src/atomic/SDL_spinlock.c
author Sam Lantinga <slouken@libsdl.org>
Fri, 08 Apr 2011 13:03:26 -0700
changeset 5535 96594ac5fd1a
parent 5328 f34a5f9ce9f6
child 5557 c1ed57cbfd66
permissions -rw-r--r--
SDL 1.3 is now under the zlib license.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2011 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_stdinc.h"
    22 
    23 #include "SDL_atomic.h"
    24 #include "SDL_mutex.h"
    25 #include "SDL_timer.h"
    26 
    27 /* Don't do the check for Visual Studio 2005, it's safe here */
    28 #ifdef __WIN32__
    29 #include "../core/windows/SDL_windows.h"
    30 #endif
    31 
    32 /* This function is where all the magic happens... */
    33 SDL_bool
    34 SDL_AtomicTryLock(SDL_SpinLock *lock)
    35 {
    36 #if SDL_ATOMIC_DISABLED
    37     /* Terrible terrible damage */
    38     static SDL_mutex *_spinlock_mutex;
    39 
    40     if (!_spinlock_mutex) {
    41         /* Race condition on first lock... */
    42         _spinlock_mutex = SDL_CreateMutex();
    43     }
    44     SDL_mutexP(_spinlock_mutex);
    45     if (*lock == 0) {
    46         *lock = 1;
    47         SDL_mutexV(_spinlock_mutex);
    48         return SDL_TRUE;
    49     } else {
    50         SDL_mutexV(_spinlock_mutex);
    51         return SDL_FALSE;
    52     }
    53 
    54 #elif defined(_MSC_VER)
    55     SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
    56     return (InterlockedExchange((long*)lock, 1) == 0);
    57 
    58 #elif defined(__MACOSX__)
    59     return OSAtomicCompareAndSwap32Barrier(0, 1, lock);
    60 
    61 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
    62     return (__sync_lock_test_and_set(lock, 1) == 0);
    63 
    64 #elif defined(__GNUC__) && defined(__arm__) && \
    65         (defined(__ARM_ARCH_4__) || defined(__ARM_ARCH_4T__) || \
    66          defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__))
    67     int result;
    68     __asm__ __volatile__ (
    69         "swp %0, %1, [%2]\n"
    70         : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");
    71     return (result == 0);
    72 
    73 #elif defined(__GNUC__) && defined(__arm__)
    74     int result;
    75     __asm__ __volatile__ (
    76         "ldrex %0, [%2]\nteq   %0, #0\nstrexeq %0, %1, [%2]"
    77         : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
    78     return (result == 0);
    79 
    80 #else
    81     /* Need CPU instructions for spinlock here! */
    82     __need_spinlock_implementation__
    83 #endif
    84 }
    85 
    86 void
    87 SDL_AtomicLock(SDL_SpinLock *lock)
    88 {
    89     /* FIXME: Should we have an eventual timeout? */
    90     while (!SDL_AtomicTryLock(lock)) {
    91         SDL_Delay(0);
    92     }
    93 }
    94 
    95 void
    96 SDL_AtomicUnlock(SDL_SpinLock *lock)
    97 {
    98 #if defined(_MSC_VER)
    99     _ReadWriteBarrier();
   100     *lock = 0;
   101 
   102 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
   103     __sync_lock_release(lock);
   104 
   105 #else
   106     *lock = 0;
   107 #endif
   108 }
   109 
   110 /* vi: set ts=4 sw=4 expandtab: */