1 | /** |
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2 | * @file |
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3 | * |
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4 | * @ingroup ScoreSMPLock |
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5 | * |
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6 | * @brief SMP Lock API |
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7 | */ |
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8 | |
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9 | /* |
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10 | * COPYRIGHT (c) 1989-2011. |
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11 | * On-Line Applications Research Corporation (OAR). |
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12 | * |
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13 | * Copyright (c) 2013-2014 embedded brains GmbH |
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14 | * |
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15 | * The license and distribution terms for this file may be |
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16 | * found in the file LICENSE in this distribution or at |
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17 | * http://www.rtems.com/license/LICENSE. |
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18 | */ |
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19 | |
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20 | #ifndef _RTEMS_SCORE_SMPLOCK_H |
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21 | #define _RTEMS_SCORE_SMPLOCK_H |
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22 | |
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23 | #include <rtems/score/cpuopts.h> |
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24 | |
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25 | #if defined( RTEMS_SMP ) |
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26 | |
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27 | #include <rtems/score/atomic.h> |
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28 | #include <rtems/score/isrlevel.h> |
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29 | |
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30 | #ifdef __cplusplus |
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31 | extern "C" { |
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32 | #endif /* __cplusplus */ |
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33 | |
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34 | /** |
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35 | * @defgroup ScoreSMPLock SMP Locks |
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36 | * |
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37 | * @ingroup Score |
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38 | * |
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39 | * @brief The SMP lock provides mutual exclusion for SMP systems at the lowest |
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40 | * level. |
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41 | * |
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42 | * The SMP lock is implemented as a ticket lock. This provides fairness in |
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43 | * case of concurrent lock attempts. |
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44 | * |
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45 | * This SMP lock API uses a local context for acquire and release pairs. Such |
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46 | * a context may be used to implement for example the Mellor-Crummey and Scott |
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47 | * (MCS) locks in the future. |
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48 | * |
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49 | * @{ |
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50 | */ |
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51 | |
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52 | /** |
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53 | * @brief SMP ticket lock control. |
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54 | */ |
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55 | typedef struct { |
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56 | Atomic_Uint next_ticket; |
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57 | Atomic_Uint now_serving; |
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58 | } SMP_ticket_lock_Control; |
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59 | |
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60 | /** |
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61 | * @brief SMP ticket lock control initializer for static initialization. |
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62 | */ |
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63 | #define SMP_TICKET_LOCK_INITIALIZER \ |
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64 | { ATOMIC_INITIALIZER_UINT( 0U ), ATOMIC_INITIALIZER_UINT( 0U ) } |
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65 | |
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66 | /** |
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67 | * @brief Initializes an SMP ticket lock. |
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68 | * |
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69 | * Concurrent initialization leads to unpredictable results. |
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70 | * |
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71 | * @param[in,out] lock The SMP ticket lock control. |
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72 | */ |
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73 | static inline void _SMP_ticket_lock_Initialize( SMP_ticket_lock_Control *lock ) |
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74 | { |
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75 | _Atomic_Init_uint( &lock->next_ticket, 0U ); |
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76 | _Atomic_Init_uint( &lock->now_serving, 0U ); |
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77 | } |
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78 | |
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79 | /** |
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80 | * @brief Destroys an SMP ticket lock. |
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81 | * |
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82 | * Concurrent destruction leads to unpredictable results. |
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83 | * |
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84 | * @param[in,out] lock The SMP ticket lock control. |
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85 | */ |
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86 | static inline void _SMP_ticket_lock_Destroy( SMP_ticket_lock_Control *lock ) |
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87 | { |
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88 | (void) lock; |
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89 | } |
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90 | |
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91 | /** |
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92 | * @brief Acquires an SMP ticket lock. |
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93 | * |
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94 | * This function will not disable interrupts. The caller must ensure that the |
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95 | * current thread of execution is not interrupted indefinite once it obtained |
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96 | * the SMP ticket lock. |
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97 | * |
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98 | * @param[in,out] lock The SMP ticket lock control. |
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99 | */ |
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100 | static inline void _SMP_ticket_lock_Acquire( SMP_ticket_lock_Control *lock ) |
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101 | { |
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102 | unsigned int my_ticket = |
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103 | _Atomic_Fetch_add_uint( &lock->next_ticket, 1U, ATOMIC_ORDER_RELAXED ); |
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104 | unsigned int now_serving; |
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105 | |
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106 | do { |
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107 | now_serving = |
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108 | _Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_ACQUIRE ); |
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109 | } while ( now_serving != my_ticket ); |
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110 | } |
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111 | |
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112 | /** |
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113 | * @brief Releases an SMP ticket lock. |
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114 | * |
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115 | * @param[in,out] lock The SMP ticket lock control. |
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116 | */ |
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117 | static inline void _SMP_ticket_lock_Release( SMP_ticket_lock_Control *lock ) |
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118 | { |
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119 | unsigned int current_ticket = |
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120 | _Atomic_Load_uint( &lock->now_serving, ATOMIC_ORDER_RELAXED ); |
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121 | unsigned int next_ticket = current_ticket + 1U; |
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122 | |
