atomic.h

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/** @file
 *  @author Bram de Greve (bram@cocamware.com)
 *  @author Tom De Muer (tom@cocamware.com)
 *
 *  *** BEGIN LICENSE INFORMATION ***
 *  
 *  The contents of this file are subject to the Common Public Attribution License 
 *  Version 1.0 (the "License"); you may not use this file except in compliance with 
 *  the License. You may obtain a copy of the License at 
 *  http://lass.sourceforge.net/cpal-license. The License is based on the 
 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover 
 *  use of software over a computer network and provide for limited attribution for 
 *  the Original Developer. In addition, Exhibit A has been modified to be consistent 
 *  with Exhibit B.
 *  
 *  Software distributed under the License is distributed on an "AS IS" basis, WITHOUT 
 *  WARRANTY OF ANY KIND, either express or implied. See the License for the specific 
 *  language governing rights and limitations under the License.
 *  
 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *  
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
 *  The Original Developer is the Initial Developer.
 *  
 *  All portions of the code written by the Initial Developer are:
 *  Copyright (C) 2004-2025 the Initial Developer.
 *  All Rights Reserved.
 *  
 *  Contributor(s):
 *
 *  Alternatively, the contents of this file may be used under the terms of the 
 *  GNU General Public License Version 2 or later (the GPL), in which case the 
 *  provisions of GPL are applicable instead of those above.  If you wish to allow use
 *  of your version of this file only under the terms of the GPL and not to allow 
 *  others to use your version of this file under the CPAL, indicate your decision by 
 *  deleting the provisions above and replace them with the notice and other 
 *  provisions required by the GPL License. If you do not delete the provisions above,
 *  a recipient may use your version of this file under either the CPAL or the GPL.
 *  
 *  *** END LICENSE INFORMATION ***
 */
 
#ifndef LASS_GUARDIAN_OF_INCLUSION_UTIL_ATOMIC_H
#define LASS_GUARDIAN_OF_INCLUSION_UTIL_ATOMIC_H
 
#include "util_common.h"
#if !defined(LASS_PROCESSOR_ARCHITECTURE_ARM64)
#   include "impl/atomic_impl.h"
#endif
 
#include <atomic>
 
#ifdef LASS_PROCESSOR_ARCHITECTURE_x86
#   if LASS_COMPILER_TYPE == LASS_COMPILER_TYPE_MSVC
#       include <intrin.h>
#       define LASS_SPIN_PAUSE _mm_pause()
#   else
#       define LASS_SPIN_PAUSE __builtin_ia32_pause()
#   endif
#else
#   define LASS_SPIN_PAUSE
#endif
 
#ifdef __cpp_lib_hardware_interference_size
#define LASS_LOCK_FREE_ALIGNMENT std::hardware_destructive_interference_size
#else
#define LASS_LOCK_FREE_ALIGNMENT 64
#endif
 
/** @defgroup atomic
 *  @brief atomic operations and tools for lock-free algorithms
 */
 
namespace lass
{
namespace util
{
 
#if !defined(LASS_PROCESSOR_ARCHITECTURE_ARM64)
 
/** @ingroup atomic
 *  
 *  Performs the following pseudocode in an atomic way (no other threads can intervene):
 *  @code
 *      if (dest != expectedValue) return false;
 *      dest = newValue;
 *      return true;
 *  @endcode
 *
 *  @deprecated Use std::atomic
 */
template <typename T>
[[deprecated("Use std::atomic")]]
bool atomicCompareAndSwap(volatile T& dest, T expectedValue, T newValue)
{
    return impl::AtomicOperations< sizeof(T) >::compareAndSwap(dest, expectedValue, newValue);
}
 
 
 
