SDL  2.0
SDL_spinlock.c
Go to the documentation of this file.
1 /*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2018 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 #include "../SDL_internal.h"
22 
23 #if defined(__WIN32__) || defined(__WINRT__)
24 #include "../core/windows/SDL_windows.h"
25 #endif
26 
27 #include "SDL_atomic.h"
28 #include "SDL_mutex.h"
29 #include "SDL_timer.h"
30 
31 #if !defined(HAVE_GCC_ATOMICS) && defined(__SOLARIS__)
32 #include <atomic.h>
33 #endif
34 
35 #if defined(__WATCOMC__) && defined(__386__)
36 SDL_COMPILE_TIME_ASSERT(locksize, 4==sizeof(SDL_SpinLock));
37 extern _inline int _SDL_xchg_watcom(volatile int *a, int v);
38 #pragma aux _SDL_xchg_watcom = \
39  "xchg [ecx], eax" \
40  parm [ecx] [eax] \
41  value [eax] \
42  modify exact [eax];
43 #endif /* __WATCOMC__ && __386__ */
44 
45 /* This function is where all the magic happens... */
48 {
49 #if SDL_ATOMIC_DISABLED
50  /* Terrible terrible damage */
51  static SDL_mutex *_spinlock_mutex;
52 
53  if (!_spinlock_mutex) {
54  /* Race condition on first lock... */
55  _spinlock_mutex = SDL_CreateMutex();
56  }
57  SDL_LockMutex(_spinlock_mutex);
58  if (*lock == 0) {
59  *lock = 1;
60  SDL_UnlockMutex(_spinlock_mutex);
61  return SDL_TRUE;
62  } else {
63  SDL_UnlockMutex(_spinlock_mutex);
64  return SDL_FALSE;
65  }
66 
67 #elif defined(_MSC_VER)
68  SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
69  return (InterlockedExchange((long*)lock, 1) == 0);
70 
71 #elif defined(__WATCOMC__) && defined(__386__)
72  return _SDL_xchg_watcom(lock, 1) == 0;
73 
74 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
75  return (__sync_lock_test_and_set(lock, 1) == 0);
76 
77 #elif defined(__GNUC__) && defined(__arm__) && \
78  (defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__) || \
79  defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__) || \
80  defined(__ARM_ARCH_5TEJ__))
81  int result;
82  __asm__ __volatile__ (
83  "swp %0, %1, [%2]\n"
84  : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");
85  return (result == 0);
86 
87 #elif defined(__GNUC__) && defined(__arm__)
88  int result;
89  __asm__ __volatile__ (
90  "ldrex %0, [%2]\nteq %0, #0\nstrexeq %0, %1, [%2]"
91  : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
92  return (result == 0);
93 
94 #elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
95  int result;
96  __asm__ __volatile__(
97  "lock ; xchgl %0, (%1)\n"
98  : "=r" (result) : "r" (lock), "0" (1) : "cc", "memory");
99  return (result == 0);
100 
101 #elif defined(__MACOSX__) || defined(__IPHONEOS__)
102  /* Maybe used for PowerPC, but the Intel asm or gcc atomics are favored. */
103  return OSAtomicCompareAndSwap32Barrier(0, 1, lock);
104 
105 #elif defined(__SOLARIS__) && defined(_LP64)
106  /* Used for Solaris with non-gcc compilers. */
107  return (SDL_bool) ((int) atomic_cas_64((volatile uint64_t*)lock, 0, 1) == 0);
108 
109 #elif defined(__SOLARIS__) && !defined(_LP64)
110  /* Used for Solaris with non-gcc compilers. */
111  return (SDL_bool) ((int) atomic_cas_32((volatile uint32_t*)lock, 0, 1) == 0);
112 
113 #else
114 #error Please implement for your platform.
115  return SDL_FALSE;
116 #endif
117 }
118 
119 void
121 {
122  /* FIXME: Should we have an eventual timeout? */
123  while (!SDL_AtomicTryLock(lock)) {
124  SDL_Delay(0);
125  }
126 }
127 
128 void
130 {
131 #if defined(_MSC_VER)
132  _ReadWriteBarrier();
133  *lock = 0;
134 
135 #elif defined(__WATCOMC__) && defined(__386__)
137  *lock = 0;
138 
139 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
140  __sync_lock_release(lock);
141 
142 #elif defined(__SOLARIS__)
143  /* Used for Solaris when not using gcc. */
144  *lock = 0;
145  membar_producer();
146 
147 #else
148  *lock = 0;
149 #endif
150 }
151 
152 /* vi: set ts=4 sw=4 expandtab: */
#define SDL_LockMutex
#define SDL_CompilerBarrier()
Definition: SDL_atomic.h:132
GLuint64EXT * result
void SDL_AtomicLock(SDL_SpinLock *lock)
Lock a spin lock by setting it to a non-zero value.
Definition: SDL_spinlock.c:120
void SDL_AtomicUnlock(SDL_SpinLock *lock)
Unlock a spin lock by setting it to 0. Always returns immediately.
Definition: SDL_spinlock.c:129
const GLdouble * v
Definition: SDL_opengl.h:2064
#define SDL_CreateMutex
unsigned long long uint64_t
#define SDL_Delay
SDL_bool
Definition: SDL_stdinc.h:139
unsigned int uint32_t
SDL_mutex * lock
Definition: SDL_events.c:78
#define SDL_UnlockMutex
int SDL_SpinLock
Definition: SDL_atomic.h:89
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
GLboolean GLboolean GLboolean GLboolean a
#define SDL_COMPILE_TIME_ASSERT(name, x)
Definition: SDL_stdinc.h:290