SDL  2.0
SDL_atomic.h
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1 /*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2017 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  * \brief Try to lock a spin lock by setting it to a non-zero value.
93  *
94  * \param lock Points to the lock.
95  *
96  * \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
97  */
98 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
99 
100 /**
101  * \brief Lock a spin lock by setting it to a non-zero value.
102  *
103  * \param lock Points to the lock.
104  */
105 extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
106 
107 /**
108  * \brief Unlock a spin lock by setting it to 0. Always returns immediately
109  *
110  * \param lock Points to the lock.
111  */
112 extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
113 
114 /* @} *//* SDL AtomicLock */
115 
116 
117 /**
118  * The compiler barrier prevents the compiler from reordering
119  * reads and writes to globally visible variables across the call.
120  */
121 #if defined(_MSC_VER) && (_MSC_VER > 1200) && !defined(__clang__)
122 void _ReadWriteBarrier(void);
123 #pragma intrinsic(_ReadWriteBarrier)
124 #define SDL_CompilerBarrier() _ReadWriteBarrier()
125 #elif (defined(__GNUC__) && !defined(__EMSCRIPTEN__)) || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
126 /* This is correct for all CPUs when using GCC or Solaris Studio 12.1+. */
127 #define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")
128 #elif defined(__WATCOMC__)
129 extern _inline void SDL_CompilerBarrier (void);
130 #pragma aux SDL_CompilerBarrier = "" parm [] modify exact [];
131 #else
132 #define SDL_CompilerBarrier() \
133 { SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); }
134 #endif
135 
136 /**
137  * Memory barriers are designed to prevent reads and writes from being
138  * reordered by the compiler and being seen out of order on multi-core CPUs.
139  *
140  * A typical pattern would be for thread A to write some data and a flag,
141  * and for thread B to read the flag and get the data. In this case you
142  * would insert a release barrier between writing the data and the flag,
143  * guaranteeing that the data write completes no later than the flag is
144  * written, and you would insert an acquire barrier between reading the
145  * flag and reading the data, to ensure that all the reads associated
146  * with the flag have completed.
147  *
148  * In this pattern you should always see a release barrier paired with
149  * an acquire barrier and you should gate the data reads/writes with a
150  * single flag variable.
151  *
152  * For more information on these semantics, take a look at the blog post:
153  * http://preshing.com/20120913/acquire-and-release-semantics
154  */
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__) || defined(__ARM_ARCH_5TE__)
166 #ifdef __thumb__
167 /* The mcr instruction isn't available in thumb mode, use real functions */
168 #define SDL_MemoryBarrierRelease() SDL_MemoryBarrierReleaseFunction()
169 #define SDL_MemoryBarrierAcquire() SDL_MemoryBarrierAcquireFunction()
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 #if (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
180 /* This is correct for all CPUs on Solaris when using Solaris Studio 12.1+. */
181 #include <mbarrier.h>
182 #define SDL_MemoryBarrierRelease() __machine_rel_barrier()
183 #define SDL_MemoryBarrierAcquire() __machine_acq_barrier()
184 #else
185 /* This is correct for the x86 and x64 CPUs, and we'll expand this over time. */
186 #define SDL_MemoryBarrierRelease() SDL_CompilerBarrier()
187 #define SDL_MemoryBarrierAcquire() SDL_CompilerBarrier()
188 #endif
189 #endif
190 
191 /**
192  * \brief A type representing an atomic integer value. It is a struct
193  * so people don't accidentally use numeric operations on it.
194  */
195 typedef struct { int value; } SDL_atomic_t;
196 
197 /**
198  * \brief Set an atomic variable to a new value if it is currently an old value.
199  *
200  * \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
201  *
202  * \note If you don't know what this function is for, you shouldn't use it!
203 */
204 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval);
205 
206 /**
207  * \brief Set an atomic variable to a value.
208  *
209  * \return The previous value of the atomic variable.
210  */
211 extern DECLSPEC int SDLCALL SDL_AtomicSet(SDL_atomic_t *a, int v);
212 
213 /**
214  * \brief Get the value of an atomic variable
215  */
217 
218 /**
219  * \brief Add to an atomic variable.
220  *
221  * \return The previous value of the atomic variable.
