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annotate include/SDL_atomic.h @ 5097:dceec93471e7

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Improvements based on feedback from Anthony Williams
author Sam Lantinga <slouken@libsdl.org>
date Tue, 25 Jan 2011 17:40:06 -0800
parents c2539ff054c8
children e4301cde4de1
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
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23 /**
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24 * \file SDL_atomic.h
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25 *
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26 * Atomic operations.
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27 *
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28 * IMPORTANT:
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29 * If you are not an expert in concurrent lockless programming, you should
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30 * only be using the atomic lock and reference counting functions in this
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31 * file. In all other cases you should be protecting your data structures
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32 * with full mutexes.
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33 *
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34 * The list of "safe" functions to use are:
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35 * SDL_AtomicLock()
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36 * SDL_AtomicUnlock()
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37 * SDL_AtomicIncRef()
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38 * SDL_AtomicDecRef()
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39 *
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40 * Seriously, here be dragons!
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41 * ^^^^^^^^^^^^^^^^^^^^^^^^^^^
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42 *
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43 * You can find out a little more about lockless programming and the
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44 * subtle issues that can arise here:
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45 * http://msdn.microsoft.com/en-us/library/ee418650%28v=vs.85%29.aspx
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46 *
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47 * These operations may or may not actually be implemented using
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48 * processor specific atomic operations. When possible they are
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49 * implemented as true processor specific atomic operations. When that
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50 * is not possible the are implemented using locks that *do* use the
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51 * available atomic operations.
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52 *
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53 * All of the atomic operations that modify memory are full memory barriers.
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54 */
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55
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56 #ifndef _SDL_atomic_h_
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57 #define _SDL_atomic_h_
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58
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59 #include "SDL_stdinc.h"
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60 #include "SDL_platform.h"
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61
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62 #include "begin_code.h"
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63
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64 /* Need to do this here because intrin.h has C++ code in it */
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65 /* Visual Studio 2005 has a bug where intrin.h conflicts with winnt.h */
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66 #if defined(_MSC_VER) && (_MSC_VER >= 1500) && !defined(_WIN32_WCE)
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67 #include <intrin.h>
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68 #define HAVE_MSC_ATOMICS
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69 #endif
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70
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71 /* Set up for C function definitions, even when using C++ */
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72 #ifdef __cplusplus
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73 /* *INDENT-OFF* */
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74 extern "C" {
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75 /* *INDENT-ON* */
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76 #endif
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77
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78 /**
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79 * \name SDL AtomicLock
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80 *
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81 * The atomic locks are efficient spinlocks using CPU instructions,
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82 * but are vulnerable to starvation and can spin forever if a thread
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83 * holding a lock has been terminated. For this reason you should
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84 * minimize the code executed inside an atomic lock and never do
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85 * expensive things like API or system calls while holding them.
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86 *
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87 * The atomic locks are not safe to lock recursively.
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88 *
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89 * Porting Note:
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90 * The spin lock functions and type are required and can not be
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91 * emulated because they are used in the atomic emulation code.
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92 */
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93 /*@{*/
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94
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95 typedef int SDL_SpinLock;
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96
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97 /**
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98 * \brief Try to lock a spin lock by setting it to a non-zero value.
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99 *
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100 * \param lock Points to the lock.
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101 *
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102 * \return SDL_TRUE if the lock succeeded, SDL_FALSE if the lock is already held.
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103 */
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104 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicTryLock(SDL_SpinLock *lock);
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105
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106 /**
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107 * \brief Lock a spin lock by setting it to a non-zero value.
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108 *
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109 * \param lock Points to the lock.
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110 */
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111 extern DECLSPEC void SDLCALL SDL_AtomicLock(SDL_SpinLock *lock);
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112
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113 /**
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114 * \brief Unlock a spin lock by setting it to 0. Always returns immediately
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115 *
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116 * \param lock Points to the lock.
