1 | /* |
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2 | * Mutex Handler |
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3 | * |
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4 | * DESCRIPTION: |
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5 | * |
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6 | * This package is the implementation of the Mutex Handler. |
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7 | * This handler provides synchronization and mutual exclusion capabilities. |
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8 | * |
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9 | * COPYRIGHT (c) 1989-1999. |
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10 | * On-Line Applications Research Corporation (OAR). |
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11 | * |
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12 | * The license and distribution terms for this file may be |
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13 | * found in the file LICENSE in this distribution or at |
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14 | * http://www.OARcorp.com/rtems/license.html. |
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15 | * |
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16 | * $Id$ |
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17 | */ |
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18 | |
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19 | #include <rtems/system.h> |
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20 | #include <rtems/score/isr.h> |
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21 | #include <rtems/score/coremutex.h> |
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22 | #include <rtems/score/states.h> |
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23 | #include <rtems/score/thread.h> |
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24 | #include <rtems/score/threadq.h> |
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25 | |
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26 | /* |
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27 | * _CORE_mutex_Surrender |
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28 | * |
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29 | * DESCRIPTION: |
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30 | * |
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31 | * This routine frees a unit to the mutex. If a task was blocked waiting for |
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32 | * a unit from this mutex, then that task will be readied and the unit |
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33 | * given to that task. Otherwise, the unit will be returned to the mutex. |
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34 | * |
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35 | * Input parameters: |
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36 | * the_mutex - the mutex to be flushed |
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37 | * id - id of parent mutex |
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38 | * api_mutex_mp_support - api dependent MP support actions |
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39 | * |
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40 | * Output parameters: |
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41 | * CORE_MUTEX_STATUS_SUCCESSFUL - if successful |
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42 | * core error code - if unsuccessful |
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43 | */ |
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44 | |
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45 | CORE_mutex_Status _CORE_mutex_Surrender( |
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46 | CORE_mutex_Control *the_mutex, |
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47 | Objects_Id id, |
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48 | CORE_mutex_API_mp_support_callout api_mutex_mp_support |
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49 | ) |
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50 | { |
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51 | Thread_Control *the_thread; |
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52 | Thread_Control *holder; |
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53 | |
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54 | holder = the_mutex->holder; |
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55 | |
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56 | /* |
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57 | * The following code allows a thread (or ISR) other than the thread |
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58 | * which acquired the mutex to release that mutex. This is only |
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59 | * allowed when the mutex in quetion is FIFO or simple Priority |
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60 | * discipline. But Priority Ceiling or Priority Inheritance mutexes |
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61 | * must be released by the thread which acquired them. |
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62 | */ |
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63 | |
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64 | if ( the_mutex->Attributes.only_owner_release ) { |
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65 | if ( !_Thread_Is_executing( holder ) ) |
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66 | return CORE_MUTEX_STATUS_NOT_OWNER_OF_RESOURCE; |
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67 | } |
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68 | |
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69 | /* XXX already unlocked -- not right status */ |
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70 | |
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71 | if ( !the_mutex->nest_count ) |
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72 | return CORE_MUTEX_STATUS_SUCCESSFUL; |
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73 | |
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74 | the_mutex->nest_count--; |
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75 | |
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76 | if ( the_mutex->nest_count != 0 ) { |
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77 | switch ( the_mutex->Attributes.lock_nesting_behavior ) { |
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78 | case CORE_MUTEX_NESTING_ACQUIRES: |
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79 | return CORE_MUTEX_STATUS_SUCCESSFUL; |
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80 | case CORE_MUTEX_NESTING_IS_ERROR: |
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81 | /* should never occur */ |
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82 | return CORE_MUTEX_STATUS_NESTING_NOT_ALLOWED; |
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83 | case CORE_MUTEX_NESTING_BLOCKS: |
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84 | /* Currently no API exercises this behavior. */ |
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85 | break; |
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86 | } |
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87 | } |
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88 | |
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89 | _Thread_Executing->resource_count--; |
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90 | the_mutex->holder = NULL; |
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91 | the_mutex->holder_id = 0; |
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92 | |
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93 | /* |
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94 | * Whether or not someone is waiting for the mutex, an |
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95 | * inherited priority must be lowered if this is the last |
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96 | * mutex (i.e. resource) this task has. |
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97 | */ |
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98 | |
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99 | switch ( the_mutex->Attributes.discipline ) { |
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100 | case CORE_MUTEX_DISCIPLINES_FIFO: |
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101 | case CORE_MUTEX_DISCIPLINES_PRIORITY: |
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102 | break; |
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103 | case CORE_MUTEX_DISCIPLINES_PRIORITY_CEILING: |
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104 | case CORE_MUTEX_DISCIPLINES_PRIORITY_INHERIT: |
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105 | if ( holder->resource_count == 0 && |
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106 | holder->real_priority != holder->current_priority ) { |
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107 | _Thread_Change_priority( holder, holder->real_priority, TRUE ); |
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108 | } |
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109 | break; |
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110 | } |
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111 | |
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112 | |
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113 | if ( ( the_thread = _Thread_queue_Dequeue( &the_mutex->Wait_queue ) ) ) { |
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114 | |
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115 | #if defined(RTEMS_MULTIPROCESSING) |
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116 | if ( !_Objects_Is_local_id( the_thread->Object.id ) ) { |
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117 | |
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118 | the_mutex->holder = NULL; |
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119 | the_mutex->holder_id = the_thread->Object.id; |
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120 | the_mutex->nest_count = 1; |
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121 | |
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122 | ( *api_mutex_mp_support)( the_thread, id ); |
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123 | |
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124 | } else |
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125 | #endif |
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126 | { |
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127 | |
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128 | the_mutex->holder = the_thread; |
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129 | the_mutex->holder_id = the_thread->Object.id; |
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130 | the_thread->resource_count++; |
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131 | the_mutex->nest_count = 1; |
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132 | |
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133 | /* |
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134 | * No special action for priority inheritance or priority ceiling |
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135 | * because the_thread is guaranteed to be the highest priority |
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136 | * thread waiting for the mutex. |
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137 | */ |
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138 | } |
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139 | } else |
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140 | the_mutex->lock = CORE_MUTEX_UNLOCKED; |
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141 | |
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142 | return CORE_MUTEX_STATUS_SUCCESSFUL; |
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143 | } |
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144 | |
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