318 lines
9.2 KiB
C
318 lines
9.2 KiB
C
/*
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Simple DirectMedia Layer
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Copyright (C) 1997-2011 Sam Lantinga <slouken@libsdl.org>
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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/**
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* \file SDL_atomic.h
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*
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* Atomic operations.
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*
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* IMPORTANT:
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* If you are not an expert in concurrent lockless programming, you should
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* only be using the atomic lock and reference counting functions in this
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* file. In all other cases you should be protecting your data structures
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* with full mutexes.
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*
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* The list of "safe" functions to use are:
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* SDL_AtomicLock()
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* SDL_AtomicUnlock()
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* SDL_AtomicIncRef()
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* SDL_AtomicDecRef()
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*
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* Seriously, here be dragons!
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* ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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*
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* You can find out a little more about lockless programming and the
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* subtle issues that can arise here:
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* http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx
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*
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* There's also lots of good information here:
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* http://www.1024cores.net/home/lock-free-algorithms
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*
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* These operations may or may not actually be implemented using
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* processor specific atomic operations. When possible they are
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* implemented as true processor specific atomic operations. When that
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* is not possible the are implemented using locks that *do* use the
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* available atomic operations.
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*
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* All of the atomic operations that modify memory are full memory barriers.
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*/
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#ifndef _SDL_atomic_h_
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#define _SDL_atomic_h_
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#include "SDL_stdinc.h"
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#include "SDL_platform.h"
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#include "begin_code.h"
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/* Need to do this here because intrin.h has C++ code in it */
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/* Visual Studio 2005 has a bug where intrin.h conflicts with winnt.h */
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#if defined(_MSC_VER) && (_MSC_VER >= 1500) && !defined(_WIN32_WCE)
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#include <intrin.h>
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#define HAVE_MSC_ATOMICS 1
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#endif
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/* Set up for C function definitions, even when using C++ */
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#ifdef __cplusplus
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/* *INDENT-OFF* */
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extern "C" {
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/* *INDENT-ON* */
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#endif
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/**
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* \name SDL AtomicLock
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*
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* The atomic locks are efficient spinlocks using CPU instructions,
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* but are vulnerable to starvation and can spin forever if a thread
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* holding a lock has been terminated. For this reason you should
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* minimize the code executed inside an atomic lock and never do
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* expensive things like API or system calls while holding them.
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*
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* The atomic locks are not safe to lock recursively.
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*
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* Porting Note:
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* The spin lock functions and type are required and can not be
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* emulated because they are used in the atomic emulation code.
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*/
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/*@{*/
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typedef int SDL_SpinLock;
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/**
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* \brief Try to lock a spin lock by setting it to a non-zero value.
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*
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* \param lock Points to the lock.
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*
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* \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
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*/
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extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
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/**
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* \brief Lock a spin lock by setting it to a non-zero value.
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*
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* \param lock Points to the lock.
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*/
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extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
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/**
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* \brief Unlock a spin lock by setting it to 0. Always returns immediately
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*
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* \param lock Points to the lock.
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*/
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extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
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/*@}*//*SDL AtomicLock*/
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/**
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* The compiler barrier prevents the compiler from reordering
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* reads and writes to globally visible variables across the call.
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*/
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#ifdef _MSC_VER
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void _ReadWriteBarrier(void);
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#pragma intrinsic(_ReadWriteBarrier)
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#define SDL_CompilerBarrier() _ReadWriteBarrier()
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#elif defined(__GNUC__)
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#define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")
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#else
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#define SDL_CompilerBarrier() \
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({ SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); })
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#endif
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/* Platform specific optimized versions of the atomic functions,
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* you can disable these by defining SDL_DISABLE_ATOMIC_INLINE
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*/
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#if defined(SDL_ATOMIC_DISABLED) && SDL_ATOMIC_DISABLED
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#define SDL_DISABLE_ATOMIC_INLINE
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#endif
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#ifndef SDL_DISABLE_ATOMIC_INLINE
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#ifdef HAVE_MSC_ATOMICS
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#define SDL_AtomicSet(a, v) _InterlockedExchange((long*)&(a)->value, (v))
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#define SDL_AtomicAdd(a, v) _InterlockedExchangeAdd((long*)&(a)->value, (v))
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#define SDL_AtomicCAS(a, oldval, newval) (_InterlockedCompareExchange((long*)&(a)->value, (newval), (oldval)) == (oldval))
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#define SDL_AtomicSetPtr(a, v) _InterlockedExchangePointer((a), (v))
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#if _M_IX86
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#define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchange((long*)(a), (long)(newval), (long)(oldval)) == (long)(oldval))
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#else
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#define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchangePointer((a), (newval), (oldval)) == (oldval))
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#endif
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#elif defined(__MACOSX__)
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#include <libkern/OSAtomic.h>
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#define SDL_AtomicCAS(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((oldval), (newval), &(a)->value)
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#if SIZEOF_VOIDP == 4
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#define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_t*)(a))
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#elif SIZEOF_VOIDP == 8
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#define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))
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#endif
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#elif defined(HAVE_GCC_ATOMICS)
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#define SDL_AtomicSet(a, v) __sync_lock_test_and_set(&(a)->value, v)
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#define SDL_AtomicAdd(a, v) __sync_fetch_and_add(&(a)->value, v)
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#define SDL_AtomicSetPtr(a, v) __sync_lock_test_and_set(a, v)
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#define SDL_AtomicCAS(a, oldval, newval) __sync_bool_compare_and_swap(&(a)->value, oldval, newval)
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#define SDL_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)
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#endif
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#endif /* !SDL_DISABLE_ATOMIC_INLINE */
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/**
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* \brief A type representing an atomic integer value. It is a struct
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* so people don't accidentally use numeric operations on it.
