1/*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2025 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(SDL_PLATFORM_WINDOWS)
24#include "../core/windows/SDL_windows.h"
25#endif
26
27#if !defined(HAVE_GCC_ATOMICS) && defined(SDL_PLATFORM_SOLARIS)
28#include <atomic.h>
29#endif
30
31#if !defined(HAVE_GCC_ATOMICS) && defined(SDL_PLATFORM_RISCOS)
32#include <unixlib/local.h>
33#endif
34
35#if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
36#include <xmmintrin.h>
37#endif
38
39#ifdef PS2
40#include <kernel.h>
41#endif
42
43#if !defined(HAVE_GCC_ATOMICS) && defined(SDL_PLATFORM_MACOS)
44#include <libkern/OSAtomic.h>
45#endif
46
47/* *INDENT-OFF* */ // clang-format off
48#if defined(__WATCOMC__) && defined(__386__)
49SDL_COMPILE_TIME_ASSERT(locksize, 4==sizeof(SDL_SpinLock));
50extern __inline int _SDL_xchg_watcom(volatile int *a, int v);
51#pragma aux _SDL_xchg_watcom = \
52 "lock xchg [ecx], eax" \
53 parm [ecx] [eax] \
54 value [eax] \
55 modify exact [eax];
56#endif // __WATCOMC__ && __386__
57/* *INDENT-ON* */ // clang-format on
58
59// This function is where all the magic happens...
60bool SDL_TryLockSpinlock(SDL_SpinLock *lock)
61{
62#if defined(HAVE_GCC_ATOMICS) || defined(HAVE_GCC_SYNC_LOCK_TEST_AND_SET)
63 return __sync_lock_test_and_set(lock, 1) == 0;
64
65#elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_ARM64))
66 return _InterlockedExchange_acq(lock, 1) == 0;
67
68#elif defined(_MSC_VER)
69 SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
70 return InterlockedExchange((long *)lock, 1) == 0;
71
72#elif defined(__WATCOMC__) && defined(__386__)
73 return _SDL_xchg_watcom(lock, 1) == 0;
74
75#elif defined(__GNUC__) && defined(__arm__) && \
76 (defined(__ARM_ARCH_3__) || defined(__ARM_ARCH_3M__) || \
77 defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__) || \
78 defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__) || \
79 defined(__ARM_ARCH_5TEJ__))
80 int result;
81
82#ifdef SDL_PLATFORM_RISCOS
83 if (__cpucap_have_rex()) {
84 __asm__ __volatile__(
85 "ldrex %0, [%2]\nteq %0, #0\nstrexeq %0, %1, [%2]"
86 : "=&r"(result)
87 : "r"(1), "r"(lock)
88 : "cc", "memory");
89 return result == 0;
90 }
91#endif
92
93 __asm__ __volatile__(
94 "swp %0, %1, [%2]\n"
95 : "=&r,&r"(result)
96 : "r,0"(1), "r,r"(lock)
97 : "memory");
98 return result == 0;
99
100#elif defined(__GNUC__) && defined(__arm__)
101 int result;
102 __asm__ __volatile__(
103 "ldrex %0, [%2]\nteq %0, #0\nstrexeq %0, %1, [%2]"
104 : "=&r"(result)
105 : "r"(1), "r"(lock)
106 : "cc", "memory");
107 return result == 0;
108
109#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
110 int result;
111 __asm__ __volatile__(
112 "lock ; xchgl %0, (%1)\n"
113 : "=r"(result)
114 : "r"(lock), "0"(1)
115 : "cc", "memory");
116 return result == 0;
117
118#elif defined(SDL_PLATFORM_MACOS) || defined(SDL_PLATFORM_IOS) || defined(SDL_PLATFORM_TVOS)
119 // Maybe used for PowerPC, but the Intel asm or gcc atomics are favored.
120 return OSAtomicCompareAndSwap32Barrier(0, 1, lock);
121
122#elif defined(SDL_PLATFORM_SOLARIS) && defined(_LP64)
123 // Used for Solaris with non-gcc compilers.
124 return ((int)atomic_cas_64((volatile uint64_t *)lock, 0, 1) == 0);
125
126#elif defined(SDL_PLATFORM_SOLARIS) && !defined(_LP64)
127 // Used for Solaris with non-gcc compilers.
128 return ((int)atomic_cas_32((volatile uint32_t *)lock, 0, 1) == 0);
129#elif defined(PS2)
130 uint32_t oldintr;
131 bool res = false;
132 // disable interruption
133 oldintr = DIntr();
134
135 if (*lock == 0) {
136 *lock = 1;
137 res = true;
138 }
139 // enable interruption
140 if (oldintr) {
141 EIntr();
142 }
143 return res;
144#else
145 // Terrible terrible damage
146 static SDL_Mutex *_spinlock_mutex;
147
148 if (!_spinlock_mutex) {
149 // Race condition on first lock...
150 _spinlock_mutex = SDL_CreateMutex();
151 }
152 SDL_LockMutex(_spinlock_mutex);
153 if (*lock == 0) {
154 *lock = 1;
155 SDL_UnlockMutex(_spinlock_mutex);
156 return true;
157 } else {
158 SDL_UnlockMutex(_spinlock_mutex);
159 return false;
160 }
161#endif
162}
163
164void SDL_LockSpinlock(SDL_SpinLock *lock)
165{
166 int iterations = 0;
167 // FIXME: Should we have an eventual timeout?
168 while (!SDL_TryLockSpinlock(lock)) {
169 if (iterations < 32) {
170 iterations++;
171 SDL_CPUPauseInstruction();
172 } else {
173 // !!! FIXME: this doesn't definitely give up the current timeslice, it does different things on various platforms.
174 SDL_Delay(0);
175 }
176 }
177}
178
179void SDL_UnlockSpinlock(SDL_SpinLock *lock)
180{
181#if defined(HAVE_GCC_ATOMICS) || defined(HAVE_GCC_SYNC_LOCK_TEST_AND_SET)
182 __sync_lock_release(lock);
183
184#elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_ARM64))
185 _InterlockedExchange_rel(lock, 0);
186
187#elif defined(_MSC_VER)
188 _ReadWriteBarrier();
189 *lock = 0;
190
191#elif defined(__WATCOMC__) && defined(__386__)
192 SDL_CompilerBarrier();
193 *lock = 0;
194
195#elif defined(SDL_PLATFORM_SOLARIS)
196 // Used for Solaris when not using gcc.
197 *lock = 0;
198 membar_producer();
199
200#else
201 *lock = 0;
202#endif
203}
204