/** @ingroup atomic
 *  
 *  Performs the following pseudocode in an atomic way (no other threads can intervene):
 *  @code
 *      if (dest1 != expectedValue1 || *(T2*)(&dest1 + sizeof(T1)) != expected2) return false;
 *      dest1 = new1;
 *      dest2 = new2;
 *      return true;
 *  @endcode
 *
 *  Does not exist for 64-bit types (there's no 128-bit CAS).
 *
 *  @deprecated Use std::atomic
 */
template <typename T1, typename T2>
[[deprecated("Use std::atomic")]]
bool atomicCompareAndSwap(volatile T1& dest1, T1 expected1, T2 expected2, T1 new1, T2 new2)
{
    static_assert(sizeof(T1) == sizeof(T2), "T1 and T2 must be of same size");
    return impl::AtomicOperations< sizeof(T1) >::compareAndSwap(
        dest1, expected1, expected2, new1, new2);
}
 
 
 
/** @ingroup atomic
 *  
 *  Performs the following pseudocode in an atomic way (no other threads can intervene):
 *  @code
 *      ++value;
 *  @endcode
 *
 *  @deprecated Use std::atomic
 */
template <typename T>
[[deprecated("Use std::atomic")]]
void atomicIncrement(volatile T& value)
{
    impl::AtomicOperations< sizeof(T) >::increment(value);
}
 
 
 
/** @ingroup atomic
 *  
 *  Performs the following pseudocode in an atomic way (no other threads can intervene):
 *  @code
 *      --value;
 *  @endcode
 *
 *  @deprecated Use std::atomic
 */
template <typename T>
[[deprecated("Use std::atomic")]]
void atomicDecrement(volatile T& value)
{
    impl::AtomicOperations< sizeof(T) >::decrement(value);
}
 
 
 
/** @ingroup atomic
 *
 *  @deprecated Use std::atomic
 */
template <typename T>
[[deprecated("Use std::atomic")]]
void atomicLock(volatile T& semaphore)
{
    T current;
    do
    {
        current = semaphore;
    }
    while (current <= 0 || !atomicCompareAndSwap(semaphore, current, current - 1));
}
 
 
 
/** @ingroup atomic
 *
 *  @deprecated Use std::atomic
 */
template <typename T>
[[deprecated("Use std::atomic")]]
bool atomicTryLock(volatile T& semaphore)
{
    T current;
    do
    {
        current = semaphore;
        if (current <= 0)
        {
            return false;
        }
    }
    while (!atomicCompareAndSwap(semaphore, current, current - 1));
    return true;
}
 
 
 
/** @ingroup atomic
 *
 *  @deprecated Use std::atomic
 */
template <typename T>
[[deprecated("Use std::atomic")]]
void atomicUnlock(volatile T& semaphore)
{
    atomicIncrement(semaphore);
}
 
#endif
 
 
/** @ingroup atomic
 */
template <typename T>
void atomicLock(std::atomic<T>& semaphore)
{
    // the load on failure (or when current==0) may be relaxed because
    // memory order is not about the atomic variable itself. It's about
    // loads and stores on _other_ locations, and there are none of these
    // inside the loop. https://stackoverflow.com/q/58635264
    T current = semaphore.load(std::memory_order_acquire);
    do
    {
        while (!current)
        {
            LASS_SPIN_PAUSE;
            current = semaphore.load(std::memory_order_relaxed);
        }
        LASS_ASSERT(current >= 0);
    }
    while (!semaphore.compare_exchange_weak(current, current - 1,
        std::memory_order_release, std::memory_order_relaxed));
}
 
 
 
/** @ingroup atomic
 */
template <typename T>
bool atomicTryLock(std::atomic<T>& semaphore)
{
    // the load on failure (or when current==0) may be relaxed because
    // memory order is not about the atomic variable itself. It's about
    // loads and stores on _other_ locations, and there are none of these
    // inside the loop. https://stackoverflow.com/q/58635264
    T current = semaphore.load(std::memory_order_acquire);
    do
    {
        LASS_ASSERT(current >= 0);
        if (!current)
        {
            return false;
        }
    }
    while (!semaphore.compare_exchange_weak(current, current - 1,
        std::memory_order_release, std::memory_order_relaxed));
    return true;
}
 
 
 
/** @ingroup atomic
 */
template <typename T>
void atomicUnlock(std::atomic<T>& semaphore)
{
    semaphore.fetch_add(1, std::memory_order_acq_rel);
}
 
