting(); }
#endif /* !DBUG_OFF */
private:
  /** Try to acquire a shared latch.
  @return the lock word value if the latch was not acquired
  @retval 0  if the latch was acquired */
  uint32_t rd_lock_try_low() noexcept
  {
    uint32_t lk= 0;
    while (!readers.compare_exchange_weak(lk, lk + 1,
                                          std::memory_order_acquire,
                                          std::memory_order_relaxed))
      if (lk & WRITER)
        return lk;
    return 0;
  }
public:

  bool rd_lock_try() noexcept { return rd_lock_try_low() == 0; }

  bool u_lock_try() noexcept { return writer.wr_lock_try(); }

  bool wr_lock_try() noexcept
  {
    if (!writer.wr_lock_try())
      return false;
    uint32_t lk= 0;
    if (readers.compare_exchange_strong(lk, WRITER,
                                        std::memory_order_acquire,
                                        std::memory_order_relaxed))
      return true;
    writer.wr_unlock();
    return false;
  }

  inline void rd_lock() noexcept;
  void u_lock() noexcept
  {
    writer.wr_lock();
  }
  void wr_lock() noexcept
  {
    writer.wr_lock();
#if defined __i386__||defined __x86_64__||defined _M_IX86||defined _M_X64
    /* On IA-32 and AMD64, a fetch_XXX() that needs to return the
    previous value of the word state can only be implemented
    efficiently for fetch_add() or fetch_sub(), both of which
    translate into a 80486 LOCK XADD instruction. Anything else would
    translate into a loop around LOCK CMPXCHG. In this particular
    case, we know that the bit was previously clear, and therefore
    setting (actually toggling) the most significant bit using
    fetch_add() or fetch_sub() is equivalent. */
    static_assert(WRITER == 1U << 31, "compatibility");
    if (uint32_t lk= readers.fetch_add(WRITER, std::memory_order_acquire))
      wr_wait(lk);
#else
    if (uint32_t lk= readers.fetch_or(WRITER, std::memory_order_acquire))
      wr_wait(lk);
#endif
  }

  bool rd_u_upgrade_try() noexcept { return writer.wr_lock_try(); }

  void u_wr_upgrade() noexcept
  {
    DBUG_ASSERT(writer.is_locked());
    uint32_t lk= readers.fetch_add(WRITER, std::memory_order_acquire);
    if (lk)
      wr_wait(lk);
  }
  void wr_u_downgrade() noexcept
  {
    DBUG_ASSERT(writer.is_locked());
    DBUG_ASSERT(is_write_locked());
    readers.store(0, std::memory_order_release);
    /* Note: Any pending rd_lock() will not be woken up until u_unlock() */
  }
  void u_rd_downgrade() noexcept
  {
    DBUG_ASSERT(writer.is_locked());
    ut_d(uint32_t lk=) readers.fetch_add(1, std::memory_order_relaxed);
    ut_ad(lk < WRITER);
    u_unlock();
  }
  void wr_rd_downgrade() noexcept { wr_u_downgrade(); u_rd_downgrade(); }

  void rd_unlock() noexcept
  {
    uint32_t lk= readers.fetch_sub(1, std::memory_order_release);
    ut_ad(~WRITER & lk);
    if (lk == WRITER + 1)
      wake();
  }
  void u_unlock() noexcept
  {
    writer.wr_unlock();
  }
  void wr_unlock() noexcept
  {
    DBUG_ASSERT(is_write_locked());
    readers.store(0, std::memory_order_release);
    writer.wr_unlock();
  }
  /** @return whether an exclusive lock may be held by any thread */
  bool is_write_locked() const noexcept
  { return readers.load(std::memory_order_acquire) == WRITER; }
  /** @return whether any lock may be held by any thread */
  bool is_locked() const noexcept
  { return readers.load(std::memory_order_acquire) != 0; }
  /** @return whether any lock may be held by any thread */
  bool is_locked_or_waiting() const noexcept
  { return is_locked() || writer.is_locked_or_waiting(); }

  void lock_shared() noexcept { rd_lock(); }
  void unlock_shared() noexcept { rd_unlock(); }
  void lock() noexcept { wr_lock(); }
  void unlock() noexcept { wr_unlock(); }
};

template<> inline void ssux_lock_impl<false>::rd_lock() noexcept
{ rd_lock_nospin(); }
template<> inline void ssux_lock_impl<true>::rd_lock() noexcept
{ if (!rd_lock_try()) rd_lock_spin(); }

