SDL  2.0
SDL_spinlock.c
Go to the documentation of this file.
1 /*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2020 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(HAVE_GCC_ATOMICS) && defined(__RISCOS__)
36 #include <unixlib/local.h>
37 #endif
38 
39 #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
40 #include <xmmintrin.h>
41 #endif
42 
43 #if defined(__WATCOMC__) && defined(__386__)
44 SDL_COMPILE_TIME_ASSERT(locksize, 4==sizeof(SDL_SpinLock));
45 extern _inline int _SDL_xchg_watcom(volatile int *a, int v);
46 #pragma aux _SDL_xchg_watcom = \
47  "lock xchg [ecx], eax" \
48  parm [ecx] [eax] \
49  value [eax] \
50  modify exact [eax];
51 #endif /* __WATCOMC__ && __386__ */
52 
53 /* This function is where all the magic happens... */
56 {
57 #if SDL_ATOMIC_DISABLED
58  /* Terrible terrible damage */
59  static SDL_mutex *_spinlock_mutex;
60 
61  if (!_spinlock_mutex) {
62  /* Race condition on first lock... */
63  _spinlock_mutex = SDL_CreateMutex();
64  }
65  SDL_LockMutex(_spinlock_mutex);
66  if (*lock == 0) {
67  *lock = 1;
68  SDL_UnlockMutex(_spinlock_mutex);
69  return SDL_TRUE;
70  } else {
71  SDL_UnlockMutex(_spinlock_mutex);
72  return SDL_FALSE;
73  }
74 
75 #elif defined(_MSC_VER)
76  SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
77  return (InterlockedExchange((long*)lock, 1) == 0);
78 
79 #elif defined(__WATCOMC__) && defined(__386__)
80  return _SDL_xchg_watcom(lock, 1) == 0;
81 
82 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
83  return (__sync_lock_test_and_set(lock, 1) == 0);
84 
85 #elif defined(__GNUC__) && defined(__arm__) && \
86  (defined(__ARM_ARCH_3__) || defined(__ARM_ARCH_3M__) || \
87  defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__) || \
88  defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__) || \
89  defined(__ARM_ARCH_5TEJ__))
90  int result;
91 
92 #if defined(__RISCOS__)
93  if (__cpucap_have_rex()) {
94  __asm__ __volatile__ (
95  "ldrex %0, [%2]\nteq %0, #0\nstrexeq %0, %1, [%2]"
96  : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
97  return (result == 0);
98  }
99 #endif
100 
101  __asm__ __volatile__ (
102  "swp %0, %1, [%2]\n"
103  : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");
104  return (result == 0);
105 
106 #elif defined(__GNUC__) && defined(__arm__)
107  int result;
108  __asm__ __volatile__ (
109  "ldrex %0, [%2]\nteq %0, #0\nstrexeq %0, %1, [%2]"
110  : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
111  return (result == 0);
112 
113 #elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
114  int result;
115  __asm__ __volatile__(
116  "lock ; xchgl %0, (%1)\n"
117  : "=r" (result) : "r" (lock), "0" (1) : "cc", "memory");
118  return (result == 0);
119 
120 #elif defined(__MACOSX__) || defined(__IPHONEOS__)
121  /* Maybe used for PowerPC, but the Intel asm or gcc atomics are favored. */
122  return OSAtomicCompareAndSwap32Barrier(0, 1, lock);
123 
124 #elif defined(__SOLARIS__) && defined(_LP64)
125  /* Used for Solaris with non-gcc compilers. */
126  return (SDL_bool) ((int) atomic_cas_64((volatile uint64_t*)lock, 0, 1) == 0);
127 
128 #elif defined(__SOLARIS__) && !defined(_LP64)
129  /* Used for Solaris with non-gcc compilers. */
130  return (SDL_bool) ((int) atomic_cas_32((volatile uint32_t*)lock, 0, 1) == 0);
131 
132 #else
133 #error Please implement for your platform.