 
#if LASS_ADDRESS_SIZE == 64
#   if LASS_HAVE_STD_ATOMIC_DWCAS_LOCK_FREE
        // std::atomic is lock free for 16 byte PODs, and will use lock cmpxchg16b
        // (or _InterlockedCompareExchange128) for it's compare_exchange (DWCAS).
        // This requires TaggedPtr to be 16-byte aligned
#       define LASS_TAGGED_PTR_ALIGN alignas(16)
#   elif LASS_ACTUAL_ADDRESS_SIZE == 48
        // std::atomic is *not* lock free for 16 byte PODs, because it will not use
        // lock cmpxchg16b, even though it may commonly exists for this architecture.
        // This is to remain ABI compatible with early 64-bit AMD processors that
        // lacked this instruction.
        // Therefore, we need to use the good old pointers-are-actually-only-48-bits
        // trick to pack a pointer and a 16-bit tag in the space of one 8 byte pointer,
        // for which std::atomic will be lock free.
#       define LASS_TAGGED_PTR_64_PACKED 1
#       define LASS_TAGGED_PTR_ALIGN alignas(8)
#   else
#       error not implemented yet
#   endif
#else
#   define LASS_TAGGED_PTR_ALIGN alignas(8)
#endif
 
/** Pointer with a tag for ABA salvation
 *  @ingroup atomic
 *  Some lock-free algorithms suffer from the ABA problem when acting on pointers.
 *  This can be solved (read: be made very unlikely) by adding a tag to the pointer.
 */
template <typename T>
class LASS_TAGGED_PTR_ALIGN TaggedPtr
{
public:
    typedef T TValue;
    typedef T* TPointer;
 
#if LASS_TAGGED_PTR_64_PACKED
 
    typedef num::Tuint16 TTag;
    TaggedPtr() = default;
    TaggedPtr(T * ptr, TTag tag): bits_((reinterpret_cast<num::Tint64>(ptr) << 16) | (tag & 0xffff)) {}
    TPointer get() const
    {
#   if defined(LASS_HAVE_INLINE_ASSEMBLY_GCC) && defined(LASS_PROCESSOR_ARCHITECTURE_x86)
        TPointer ptr;
        __asm__ ("sarq $16, %0;" : "=q"(ptr) : "0"(bits_) : "cc");
        return ptr;
#   elif LASS_COMPILER_TYPE == LASS_COMPILER_TYPE_MSVC
        return reinterpret_cast<TPointer>(__ll_rshift(bits_, 16));
#   else
        return ((bits_ & 0xa000000000000000) == 0) ?
            reinterpret_cast<TPointer>(bits_ >> 16) :
            reinterpret_cast<TPointer>((bits_ >> 16) | 0xffff000000000000);
#   endif
    }
    TTag tag() const { return static_cast<TTag>(bits_ & 0xffff); }
    TTag nextTag() const { return static_cast<TTag>(static_cast<size_t>(tag() + 1) & 0xffff); }
    bool operator==(const TaggedPtr& other) const { return bits_ == other.bits_; }
private:
    num::Tint64 bits_ = 0;
 
#else
 
    typedef num::TuintPtr TTag;
    TaggedPtr() = default;
    TaggedPtr(TPointer ptr, TTag tag) : ptr_(ptr), tag_(tag) {}
    TPointer get() const { return ptr_; }
    TTag tag() const { return tag_; }
    TTag nextTag() const { return tag_ + 1; }
    bool operator==(const TaggedPtr& other) const { return ptr_ == other.ptr_ && tag_ == other.tag_; }
private:
    TPointer ptr_ = nullptr;
    TTag tag_ = 0;
 
#endif
 
public:
    TPointer operator->() const { LASS_ASSERT(get()); return get(); }
    bool operator!() const { return get() == nullptr; }
    explicit operator bool() const { return get() != nullptr; }
    bool operator!=(const TaggedPtr& other) const { return !(*this == other); }
};
 
 
}
}
 
#endif
 
// EOF