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1 //========================================================================== |
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2 // |
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3 // sync/cnt_sem.cxx |
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4 // |
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5 // Counting semaphore implementation |
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6 // |
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7 //========================================================================== |
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8 //####COPYRIGHTBEGIN#### |
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9 // |
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10 // ------------------------------------------- |
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11 // The contents of this file are subject to the Cygnus eCos Public License |
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12 // Version 1.0 (the "License"); you may not use this file except in |
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13 // compliance with the License. You may obtain a copy of the License at |
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14 // http://sourceware.cygnus.com/ecos |
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15 // |
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16 // Software distributed under the License is distributed on an "AS IS" |
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17 // basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the |
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18 // License for the specific language governing rights and limitations under |
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19 // the License. |
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20 // |
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21 // The Original Code is eCos - Embedded Cygnus Operating System, released |
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22 // September 30, 1998. |
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23 // |
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24 // The Initial Developer of the Original Code is Cygnus. Portions created |
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25 // by Cygnus are Copyright (C) 1998,1999 Cygnus Solutions. All Rights Reserved. |
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26 // ------------------------------------------- |
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27 // |
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28 //####COPYRIGHTEND#### |
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29 //========================================================================== |
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30 //#####DESCRIPTIONBEGIN#### |
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31 // |
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32 // Author(s): nickg |
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33 // Contributors: nickg |
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34 // Date: 1997-09-24 |
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35 // Purpose: Cyg_Counting_Semaphore implementation |
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36 // Description: This file contains the implementations of the counting semaphore |
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37 // class. |
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38 // |
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39 //####DESCRIPTIONEND#### |
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40 // |
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41 //========================================================================== |
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42 |
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43 #include <pkgconf/kernel.h> |
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44 |
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45 #include <cyg/kernel/ktypes.h> // base kernel types |
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46 #include <cyg/infra/cyg_trac.h> // tracing macros |
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47 #include <cyg/infra/cyg_ass.h> // assertion macros |
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48 #include <cyg/kernel/instrmnt.h> // instrumentation |
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49 |
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50 #include <cyg/kernel/thread.inl> // Cyg_Thread inlines |
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51 |
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52 #include <cyg/kernel/sema.hxx> // our header |
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53 |
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54 #include <cyg/kernel/sched.inl> // scheduler inlines |
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55 |
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56 // ------------------------------------------------------------------------- |
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57 // Constructor |
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58 |
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59 Cyg_Counting_Semaphore::Cyg_Counting_Semaphore( |
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60 cyg_count32 init_count // Initial count value |
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61 ) |
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62 { |
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63 count = init_count; |
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64 } |
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65 |
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66 // ------------------------------------------------------------------------- |
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67 // Destructor |
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68 |
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69 Cyg_Counting_Semaphore::~Cyg_Counting_Semaphore() |
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70 { |
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71 CYG_ASSERT( queue.empty(), "Destroying semaphore with waiting threads"); |
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72 } |
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73 |
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74 // ------------------------------------------------------------------------- |
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75 // Wait until the count can be decremented without it becoming |
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76 // negative. |
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77 |
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78 cyg_bool Cyg_Counting_Semaphore::wait() |
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79 { |
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80 cyg_bool result = true; |
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81 Cyg_Thread *self = Cyg_Thread::self(); |
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82 |
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83 // Prevent preemption |
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84 Cyg_Scheduler::lock(); |
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85 |
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86 CYG_INSTRUMENT_CNTSEM( CLAIM, this, count ); |
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87 |
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88 while( count == 0 && result ) |
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89 { |
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90 self->set_sleep_reason( Cyg_Thread::WAIT ); |
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91 |
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92 self->sleep(); |
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93 |
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94 queue.enqueue( self ); |
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95 |
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96 CYG_INSTRUMENT_CNTSEM( WAIT, this, 0 ); |
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97 |
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98 CYG_ASSERT( Cyg_Scheduler::get_sched_lock() == 1, "Called with non-zero scheduler lock"); |
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99 |
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100 Cyg_Scheduler::unlock(); |
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101 Cyg_Scheduler::lock(); |
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102 |
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103 CYG_INSTRUMENT_CNTSEM( WOKE, this, count ); |
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104 |
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105 switch( self->get_wake_reason() ) |
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106 { |
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107 case Cyg_Thread::DESTRUCT: |
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108 case Cyg_Thread::BREAK: |
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109 result = false; |
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110 break; |
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111 |
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112 case Cyg_Thread::EXIT: |
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113 self->exit(); |
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114 break; |
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115 |
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116 default: |
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117 break; |
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118 } |
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119 } |
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120 |
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121 if( result ) count--; |
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122 |
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123 // Unlock the scheduler |
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124 Cyg_Scheduler::unlock(); |
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125 |
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126 return result; |
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127 } |
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128 |
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129 // ------------------------------------------------------------------------- |
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130 // Wait until the count can be decremented without it becoming |
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131 // negative. |
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132 |
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133 #ifdef CYGFUN_KERNEL_THREADS_TIMER |