134  return SDL_FALSE;
135 #endif
136 }
137 
138 /* "REP NOP" is PAUSE, coded for tools that don't know it by that name. */
139 #if (defined(__GNUC__) || defined(__clang__)) && (defined(__i386__) || defined(__x86_64__))
140  #define PAUSE_INSTRUCTION() __asm__ __volatile__("pause\n") /* Some assemblers can't do REP NOP, so go with PAUSE. */
141 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
142  #define PAUSE_INSTRUCTION() _mm_pause() /* this is actually "rep nop" and not a SIMD instruction. No inline asm in MSVC x86-64! */
143 #elif defined(__WATCOMC__) && defined(__386__)
144  /* watcom assembler rejects PAUSE if CPU < i686, and it refuses REP NOP as an invalid combination. Hardcode the bytes. */
145  extern _inline void PAUSE_INSTRUCTION(void);
146  #pragma aux PAUSE_INSTRUCTION = "db 0f3h,90h"
147 #else
148  #define PAUSE_INSTRUCTION()
149 #endif
150 
151 void
153 {
154  int iterations = 0;
155  /* FIXME: Should we have an eventual timeout? */
156  while (!SDL_AtomicTryLock(lock)) {
157  if (iterations < 32) {
158  iterations++;
160  } else {
161  /* !!! FIXME: this doesn't definitely give up the current timeslice, it does different things on various platforms. */
162  SDL_Delay(0);
163  }
164  }
165 }
166 
167 void
169 {
170 #if defined(_MSC_VER)
171  _ReadWriteBarrier();
172  *lock = 0;
173 
174 #elif defined(__WATCOMC__) && defined(__386__)
176  *lock = 0;
177 
178 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
179  __sync_lock_release(lock);
180 
181 #elif defined(__SOLARIS__)
182  /* Used for Solaris when not using gcc. */
183  *lock = 0;
184  membar_producer();
185 
186 #else
187  *lock = 0;
188 #endif
189 }
190 
191 /* vi: set ts=4 sw=4 expandtab: */
SDL_AtomicLock
void SDL_AtomicLock(SDL_SpinLock *lock)
Lock a spin lock by setting it to a non-zero value.
Definition: SDL_spinlock.c:152
SDL_LockMutex
#define SDL_LockMutex
Definition: SDL_dynapi_overrides.h:260
SDL_atomic.h
SDL_timer.h
SDL_mutex
Definition: SDL_sysmutex.c:29
iterations
static int iterations
Definition: testsprite2.c:45
SDL_CreateMutex
#define SDL_CreateMutex
Definition: SDL_dynapi_overrides.h:259
SDL_AtomicTryLock
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:55
a
GLboolean GLboolean GLboolean GLboolean a
Definition: SDL_opengl_glext.h:1112
v
const GLdouble * v
Definition: SDL_opengl.h:2064
result
GLuint64EXT * result
Definition: SDL_opengl_glext.h:9435
SDL_AtomicUnlock
void SDL_AtomicUnlock(SDL_SpinLock *lock)
Unlock a spin lock by setting it to 0. Always returns immediately.
Definition: SDL_spinlock.c:168
SDL_FALSE
@ SDL_FALSE
Definition: SDL_stdinc.h:163
SDL_COMPILE_TIME_ASSERT
#define SDL_COMPILE_TIME_ASSERT(name, x)
Definition: SDL_stdinc.h:312
SDL_mutex.h
SDL_CompilerBarrier
#define SDL_CompilerBarrier()
Definition: SDL_atomic.h:132
SDL_Delay
#define SDL_Delay
Definition: SDL_dynapi_overrides.h:486
SDL_SpinLock
int SDL_SpinLock
Definition: SDL_atomic.h:89
uint32_t
unsigned int uint32_t
Definition: SDL_config_windows.h:63
SDL_TRUE
@ SDL_TRUE
Definition: SDL_stdinc.h:164
PAUSE_INSTRUCTION
#define PAUSE_INSTRUCTION()
Definition: SDL_spinlock.c:148
SDL_UnlockMutex
#define SDL_UnlockMutex
Definition: SDL_dynapi_overrides.h:262
uint64_t
unsigned long long uint64_t
Definition: SDL_config_windows.h:65
SDL_bool
SDL_bool
Definition: SDL_stdinc.h:161
lock
SDL_mutex * lock
Definition: SDL_events.c:83