2 FreeRTOS.org V5.1.0 - Copyright (C) 2003-2008 Richard Barry.
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4 This file is part of the FreeRTOS.org distribution.
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6 FreeRTOS.org is free software; you can redistribute it and/or modify
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7 it under the terms of the GNU General Public License as published by
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8 the Free Software Foundation; either version 2 of the License, or
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9 (at your option) any later version.
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11 FreeRTOS.org is distributed in the hope that it will be useful,
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12 but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 GNU General Public License for more details.
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16 You should have received a copy of the GNU General Public License
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17 along with FreeRTOS.org; if not, write to the Free Software
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18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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20 A special exception to the GPL can be applied should you wish to distribute
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21 a combined work that includes FreeRTOS.org, without being obliged to provide
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22 the source code for any proprietary components. See the licensing section
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23 of http://www.FreeRTOS.org for full details of how and when the exception
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26 ***************************************************************************
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27 ***************************************************************************
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29 * SAVE TIME AND MONEY! We can port FreeRTOS.org to your own hardware, *
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30 * and even write all or part of your application on your behalf. *
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31 * See http://www.OpenRTOS.com for details of the services we provide to *
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32 * expedite your project. *
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34 ***************************************************************************
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35 ***************************************************************************
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37 Please ensure to read the configuration and relevant port sections of the
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38 online documentation.
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40 http://www.FreeRTOS.org - Documentation, latest information, license and
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43 http://www.SafeRTOS.com - A version that is certified for use in safety
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46 http://www.OpenRTOS.com - Commercial support, development, porting,
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47 licensing and training services.
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51 The tasks defined on this page demonstrate the use of recursive mutexes.
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53 For recursive mutex functionality the created mutex should be created using
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54 xSemaphoreCreateRecursiveMutex(), then be manipulated
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55 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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58 This demo creates three tasks all of which access the same recursive mutex:
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60 prvRecursiveMutexControllingTask() has the highest priority so executes
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61 first and grabs the mutex. It then performs some recursive accesses -
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62 between each of which it sleeps for a short period to let the lower
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63 priority tasks execute. When it has completed its demo functionality
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64 it gives the mutex back before suspending itself.
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66 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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67 a blocking 'take'. The blocking task has a lower priority than the
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68 controlling task so by the time it executes the mutex has already been
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69 taken by the controlling task, causing the blocking task to block. It
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70 does not unblock until the controlling task has given the mutex back,
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71 and it does not actually run until the controlling task has suspended
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72 itself (due to the relative priorities). When it eventually does obtain
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73 the mutex all it does is give the mutex back prior to also suspending
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74 itself. At this point both the controlling task and the blocking task are
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77 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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78 a tight loop attempting to obtain the mutex with a non-blocking call. As
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79 the lowest priority task it will not successfully obtain the mutex until
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80 both the controlling and blocking tasks are suspended. Once it eventually
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81 does obtain the mutex it first unsuspends both the controlling task and
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82 blocking task prior to giving the mutex back - resulting in the polling
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83 task temporarily inheriting the controlling tasks priority.
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86 /* Scheduler include files. */
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87 #include "FreeRTOS.h"
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91 /* Demo app include files. */
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92 #include "recmutex.h"
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94 /* Priorities assigned to the three tasks. */
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95 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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96 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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97 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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99 /* The recursive call depth. */
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100 #define recmuMAX_COUNT ( 10 )
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103 #define recmuSHORT_DELAY ( 20 / portTICK_RATE_MS )
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104 #define recmuNO_DELAY ( ( portTickType ) 0 )
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105 #define recmuTWO_TICK_DELAY ( ( portTickType ) 2 )
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107 /* The three tasks as described at the top of this file. */
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108 static void prvRecursiveMutexControllingTask( void *pvParameters );
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109 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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110 static void prvRecursiveMutexPollingTask( void *pvParameters );
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112 /* The mutex used by the demo. */
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113 static xSemaphoreHandle xMutex;
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115 /* Variables used to detect and latch errors. */
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116 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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117 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles, uxPollingCycles = 0;
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119 /* Handles of the two higher priority tasks, required so they can be resumed
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121 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
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123 /*-----------------------------------------------------------*/
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125 void vStartRecursiveMutexTasks( void )
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127 /* Just creates the mutex and the three tasks. */
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129 xMutex = xSemaphoreCreateRecursiveMutex();
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131 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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132 in use. The registry is provided as a means for kernel aware
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133 debuggers to locate mutex and has no purpose if a kernel aware debugger
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134 is not being used. The call to vQueueAddToRegistry() will be removed
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135 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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136 defined to be less than 1. */
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137 vQueueAddToRegistry( ( xQueueHandle ) xMutex, ( signed portCHAR * ) "Recursive_Mutex" );
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140 if( xMutex != NULL )
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142 xTaskCreate( prvRecursiveMutexControllingTask, ( signed portCHAR * ) "Rec1", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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143 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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144 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
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147 /*-----------------------------------------------------------*/
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149 static void prvRecursiveMutexControllingTask( void *pvParameters )
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151 unsigned portBASE_TYPE ux;
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153 /* Just to remove compiler warning. */
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154 ( void ) pvParameters;
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158 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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160 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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162 xErrorOccurred = pdTRUE;
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165 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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167 /* We should now be able to take the mutex as many times as
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168 we like. A one tick delay is used so the polling task will
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169 inherit our priority on all but the first cycle of this task.
