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annotate src/atomic/SDL_spinlock.c @ 5230:5d01d426f2ea

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It's now possible to disable the fast atomic operations, at a huge performance penalty.
author Sam Lantinga <slouken@libsdl.org>
date Mon, 07 Feb 2011 22:57:33 -0800
parents b938ad843e52
children b530ef003506
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2010 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with this library; if not, write to the Free Software
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18
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19 Sam Lantinga
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20 slouken@libsdl.org
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21 */
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22 #include "SDL_stdinc.h"
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23
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24 #include "SDL_atomic.h"
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25 #include "SDL_mutex.h"
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26 #include "SDL_timer.h"
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27
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28 /* Don't do the check for Visual Studio 2005, it's safe here */
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29 #ifdef __WIN32__
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30 #include "../core/windows/SDL_windows.h"
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31 #endif
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32
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33 /* This function is where all the magic happens... */
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34 SDL_bool
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35 SDL_AtomicTryLock(SDL_SpinLock *lock)
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36 {
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37 #if SDL_ATOMIC_DISABLED
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38 /* Terrible terrible damage */
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39 static SDL_mutex *_spinlock_mutex;
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40
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41 if (!_spinlock_mutex) {
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42 /* Race condition on first lock... */
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43 _spinlock_mutex = SDL_CreateMutex();
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44 }
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45 SDL_mutexP(_spinlock_mutex);
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46 if (*lock == 0) {
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47 *lock = 1;
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48 SDL_mutexV(_spinlock_mutex);
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49 return SDL_TRUE;
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50 } else {
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51 SDL_mutexV(_spinlock_mutex);
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52 return SDL_FALSE;
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53 }
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54
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55 #elif defined(_MSC_VER)
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56 SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
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57 return (InterlockedExchange((long*)lock, 1) == 0);
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58
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59 #elif defined(__MACOSX__)
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60 return OSAtomicCompareAndSwap32Barrier(0, 1, lock);
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61
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62 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
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63 return (__sync_lock_test_and_set(lock, 1) == 0);
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64
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65 #elif defined(__GNUC__) && defined(__arm__) && defined(__ARM_ARCH_5__)
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66 int result;
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67 __asm__ __volatile__ (
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68 "swp %0, %1, [%2]\n"
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69 : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");
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70 return (result == 0);
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71
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72 #elif defined(__GNUC__) && defined(__arm__)
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73 int result;
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74 __asm__ __volatile__ (
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75 "ldrex %0, [%2]\nteq %0, #0\nstrexeq %0, %1, [%2]"
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76 : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
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77 return (result == 0);
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78
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79 #else
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80 /* Need CPU instructions for spinlock here! */
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81 __need_spinlock_implementation__
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82 #endif
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83 }
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84
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85 void
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86 SDL_AtomicLock(SDL_SpinLock *lock)
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87 {
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88 /* FIXME: Should we have an eventual timeout? */
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89 while (!SDL_AtomicTryLock(lock)) {
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90 SDL_Delay(0);
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91 }
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92 }
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93
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94 void
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95 SDL_AtomicUnlock(SDL_SpinLock *lock)
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96 {
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97 #if defined(_MSC_VER)
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98 _ReadWriteBarrier();
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99 *lock = 0;
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100
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101 #elif HAVE_GCC_ATOMICS || HAVE_GCC_SYNC_LOCK_TEST_AND_SET
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102 __sync_lock_release(lock);
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103
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104 #else
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105 *lock = 0;
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106 #endif
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107 }
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108
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109 /* vi: set ts=4 sw=4 expandtab: */