atomic_ptr.hpp

/*
    Copyright (c) 2007-2015 Contributors as noted in the AUTHORS file

    This file is part of libzmq, the ZeroMQ core engine in C++.

    libzmq is free software; you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    As a special exception, the Contributors give you permission to link
    this library with independent modules to produce an executable,
    regardless of the license terms of these independent modules, and to
    copy and distribute the resulting executable under terms of your choice,
    provided that you also meet, for each linked independent module, the
    terms and conditions of the license of that module. An independent
    module is a module which is not derived from or based on this library.
    If you modify this library, you must extend this exception to your
    version of the library.

    libzmq 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 Lesser General Public
    License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef __ZMQ_ATOMIC_PTR_HPP_INCLUDED__
#define __ZMQ_ATOMIC_PTR_HPP_INCLUDED__

#include "platform.hpp"

#if defined ZMQ_FORCE_MUTEXES
#define ZMQ_ATOMIC_PTR_MUTEX
#elif defined ZMQ_HAVE_ATOMIC_INTRINSICS
#define ZMQ_ATOMIC_PTR_INTRINSIC
#elif (defined ZMQ_CXX11 && defined __cplusplus && __cplusplus >= 201103L)
#define ZMQ_ATOMIC_PTR_CXX11
#elif (defined __i386__ || defined __x86_64__) && defined __GNUC__
#define ZMQ_ATOMIC_PTR_X86
#elif defined __ARM_ARCH_7A__ && defined __GNUC__
#define ZMQ_ATOMIC_PTR_ARM
#elif defined __tile__
#define ZMQ_ATOMIC_PTR_TILE
#elif defined ZMQ_HAVE_WINDOWS
#define ZMQ_ATOMIC_PTR_WINDOWS
#elif (defined ZMQ_HAVE_SOLARIS || defined ZMQ_HAVE_NETBSD)
#define ZMQ_ATOMIC_PTR_ATOMIC_H
#else
#define ZMQ_ATOMIC_PTR_MUTEX
#endif

#if defined ZMQ_ATOMIC_PTR_MUTEX
#include "mutex.hpp"
#elif defined ZMQ_ATOMIC_PTR_CXX11
#include <atomic>
#elif defined ZMQ_ATOMIC_PTR_WINDOWS
#include "windows.hpp"
#elif defined ZMQ_ATOMIC_PTR_ATOMIC_H
#include <atomic.h>
#elif defined ZMQ_ATOMIC_PTR_TILE
#include <arch/atomic.h>
#endif

namespace zmq
{

    //  This class encapsulates several atomic operations on pointers.

    template <typename T> class atomic_ptr_t
    {
    public:

        //  Initialise atomic pointer
        inline atomic_ptr_t ()
        {
            ptr = NULL;
        }

        //  Destroy atomic pointer
        inline ~atomic_ptr_t ()
        {
        }

        //  Set value of atomic pointer in a non-threadsafe way
        //  Use this function only when you are sure that at most one
        //  thread is accessing the pointer at the moment.
        inline void set (T *ptr_)
        {
            this->ptr = ptr_;
        }

        //  Perform atomic 'exchange pointers' operation. Pointer is set
        //  to the 'val' value. Old value is returned.
        inline T *xchg (T *val_)
        {
#if defined ZMQ_ATOMIC_PTR_WINDOWS
            return (T*) InterlockedExchangePointer ((PVOID*) &ptr, val_);
#elif defined ZMQ_ATOMIC_PTR_INTRINSIC
            return (T*) __atomic_exchange_n (&ptr, val_, __ATOMIC_ACQ_REL);
#elif defined ZMQ_ATOMIC_PTR_CXX11
            return ptr.exchange(val_, std::memory_order_acq_rel);
#elif defined ZMQ_ATOMIC_PTR_ATOMIC_H
            return (T*) atomic_swap_ptr (&ptr, val_);
#elif defined ZMQ_ATOMIC_PTR_TILE
            return (T*) arch_atomic_exchange (&ptr, val_);
#elif defined ZMQ_ATOMIC_PTR_X86
            T *old;
            __asm__ volatile (
                "lock; xchg %0, %2"
                : "=r" (old), "=m" (ptr)
                : "m" (ptr), "0" (val_));
            return old;
#elif defined ZMQ_ATOMIC_PTR_ARM
            T* old;
            unsigned int flag;
            __asm__ volatile (
                "       dmb     sy\n\t"
                "1:     ldrex   %1, [%3]\n\t"
                "       strex   %0, %4, [%3]\n\t"
                "       teq     %0, #0\n\t"
                "       bne     1b\n\t"
                "       dmb     sy\n\t"
                : "=&r"(flag), "=&r"(old), "+Qo"(ptr)
                : "r"(&ptr), "r"(val_)
                : "cc");
            return old;
#elif defined ZMQ_ATOMIC_PTR_MUTEX
            sync.lock ();
            T *old = (T*) ptr;
            ptr = val_;
            sync.unlock ();
            return old;
#else
#error atomic_ptr is not implemented for this platform
#endif
        }