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170 If we did not block attempting to receive the mutex then no
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171 priority inheritance would occur. */
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172 if( xSemaphoreTakeRecursive( xMutex, recmuTWO_TICK_DELAY ) != pdPASS )
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174 xErrorOccurred = pdTRUE;
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177 /* Ensure the other task attempting to access the mutex (and the
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178 other demo tasks) are able to execute. */
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179 vTaskDelay( recmuSHORT_DELAY );
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182 /* For each time we took the mutex, give it back. */
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183 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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185 /* Ensure the other task attempting to access the mutex (and the
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186 other demo tasks) are able to execute. */
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187 vTaskDelay( recmuSHORT_DELAY );
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189 /* We should now be able to give the mutex as many times as we
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191 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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193 xErrorOccurred = pdTRUE;
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197 /* Having given it back the same number of times as it was taken, we
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198 should no longer be the mutex owner, so the next give sh ould fail. */
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199 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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201 xErrorOccurred = pdTRUE;
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204 /* Keep count of the number of cycles this task has performed so a
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205 stall can be detected. */
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206 uxControllingCycles++;
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208 /* Suspend ourselves to the blocking task can execute. */
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209 xControllingIsSuspended = pdTRUE;
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210 vTaskSuspend( NULL );
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211 xControllingIsSuspended = pdFALSE;
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214 /*-----------------------------------------------------------*/
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216 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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218 /* Just to remove compiler warning. */
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219 ( void ) pvParameters;
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223 /* Attempt to obtain the mutex. We should block until the
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224 controlling task has given up the mutex, and not actually execute
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225 past this call until the controlling task is suspended. */
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226 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
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228 if( xControllingIsSuspended != pdTRUE )
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230 /* Did not expect to execute until the controlling task was
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232 xErrorOccurred = pdTRUE;
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236 /* Give the mutex back before suspending ourselves to allow
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237 the polling task to obtain the mutex. */
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238 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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240 xErrorOccurred = pdTRUE;
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243 xBlockingIsSuspended = pdTRUE;
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244 vTaskSuspend( NULL );
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245 xBlockingIsSuspended = pdFALSE;
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250 /* We should not leave the xSemaphoreTakeRecursive() function
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251 until the mutex was obtained. */
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252 xErrorOccurred = pdTRUE;
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255 /* The controlling and blocking tasks should be in lock step. */
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256 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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258 xErrorOccurred = pdTRUE;
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261 /* Keep count of the number of cycles this task has performed so a
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262 stall can be detected. */
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263 uxBlockingCycles++;
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266 /*-----------------------------------------------------------*/
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268 static void prvRecursiveMutexPollingTask( void *pvParameters )
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270 /* Just to remove compiler warning. */
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271 ( void ) pvParameters;
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275 /* Keep attempting to obtain the mutex. We should only obtain it when
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276 the blocking task has suspended itself. */
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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 )
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282 xErrorOccurred = pdTRUE;
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286 /* Keep count of the number of cycles this task has performed so
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287 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. */
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295 vTaskResume( xBlockingTaskHandle );
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296 vTaskResume( xControllingTaskHandle );
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298 /* Release the mutex, disinheriting the higher priority again. */
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299 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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301 xErrorOccurred = pdTRUE;
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306 #if configUSE_PREEMPTION == 0
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313 /*-----------------------------------------------------------*/
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315 /* This is called to check that all the created tasks are still running. */
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316 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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318 portBASE_TYPE xReturn;
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319 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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321 /* Is the controlling task still cycling? */
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322 if( uxLastControllingCycles == uxControllingCycles )
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324 xErrorOccurred = pdTRUE;
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328 uxLastControllingCycles = uxControllingCycles;
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331 /* Is the blocking task still cycling? */
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332 if( uxLastBlockingCycles == uxBlockingCycles )
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334 xErrorOccurred = pdTRUE;
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338 uxLastBlockingCycles = uxBlockingCycles;
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341 /* Is the polling task still cycling? */
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342 if( uxLastPollingCycles == uxPollingCycles )
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344 xErrorOccurred = pdTRUE;
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348 uxLastPollingCycles = uxPollingCycles;
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351 if( xErrorOccurred == pdTRUE )
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