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123 | _Atomic_Store_uint( &lock->now_serving, next_ticket, ATOMIC_ORDER_RELEASE ); |
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124 | } |
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125 | |
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126 | /** |
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127 | * @brief SMP lock control. |
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128 | */ |
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129 | typedef struct { |
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130 | SMP_ticket_lock_Control ticket_lock; |
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131 | } SMP_lock_Control; |
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132 | |
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133 | /** |
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134 | * @brief Local SMP lock context for acquire and release pairs. |
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135 | */ |
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136 | typedef struct { |
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137 | ISR_Level isr_level; |
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138 | } SMP_lock_Context; |
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139 | |
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140 | /** |
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141 | * @brief SMP lock control initializer for static initialization. |
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142 | */ |
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143 | #define SMP_LOCK_INITIALIZER { SMP_TICKET_LOCK_INITIALIZER } |
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144 | |
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145 | /** |
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146 | * @brief Initializes an SMP lock. |
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147 | * |
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148 | * Concurrent initialization leads to unpredictable results. |
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149 | * |
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150 | * @param[in,out] lock The SMP lock control. |
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151 | */ |
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152 | static inline void _SMP_lock_Initialize( SMP_lock_Control *lock ) |
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153 | { |
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154 | _SMP_ticket_lock_Initialize( &lock->ticket_lock ); |
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155 | } |
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156 | |
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157 | /** |
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158 | * @brief Destroys an SMP lock. |
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159 | * |
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160 | * Concurrent destruction leads to unpredictable results. |
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161 | * |
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162 | * @param[in,out] lock The SMP lock control. |
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163 | */ |
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164 | static inline void _SMP_lock_Destroy( SMP_lock_Control *lock ) |
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165 | { |
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166 | _SMP_ticket_lock_Destroy( &lock->ticket_lock ); |
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167 | } |
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168 | |
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169 | /** |
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170 | * @brief Acquires an SMP lock. |
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171 | * |
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172 | * This function will not disable interrupts. The caller must ensure that the |
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173 | * current thread of execution is not interrupted indefinite once it obtained |
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174 | * the SMP lock. |
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175 | * |
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176 | * @param[in,out] lock The SMP lock control. |
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177 | * @param[in,out] context The local SMP lock context for an acquire and release |
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178 | * pair. |
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179 | */ |
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180 | static inline void _SMP_lock_Acquire( |
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181 | SMP_lock_Control *lock, |
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182 | SMP_lock_Context *context |
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183 | ) |
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184 | { |
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185 | (void) context; |
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186 | _SMP_ticket_lock_Acquire( &lock->ticket_lock ); |
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187 | } |
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188 | |
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189 | /** |
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190 | * @brief Releases an SMP lock. |
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191 | * |
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192 | * @param[in,out] lock The SMP lock control. |
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193 | * @param[in,out] context The local SMP lock context for an acquire and release |
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194 | * pair. |
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195 | */ |
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196 | static inline void _SMP_lock_Release( |
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197 | SMP_lock_Control *lock, |
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198 | SMP_lock_Context *context |
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199 | ) |
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200 | { |
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201 | (void) context; |
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202 | _SMP_ticket_lock_Release( &lock->ticket_lock ); |
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203 | } |
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204 | |
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205 | /** |
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206 | * @brief Disables interrupts and acquires the SMP lock. |
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207 | * |
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208 | * @param[in,out] lock The SMP lock control. |
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209 | * @param[in,out] context The local SMP lock context for an acquire and release |
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210 | * pair. |
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211 | */ |
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212 | static inline void _SMP_lock_ISR_disable_and_acquire( |
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213 | SMP_lock_Control *lock, |
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214 | SMP_lock_Context *context |
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215 | ) |
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216 | { |
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217 | _ISR_Disable_without_giant( context->isr_level ); |
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218 | _SMP_lock_Acquire( lock, context ); |
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219 | } |
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220 | |
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221 | /** |
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222 | * @brief Releases the SMP lock and enables interrupts. |
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223 | * |
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224 | * @param[in,out] lock The SMP lock control. |
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225 | * @param[in,out] context The local SMP lock context for an acquire and release |
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226 | * pair. |
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227 | */ |
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228 | static inline void _SMP_lock_Release_and_ISR_enable( |
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229 | SMP_lock_Control *lock, |
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230 | SMP_lock_Context *context |
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231 | ) |
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232 | { |
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233 | _SMP_lock_Release( lock, context ); |
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234 | _ISR_Enable_without_giant( context->isr_level ); |
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235 | } |
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236 | |
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237 | /**@}*/ |
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238 | |
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239 | #ifdef __cplusplus |
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240 | } |
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241 | #endif /* __cplusplus */ |
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242 | |
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243 | #endif /* defined( RTEMS_SMP ) */ |
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244 | |
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245 | #endif /* _RTEMS_SCORE_SMPLOCK_H */ |
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