222  *
223  * \note This same style can be used for any number operation
224  */
225 extern DECLSPEC int SDLCALL SDL_AtomicAdd(SDL_atomic_t *a, int v);
226 
227 /**
228  * \brief Increment an atomic variable used as a reference count.
229  */
230 #ifndef SDL_AtomicIncRef
231 #define SDL_AtomicIncRef(a) SDL_AtomicAdd(a, 1)
232 #endif
233 
234 /**
235  * \brief Decrement an atomic variable used as a reference count.
236  *
237  * \return SDL_TRUE if the variable reached zero after decrementing,
238  * SDL_FALSE otherwise
239  */
240 #ifndef SDL_AtomicDecRef
241 #define SDL_AtomicDecRef(a) (SDL_AtomicAdd(a, -1) == 1)
242 #endif
243 
244 /**
245  * \brief Set a pointer to a new value if it is currently an old value.
246  *
247  * \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
248  *
249  * \note If you don't know what this function is for, you shouldn't use it!
250 */
251 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr(void **a, void *oldval, void *newval);
252 
253 /**
254  * \brief Set a pointer to a value atomically.
255  *
256  * \return The previous value of the pointer.
257  */
258 extern DECLSPEC void* SDLCALL SDL_AtomicSetPtr(void **a, void* v);
259 
260 /**
261  * \brief Get the value of a pointer atomically.
262  */
263 extern DECLSPEC void* SDLCALL SDL_AtomicGetPtr(void **a);
264 
265 /* Ends C function definitions when using C++ */
266 #ifdef __cplusplus
267 }
268 #endif
269 
270 #include "close_code.h"
271 
272 #endif /* SDL_atomic_h_ */
273 
274 /* vi: set ts=4 sw=4 expandtab: */
#define SDL_CompilerBarrier()
Definition: SDL_atomic.h:132
void * SDL_AtomicGetPtr(void **a)
Get the value of a pointer atomically.
Definition: SDL_atomic.c:278
SDL_bool SDL_AtomicCASPtr(void **a, void *oldval, void *newval)
Set a pointer to a new value if it is currently an old value.
Definition: SDL_atomic.c:160
const GLdouble * v
Definition: SDL_opengl.h:2064
int SDL_AtomicAdd(SDL_atomic_t *a, int v)
Add to an atomic variable.
Definition: SDL_atomic.c:237
A type representing an atomic integer value. It is a struct so people don&#39;t accidentally use numeric ...
Definition: SDL_atomic.h:195
#define DECLSPEC
Definition: SDL_internal.h:44
int SDL_AtomicGet(SDL_atomic_t *a)
Get the value of an atomic variable.
Definition: SDL_atomic.c:264
int SDL_AtomicSet(SDL_atomic_t *a, int v)
Set an atomic variable to a value.
Definition: SDL_atomic.c:193
SDL_bool SDL_AtomicCAS(SDL_atomic_t *a, int oldval, int newval)
Set an atomic variable to a new value if it is currently an old value.
Definition: SDL_atomic.c:129
void SDL_AtomicLock(SDL_SpinLock *lock)
Lock a spin lock by setting it to a non-zero value.
Definition: SDL_spinlock.c:120
SDL_bool
Definition: SDL_stdinc.h:139
SDL_bool SDL_AtomicTryLock(SDL_SpinLock *lock)
Try to lock a spin lock by setting it to a non-zero value.
Definition: SDL_spinlock.c:47
void * SDL_AtomicSetPtr(void **a, void *v)
Set a pointer to a value atomically.
Definition: SDL_atomic.c:215
void SDL_AtomicUnlock(SDL_SpinLock *lock)
Unlock a spin lock by setting it to 0. Always returns immediately.
Definition: SDL_spinlock.c:129
SDL_mutex * lock
Definition: SDL_events.c:77
void SDL_MemoryBarrierAcquireFunction(void)
Definition: SDL_atomic.c:298
int SDL_SpinLock
Definition: SDL_atomic.h:89
GLboolean GLboolean GLboolean GLboolean a
#define SDLCALL
Definition: SDL_internal.h:45
void SDL_MemoryBarrierReleaseFunction(void)
Definition: SDL_atomic.c:292