2 * FreeRTOS Kernel V10.2.0
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3 * Copyright (C) 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
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5 * Permission is hereby granted, free of charge, to any person obtaining a copy of
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6 * this software and associated documentation files (the "Software"), to deal in
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7 * the Software without restriction, including without limitation the rights to
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8 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
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9 * the Software, and to permit persons to whom the Software is furnished to do so,
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10 * subject to the following conditions:
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12 * The above copyright notice and this permission notice shall be included in all
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13 * copies or substantial portions of the Software.
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15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
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17 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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18 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
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19 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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20 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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22 * http://www.FreeRTOS.org
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23 * http://aws.amazon.com/freertos
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25 * 1 tab == 4 spaces!
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29 The tasks defined on this page demonstrate the use of recursive mutexes.
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31 For recursive mutex functionality the created mutex should be created using
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32 xSemaphoreCreateRecursiveMutex(), then be manipulated
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33 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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36 This demo creates three tasks all of which access the same recursive mutex:
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38 prvRecursiveMutexControllingTask() has the highest priority so executes
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39 first and grabs the mutex. It then performs some recursive accesses -
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40 between each of which it sleeps for a short period to let the lower
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41 priority tasks execute. When it has completed its demo functionality
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42 it gives the mutex back before suspending itself.
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44 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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45 a blocking 'take'. The blocking task has a lower priority than the
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46 controlling task so by the time it executes the mutex has already been
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47 taken by the controlling task, causing the blocking task to block. It
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48 does not unblock until the controlling task has given the mutex back,
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49 and it does not actually run until the controlling task has suspended
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50 itself (due to the relative priorities). When it eventually does obtain
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51 the mutex all it does is give the mutex back prior to also suspending
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52 itself. At this point both the controlling task and the blocking task are
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55 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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56 a tight loop attempting to obtain the mutex with a non-blocking call. As
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57 the lowest priority task it will not successfully obtain the mutex until
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58 both the controlling and blocking tasks are suspended. Once it eventually
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59 does obtain the mutex it first unsuspends both the controlling task and
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60 blocking task prior to giving the mutex back - resulting in the polling
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61 task temporarily inheriting the controlling tasks priority.
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64 /* Scheduler include files. */
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65 #include "FreeRTOS.h"
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69 /* Demo app include files. */
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70 #include "recmutex.h"
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72 /* Priorities assigned to the three tasks. */
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73 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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74 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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75 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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77 /* In this version the tick period is very long, so the short delay cannot be
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78 for too many ticks, or the check task will execute and find that the recmutex
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79 tasks have not completed their functionality and then signal an error. The
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80 delay does however have to be long enough to allow the lower priority tasks
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81 a chance of executing - this is basically achieved by reducing the number
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82 of times the loop that takes/gives the recursive mutex executes. */
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83 #define recmuMAX_COUNT ( 2 )
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84 #define recmuSHORT_DELAY ( 20 )
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85 #define recmuNO_DELAY ( ( TickType_t ) 0 )
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86 #define recmuFIVE_TICK_DELAY ( ( TickType_t ) 5 )
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88 /* The three tasks as described at the top of this file. */
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89 static void prvRecursiveMutexControllingTask( void *pvParameters );
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90 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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91 static void prvRecursiveMutexPollingTask( void *pvParameters );
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93 /* The mutex used by the demo. */
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94 static SemaphoreHandle_t xMutex;
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96 /* Variables used to detect and latch errors. */
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97 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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98 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles = 0, uxPollingCycles = 0;
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100 /* Handles of the two higher priority tasks, required so they can be resumed
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102 static TaskHandle_t xControllingTaskHandle, xBlockingTaskHandle, xPollingTaskHandle;
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104 /*-----------------------------------------------------------*/
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106 void vStartRecursiveMutexTasks( void )
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108 /* Just creates the mutex and the three tasks. */
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110 xMutex = xSemaphoreCreateRecursiveMutex();
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112 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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113 in use. The registry is provided as a means for kernel aware
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114 debuggers to locate mutex and has no purpose if a kernel aware debugger
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115 is not being used. The call to vQueueAddToRegistry() will be removed
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116 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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117 defined to be less than 1. */
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118 vQueueAddToRegistry( ( QueueHandle_t ) xMutex, "Recursive_Mutex" );
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121 if( xMutex != NULL )
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123 xTaskCreate( prvRecursiveMutexControllingTask, "Rec1Ctrl", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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124 xTaskCreate( prvRecursiveMutexBlockingTask, "Rec2Blck", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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125 xTaskCreate( prvRecursiveMutexPollingTask, "Rec3Poll", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, &xPollingTaskHandle );
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128 /*-----------------------------------------------------------*/
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130 static void prvRecursiveMutexControllingTask( void *pvParameters )
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132 unsigned portBASE_TYPE ux;
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134 /* Just to remove compiler warning. */
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135 ( void ) pvParameters;
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139 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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140 it. The first time through, the mutex will not have been used yet,
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141 subsequent times through, at this point the mutex will be held by the
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143 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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145 xErrorOccurred = pdTRUE;
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148 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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150 /* We should now be able to take the mutex as many times as
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153 The first time through the mutex will be immediately available, on
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154 subsequent times through the mutex will be held by the polling task
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155 at this point and this Take will cause the polling task to inherit
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156 the priority of this task. In this case the block time must be
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157 long enough to ensure the polling task will execute again before the
