Utilities/std/cm/shared_mutex

// -*-c++-*-
// vim: set ft=cpp:

/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
   file LICENSE.rst or https://cmake.org/licensing for details.  */
#pragma once

#if __cplusplus >= 201402L || defined(_MSVC_LANG) && _MSVC_LANG >= 201402L
#  define CMake_HAVE_CXX_SHARED_LOCK
#endif
#if __cplusplus >= 201703L || defined(_MSVC_LANG) && _MSVC_LANG >= 201703L
#  define CMake_HAVE_CXX_SHARED_MUTEX
#endif

#if defined(CMake_HAVE_CXX_SHARED_LOCK)
#  include <shared_mutex> // IWYU pragma: export
#endif
#if !defined(CMake_HAVE_CXX_SHARED_MUTEX)
#  include <cm3p/uv.h>
#endif

namespace cm {
#if defined(CMake_HAVE_CXX_SHARED_MUTEX)
using std::shared_mutex;
#else
class shared_mutex
{
  uv_rwlock_t _M_;

public:
  using native_handle_type = uv_rwlock_t*;

  shared_mutex() { uv_rwlock_init(&_M_); }
  ~shared_mutex() { uv_rwlock_destroy(&_M_); }

  shared_mutex(shared_mutex const&) = delete;
  shared_mutex& operator=(shared_mutex const&) = delete;

  void lock() { uv_rwlock_wrlock(&_M_); }
  bool try_lock() { return uv_rwlock_trywrlock(&_M_) == 0; }
  void unlock() { uv_rwlock_wrunlock(&_M_); }

  void lock_shared() { uv_rwlock_rdlock(&_M_); }
  void unlock_shared() { uv_rwlock_rdunlock(&_M_); }

  native_handle_type native_handle() { return &_M_; }
};
#endif

#if defined(CMake_HAVE_CXX_SHARED_LOCK)
using std::shared_lock;
#else
template <typename T>
class shared_lock
{
  T& _mutex;

public:
  using mutex_type = T;

  shared_lock(T& m)
    : _mutex(m)
  {
    _mutex.lock_shared();
  }

  ~shared_lock() { _mutex.unlock_shared(); }

  shared_lock(shared_lock const&) = delete;
  shared_lock& operator=(shared_lock const&) = delete;
};
#endif
}