        //  Perform atomic 'compare and swap' operation on the pointer.
        //  The pointer is compared to 'cmp' argument and if they are
        //  equal, its value is set to 'val'. Old value of the pointer
        //  is returned.
        inline T *cas (T *cmp_, T *val_)
        {
#if defined ZMQ_ATOMIC_PTR_WINDOWS
            return (T*) InterlockedCompareExchangePointer (
                (volatile PVOID*) &ptr, val_, cmp_);
#elif defined ZMQ_ATOMIC_PTR_INTRINSIC
            T *old = cmp_;
            __atomic_compare_exchange_n (&ptr, (volatile T**) &old, val_, false,
                    __ATOMIC_RELEASE, __ATOMIC_ACQUIRE);
            return old;
#elif defined ZMQ_ATOMIC_PTR_CXX11
            ptr.compare_exchange_strong(cmp_, val_, std::memory_order_acq_rel);
            return cmp_;
#elif defined ZMQ_ATOMIC_PTR_ATOMIC_H
            return (T*) atomic_cas_ptr (&ptr, cmp_, val_);
#elif defined ZMQ_ATOMIC_PTR_TILE
            return (T*) arch_atomic_val_compare_and_exchange (&ptr, cmp_, val_);
#elif defined ZMQ_ATOMIC_PTR_X86
            T *old;
            __asm__ volatile (
                "lock; cmpxchg %2, %3"
                : "=a" (old), "=m" (ptr)
                : "r" (val_), "m" (ptr), "0" (cmp_)
                : "cc");
            return old;
#elif defined ZMQ_ATOMIC_PTR_ARM
            T *old;
            unsigned int flag;
            __asm__ volatile (
                "       dmb     sy\n\t"
                "1:     ldrex   %1, [%3]\n\t"
                "       mov     %0, #0\n\t"
                "       teq     %1, %4\n\t"
                "       it      eq\n\t"
                "       strexeq %0, %5, [%3]\n\t"
                "       teq     %0, #0\n\t"
                "       bne     1b\n\t"
                "       dmb     sy\n\t"
                : "=&r"(flag), "=&r"(old), "+Qo"(ptr)
                : "r"(&ptr), "r"(cmp_), "r"(val_)
                : "cc");
            return old;
#elif defined ZMQ_ATOMIC_PTR_MUTEX
            sync.lock ();
            T *old = (T*) ptr;
            if (ptr == cmp_)
                ptr = val_;
            sync.unlock ();
            return old;
#else
#error atomic_ptr is not implemented for this platform
#endif
        }

    private:

#if defined ZMQ_ATOMIC_PTR_CXX11
        std::atomic<T*> ptr;
#else
        volatile T *ptr;
#endif

#if defined ZMQ_ATOMIC_PTR_MUTEX
        mutex_t sync;
#endif

#if ! defined ZMQ_ATOMIC_PTR_CXX11
        atomic_ptr_t (const atomic_ptr_t&);
        const atomic_ptr_t &operator = (const atomic_ptr_t&);
#endif
    };

}

//  Remove macros local to this file.
#undef ZMQ_ATOMIC_PTR_MUTEX
#undef ZMQ_ATOMIC_PTR_INTRINSIC
#undef ZMQ_ATOMIC_PTR_CXX11
#undef ZMQ_ATOMIC_PTR_X86
#undef ZMQ_ATOMIC_PTR_ARM
#undef ZMQ_ATOMIC_PTR_TILE
#undef ZMQ_ATOMIC_PTR_WINDOWS
#undef ZMQ_ATOMIC_PTR_ATOMIC_H

#endif