include/SDL_atomic.h
author Sam Lantinga <slouken@libsdl.org>
Wed, 10 Jul 2013 18:31:17 -0700
changeset 7393 358696c354a8
parent 7191 75360622e65f
child 7394 38dc4961ab15
permissions -rw-r--r--
Added release/acquire memory barriers to the atomic API
* Added a destructor to clean up TLS memory at thread shutdown
* Refactored the TLS code to have platform independent code and a small platform dependent core with a fallback to generic code if platform dependent functions fail.
* Fixed recursion issues with SDL_GetErrBuf()
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/*
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  Simple DirectMedia Layer
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  Copyright (C) 1997-2013 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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 * http://preshing.com/
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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)
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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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extern "C" {
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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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#if defined(_MSC_VER) && (_MSC_VER > 1200)
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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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/**
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 * Memory barriers are designed to prevent reads and writes from being
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 * reordered by the compiler and being seen out of order on multi-core CPUs.
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 *
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 * A typical pattern would be for thread A to write some data and a flag,
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 * and for thread B to read the flag and get the data. In this case you
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 * would insert a release barrier between writing the data and the flag,
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 * guaranteeing that the data write completes no later than the flag is
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 * written, and you would insert an acquire barrier between reading the
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 * flag and reading the data, to ensure that all the reads associated
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 * with the flag have completed.
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 *
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 * In this pattern you should always see a release barrier paired with
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 * an acquire barrier and you should gate the data reads/writes with a
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 * single flag variable.
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 *
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 * For more information on these semantics, take a look at the blog post:
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 * http://preshing.com/20120913/acquire-and-release-semantics
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 */
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/* FIXME: This is correct for x86 and x64 but not other CPUs
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   For PPC we need the lwsync instruction, and on ARM some variant of dmb
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 */
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#define SDL_MemoryBarrierRelease()  SDL_CompilerBarrier()
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#define SDL_MemoryBarrierAcquire()  SDL_CompilerBarrier()
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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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#ifdef __LP64__
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#define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))
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#else
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#define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_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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extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
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#endif
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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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SDL_FORCE_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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SDL_FORCE_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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SDL_FORCE_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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extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void* *a, void *oldval, void *newval);
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#endif
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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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SDL_FORCE_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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SDL_FORCE_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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}
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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: */