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117 */
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118 extern DECLSPEC void SDLCALL SDL_AtomicUnlock(SDL_SpinLock *lock);
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119
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120 /*@}*//*SDL AtomicLock*/
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121
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122
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123 /* The compiler barrier prevents the compiler from reordering
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124 reads and writes to globally visible variables across the call.
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125 */
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126 #ifdef _MSC_VER
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127 void _ReadWriteBarrier(void);
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128 #pragma intrinsic(_ReadWriteBarrier)
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129 #define SDL_CompilerBarrier() _ReadWriteBarrier()
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130 #elif __GNUC__
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131 #define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")
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132 #else
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133 #define SDL_CompilerBarrier() \
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134 ({ SDL_SpinLock _tmp = 0; SDL_AtomicLock(&_tmp); SDL_AtomicUnlock(&_tmp); })
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135 #endif
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136
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137 /* Platform specific optimized versions of the atomic functions,
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138 * you can disable these by defining SDL_DISABLE_ATOMIC_INLINE
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139 */
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140 #ifndef SDL_DISABLE_ATOMIC_INLINE
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141
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142 #if HAVE_MSC_ATOMICS
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143
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144 #define SDL_AtomicSet(a, v) _InterlockedExchange((long*)&(a)->value, (v))
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145 #define SDL_AtomicAdd(a, v) _InterlockedExchangeAdd((long*)&(a)->value, (v))
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146 #define SDL_AtomicCAS(a, oldval, newval) (_InterlockedCompareExchange((long*)&(a)->value, (newval), (oldval)) == (oldval))
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147 #define SDL_AtomicSetPtr(a, v) _InterlockedExchangePointer((a), (v))
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148 #if _M_IX86
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149 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchange((long*)(a), (long)(newval), (long)(oldval)) == (long)(oldval))
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150 #else
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151 #define SDL_AtomicCASPtr(a, oldval, newval) (_InterlockedCompareExchangePointer((a), (newval), (oldval)) == (oldval))
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152 #endif
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153
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154 #elif __MACOSX__
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155 #include <libkern/OSAtomic.h>
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156
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157 #define SDL_AtomicCAS(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((oldval), (newval), &(a)->value)
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158 #if SIZEOF_VOIDP == 4
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159 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap32Barrier((int32_t)(oldval), (int32_t)(newval), (int32_t*)(a))
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160 #elif SIZEOF_VOIDP == 8
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161 #define SDL_AtomicCASPtr(a, oldval, newval) OSAtomicCompareAndSwap64Barrier((int64_t)(oldval), (int64_t)(newval), (int64_t*)(a))
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162 #endif
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163
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164 #elif HAVE_GCC_ATOMICS
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165
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166 #define SDL_AtomicSet(a, v) __sync_lock_test_and_set(&(a)->value, v)
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167 #define SDL_AtomicAdd(a, v) __sync_fetch_and_add(&(a)->value, v)
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168 #define SDL_AtomicSetPtr(a, v) __sync_lock_test_and_set(a, v)
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169 #define SDL_AtomicCAS(a, oldval, newval) __sync_bool_compare_and_swap(&(a)->value, oldval, newval)
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170 #define SDL_AtomicCASPtr(a, oldval, newval) __sync_bool_compare_and_swap(a, oldval, newval)
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171
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172 #endif
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173
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174 #endif /* !SDL_DISABLE_ATOMIC_INLINE */
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175
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176
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177 /**
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178 * \brief A type representing an atomic integer value. It is a struct
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179 * so people don't accidentally use numeric operations on it.
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180 */
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181 #ifndef SDL_atomic_t_defined
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182 typedef struct { int value; } SDL_atomic_t;
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183 #endif
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184
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185 /**
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186 * \brief Set an atomic variable to a value.
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187 *
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188 * \return The previous value of the atomic variable.