#if defined _WIN32 || defined SUX_LOCK_GENERIC
/** Slim read-write lock */
template<bool spinloop>
class srw_lock_
{
# ifdef UNIV_PFS_RWLOCK
  friend srw_lock_impl<spinloop>;
# endif
# ifdef _WIN32
  SRWLOCK lk;
# else
  rw_lock_t lk;
# endif

  void rd_wait() noexcept;
  void wr_wait() noexcept;
public:
  void init() noexcept { IF_WIN(,my_rwlock_init(&lk, nullptr)); }
  void destroy() noexcept { IF_WIN(,rwlock_destroy(&lk)); }
  inline void rd_lock() noexcept;
  inline void wr_lock() noexcept;
  bool rd_lock_try() noexcept
  { return IF_WIN(TryAcquireSRWLockShared(&lk), !rw_tryrdlock(&lk)); }
  void rd_unlock() noexcept
  { IF_WIN(ReleaseSRWLockShared(&lk), rw_unlock(&lk)); }
  bool wr_lock_try() noexcept
  { return IF_WIN(TryAcquireSRWLockExclusive(&lk), !rw_trywrlock(&lk)); }
  void wr_unlock() noexcept
  { IF_WIN(ReleaseSRWLockExclusive(&lk), rw_unlock(&lk)); }
#ifdef _WIN32
  /** @return whether any lock may be held by any thread */
  bool is_locked_or_waiting() const noexcept { return (size_t&)(lk) != 0; }
  /** @return whether any lock may be held by any thread */
  bool is_locked() const noexcept { return is_locked_or_waiting(); }
  /** @return whether an exclusive lock may be held by any thread */
  bool is_write_locked() const noexcept
  {
    // FIXME: this returns false positives for shared locks
    return is_locked();
  }

  void lock_shared() noexcept { rd_lock(); }
  void unlock_shared() noexcept { rd_unlock(); }
  void lock() noexcept { wr_lock(); }
  void unlock() noexcept { wr_unlock(); }
#endif
};

template<> void srw_lock_<true>::rd_wait() noexcept;
template<> void srw_lock_<true>::wr_wait() noexcept;

template<>
inline void srw_lock_<false>::rd_lock() noexcept
{ IF_WIN(AcquireSRWLockShared(&lk), rw_rdlock(&lk)); }
template<>
inline void srw_lock_<false>::wr_lock() noexcept
{ IF_WIN(AcquireSRWLockExclusive(&lk), rw_wrlock(&lk)); }

template<>
inline void srw_lock_<true>::rd_lock() noexcept { if (!rd_lock_try()) rd_wait(); }
template<>
inline void srw_lock_<true>::wr_lock() noexcept { if (!wr_lock_try()) wr_wait(); }

typedef srw_lock_<false> srw_lock_low;
typedef srw_lock_<true> srw_spin_lock_low;
#else
typedef ssux_lock_impl<false> srw_lock_low;
typedef ssux_lock_impl<true> srw_spin_lock_low;
#endif

#ifndef UNIV_PFS_RWLOCK
typedef srw_lock_low srw_lock;
typedef srw_spin_lock_low srw_spin_lock;
#else
/** Slim shared-update-exclusive lock with PERFORMANCE_SCHEMA instrumentation */
class ssux_lock
{
  PSI_rwlock *pfs_psi;
  ssux_lock_impl<true> lock;

