/*

SDL - Simple DirectMedia Layer

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!

* You can find out a little more about lockless programming and the

* subtle issues that can arise here:

* http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx

*

* There's also lots of good information here:

* http://www.1024cores.net/home/lock-free-algorithms

*

* 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"

/* Need to do this here because intrin.h has C++ code in it */

/* Visual Studio 2005 has a bug where intrin.h conflicts with winnt.h */

#endif

/* 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_AtomicUnlock(SDL_SpinLock *lock);

/**

* The compiler barrier prevents the compiler from reordering

* reads and writes to globally visible variables across the call.

*/

#ifdef _MSC_VER

void _ReadWriteBarrier(void);

#pragma intrinsic(_ReadWriteBarrier)

#define SDL_CompilerBarrier() _ReadWriteBarrier()

#define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")

#else

#define SDL_CompilerBarrier() \

({ SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); })

#endif

/* Platform specific optimized versions of the atomic functions,

* you can disable these by defining SDL_DISABLE_ATOMIC_INLINE

*/

#ifndef SDL_DISABLE_ATOMIC_INLINE

#define SDL_AtomicSet(a, v) _InterlockedExchange((long*)&(a)->value, (v))

#define SDL_AtomicAdd(a, v) _InterlockedExchangeAdd((long*)&(a)->value, (v))

#define SDL_AtomicCAS(a, oldval, newval) (_InterlockedCompareExchange((long*)&(a)->value, (newval), (oldval)) == (oldval))

#if _M_IX86

#define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchange((long*)(a), (long)(newval), (long)(oldval)) == (long)(oldval))

#else

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

#endif

#include <libkern/OSAtomic.h>

#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

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

#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_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)

#endif

#endif /* !SDL_DISABLE_ATOMIC_INLINE */

* \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 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

#define SDL_AtomicCAS SDL_AtomicCAS_

#endif

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

* \brief Set an atomic variable to a value.

*

* \return The previous value of the atomic variable.

static __inline__ int SDL_AtomicSet(SDL_atomic_t *a, int v)

{

int value;

do {

value = a->value;

} while (!SDL_AtomicCAS(a, value, v));

return value;

}

static __inline__ int SDL_AtomicGet(SDL_atomic_t *a)

{

int value = a->value;

SDL_CompilerBarrier();

return value;

}

*

* \return The previous value of the atomic variable.

*

* \note This same style can be used for any number operation

static __inline__ int SDL_AtomicAdd(SDL_atomic_t *a, int v)

{

int value;

do {

value = a->value;

} while (!SDL_AtomicCAS(a, value, (value + v)));

return value;

}

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

*

*

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

*/

#ifndef SDL_AtomicCASPtr

#define SDL_AtomicCASPtr SDL_AtomicCASPtr_

*

* \return The previous value of the pointer.

static __inline__ void* SDL_AtomicSetPtr(void* *a, void* v)

{

void* value;

do {

value = *a;

} while (!SDL_AtomicCASPtr(a, value, v));

return value;

}

static __inline__ void* SDL_AtomicGetPtr(void* *a)

{

void* value = *a;

SDL_CompilerBarrier();

return value;

}

/* 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: */