1 | @c |
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2 | @c COPYRIGHT (c) 1996. |
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3 | @c On-Line Applications Research Corporation (OAR). |
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4 | @c All rights reserved. |
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5 | @c |
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6 | |
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7 | @ifinfo |
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8 | @node Scheduler Manager, Scheduler Manager Introduction, time, Top |
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9 | @end ifinfo |
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10 | @chapter Scheduler Manager |
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11 | @ifinfo |
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12 | @menu |
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13 | * Scheduler Manager Introduction:: |
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14 | * Scheduler Manager Background:: |
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15 | * Scheduler Manager Operations:: |
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16 | * Scheduler Manager Directives:: |
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17 | @end menu |
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18 | @end ifinfo |
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19 | |
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20 | @ifinfo |
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21 | @node Scheduler Manager Introduction, Scheduler Manager Background, Scheduler Manager, Scheduler Manager |
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22 | @end ifinfo |
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23 | @section Introduction |
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24 | |
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25 | The scheduler manager ... |
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26 | |
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27 | The directives provided by the scheduler manager are: |
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28 | |
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29 | @itemize @bullet |
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30 | @item @code{sched_get_priority_min} - |
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31 | @item @code{sched_get_priority_max} - |
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32 | @item @code{sched_rr_get_interval} - |
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33 | @item @code{sched_yield} - |
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34 | @end itemize |
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35 | |
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36 | @ifinfo |
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37 | @node Scheduler Manager Background, Priority, Scheduler Manager Introduction, Scheduler Manager |
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38 | @end ifinfo |
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39 | @section Background |
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40 | @ifinfo |
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41 | @menu |
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42 | * Priority:: |
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43 | * Scheduling Policies:: |
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44 | @end menu |
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45 | @end ifinfo |
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46 | |
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47 | @ifinfo |
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48 | @node Priority, Scheduling Policies, Scheduler Manager Background, Scheduler Manager Background |
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49 | @end ifinfo |
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50 | @subsection Priority |
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51 | |
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52 | In the RTEMS implementation of the POSIX API, the priorities range from |
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53 | the low priority of sched_get_priority_min() to the highest priority of |
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54 | sched_get_priority_max(). Numerically higher values represent higher |
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55 | priorities. |
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56 | |
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57 | @ifinfo |
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58 | @node Scheduling Policies, Scheduler Manager Operations, Priority, Scheduler Manager Background |
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59 | @end ifinfo |
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60 | @subsection Scheduling Policies |
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61 | |
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62 | The following scheduling policies are available: |
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63 | |
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64 | @table @b |
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65 | @item SCHED_FIFO |
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66 | Priority-based, preemptive scheduling with no timeslicing. This is equivalent |
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67 | to what is called "manual round-robin" scheduling. |
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68 | |
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69 | @item SCHED_RR |
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70 | Priority-based, preemptive scheduling with timeslicing. Time quantums are |
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71 | maintained on a per-thread basis and are not reset at each context switch. |
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72 | Thus, a thread which is preempted and subsequently resumes execution will |
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73 | attempt to complete the unused portion of its time quantum. |
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74 | |
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75 | @item SCHED_OTHER |
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76 | Priority-based, preemptive scheduling with timeslicing. Time quantums are |
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77 | maintained on a per-thread basis and are reset at each context switch. |
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78 | |
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79 | @item SCHED_SPORADIC |
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80 | Priority-based, preemptive scheduling utilizing three additional parameters: |
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81 | budget, replenishment period, and low priority. Under this policy, the |
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82 | thread is allowed to execute for "budget" amount of time before its priority |
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83 | is lowered to "low priority". At the end of each replenishment period, |
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84 | the thread resumes its initial priority and has its budget replenished. |
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85 | |
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86 | @end table |
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87 | |
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88 | @ifinfo |
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89 | @node Scheduler Manager Operations, Scheduler Manager Directives, Scheduling Policies, Scheduler Manager |
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90 | @end ifinfo |
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91 | @section Operations |
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92 | |
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93 | @ifinfo |
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94 | @node Scheduler Manager Directives, sched_get_priority_min, Scheduler Manager Operations, Scheduler Manager |
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95 | @end ifinfo |
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96 | @section Directives |
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97 | @ifinfo |
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98 | @menu |
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99 | * sched_get_priority_min:: |
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100 | * sched_get_priority_max:: |
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101 | * sched_rr_get_interval:: |
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102 | * sched_yield:: |
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103 | @end menu |
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104 | @end ifinfo |
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105 | |
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106 | This section details the scheduler manager's directives. |