  ATTRIBUTE_NOINLINE void psi_rd_lock(const char *file, unsigned line) noexcept;
  ATTRIBUTE_NOINLINE void psi_wr_lock(const char *file, unsigned line) noexcept;
  ATTRIBUTE_NOINLINE void psi_u_lock(const char *file, unsigned line) noexcept;
  ATTRIBUTE_NOINLINE void psi_u_wr_upgrade(const char *file, unsigned line) noexcept;
public:
  void init(mysql_pfs_key_t key) noexcept
  {
    pfs_psi= PSI_RWLOCK_CALL(init_rwlock)(key, this);
    lock.init();
  }
  void destroy() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
    {
      PSI_RWLOCK_CALL(destroy_rwlock)(pfs_psi);
      pfs_psi= nullptr;
    }
    lock.destroy();
  }
  void rd_lock(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      psi_rd_lock(file, line);
    else
      lock.rd_lock();
  }
  void rd_unlock() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      PSI_RWLOCK_CALL(unlock_rwlock)(pfs_psi);
    lock.rd_unlock();
  }
  void u_lock(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      psi_u_lock(file, line);
    else
      lock.u_lock();
  }
  void u_unlock() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      PSI_RWLOCK_CALL(unlock_rwlock)(pfs_psi);
    lock.u_unlock();
  }
  void wr_lock(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      psi_wr_lock(file, line);
    else
      lock.wr_lock();
  }
  void wr_unlock() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      PSI_RWLOCK_CALL(unlock_rwlock)(pfs_psi);
    lock.wr_unlock();
  }
  void u_wr_upgrade(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      psi_u_wr_upgrade(file, line);
    else
      lock.u_wr_upgrade();
  }
  bool rd_lock_try() noexcept { return lock.rd_lock_try(); }
  bool u_lock_try() noexcept { return lock.u_lock_try(); }
  bool wr_lock_try() noexcept { return lock.wr_lock_try(); }
  bool is_waiting() const noexcept { return lock.is_waiting(); }
};

/** Slim reader-writer lock with PERFORMANCE_SCHEMA instrumentation */
template<bool spinloop>
class srw_lock_impl
{
  PSI_rwlock *pfs_psi;
# if defined _WIN32 || defined SUX_LOCK_GENERIC
  srw_lock_<spinloop> lock;
# else
  ssux_lock_impl<spinloop> lock;
# endif

  ATTRIBUTE_NOINLINE void psi_rd_lock(const char *file, unsigned line) noexcept;
  ATTRIBUTE_NOINLINE void psi_wr_lock(const char *file, unsigned line) noexcept;
public:
  void init(mysql_pfs_key_t key) noexcept
  {
    pfs_psi= PSI_RWLOCK_CALL(init_rwlock)(key, this);
    lock.init();
  }
  void destroy() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
    {
      PSI_RWLOCK_CALL(destroy_rwlock)(pfs_psi);
      pfs_psi= nullptr;
    }
    lock.destroy();
  }
  void rd_lock(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      psi_rd_lock(file, line);
    else
      lock.rd_lock();
  }
  void rd_unlock() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      PSI_RWLOCK_CALL(unlock_rwlock)(pfs_psi);
    lock.rd_unlock();
  }
  void wr_lock(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      psi_wr_lock(file, line);
    else
      lock.wr_lock();
  }
  void wr_unlock() noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
      PSI_RWLOCK_CALL(unlock_rwlock)(pfs_psi);
    lock.wr_unlock();
  }
# if defined _WIN32 || defined SUX_LOCK_GENERIC
# else
  void wr_rd_downgrade(const char *file, unsigned line) noexcept
  {
    if (psi_likely(pfs_psi != nullptr))
    {
      PSI_RWLOCK_CALL(unlock_rwlock)(pfs_psi);
      PSI_rwlock_locker_state state;
      if (PSI_rwlock_locker *locker=
          PSI_RWLOCK_CALL(start_rwlock_rdwait)
          (&state, pfs_psi, PSI_RWLOCK_READLOCK, file, line))
        PSI_RWLOCK_CALL(end_rwlock_rdwait)(locker, 0);
    }

    lock.wr_rd_downgrade();
  }
#endif
  bool rd_lock_try() noexcept { return lock.rd_lock_try(); }
  bool wr_lock_try() noexcept { return lock.wr_lock_try(); }
  void lock_shared() noexcept { return rd_lock(SRW_LOCK_CALL); }
  void unlock_shared() noexcept { return rd_unlock(); }
#ifndef SUX_LOCK_GENERIC
  /** @return whether any lock may be held by any thread */
  bool is_locked_or_waiting() const noexcept
  { return lock.is_locked_or_waiting(); }
  /** @return whether a shared or exclusive lock may be held by any thread */
  bool is_locked() const noexcept { return lock.is_locked(); }
  /** @return whether an exclusive lock may be held by any thread */
  bool is_write_locked() const noexcept { return lock.is_write_locked(); }
#endif
};

typedef srw_lock_impl<false> srw_lock;
typedef srw_lock_impl<true> srw_spin_lock;