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*/
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#ifndef SDL_atomic_t_defined
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typedef struct { int value; } SDL_atomic_t;
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#endif
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/**
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* \brief Set an atomic variable to a new value if it is currently an old value.
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*
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* \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
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*
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* \note If you don't know what this function is for, you shouldn't use it!
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*/
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#ifndef SDL_AtomicCAS
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#define SDL_AtomicCAS SDL_AtomicCAS_
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#endif
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extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS_(SDL_atomic_t *a, int oldval, int newval);
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/**
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* \brief Set an atomic variable to a value.
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*
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* \return The previous value of the atomic variable.
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*/
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#ifndef SDL_AtomicSet
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static __inline__ int SDL_AtomicSet(SDL_atomic_t *a, int v)
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{
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int value;
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do {
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value = a->value;
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} while (!SDL_AtomicCAS(a, value, v));
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return value;
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}
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#endif
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/**
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* \brief Get the value of an atomic variable
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*/
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#ifndef SDL_AtomicGet
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static __inline__ int SDL_AtomicGet(SDL_atomic_t *a)
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{
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int value = a->value;
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SDL_CompilerBarrier();
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return value;
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}
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#endif
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/**
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* \brief Add to an atomic variable.
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*
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* \return The previous value of the atomic variable.
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*
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* \note This same style can be used for any number operation
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*/
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#ifndef SDL_AtomicAdd
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static __inline__ int SDL_AtomicAdd(SDL_atomic_t *a, int v)
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{
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int value;
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do {
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value = a->value;
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} while (!SDL_AtomicCAS(a, value, (value + v)));
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return value;
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}
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#endif
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/**
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* \brief Increment an atomic variable used as a reference count.
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*/
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#ifndef SDL_AtomicIncRef
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#define SDL_AtomicIncRef(a) SDL_AtomicAdd(a, 1)
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#endif
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/**
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* \brief Decrement an atomic variable used as a reference count.
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*
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* \return SDL_TRUE if the variable reached zero after decrementing,
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* SDL_FALSE otherwise
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*/
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#ifndef SDL_AtomicDecRef
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#define SDL_AtomicDecRef(a) (SDL_AtomicAdd(a, -1) == 1)
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#endif
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/**
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* \brief Set a pointer to a new value if it is currently an old value.
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*
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* \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
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*
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* \note If you don't know what this function is for, you shouldn't use it!
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*/
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#ifndef SDL_AtomicCASPtr
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#define SDL_AtomicCASPtr SDL_AtomicCASPtr_
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#endif
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extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr_(void* *a, void *oldval, void *newval);
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/**
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* \brief Set a pointer to a value atomically.
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*
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* \return The previous value of the pointer.
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*/
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#ifndef SDL_AtomicSetPtr
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static __inline__ void* SDL_AtomicSetPtr(void* *a, void* v)
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{
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void* value;
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do {
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value = *a;
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} while (!SDL_AtomicCASPtr(a, value, v));
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return value;
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}
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#endif
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/**
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* \brief Get the value of a pointer atomically.
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*/
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#ifndef SDL_AtomicGetPtr
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static __inline__ void* SDL_AtomicGetPtr(void* *a)
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{
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void* value = *a;
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SDL_CompilerBarrier();
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return value;
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}
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#endif
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/* Ends C function definitions when using C++ */
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#ifdef __cplusplus
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/* *INDENT-OFF* */
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}
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/* *INDENT-ON* */
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#endif
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#include "close_code.h"
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#endif /* _SDL_atomic_h_ */
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/* vi: set ts=4 sw=4 expandtab: */
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