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189 */
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190 #ifndef SDL_AtomicSet
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191 #define SDL_AtomicSet(a, v) \
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192 ({ \
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193 int _value; \
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194 do { \
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195 _value = (a)->value; \
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196 } while (!SDL_AtomicCAS(a, _value, (v))); \
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197 _value; \
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198 })
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199 #endif
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200
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201 /**
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202 * \brief Get the value of an atomic variable
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203 */
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204 #ifndef SDL_AtomicGet
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205 #define SDL_AtomicGet(a) \
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206 ({ \
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207 int _value = (a)->value; \
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208 SDL_CompilerBarrier(); \
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209 _value; \
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210 })
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211 #endif
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212
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213 /**
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214 * \brief Add to an atomic variable.
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215 *
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216 * \return The previous value of the atomic variable.
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217 *
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218 * \note This same style can be used for any number operation
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219 */
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220 #ifndef SDL_AtomicAdd
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221 #define SDL_AtomicAdd(a, v) \
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222 ({ \
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223 int _value; \
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224 do { \
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225 _value = (a)->value; \
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226 } while (!SDL_AtomicCAS(a, _value, (_value + (v)))); \
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227 _value; \
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228 })
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229 #endif
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230
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231 /**
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232 * \brief Increment an atomic variable used as a reference count.
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233 */
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234 #ifndef SDL_AtomicIncRef
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235 #define SDL_AtomicIncRef(a) SDL_AtomicAdd(a, 1)
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236 #endif
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237
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238 /**
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239 * \brief Decrement an atomic variable used as a reference count.
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240 *
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241 * \return SDL_TRUE if the variable reached zero after decrementing,
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242 * SDL_FALSE otherwise
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243 */
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244 #ifndef SDL_AtomicDecRef
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245 #define SDL_AtomicDecRef(a) (SDL_AtomicAdd(a, -1) == 1)
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246 #endif
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247
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248 /**
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249 * \brief Set an atomic variable to a new value if it is currently an old value.
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250 *
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251 * \return SDL_TRUE if the atomic variable was set, SDL_FALSE otherwise.
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252 *
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253 * \note If you don't know what this function is for, you shouldn't use it!
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254 */
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255 #ifndef SDL_AtomicCAS
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256 #define SDL_AtomicCAS SDL_AtomicCAS_
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257 #endif
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258 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCAS_(SDL_atomic_t *a, int oldval, int newval);
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259
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260 /**
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261 * \brief Set a pointer to a value atomically.
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262 *
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263 * \return The previous value of the pointer.
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264 */
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265 #ifndef SDL_AtomicSetPtr
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266 #define SDL_AtomicSetPtr(a, v) \
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267 ({ \
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268 void* _value; \
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269 do { \
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270 _value = *(a); \
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271 } while (!SDL_AtomicCASPtr(a, _value, (v))); \
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272 _value; \
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273 })
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274 #endif
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275
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276 /**
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277 * \brief Get the value of a pointer atomically.
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278 */
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279 #ifndef SDL_AtomicGetPtr
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280 #define SDL_AtomicGetPtr(a) \
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281 ({ \
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282 void* _value = *(a); \
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283 SDL_CompilerBarrier(); \
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284 _value; \
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285 })
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286 #endif
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287
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288 /**
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289 * \brief Set a pointer to a new value if it is currently an old value.
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290 *
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291 * \return SDL_TRUE if the pointer was set, SDL_FALSE otherwise.
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292 *
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293 * \note If you don't know what this function is for, you shouldn't use it!
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294 */
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295 #ifndef SDL_AtomicCASPtr
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296 #define SDL_AtomicCASPtr SDL_AtomicCASPtr_
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297 #endif
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298 extern DECLSPEC SDL_bool SDLCALL SDL_AtomicCASPtr_(void **a, void *oldval, void *newval);
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299
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300 /* Ends C function definitions when using C++ */
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301 #ifdef __cplusplus
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302 /* *INDENT-OFF* */
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303 }
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304 /* *INDENT-ON* */
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305 #endif
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306
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307 #include "close_code.h"
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308
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309 #endif /* _SDL_atomic_h_ */
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310
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311 /* vi: set ts=4 sw=4 expandtab: */