dep/sdl/include/SDL_atomic.h

   1 /*
   2   Simple DirectMedia Layer
   3   Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
   4
   5   This software is provided 'as-is', without any express or implied
   6   warranty.  In no event will the authors be held liable for any damages
   7   arising from the use of this software.
   8
   9   Permission is granted to anyone to use this software for any purpose,
  10   including commercial applications, and to alter it and redistribute it
  11   freely, subject to the following restrictions:
  12
  13   1. The origin of this software must not be misrepresented; you must not
  14      claim that you wrote the original software. If you use this software
  15      in a product, an acknowledgment in the product documentation would be
  16      appreciated but is not required.
  17   2. Altered source versions must be plainly marked as such, and must not be
  18      misrepresented as being the original software.
  19   3. This notice may not be removed or altered from any source distribution.
  20 */
  21
  22 /**
  23  * \file SDL_atomic.h
  24  *
  25  * Atomic operations.
  26  *
  27  * IMPORTANT:
  28  * If you are not an expert in concurrent lockless programming, you should
  29  * only be using the atomic lock and reference counting functions in this
  30  * file.  In all other cases you should be protecting your data structures
  31  * with full mutexes.
  32  *
  33  * The list of "safe" functions to use are:
  34  *  SDL_AtomicLock()
  35  *  SDL_AtomicUnlock()
  36  *  SDL_AtomicIncRef()
  37  *  SDL_AtomicDecRef()
  38  *
  39  * Seriously, here be dragons!
  40  * ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  41  *
  42  * You can find out a little more about lockless programming and the
  43  * subtle issues that can arise here:
  44  * http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx
  45  *
  46  * There's also lots of good information here:
  47  * http://www.1024cores.net/home/lock-free-algorithms
  48  * http://preshing.com/
  49  *
  50  * These operations may or may not actually be implemented using
  51  * processor specific atomic operations. When possible they are
  52  * implemented as true processor specific atomic operations. When that
  53  * is not possible the are implemented using locks that *do* use the
  54  * available atomic operations.
  55  *
  56  * All of the atomic operations that modify memory are full memory barriers.
  57  */
  58
  59 #ifndef SDL_atomic_h_
  60 #define SDL_atomic_h_
  61
  62 #include "SDL_stdinc.h"
  63 #include "SDL_platform.h"
  64
  65 #include "begin_code.h"
  66
  67 /* Set up for C function definitions, even when using C++ */
  68 #ifdef __cplusplus
  69 extern "C" {
  70 #endif
  71
  72 /**
  73  * \name SDL AtomicLock
  74  *
  75  * The atomic locks are efficient spinlocks using CPU instructions,
  76  * but are vulnerable to starvation and can spin forever if a thread
  77  * holding a lock has been terminated.  For this reason you should
  78  * minimize the code executed inside an atomic lock and never do
  79  * expensive things like API or system calls while holding them.
  80  *
  81  * The atomic locks are not safe to lock recursively.
  82  *
  83  * Porting Note:
  84  * The spin lock functions and type are required and can not be
  85  * emulated because they are used in the atomic emulation code.
  86  */
  87 /* @{ */
  88
  89 typedef int SDL_SpinLock;
  90
  91 /**
  92  * Try to lock a spin lock by setting it to a non-zero value.
  93  *
  94  * ***Please note that spinlocks are dangerous if you don't know what you're
  95  * doing. Please be careful using any sort of spinlock!***
  96  *
  97  * \param lock a pointer to a lock variable
  98  * \returns SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already
  99  *          held.
 100  *
 101  * \since This function is available since SDL 2.0.0.
 102  *
 103  * \sa SDL_AtomicLock
 104  * \sa SDL_AtomicUnlock
 105  */
 106 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
 107
 108 /**
 109  * Lock a spin lock by setting it to a non-zero value.
 110  *
 111  * ***Please note that spinlocks are dangerous if you don't know what you're
 112  * doing. Please be careful using any sort of spinlock!***
 113  *
 114  * \param lock a pointer to a lock variable
 115  *
 116  * \since This function is available since SDL 2.0.0.
 117  *
 118  * \sa SDL_AtomicTryLock
 119  * \sa SDL_AtomicUnlock
 120  */
 121 extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
 122
 123 /**
 124  * Unlock a spin lock by setting it to 0.
 125  *
 126  * Always returns immediately.
