llvm/llvm/include/llvm/Support/RWMutex.h

//===- RWMutex.h - Reader/Writer Mutual Exclusion Lock ----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file declares the llvm::sys::RWMutex class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_SUPPORT_RWMUTEX_H
#define LLVM_SUPPORT_RWMUTEX_H

#include "llvm/Config/llvm-config.h"
#include "llvm/Support/Threading.h"
#include <cassert>
#include <mutex>
#include <shared_mutex>

#if defined(__APPLE__)
#define LLVM_USE_RW_MUTEX_IMPL
#endif

namespace llvm {
namespace sys {

#if defined(LLVM_USE_RW_MUTEX_IMPL)
/// Platform agnostic RWMutex class.
class RWMutexImpl {
  /// @name Constructors
  /// @{
public:
  /// Initializes the lock but doesn't acquire it.
  /// Default Constructor.
  explicit RWMutexImpl();

  /// @}
  /// @name Do Not Implement
  /// @{
  RWMutexImpl(const RWMutexImpl &original) = delete;
  RWMutexImpl &operator=(const RWMutexImpl &) = delete;
  /// @}

  /// Releases and removes the lock
  /// Destructor
  ~RWMutexImpl();

  /// @}
  /// @name Methods
  /// @{
public:
  /// Attempts to unconditionally acquire the lock in reader mode. If the
  /// lock is held by a writer, this method will wait until it can acquire
  /// the lock.
  /// @returns false if any kind of error occurs, true otherwise.
  /// Unconditionally acquire the lock in reader mode.
  bool lock_shared();

  /// Attempts to release the lock in reader mode.
  /// @returns false if any kind of error occurs, true otherwise.
  /// Unconditionally release the lock in reader mode.
  bool unlock_shared();

  /// Attempts to acquire the lock in reader mode. Returns immediately.
  /// @returns true on successful lock acquisition, false otherwise.
  bool try_lock_shared();

  /// Attempts to unconditionally acquire the lock in reader mode. If the
  /// lock is held by any readers, this method will wait until it can
  /// acquire the lock.
  /// @returns false if any kind of error occurs, true otherwise.
  /// Unconditionally acquire the lock in writer mode.
  bool lock();

  /// Attempts to release the lock in writer mode.
  /// @returns false if any kind of error occurs, true otherwise.
  /// Unconditionally release the lock in write mode.
  bool unlock();

  /// Attempts to acquire the lock in writer mode. Returns immediately.
  /// @returns true on successful lock acquisition, false otherwise.
  bool try_lock();

  //@}
  /// @name Platform Dependent Data
  /// @{
private:
#if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
  void *data_ = nullptr; ///< We don't know what the data will be
#endif
};
#endif

/// SmartMutex - An R/W mutex with a compile time constant parameter that
/// indicates whether this mutex should become a no-op when we're not
/// running in multithreaded mode.
template <bool mt_only> class SmartRWMutex { … };

RWMutex;

/// ScopedReader - RAII acquisition of a reader lock
#if !defined(LLVM_USE_RW_MUTEX_IMPL)
SmartScopedReader;
#else
template <bool mt_only> struct SmartScopedReader {
  SmartRWMutex<mt_only> &mutex;

  explicit SmartScopedReader(SmartRWMutex<mt_only> &m) : mutex(m) {
    mutex.lock_shared();
  }

  ~SmartScopedReader() { mutex.unlock_shared(); }
};
#endif
ScopedReader;

/// ScopedWriter - RAII acquisition of a writer lock
#if !defined(LLVM_USE_RW_MUTEX_IMPL)
SmartScopedWriter;
#else
template <bool mt_only> struct SmartScopedWriter {
  SmartRWMutex<mt_only> &mutex;

  explicit SmartScopedWriter(SmartRWMutex<mt_only> &m) : mutex(m) {
    mutex.lock();
  }

  ~SmartScopedWriter() { mutex.unlock(); }
};
#endif
ScopedWriter;

} // end namespace sys
} // end namespace llvm

#endif // LLVM_SUPPORT_RWMUTEX_H