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1 /*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2013 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 /* Need to do this here because intrin.h has C++ code in it */
68 /* Visual Studio 2005 has a bug where intrin.h conflicts with winnt.h */
69 #if defined(_MSC_VER) && (_MSC_VER >= 1500)
70 #include <intrin.h>
71 #define HAVE_MSC_ATOMICS 1
72 #endif
73
74 /* Set up for C function definitions, even when using C++ */
75 #ifdef __cplusplus
76 extern "C" {
77 #endif
78
79 /**
80 * \name SDL AtomicLock
81 *
82 * The atomic locks are efficient spinlocks using CPU instructions,
83 * but are vulnerable to starvation and can spin forever if a thread
84 * holding a lock has been terminated. For this reason you should
85 * minimize the code executed inside an atomic lock and never do
86 * expensive things like API or system calls while holding them.
87 *
88 * The atomic locks are not safe to lock recursively.
89 *
90 * Porting Note:
91 * The spin lock functions and type are required and can not be
92 * emulated because they are used in the atomic emulation code.
93 */
94 /*@{*/
95
96 typedef int SDL_SpinLock;
97
98 /**
99 * \brief Try to lock a spin lock by setting it to a non-zero value.
100 *
101 * \param lock Points to the lock.
102 *
103 * \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
104 */
105 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
106
107 /**
108 * \brief Lock a spin lock by setting it to a non-zero value.
109 *
110 * \param lock Points to the lock.
111 */
112 extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
113
114 /**
115 * \brief Unlock a spin lock by setting it to 0. Always returns immediately
116 *
117 * \param lock Points to the lock.
118 */
119 extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
120
121 /*@}*//*SDL AtomicLock*/
122
123
124 /**
125 * The compiler barrier prevents the compiler from reordering
126 * reads and writes to globally visible variables across the call.
127 */
128 #if defined(_MSC_VER) && (_MSC_VER > 1200)
129 void _ReadWriteBarrier(void);
130 #pragma intrinsic(_ReadWriteBarrier)
131 #define SDL_CompilerBarrier() _ReadWriteBarrier()
132 #elif defined(__GNUC__)
133 #define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")
134 #else
135 #define SDL_CompilerBarrier() \
136 { SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); }
137 #endif
138
139 /**
140 * Memory barriers are designed to prevent reads and writes from being
141 * reordered by the compiler and being seen out of order on multi-core CPUs.
142 *
143 * A typical pattern would be for thread A to write some data and a flag,
144 * and for thread B to read the flag and get the data. In this case you
145 * would insert a release barrier between writing the data and the flag,
146 * guaranteeing that the data write completes no later than the flag is
147 * written, and you would insert an acquire barrier between reading the
148 * flag and reading the data, to ensure that all the reads associated
149 * with the flag have completed.
150 *
151 * In this pattern you should always see a release barrier paired with
152 * an acquire barrier and you should gate the data reads/writes with a
153 * single flag variable.
154 *
155 * For more information on these semantics, take a look at the blog post:
156 * http://preshing.com/20120913/acquire-and-release-semantics
157 */
158 #if defined(__GNUC__) && (defined(__powerpc__) || defined(__ppc__))
159 #define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("lwsync" : : : "memory")
160 #define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("lwsync" : : : "memory")
161 #elif defined(__GNUC__) && defined(__arm__)
162 #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__)
163 #define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("dmb ish" : : : "memory")
164 #define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("dmb ish" : : : "memory")
165 #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__)
166 #ifdef __thumb__
167 /* The mcr instruction isn't available in thumb mode, use real functions */
168 extern DECLSPEC void SDLCALL SDL_MemoryBarrierRelease();
169 extern DECLSPEC void SDLCALL SDL_MemoryBarrierAcquire();
170 #else
171 #define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
172 #define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
173 #endif /* __thumb__ */
174 #else
175 #define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("" : : : "memory")
176 #define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("" : : : "memory")
177 #endif /* __GNUC__ && __arm__ */
178 #else
179 /* This is correct for the x86 and x64 CPUs, and we'll expand this over time. */
180 #define SDL_MemoryBarrierRelease() SDL_CompilerBarrier()
181 #define SDL_MemoryBarrierAcquire() SDL_CompilerBarrier()
182 #endif
183
184
185 /* Platform specific optimized versions of the atomic functions,
186 * you can disable these by defining SDL_DISABLE_ATOMIC_INLINE
187 */
188 #if defined(SDL_ATOMIC_DISABLED) && SDL_ATOMIC_DISABLED
189 #define SDL_DISABLE_ATOMIC_INLINE
190 #endif
191 #ifndef SDL_DISABLE_ATOMIC_INLINE
192
193 #ifdef HAVE_MSC_ATOMICS
194
195 #define SDL_AtomicSet(a, v) _InterlockedExchange((long*)&(a)->value, (v))
196 #define SDL_AtomicAdd(a, v) _InterlockedExchangeAdd((long*)&(a)->value, (v))
197 #define SDL_AtomicCAS(a, oldval, newval) (_InterlockedCompareExchange((long*)&(a)->value, (newval), (oldval)) == (oldval))
198 #define SDL_AtomicSetPtr(a, v) _InterlockedExchangePointer((a), (v))
199 #if _M_IX86
200 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchange((long*)(a), (long)(newval), (long)(oldval)) == (long)(oldval))
201 #else
202 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchangePointer((a), (newval), (oldval)) == (oldval))
203 #endif
204
205 #elif defined(__MACOSX__)
206 #include <libkern/OSAtomic.h>
207
208 #define SDL_AtomicCAS(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((oldval), (newval), &(a)->value)
209 #ifdef __LP64__
210 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))
211 #else
212 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_t*)(a))
213 #endif
214
215 #elif defined(HAVE_GCC_ATOMICS)
216
217 #define SDL_AtomicSet(a, v) __sync_lock_test_and_set(&(a)->value, v)
218 #define SDL_AtomicAdd(a, v) __sync_fetch_and_add(&(a)->value, v)
219 #define SDL_AtomicSetPtr(a, v) __sync_lock_test_and_set(a, v)
220 #define SDL_AtomicCAS(a, oldval, newval) __sync_bool_compare_and_swap(&(a)->value, oldval, newval)
221 #define SDL_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)
222
223 #endif
224
225 #endif /* !SDL_DISABLE_ATOMIC_INLINE */
226
227
228 /**
229 * \brief A type representing an atomic integer value. It is a struct
230 * so people don't accidentally use numeric operations on it.
