/*

    SDL - Simple DirectMedia Layer

    Copyright (C) 1997-2010 Sam Lantinga

    This library is free software; you can redistribute it and/or

    modify it under the terms of the GNU Lesser General Public

    License as published by the Free Software Foundation; either

    version 2.1 of the License, or (at your option) any later version.

    This library 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 library; if not, write to the Free Software

    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga

    slouken@libsdl.org

 */

/**

 * \file SDL_atomic.h

 * 

 * Atomic operations.

 * 

 * IMPORTANT:

 * If you are not an expert in concurrent lockless programming, you should

 * only be using the atomic lock and reference counting functions in this

 * file.  In all other cases you should be protecting your data structures

 * with full mutexes.

 * 

 * The list of "safe" functions to use are:

 *  SDL_AtomicLock()

 *  SDL_AtomicUnlock()

 *  SDL_AtomicIncRef()

 *  SDL_AtomicDecRef()

 * 

 * Seriously, here be dragons!

 *

 * These operations may, or may not, actually be implemented using

 * processor specific atomic operations. When possible they are

 * implemented as true processor specific atomic operations. When that

 * is not possible the are implemented using locks that *do* use the

 * available atomic operations.

 *

 * All of the atomic operations that modify memory are full memory barriers.

 */

#ifndef _SDL_atomic_h_

#define _SDL_atomic_h_

#include "SDL_stdinc.h"

#include "SDL_platform.h"

#include "begin_code.h"

/* Set up for C function definitions, even when using C++ */

#ifdef __cplusplus

/* *INDENT-OFF* */

extern "C" {

/* *INDENT-ON* */

#endif

/**

 * \name SDL AtomicLock

 * 

 * The atomic locks are efficient spinlocks using CPU instructions,

 * but are vulnerable to starvation and can spin forever if a thread

 * holding a lock has been terminated.  For this reason you should

 * minimize the code executed inside an atomic lock and never do

 * expensive things like API or system calls while holding them.

 *

 * The atomic locks are not safe to lock recursively.

 *

 * Porting Note:

 * The spin lock functions and type are required and can not be

 * emulated because they are used in the atomic emulation code.

 */

/*@{*/

typedef int SDL_SpinLock;

/**

 * \brief Try to lock a spin lock by setting it to a non-zero value.

 * 

 * \param lock Points to the lock.

 *

 * \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.

 */

extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);

/**

 * \brief Lock a spin lock by setting it to a non-zero value.

 * 

 * \param lock Points to the lock.

 */

extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);

/**

 * \brief Unlock a spin lock by setting it to 0. Always returns immediately

 *

 * \param lock Points to the lock.

 */

extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);

/*@}*//*SDL AtomicLock*/

/* Platform specific optimized versions of the atomic functions */

#define WIN32_LEAN_AND_MEAN

#include <windows.h>

#define SDL_AtomicSet(a, v)     InterlockedExchange(&(a)->value, v)

#define SDL_AtomicGet(a)        ((a)->value)

#define SDL_AtomicAdd(a, v)     InterlockedAdd(&(a)->value, v)

#define SDL_AtomicCAS(a, oldval, newval) (InterlockedCompareExchange(&(a)->value, newval, oldval) == (oldval))

#define SDL_AtomicSetPtr(a, v)  InterlockedExchangePointer(a, v)

#define SDL_AtomicGetPtr(a)     (*(a))

#define SDL_AtomicCASPtr(a, oldval, newval) (InterlockedCompareExchangePointer(a, newval, oldval) == (oldval))

#elif defined(__MACOSX__)

#include <libkern/OSAtomic.h>

#define SDL_AtomicSet(a, v) \

({                          \

    int oldvalue;           \

                            \

    do {                    \

        oldvalue = (a)->value; \

    } while (!OSAtomicCompareAndSwap32Barrier(oldvalue, v, &(a)->value)); \

                            \

    oldvalue;               \

})

#define SDL_AtomicGet(a)        ((a)->value)