 127  *
 128  * ***Please note that spinlocks are dangerous if you don't know what you're
 129  * doing. Please be careful using any sort of spinlock!***
 130  *
 131  * \param lock a pointer to a lock variable
 132  *
 133  * \since This function is available since SDL 2.0.0.
 134  *
 135  * \sa SDL_AtomicLock
 136  * \sa SDL_AtomicTryLock
 137  */
 138 extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
 139
 140 /* @} *//* SDL AtomicLock */
 141
 142
 143 /**
 144  * The compiler barrier prevents the compiler from reordering
 145  * reads and writes to globally visible variables across the call.
 146  */
 147 #if defined(_MSC_VER) && (_MSC_VER > 1200) && !defined(__clang__)
 148 void _ReadWriteBarrier(void);
 149 #pragma intrinsic(_ReadWriteBarrier)
 150 #define SDL_CompilerBarrier()   _ReadWriteBarrier()
 151 #elif (defined(__GNUC__) && !defined(__EMSCRIPTEN__)) || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
 152 /* This is correct for all CPUs when using GCC or Solaris Studio 12.1+. */
 153 #define SDL_CompilerBarrier()   __asm__ __volatile__ ("" : : : "memory")
 154 #elif defined(__WATCOMC__)
 155 extern __inline void SDL_CompilerBarrier(void);
 156 #pragma aux SDL_CompilerBarrier = "" parm [] modify exact [];
 157 #else
 158 #define SDL_CompilerBarrier()   \
 159 { SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); }
 160 #endif
 161
 162 /**
 163  * Memory barriers are designed to prevent reads and writes from being
 164  * reordered by the compiler and being seen out of order on multi-core CPUs.
 165  *
 166  * A typical pattern would be for thread A to write some data and a flag, and
 167  * for thread B to read the flag and get the data. In this case you would
 168  * insert a release barrier between writing the data and the flag,
 169  * guaranteeing that the data write completes no later than the flag is
 170  * written, and you would insert an acquire barrier between reading the flag
 171  * and reading the data, to ensure that all the reads associated with the flag
 172  * have completed.
 173  *
 174  * In this pattern you should always see a release barrier paired with an
 175  * acquire barrier and you should gate the data reads/writes with a single
 176  * flag variable.
 177  *
 178  * For more information on these semantics, take a look at the blog post:
 179  * http://preshing.com/20120913/acquire-and-release-semantics
 180  *
 181  * \since This function is available since SDL 2.0.6.
 182  */
 183 extern DECLSPEC void SDLCALL SDL_MemoryBarrierReleaseFunction(void);
 184 extern DECLSPEC void SDLCALL SDL_MemoryBarrierAcquireFunction(void);
 185
 186 #if defined(__GNUC__) && (defined(__powerpc__) || defined(__ppc__))
 187 #define SDL_MemoryBarrierRelease()   __asm__ __volatile__ ("lwsync" : : : "memory")
 188 #define SDL_MemoryBarrierAcquire()   __asm__ __volatile__ ("lwsync" : : : "memory")
 189 #elif defined(__GNUC__) && defined(__aarch64__)
 190 #define SDL_MemoryBarrierRelease()   __asm__ __volatile__ ("dmb ish" : : : "memory")
 191 #define SDL_MemoryBarrierAcquire()   __asm__ __volatile__ ("dmb ish" : : : "memory")
 192 #elif defined(__GNUC__) && defined(__arm__)
 193 #if 0 /* defined(__LINUX__) || defined(__ANDROID__) */
 194 /* Information from:
 195    https://chromium.googlesource.com/chromium/chromium/+/trunk/base/atomicops_internals_arm_gcc.h#19
 196
 197    The Linux kernel provides a helper function which provides the right code for a memory barrier,
 198    hard-coded at address 0xffff0fa0
 199 */
 200 typedef void (*SDL_KernelMemoryBarrierFunc)();
 201 #define SDL_MemoryBarrierRelease()      ((SDL_KernelMemoryBarrierFunc)0xffff0fa0)()
 202 #define SDL_MemoryBarrierAcquire()      ((SDL_KernelMemoryBarrierFunc)0xffff0fa0)()
 203 #elif 0 /* defined(__QNXNTO__) */
 204 #include <sys/cpuinline.h>
 205
 206 #define SDL_MemoryBarrierRelease()   __cpu_membarrier()
 207 #define SDL_MemoryBarrierAcquire()   __cpu_membarrier()
 208 #else
