+++ /dev/null
-/*
- Simple DirectMedia Layer
- Copyright (C) 1997-2019 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
- * http://preshing.com/
- *
- * 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
-extern "C" {
-#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 */
-
-
-/**
- * The compiler barrier prevents the compiler from reordering
- * reads and writes to globally visible variables across the call.
- */
-#if defined(_MSC_VER) && (_MSC_VER > 1200) && !defined(__clang__)
-void _ReadWriteBarrier(void);
-#pragma intrinsic(_ReadWriteBarrier)
-#define SDL_CompilerBarrier() _ReadWriteBarrier()
-#elif (defined(__GNUC__) && !defined(__EMSCRIPTEN__)) || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
-/* This is correct for all CPUs when using GCC or Solaris Studio 12.1+. */
-#define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")
-#elif defined(__WATCOMC__)
-extern _inline void SDL_CompilerBarrier (void);
-#pragma aux SDL_CompilerBarrier = "" parm [] modify exact [];
-#else
-#define SDL_CompilerBarrier() \
-{ SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); }
-#endif
-
-/**
- * Memory barriers are designed to prevent reads and writes from being
- * reordered by the compiler and being seen out of order on multi-core CPUs.
- *
- * A typical pattern would be for thread A to write some data and a flag,
- * and for thread B to read the flag and get the data. In this case you
- * would insert a release barrier between writing the data and the flag,
- * guaranteeing that the data write completes no later than the flag is
- * written, and you would insert an acquire barrier between reading the
- * flag and reading the data, to ensure that all the reads associated
- * with the flag have completed.
- *
- * In this pattern you should always see a release barrier paired with
- * an acquire barrier and you should gate the data reads/writes with a
- * single flag variable.
- *
- * For more information on these semantics, take a look at the blog post:
- * http://preshing.com/20120913/acquire-and-release-semantics
- */
-extern DECLSPEC void SDLCALL SDL_MemoryBarrierReleaseFunction(void);
-extern DECLSPEC void SDLCALL SDL_MemoryBarrierAcquireFunction(void);
-
-#if defined(__GNUC__) && (defined(__powerpc__) || defined(__ppc__))
-#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("lwsync" : : : "memory")
-#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("lwsync" : : : "memory")
-#elif defined(__GNUC__) && defined(__aarch64__)
-#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("dmb ish" : : : "memory")
-#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("dmb ish" : : : "memory")
-#elif defined(__GNUC__) && defined(__arm__)
-#if 0 /* defined(__LINUX__) || defined(__ANDROID__) */
-/* Information from:
- https://chromium.googlesource.com/chromium/chromium/+/trunk/base/atomicops_internals_arm_gcc.h#19
-
- The Linux kernel provides a helper function which provides the right code for a memory barrier,
- hard-coded at address 0xffff0fa0
-*/
-typedef void (*SDL_KernelMemoryBarrierFunc)();
-#define SDL_MemoryBarrierRelease() ((SDL_KernelMemoryBarrierFunc)0xffff0fa0)()
-#define SDL_MemoryBarrierAcquire() ((SDL_KernelMemoryBarrierFunc)0xffff0fa0)()
-#elif 0 /* defined(__QNXNTO__) */
-#include <sys/cpuinline.h>
-
-#define SDL_MemoryBarrierRelease() __cpu_membarrier()
-#define SDL_MemoryBarrierAcquire() __cpu_membarrier()
-#else
-#if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) || defined(__ARM_ARCH_7EM__) || defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7S__) || defined(__ARM_ARCH_8A__)
-#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("dmb ish" : : : "memory")
-#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("dmb ish" : : : "memory")
-#elif defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6T2__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__) || defined(__ARM_ARCH_5TE__)
-#ifdef __thumb__
-/* The mcr instruction isn't available in thumb mode, use real functions */
-#define SDL_MEMORY_BARRIER_USES_FUNCTION
-#define SDL_MemoryBarrierRelease() SDL_MemoryBarrierReleaseFunction()
-#define SDL_MemoryBarrierAcquire() SDL_MemoryBarrierAcquireFunction()
-#else
-#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
-#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
-#endif /* __thumb__ */
-#else
-#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("" : : : "memory")
-#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("" : : : "memory")
-#endif /* __LINUX__ || __ANDROID__ */
-#endif /* __GNUC__ && __arm__ */
-#else
-#if (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
-/* This is correct for all CPUs on Solaris when using Solaris Studio 12.1+. */
-#include <mbarrier.h>
-#define SDL_MemoryBarrierRelease() __machine_rel_barrier()
-#define SDL_MemoryBarrierAcquire() __machine_acq_barrier()
-#else
-/* This is correct for the x86 and x64 CPUs, and we'll expand this over time. */
-#define SDL_MemoryBarrierRelease() SDL_CompilerBarrier()
-#define SDL_MemoryBarrierAcquire() SDL_CompilerBarrier()
-#endif
-#endif
-
-/**
- * \brief A type representing an atomic integer value. It is a struct
- * so people don't accidentally use numeric operations on it.
- */
-typedef struct { int value; } SDL_atomic_t;
-
-/**
- * \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!
-*/
-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.
- */
-extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int v);
-
-/**
- * \brief Get the value of an atomic variable
- */
-extern DECLSPEC int SDLCALL SDL_AtomicGet(SDL_atomic_t *a);
-
-/**
- * \brief Add to an atomic variable.
- *
- * \return The previous value of the atomic variable.
- *
- * \note This same style can be used for any number operation
- */
-extern DECLSPEC int SDLCALL SDL_AtomicAdd(SDL_atomic_t *a, int v);
-
-/**
- * \brief Increment an atomic variable used as a reference count.
- */
-#ifndef SDL_AtomicIncRef
-#define SDL_AtomicIncRef(a) SDL_AtomicAdd(a, 1)
-#endif
-
-/**
- * \brief Decrement an atomic variable used as a reference count.
- *
- * \return SDL_TRUE if the variable reached zero after decrementing,
- * SDL_FALSE otherwise
- */
-#ifndef SDL_AtomicDecRef
-#define SDL_AtomicDecRef(a) (SDL_AtomicAdd(a, -1) == 1)
-#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!
-*/
-extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);
-
-/**
- * \brief Set a pointer to a value atomically.
- *
- * \return The previous value of the pointer.
- */
-extern DECLSPEC void* SDLCALL SDL_AtomicSetPtr(void **a, void* v);
-
-/**
- * \brief Get the value of a pointer atomically.
- */
-extern DECLSPEC void* SDLCALL SDL_AtomicGetPtr(void **a);
-
-/* Ends C function definitions when using C++ */
-#ifdef __cplusplus
-}
-#endif
-
-#include "close_code.h"
-
-#endif /* SDL_atomic_h_ */
-
-/* vi: set ts=4 sw=4 expandtab: */
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