Simple DirectMedia Layer

Copyright (C) 1997-2011 Sam Lantinga <slouken@libsdl.org>

This software is provided 'as-is', without any express or implied

warranty. In no event will the authors be held liable for any damages

arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,

including commercial applications, and to alter it and redistribute it

freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not

claim that you wrote the original software. If you use this software

in a product, an acknowledgment in the product documentation would be

appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not be

misrepresented as being the original software.

3. This notice may not be removed or altered from any source distribution.

*/

/**

* \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

*/

#if SDL_ATOMIC_DISABLED

#define SDL_DISABLE_ATOMIC_INLINE

#endif

#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: */