src/atomic/SDL_spinlock.c
author Sylvain Becker
Tue, 27 Oct 2020 21:14:49 +0100
changeset 14207 7225f02f0055
parent 13526 2b708d63875d
permissions -rw-r--r--
Android: apply code simplications found with lint / Android Studio
     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
    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
   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
   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: */