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158 block time expires. If the block time does expire then the error
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159 flag will be set here. */
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160 if( xSemaphoreTakeRecursive( xMutex, recmuFIVE_TICK_DELAY ) != pdPASS )
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162 xErrorOccurred = pdTRUE;
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165 /* Ensure the other task attempting to access the mutex (and the
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166 other demo tasks) are able to execute to ensure they either block
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167 (where a block time is specified) or return an error (where no
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168 block time is specified) as the mutex is held by this task. */
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169 vTaskDelay( recmuSHORT_DELAY );
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172 /* For each time we took the mutex, give it back. */
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173 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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175 /* Ensure the other task attempting to access the mutex (and the
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176 other demo tasks) are able to execute. */
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177 vTaskDelay( recmuSHORT_DELAY );
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179 /* We should now be able to give the mutex as many times as we
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180 took it. When the mutex is available again the Blocking task
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181 should be unblocked but not run because it has a lower priority
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182 than this task. The polling task should also not run at this point
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183 as it too has a lower priority than this task. */
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184 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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186 xErrorOccurred = pdTRUE;
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189 #if configUSE_PREEMPTION == 0
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194 /* Having given it back the same number of times as it was taken, we
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195 should no longer be the mutex owner, so the next give should fail. */
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196 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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198 xErrorOccurred = pdTRUE;
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201 /* Keep count of the number of cycles this task has performed so a
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202 stall can be detected. */
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203 uxControllingCycles++;
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205 /* Suspend ourselves so the blocking task can execute. */
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206 xControllingIsSuspended = pdTRUE;
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207 vTaskSuspend( NULL );
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208 xControllingIsSuspended = pdFALSE;
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211 /*-----------------------------------------------------------*/
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213 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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215 /* Just to remove compiler warning. */
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216 ( void ) pvParameters;
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220 /* This task will run while the controlling task is blocked, and the
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221 controlling task will block only once it has the mutex - therefore
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222 this call should block until the controlling task has given up the
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223 mutex, and not actually execute past this call until the controlling
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224 task is suspended. */
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225 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
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227 if( xControllingIsSuspended != pdTRUE )
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229 /* Did not expect to execute until the controlling task was
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231 xErrorOccurred = pdTRUE;
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235 /* Give the mutex back before suspending ourselves to allow
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236 the polling task to obtain the mutex. */
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237 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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239 xErrorOccurred = pdTRUE;
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242 xBlockingIsSuspended = pdTRUE;
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243 vTaskSuspend( NULL );
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244 xBlockingIsSuspended = pdFALSE;
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249 /* We should not leave the xSemaphoreTakeRecursive() function
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250 until the mutex was obtained. */
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251 xErrorOccurred = pdTRUE;
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254 /* The controlling and blocking tasks should be in lock step. */
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255 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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257 xErrorOccurred = pdTRUE;
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260 /* Keep count of the number of cycles this task has performed so a
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261 stall can be detected. */
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262 uxBlockingCycles++;
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265 /*-----------------------------------------------------------*/
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267 static void prvRecursiveMutexPollingTask( void *pvParameters )
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269 /* Just to remove compiler warning. */
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270 ( void ) pvParameters;
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274 /* Keep attempting to obtain the mutex. We should only obtain it when
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275 the blocking task has suspended itself, which in turn should only
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276 happen when the controlling task is also suspended. */
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277 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
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279 /* Is the blocking task suspended? */
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280 if( ( xBlockingIsSuspended != pdTRUE ) || ( xControllingIsSuspended != pdTRUE ) )
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282 xErrorOccurred = pdTRUE;
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286 /* Keep count of the number of cycles this task has performed
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287 so a stall can be detected. */
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290 /* We can resume the other tasks here even though they have a
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291 higher priority than the polling task. When they execute they
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292 will attempt to obtain the mutex but fail because the polling
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293 task is still the mutex holder. The polling task (this task)
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294 will then inherit the higher priority. The Blocking task will
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295 block indefinitely when it attempts to obtain the mutex, the
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296 Controlling task will only block for a fixed period and an
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297 error will be latched if the polling task has not returned the
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298 mutex by the time this fixed period has expired. */
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299 vTaskResume( xBlockingTaskHandle );
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300 #if configUSE_PREEMPTION == 0
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304 vTaskResume( xControllingTaskHandle );
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305 #if configUSE_PREEMPTION == 0
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309 /* The other two tasks should now have executed and no longer
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311 if( ( xBlockingIsSuspended == pdTRUE ) || ( xControllingIsSuspended == pdTRUE ) )
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313 xErrorOccurred = pdTRUE;
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316 /* Release the mutex, disinheriting the higher priority again. */
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317 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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319 xErrorOccurred = pdTRUE;
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322 #if configUSE_PREEMPTION == 0
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328 #if configUSE_PREEMPTION == 0
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335 /*-----------------------------------------------------------*/
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337 /* This is called to check that all the created tasks are still running. */
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338 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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340 portBASE_TYPE xReturn;
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341 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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343 /* Is the controlling task still cycling? */
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344 if( uxLastControllingCycles == uxControllingCycles )
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346 xErrorOccurred = pdTRUE;
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350 uxLastControllingCycles = uxControllingCycles;
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353 /* Is the blocking task still cycling? */
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354 if( uxLastBlockingCycles == uxBlockingCycles )
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356 xErrorOccurred = pdTRUE;
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360 uxLastBlockingCycles = uxBlockingCycles;
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363 /* Is the polling task still cycling? */
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364 if( uxLastPollingCycles == uxPollingCycles )
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366 xErrorOccurred = pdTRUE;
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370 uxLastPollingCycles = uxPollingCycles;
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373 if( xErrorOccurred == pdTRUE )
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