//===- 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>
// std::shared_timed_mutex is only availble on macOS 10.12 and later.
#if defined(__APPLE__) && defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__)
#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
#define LLVM_USE_RW_MUTEX_IMPL
#endif
#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 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();
//@}
/// @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 {
#if !defined(LLVM_USE_RW_MUTEX_IMPL)
std::shared_mutex impl;
#else
RWMutexImpl impl;
#endif
unsigned readers = 0;
unsigned writers = 0;
public:
bool lock_shared() {
if (!mt_only || llvm_is_multithreaded()) {
impl.lock_shared();
return true;
}
// Single-threaded debugging code. This would be racy in multithreaded
// mode, but provides not basic checks in single threaded mode.
++readers;
return true;
}
bool unlock_shared() {
if (!mt_only || llvm_is_multithreaded()) {
impl.unlock_shared();
return true;
}
// Single-threaded debugging code. This would be racy in multithreaded
// mode, but provides not basic checks in single threaded mode.
assert(readers > 0 && "Reader lock not acquired before release!");
--readers;
return true;
}
bool lock() {
if (!mt_only || llvm_is_multithreaded()) {
impl.lock();
return true;
}
// Single-threaded debugging code. This would be racy in multithreaded
// mode, but provides not basic checks in single threaded mode.
assert(writers == 0 && "Writer lock already acquired!");
++writers;
return true;
}
bool unlock() {
if (!mt_only || llvm_is_multithreaded()) {
impl.unlock();
return true;
}
// Single-threaded debugging code. This would be racy in multithreaded
// mode, but provides not basic checks in single threaded mode.
assert(writers == 1 && "Writer lock not acquired before release!");
--writers;
return true;
}
};
typedef SmartRWMutex<false> RWMutex;
/// ScopedReader - RAII acquisition of a reader lock
#if !defined(LLVM_USE_RW_MUTEX_IMPL)
template <bool mt_only>
using SmartScopedReader = const std::shared_lock<SmartRWMutex<mt_only>>;
#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
typedef SmartScopedReader<false> ScopedReader;
/// ScopedWriter - RAII acquisition of a writer lock
#if !defined(LLVM_USE_RW_MUTEX_IMPL)
template <bool mt_only>
using SmartScopedWriter = std::lock_guard<SmartRWMutex<mt_only>>;
#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
typedef SmartScopedWriter<false> ScopedWriter;
} // end namespace sys
} // end namespace llvm
#endif // LLVM_SUPPORT_RWMUTEX_H