#define SDL_AtomicAdd(a, v) \

({                          \

    int oldvalue;           \

                            \

    do {                    \

        oldvalue = (a)->value; \

    } while (!OSAtomicCompareAndSwap32Barrier(oldvalue, oldvalue+v, &(a)->value)); \

                            \

    oldvalue;               \

})

#define SDL_AtomicCAS(a, oldval, newval) OSAtomicCompareAndSwap32Barrier(oldval, newval, &(a)->value)

#define SDL_AtomicSetPtr(a, v)  (*(a) = v, OSMemoryBarrier())

#define SDL_AtomicGetPtr(a)     (*(a))

#if SIZEOF_VOIDP == 4

#define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_t*)(a))

#elif SIZEOF_VOIDP == 8

#define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))

#endif

#elif defined(HAVE_GCC_ATOMICS)

#define SDL_AtomicSet(a, v)     __sync_lock_test_and_set(&(a)->value, v)

#define SDL_AtomicGet(a)        ((a)->value)

#define SDL_AtomicAdd(a, v)     __sync_fetch_and_add(&(a)->value, v)

#define SDL_AtomicCAS(a, oldval, newval) __sync_bool_compare_and_swap(&(a)->value, oldval, newval)

#define SDL_AtomicSetPtr(a, v)  (*(a) = v, __sync_synchronize())

#define SDL_AtomicGetPtr(a)     (*(a))

#define SDL_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)

#endif

/**

 * \brief A type representing an atomic integer value.  It is a struct

 *        so people don't accidentally use numeric operations on it.

 */

#ifndef SDL_atomic_t_defined

typedef struct { int value; } SDL_atomic_t;

#endif

/**

 * \brief Set an atomic variable to a value.

 *

 * \return The previous value of the atomic variable.

 */

#ifndef SDL_AtomicSet

extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int value);

#endif

/**

 * \brief Get the value of an atomic variable

 */

#ifndef SDL_AtomicGet

extern DECLSPEC int SDLCALL SDL_AtomicGet(SDL_atomic_t *a);

#endif

/**

 * \brief  Add to an atomic variable.

 *

 * \return The previous value of the atomic variable.

 */

#ifndef SDL_AtomicAdd

extern DECLSPEC int SDLCALL SDL_AtomicAdd(SDL_atomic_t *a, int value);

#endif

/**

 * \brief Increment an atomic variable used as a reference count.

 */

#ifndef SDL_AtomicIncRef

extern DECLSPEC void SDLCALL SDL_AtomicIncRef(SDL_atomic_t *a);

#endif

/**

 * \brief Decrement an atomic variable used as a reference count.

 *

 * \return SDL_TRUE if the variable has reached zero after decrementing,

 *         SDL_FALSE otherwise

 */

#ifndef SDL_AtomicDecRef

extern DECLSPEC SDL_bool SDLCALL SDL_AtomicDecRef(SDL_atomic_t *a);

#endif

/**

 * \brief Set an atomic variable to a new value if it is currently an old value.

 *

 * \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.

 *

 * \note If you don't know what this function is for, you shouldn't use it!

*/

#ifndef SDL_AtomicCAS

extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);

#endif

/**

 * \brief Set a pointer to a value atomically.

 */

#ifndef SDL_AtomicSetPtr

extern DECLSPEC void SDLCALL SDL_AtomicSetPtr(void** a, void* value);

#endif

/**

 * \brief Get the value of a pointer atomically.

 */

#ifndef SDL_AtomicGetPtr

extern DECLSPEC void* SDLCALL SDL_AtomicGetPtr(void** a);

#endif

/**

 * \brief Set a pointer to a new value if it is currently an old value.

 *

 * \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.

 *

 * \note If you don't know what this function is for, you shouldn't use it!

*/

#ifndef SDL_AtomicCASPtr

extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);

#endif

/* Ends C function definitions when using C++ */

#ifdef __cplusplus

/* *INDENT-OFF* */

}

/* *INDENT-ON* */

#endif

#include "close_code.h"

#endif /* _SDL_atomic_h_ */

/* vi: set ts=4 sw=4 expandtab: */