 209 #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__)
 210 #define SDL_MemoryBarrierRelease()   __asm__ __volatile__ ("dmb ish" : : : "memory")
 211 #define SDL_MemoryBarrierAcquire()   __asm__ __volatile__ ("dmb ish" : : : "memory")
 212 #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__)
 213 #ifdef __thumb__
 214 /* The mcr instruction isn't available in thumb mode, use real functions */
 215 #define SDL_MEMORY_BARRIER_USES_FUNCTION
 216 #define SDL_MemoryBarrierRelease()   SDL_MemoryBarrierReleaseFunction()
 217 #define SDL_MemoryBarrierAcquire()   SDL_MemoryBarrierAcquireFunction()
 218 #else
 219 #define SDL_MemoryBarrierRelease()   __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
 220 #define SDL_MemoryBarrierAcquire()   __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
 221 #endif /* __thumb__ */
 222 #else
 223 #define SDL_MemoryBarrierRelease()   __asm__ __volatile__ ("" : : : "memory")
 224 #define SDL_MemoryBarrierAcquire()   __asm__ __volatile__ ("" : : : "memory")
 225 #endif /* __LINUX__ || __ANDROID__ */
 226 #endif /* __GNUC__ && __arm__ */
 227 #else
 228 #if (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
 229 /* This is correct for all CPUs on Solaris when using Solaris Studio 12.1+. */
 230 #include <mbarrier.h>
 231 #define SDL_MemoryBarrierRelease()  __machine_rel_barrier()
 232 #define SDL_MemoryBarrierAcquire()  __machine_acq_barrier()
 233 #else
 234 /* This is correct for the x86 and x64 CPUs, and we'll expand this over time. */
 235 #define SDL_MemoryBarrierRelease()  SDL_CompilerBarrier()
 236 #define SDL_MemoryBarrierAcquire()  SDL_CompilerBarrier()
 237 #endif
 238 #endif
 239
 240 /* "REP NOP" is PAUSE, coded for tools that don't know it by that name. */
 241 #if (defined(__GNUC__) || defined(__clang__)) && (defined(__i386__) || defined(__x86_64__))
 242     #define SDL_CPUPauseInstruction() __asm__ __volatile__("pause\n")  /* Some assemblers can't do REP NOP, so go with PAUSE. */
 243 #elif (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__)
 244     #define SDL_CPUPauseInstruction() __asm__ __volatile__("yield" ::: "memory")
 245 #elif (defined(__powerpc__) || defined(__powerpc64__))
 246     #define SDL_CPUPauseInstruction() __asm__ __volatile__("or 27,27,27");
 247 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
 248     #define SDL_CPUPauseInstruction() _mm_pause()  /* this is actually "rep nop" and not a SIMD instruction. No inline asm in MSVC x86-64! */
 249 #elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_ARM64))
 250     #define SDL_CPUPauseInstruction() __yield()
 251 #elif defined(__WATCOMC__) && defined(__386__)
 252     /* watcom assembler rejects PAUSE if CPU < i686, and it refuses REP NOP as an invalid combination. Hardcode the bytes.  */
 253     extern __inline void SDL_CPUPauseInstruction(void);
 254     #pragma aux SDL_CPUPauseInstruction = "db 0f3h,90h"
 255 #else
 256     #define SDL_CPUPauseInstruction()
 257 #endif
 258
 259
 260 /**
 261  * \brief A type representing an atomic integer value.  It is a struct
 262  *        so people don't accidentally use numeric operations on it.
 263  */
 264 typedef struct { int value; } SDL_atomic_t;
 265
 266 /**
 267  * Set an atomic variable to a new value if it is currently an old value.
 268  *
 269  * ***Note: If you don't know what this function is for, you shouldn't use
 270  * it!***
 271  *
 272  * \param a a pointer to an SDL_atomic_t variable to be modified
 273  * \param oldval the old value
 274  * \param newval the new value
 275  * \returns SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
 276  *
 277  * \since This function is available since SDL 2.0.0.
 278  *
 279  * \sa SDL_AtomicCASPtr
 280  * \sa SDL_AtomicGet
 281  * \sa SDL_AtomicSet
 282  */
 283 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
 284
 285 /**
 286  * Set an atomic variable to a value.
 287  *
 288  * This function also acts as a full memory barrier.