#endif

#ifdef UNIV_DEBUG
# include <unordered_set>

class srw_lock_debug : private srw_lock
{
  /** The owner of the exclusive lock (0 if none) */
  std::atomic<pthread_t> writer;
  /** Protects readers */
  mutable srw_mutex readers_lock;
  /** Threads that hold the lock in shared mode */
  std::atomic<std::unordered_multiset<pthread_t>*> readers;

  /** Register a read lock. */
  void readers_register() noexcept;

public:
  void SRW_LOCK_INIT(mysql_pfs_key_t key) noexcept;
  void destroy() noexcept;

# ifndef SUX_LOCK_GENERIC
  /** @return whether any lock may be held by any thread */
  bool is_locked_or_waiting() const noexcept
  { return srw_lock::is_locked_or_waiting(); }
  /** @return whether an exclusive lock may be held by any thread */
  bool is_write_locked() const noexcept { return srw_lock::is_write_locked(); }
# endif

  /** Acquire an exclusive lock */
  void wr_lock(SRW_LOCK_ARGS(const char *file, unsigned line)) noexcept;
  /** @return whether an exclusive lock was acquired */
  bool wr_lock_try() noexcept;
  /** Release after wr_lock() */
  void wr_unlock() noexcept;
# if defined _WIN32 || defined SUX_LOCK_GENERIC
# else
  /** Downgrade wr_lock() to rd_lock() */
  void wr_rd_downgrade(SRW_LOCK_ARGS(const char*,unsigned)) noexcept;
# endif
  /** Acquire a shared lock */
  void rd_lock(SRW_LOCK_ARGS(const char *file, unsigned line)) noexcept;
  /** @return whether a shared lock was acquired */
  bool rd_lock_try() noexcept;
  /** Release after rd_lock() */
  void rd_unlock() noexcept;
  /** @return whether this thread is between rd_lock() and rd_unlock() */
  bool have_rd() const noexcept;
  /** @return whether this thread is between wr_lock() and wr_unlock() */
  bool have_wr() const noexcept;
  /** @return whether this thread is holding rd_lock() or wr_lock() */
  bool have_any() const noexcept;
};

# ifndef LOG_LATCH_DEBUG
# elif !defined UNIV_PFS_RWLOCK
typedef srw_lock_debug srw_lock_debug_simple;
# else
class srw_lock_debug_simple : private ssux_lock_impl<false>
{
  /** The owner of the exclusive lock (0 if none) */
  std::atomic<pthread_t> writer;
  /** Protects readers */
  mutable srw_mutex readers_lock;
  /** Threads that hold the lock in shared mode */
  std::atomic<std::unordered_multiset<pthread_t>*> readers;

  /** Register a read lock. */
  void readers_register() noexcept;

public:
  void init() noexcept;
  void destroy() noexcept;

#ifndef SUX_LOCK_GENERIC
  /** @return whether any lock may be held by any thread */
  bool is_locked_or_waiting() const noexcept
  { return ssux_lock_impl::is_locked_or_waiting(); }
  /** @return whether an exclusive lock may be held by any thread */
  bool is_write_locked() const noexcept
  { return ssux_lock_impl::is_write_locked(); }
#endif

  /** Acquire an exclusive lock */
  void wr_lock() noexcept;
  /** @return whether an exclusive lock was acquired */
  bool wr_lock_try() noexcept;
  /** Release after wr_lock() */
  void wr_unlock() noexcept;
  /** Acquire a shared lock */
  void rd_lock() noexcept;
  /** @return whether a shared lock was acquired */
  bool rd_lock_try() noexcept;
  /** Release after rd_lock() */
  void rd_unlock() noexcept;
  /** @return whether this thread is between rd_lock() and rd_unlock() */
  bool have_rd() const noexcept;
  /** @return whether this thread is between wr_lock() and wr_unlock() */
  bool have_wr() const noexcept;
  /** @return whether this thread is holding rd_lock() or wr_lock() */
  bool have_any() const noexcept;
};
# endif
#endif
