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... */
54 SDL_bool
SDL_AtomicTryLock(SDL_SpinLock * lock)55 SDL_AtomicTryLock(SDL_SpinLock *lock)
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
SDL_AtomicLock(SDL_SpinLock * lock)152 SDL_AtomicLock(SDL_SpinLock *lock)
153 {
154     int iterations = 0;
155     /* FIXME: Should we have an eventual timeout? */
156     while (!SDL_AtomicTryLock(lock)) {
157         if (iterations < 32) {
158             iterations++;
159             PAUSE_INSTRUCTION();
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
SDL_AtomicUnlock(SDL_SpinLock * lock)168 SDL_AtomicUnlock(SDL_SpinLock *lock)
169 {
170 #if defined(_MSC_VER)
171     _ReadWriteBarrier();
172     *lock = 0;
173 
174 #elif defined(__WATCOMC__) && defined(__386__)
175     SDL_CompilerBarrier ();
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: */
192