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107 | A subsection is dedicated to each of this manager's directives |
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108 | and describes the calling sequence, related constants, usage, |
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109 | and status codes. |
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110 | |
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111 | @page |
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112 | @ifinfo |
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113 | @node sched_get_priority_min, sched_get_priority_max, Scheduler Manager Directives, Scheduler Manager Directives |
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114 | @end ifinfo |
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115 | @subsection sched_get_priority_min |
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116 | |
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117 | @subheading CALLING SEQUENCE: |
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118 | |
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119 | @example |
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120 | #include <sched.h> |
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121 | |
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122 | int sched_get_priority_min( |
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123 | int policy |
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124 | ); |
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125 | @end example |
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126 | |
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127 | @subheading STATUS CODES: |
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128 | |
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129 | On error, this routine returns -1 and sets errno to one of the following: |
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130 | |
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131 | @table @b |
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132 | @item EINVAL |
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133 | The indicated policy is invalid. |
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134 | |
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135 | @end table |
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136 | |
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137 | @subheading DESCRIPTION: |
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138 | |
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139 | @subheading NOTES: |
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140 | |
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141 | @page |
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142 | @ifinfo |
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143 | @node sched_get_priority_max, sched_rr_get_interval, sched_get_priority_min, Scheduler Manager Directives |
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144 | @end ifinfo |
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145 | @subsection sched_get_priority_max |
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146 | |
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147 | @subheading CALLING SEQUENCE: |
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148 | |
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149 | @example |
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150 | #include <sched.h> |
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151 | |
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152 | int sched_get_priority_max( |
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153 | int policy |
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154 | ); |
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155 | @end example |
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156 | |
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157 | @subheading STATUS CODES: |
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158 | |
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159 | On error, this routine returns -1 and sets errno to one of the following: |
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160 | |
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161 | @table @b |
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162 | @item EINVAL |
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163 | The indicated policy is invalid. |
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164 | |
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165 | @end table |
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166 | |
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167 | @subheading DESCRIPTION: |
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168 | |
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169 | @subheading NOTES: |
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170 | |
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171 | @page |
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172 | @ifinfo |
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173 | @node sched_rr_get_interval, sched_yield, sched_get_priority_max, Scheduler Manager Directives |
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174 | @end ifinfo |
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175 | @subsection sched_rr_get_interval |
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176 | |
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177 | @subheading CALLING SEQUENCE: |
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178 | |
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179 | @example |
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180 | #include <sched.h> |
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181 | |
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182 | int sched_rr_get_interval( |
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183 | pid_t pid, |
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184 | struct timespec *interval |
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185 | ); |
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186 | @end example |
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187 | |
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188 | @subheading STATUS CODES: |
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189 | |
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190 | On error, this routine returns -1 and sets errno to one of the following: |
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191 | |
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192 | @table @b |
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193 | @item ESRCH |
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194 | The indicated process id is invalid. |
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195 | |
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196 | @item EINVAL |
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197 | The specified interval pointer parameter is invalid. |
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198 | |
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199 | @end table |
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200 | |
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201 | @subheading DESCRIPTION: |
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202 | |
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203 | @subheading NOTES: |
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204 | |
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205 | @page |
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206 | @ifinfo |
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207 | @node sched_yield, Command and Variable Index, sched_rr_get_interval, Scheduler Manager Directives |
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208 | @end ifinfo |
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209 | @subsection sched_yield |
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210 | |
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211 | @subheading CALLING SEQUENCE: |
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212 | |
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213 | @example |
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214 | #include <sched.h> |
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215 | |
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216 | int sched_yield( void ); |
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217 | @end example |
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218 | |
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219 | @subheading STATUS CODES: |
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220 | |
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221 | This routine always returns zero to indicate success. |
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222 | |
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223 | @subheading DESCRIPTION: |
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224 | |
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225 | @subheading NOTES: |
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226 | |
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