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134 |
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135 cyg_bool |
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136 Cyg_Counting_Semaphore::wait( cyg_tick_count timeout ) |
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137 { |
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138 cyg_bool result = true; |
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139 Cyg_Thread *self = Cyg_Thread::self(); |
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140 |
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141 // Prevent preemption |
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142 Cyg_Scheduler::lock(); |
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143 |
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144 CYG_INSTRUMENT_CNTSEM( CLAIM, this, count ); |
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145 |
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146 // Set the timer _once_ outside the loop. |
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147 self->set_timer( timeout, Cyg_Thread::TIMEOUT ); |
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148 |
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149 // If the timeout is in the past, the wake reason will have been |
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150 // set to something other than NONE already. Set the result false |
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151 // to force an immediate return. |
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152 |
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153 if( self->get_wake_reason() != Cyg_Thread::NONE ) |
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154 result = false; |
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155 |
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156 while ( 0 == count && result ) { |
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157 |
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158 // must reset the sleep reason every time |
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159 self->set_sleep_reason( Cyg_Thread::TIMEOUT ); |
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160 |
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161 self->sleep(); |
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162 |
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163 queue.enqueue( self ); |
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164 |
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165 CYG_INSTRUMENT_CNTSEM( WAIT, this, 0 ); |
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166 |
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167 CYG_ASSERT( Cyg_Scheduler::get_sched_lock() == 1, |
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168 "Called with non-zero scheduler lock"); |
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169 |
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170 Cyg_Scheduler::unlock(); |
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171 Cyg_Scheduler::lock(); |
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172 |
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173 CYG_INSTRUMENT_CNTSEM( WOKE, this, count ); |
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174 |
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175 switch( self->get_wake_reason() ) |
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176 { |
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177 case Cyg_Thread::TIMEOUT: |
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178 result = false; |
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179 CYG_INSTRUMENT_CNTSEM( TIMEOUT, this, count); |
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180 break; |
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181 |
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182 case Cyg_Thread::DESTRUCT: |
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183 case Cyg_Thread::BREAK: |
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184 result = false; |
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185 break; |
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186 |
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187 case Cyg_Thread::EXIT: |
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188 self->exit(); |
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189 break; |
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190 |
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191 default: |
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192 break; |
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193 } |
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194 } |
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195 |
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196 // Clear the timeout. It is irrelevant whether the alarm has |
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197 // actually gone off or not. |
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198 self->clear_timer(); |
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199 |
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200 if ( result ) count--; |
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201 |
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202 // Unlock the scheduler and maybe switch threads |
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203 Cyg_Scheduler::unlock(); |
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204 |
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205 return result; |
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206 } |
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207 |
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208 #endif // CYGFUN_KERNEL_THREADS_TIMER |
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209 |
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210 // ------------------------------------------------------------------------- |
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211 // Try to decrement, but fail if not possible |
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212 |
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213 cyg_bool Cyg_Counting_Semaphore::trywait() |
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214 { |
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215 cyg_bool result = true; |
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216 |
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217 // Prevent preemption |
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218 Cyg_Scheduler::lock(); |
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219 |
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220 if( count > 0 ) count--; |
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221 else result = false; |
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222 |
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223 CYG_INSTRUMENT_CNTSEM( TRY, this, result ); |
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224 |
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225 // Unlock the scheduler and maybe switch threads |
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226 Cyg_Scheduler::unlock(); |
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227 |
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228 return result; |
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229 } |
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230 |
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231 // ------------------------------------------------------------------------- |
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232 // Increment count |
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233 |
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234 void Cyg_Counting_Semaphore::post() |
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235 { |
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236 // Prevent preemption |
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237 Cyg_Scheduler::lock(); |
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238 |
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239 CYG_INSTRUMENT_CNTSEM( POST, this, 0 ); |
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240 |
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241 count++; |
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242 |
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243 if( !queue.empty() ) { |
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244 |
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245 // The queue is non-empty, so grab the next |
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246 // thread from it and wake it up. The waiter |
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247 // will decrement the count when he is awakened. |
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248 |
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249 Cyg_Thread *thread = queue.dequeue(); |
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250 |
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251 thread->set_wake_reason( Cyg_Thread::DONE ); |
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252 |
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253 thread->wake(); |
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254 |
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255 CYG_INSTRUMENT_CNTSEM( WAKE, this, thread ); |
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256 } |
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257 |
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258 // Unlock the scheduler and maybe switch threads |
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259 Cyg_Scheduler::unlock(); |
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260 } |
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261 |
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262 // ------------------------------------------------------------------------- |
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263 // Get current count value |
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264 |
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265 cyg_count32 Cyg_Counting_Semaphore::peek() |
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266 { |
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267 // This is a single read of the value of count. |
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268 // This is already atomic, hence there is no need |
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269 // to lock the scheduler. |
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270 |
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271 return count; |
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272 } |
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273 |
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274 // ------------------------------------------------------------------------- |
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275 // EOF sync/cnt_sem.cxx |
