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+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2022 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;
+
+/**
+ * Try to lock a spin lock by setting it to a non-zero value.
+ *
+ * ***Please note that spinlocks are dangerous if you don't know what you're
+ * doing. Please be careful using any sort of spinlock!***
+ *
+ * \param lock a pointer to a lock variable
+ * \returns SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already
+ *          held.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_AtomicLock
+ * \sa SDL_AtomicUnlock
+ */
+extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
+
+/**
+ * Lock a spin lock by setting it to a non-zero value.
+ *
+ * ***Please note that spinlocks are dangerous if you don't know what you're
+ * doing. Please be careful using any sort of spinlock!***
+ *
+ * \param lock a pointer to a lock variable
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_AtomicTryLock
+ * \sa SDL_AtomicUnlock
+ */
+extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
+
+/**
+ * Unlock a spin lock by setting it to 0.
+ *
+ * Always returns immediately.
+ *
+ * ***Please note that spinlocks are dangerous if you don't know what you're
+ * doing. Please be careful using any sort of spinlock!***
+ *
+ * \param lock a pointer to a lock variable
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_AtomicLock
+ * \sa SDL_AtomicTryLock
+ */
+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
+ *
+ * \since This function is available since SDL 2.0.6.
+ */
+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;
+
+/**
+ * Set an atomic variable to a new value if it is currently an old value.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to an SDL_atomic_t variable to be modified
+ * \param oldval the old value
+ * \param newval the new value
+ * \returns SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_AtomicCASPtr
+ * \sa SDL_AtomicGet
+ * \sa SDL_AtomicSet
+ */
+extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
+
+/**
+ * Set an atomic variable to a value.
+ *
+ * This function also acts as a full memory barrier.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to an SDL_atomic_t variable to be modified
+ * \param v the desired value
+ * \returns the previous value of the atomic variable.
+ *
+ * \since This function is available since SDL 2.0.2.
+ *
+ * \sa SDL_AtomicGet
+ */
+extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int v);
+
+/**
+ * Get the value of an atomic variable.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to an SDL_atomic_t variable
+ * \returns the current value of an atomic variable.
+ *
+ * \since This function is available since SDL 2.0.2.
+ *
+ * \sa SDL_AtomicSet
+ */
+extern DECLSPEC int SDLCALL SDL_AtomicGet(SDL_atomic_t *a);
+
+/**
+ * Add to an atomic variable.
+ *
+ * This function also acts as a full memory barrier.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to an SDL_atomic_t variable to be modified
+ * \param v the desired value to add
+ * \returns the previous value of the atomic variable.
+ *
+ * \since This function is available since SDL 2.0.2.
+ *
+ * \sa SDL_AtomicDecRef
+ * \sa SDL_AtomicIncRef
+ */
+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
+
+/**
+ * Set a pointer to a new value if it is currently an old value.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to a pointer
+ * \param oldval the old pointer value
+ * \param newval the new pointer value
+ * \returns SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
+ *
+ * \since This function is available since SDL 2.0.0.
+ *
+ * \sa SDL_AtomicCAS
+ * \sa SDL_AtomicGetPtr
+ * \sa SDL_AtomicSetPtr
+ */
+extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);
+
+/**
+ * Set a pointer to a value atomically.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to a pointer
+ * \param v the desired pointer value
+ * \returns the previous value of the pointer.
+ *
+ * \since This function is available since SDL 2.0.2.
+ *
+ * \sa SDL_AtomicCASPtr
+ * \sa SDL_AtomicGetPtr
+ */
+extern DECLSPEC void* SDLCALL SDL_AtomicSetPtr(void **a, void* v);
+
+/**
+ * Get the value of a pointer atomically.
+ *
+ * ***Note: If you don't know what this function is for, you shouldn't use
+ * it!***
+ *
+ * \param a a pointer to a pointer
+ * \returns the current value of a pointer.
+ *
+ * \since This function is available since SDL 2.0.2.
+ *
+ * \sa SDL_AtomicCASPtr
+ * \sa SDL_AtomicSetPtr
+ */
+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: */