 289  *
 290  * ***Note: If you don't know what this function is for, you shouldn't use
 291  * it!***
 292  *
 293  * \param a a pointer to an SDL_atomic_t variable to be modified
 294  * \param v the desired value
 295  * \returns the previous value of the atomic variable.
 296  *
 297  * \since This function is available since SDL 2.0.2.
 298  *
 299  * \sa SDL_AtomicGet
 300  */
 301 extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int v);
 302
 303 /**
 304  * Get the value of an atomic variable.
 305  *
 306  * ***Note: If you don't know what this function is for, you shouldn't use
 307  * it!***
 308  *
 309  * \param a a pointer to an SDL_atomic_t variable
 310  * \returns the current value of an atomic variable.
 311  *
 312  * \since This function is available since SDL 2.0.2.
 313  *
 314  * \sa SDL_AtomicSet
 315  */
 316 extern DECLSPEC int SDLCALL SDL_AtomicGet(SDL_atomic_t *a);
 317
 318 /**
 319  * Add to an atomic variable.
 320  *
 321  * This function also acts as a full memory barrier.
 322  *
 323  * ***Note: If you don't know what this function is for, you shouldn't use
 324  * it!***
 325  *
 326  * \param a a pointer to an SDL_atomic_t variable to be modified
 327  * \param v the desired value to add
 328  * \returns the previous value of the atomic variable.
 329  *
 330  * \since This function is available since SDL 2.0.2.
 331  *
 332  * \sa SDL_AtomicDecRef
 333  * \sa SDL_AtomicIncRef
 334  */
 335 extern DECLSPEC int SDLCALL SDL_AtomicAdd(SDL_atomic_t *a, int v);
 336
 337 /**
 338  * \brief Increment an atomic variable used as a reference count.
 339  */
 340 #ifndef SDL_AtomicIncRef
 341 #define SDL_AtomicIncRef(a)    SDL_AtomicAdd(a, 1)
 342 #endif
 343
 344 /**
 345  * \brief Decrement an atomic variable used as a reference count.
 346  *
 347  * \return SDL_TRUE if the variable reached zero after decrementing,
 348  *         SDL_FALSE otherwise
 349  */
 350 #ifndef SDL_AtomicDecRef
 351 #define SDL_AtomicDecRef(a)    (SDL_AtomicAdd(a, -1) == 1)
 352 #endif
 353
 354 /**
 355  * Set a pointer to a new value if it is currently an old value.
 356  *
 357  * ***Note: If you don't know what this function is for, you shouldn't use
 358  * it!***
 359  *
 360  * \param a a pointer to a pointer
 361  * \param oldval the old pointer value
 362  * \param newval the new pointer value
 363  * \returns SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
 364  *
 365  * \since This function is available since SDL 2.0.0.
 366  *
 367  * \sa SDL_AtomicCAS
 368  * \sa SDL_AtomicGetPtr
 369  * \sa SDL_AtomicSetPtr
 370  */
 371 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);
 372
 373 /**
 374  * Set a pointer to a value atomically.
 375  *
 376  * ***Note: If you don't know what this function is for, you shouldn't use
 377  * it!***
 378  *
 379  * \param a a pointer to a pointer
 380  * \param v the desired pointer value
 381  * \returns the previous value of the pointer.
 382  *
 383  * \since This function is available since SDL 2.0.2.
 384  *
 385  * \sa SDL_AtomicCASPtr
 386  * \sa SDL_AtomicGetPtr
 387  */
 388 extern DECLSPEC void* SDLCALL SDL_AtomicSetPtr(void **a, void* v);
 389
 390 /**
 391  * Get the value of a pointer atomically.
 392  *
 393  * ***Note: If you don't know what this function is for, you shouldn't use
 394  * it!***
 395  *
 396  * \param a a pointer to a pointer
 397  * \returns the current value of a pointer.
 398  *
 399  * \since This function is available since SDL 2.0.2.
 400  *
 401  * \sa SDL_AtomicCASPtr
 402  * \sa SDL_AtomicSetPtr
 403  */
 404 extern DECLSPEC void* SDLCALL SDL_AtomicGetPtr(void **a);
 405
 406 /* Ends C function definitions when using C++ */
 407 #ifdef __cplusplus
 408 }
 409 #endif
 410
 411 #include "close_code.h"
 412
 413 #endif /* SDL_atomic_h_ */
 414
 415 /* vi: set ts=4 sw=4 expandtab: */