231 */
232 #ifndef SDL_atomic_t_defined
233 typedef struct { int value; } SDL_atomic_t;
234 #endif
235
236 /**
237 * \brief Set an atomic variable to a new value if it is currently an old value.
238 *
239 * \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
240 *
241 * \note If you don't know what this function is for, you shouldn't use it!
242 */
243 #ifndef SDL_AtomicCAS
244 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
245 #endif
246
247 /**
248 * \brief Set an atomic variable to a value.
249 *
250 * \return The previous value of the atomic variable.
251 */
252 #ifndef SDL_AtomicSet
253 SDL_FORCE_INLINE int SDL_AtomicSet(SDL_atomic_t *a, int v)
254 {
255 int value;
256 do {
257 value = a->value;
258 } while (!SDL_AtomicCAS(a, value, v));
259 return value;
260 }
261 #endif
262
263 /**
264 * \brief Get the value of an atomic variable
265 */
266 #ifndef SDL_AtomicGet
267 SDL_FORCE_INLINE int SDL_AtomicGet(SDL_atomic_t *a)
268 {
269 int value = a->value;
270 SDL_CompilerBarrier();
271 return value;
272 }
273 #endif
274
275 /**
276 * \brief Add to an atomic variable.
277 *
278 * \return The previous value of the atomic variable.
279 *
280 * \note This same style can be used for any number operation
281 */
282 #ifndef SDL_AtomicAdd
283 SDL_FORCE_INLINE int SDL_AtomicAdd(SDL_atomic_t *a, int v)
284 {
285 int value;
286 do {
287 value = a->value;
288 } while (!SDL_AtomicCAS(a, value, (value + v)));
289 return value;
290 }
291 #endif
292
293 /**
294 * \brief Increment an atomic variable used as a reference count.
295 */
296 #ifndef SDL_AtomicIncRef
297 #define SDL_AtomicIncRef(a) SDL_AtomicAdd(a, 1)
298 #endif
299
300 /**
301 * \brief Decrement an atomic variable used as a reference count.
302 *
303 * \return SDL_TRUE if the variable reached zero after decrementing,
304 * SDL_FALSE otherwise
305 */
306 #ifndef SDL_AtomicDecRef
307 #define SDL_AtomicDecRef(a) (SDL_AtomicAdd(a, -1) == 1)
308 #endif
309
310 /**
311 * \brief Set a pointer to a new value if it is currently an old value.
312 *
313 * \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
314 *
315 * \note If you don't know what this function is for, you shouldn't use it!
316 */
317 #ifndef SDL_AtomicCASPtr
318 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void* *a, void *oldval, void *newval);
319 #endif
320
321 /**
322 * \brief Set a pointer to a value atomically.
323 *
324 * \return The previous value of the pointer.
325 */
326 #ifndef SDL_AtomicSetPtr
327 SDL_FORCE_INLINE void* SDL_AtomicSetPtr(void* *a, void* v)
328 {
329 void* value;
330 do {
331 value = *a;
332 } while (!SDL_AtomicCASPtr(a, value, v));
333 return value;
334 }
335 #endif
336
337 /**
338 * \brief Get the value of a pointer atomically.
339 */
340 #ifndef SDL_AtomicGetPtr
341 SDL_FORCE_INLINE void* SDL_AtomicGetPtr(void* *a)
342 {
343 void* value = *a;
344 SDL_CompilerBarrier();
345 return value;
346 }
347 #endif
348
349
350 /* Ends C function definitions when using C++ */
351 #ifdef __cplusplus
352 }
353 #endif
354
355 #include "close_code.h"
356
357 #endif /* _SDL_atomic_h_ */
358
359 /* vi: set ts=4 sw=4 expandtab: */