2 FreeRTOS V7.5.3 - Copyright (C) 2013 Real Time Engineers Ltd.
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5 VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
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7 ***************************************************************************
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9 * FreeRTOS provides completely free yet professionally developed, *
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10 * robust, strictly quality controlled, supported, and cross *
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11 * platform software that has become a de facto standard. *
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13 * Help yourself get started quickly and support the FreeRTOS *
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14 * project by purchasing a FreeRTOS tutorial book, reference *
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15 * manual, or both from: http://www.FreeRTOS.org/Documentation *
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19 ***************************************************************************
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21 This file is part of the FreeRTOS distribution.
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23 FreeRTOS is free software; you can redistribute it and/or modify it under
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24 the terms of the GNU General Public License (version 2) as published by the
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25 Free Software Foundation >>!AND MODIFIED BY!<< the FreeRTOS exception.
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27 >>! NOTE: The modification to the GPL is included to allow you to distribute
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28 >>! a combined work that includes FreeRTOS without being obliged to provide
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29 >>! the source code for proprietary components outside of the FreeRTOS
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32 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
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33 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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34 FOR A PARTICULAR PURPOSE. Full license text is available from the following
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35 link: http://www.freertos.org/a00114.html
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39 ***************************************************************************
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41 * Having a problem? Start by reading the FAQ "My application does *
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42 * not run, what could be wrong?" *
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44 * http://www.FreeRTOS.org/FAQHelp.html *
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46 ***************************************************************************
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48 http://www.FreeRTOS.org - Documentation, books, training, latest versions,
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49 license and Real Time Engineers Ltd. contact details.
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51 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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52 including FreeRTOS+Trace - an indispensable productivity tool, a DOS
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53 compatible FAT file system, and our tiny thread aware UDP/IP stack.
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55 http://www.OpenRTOS.com - Real Time Engineers ltd license FreeRTOS to High
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56 Integrity Systems to sell under the OpenRTOS brand. Low cost OpenRTOS
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57 licenses offer ticketed support, indemnification and middleware.
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59 http://www.SafeRTOS.com - High Integrity Systems also provide a safety
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60 engineered and independently SIL3 certified version for use in safety and
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61 mission critical applications that require provable dependability.
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67 The tasks defined on this page demonstrate the use of recursive mutexes.
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69 For recursive mutex functionality the created mutex should be created using
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70 xSemaphoreCreateRecursiveMutex(), then be manipulated
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71 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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74 This demo creates three tasks all of which access the same recursive mutex:
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76 prvRecursiveMutexControllingTask() has the highest priority so executes
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77 first and grabs the mutex. It then performs some recursive accesses -
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78 between each of which it sleeps for a short period to let the lower
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79 priority tasks execute. When it has completed its demo functionality
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80 it gives the mutex back before suspending itself.
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82 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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83 a blocking 'take'. The blocking task has a lower priority than the
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84 controlling task so by the time it executes the mutex has already been
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85 taken by the controlling task, causing the blocking task to block. It
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86 does not unblock until the controlling task has given the mutex back,
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87 and it does not actually run until the controlling task has suspended
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88 itself (due to the relative priorities). When it eventually does obtain
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89 the mutex all it does is give the mutex back prior to also suspending
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90 itself. At this point both the controlling task and the blocking task are
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93 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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94 a tight loop attempting to obtain the mutex with a non-blocking call. As
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95 the lowest priority task it will not successfully obtain the mutex until
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96 both the controlling and blocking tasks are suspended. Once it eventually
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97 does obtain the mutex it first unsuspends both the controlling task and
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98 blocking task prior to giving the mutex back - resulting in the polling
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99 task temporarily inheriting the controlling tasks priority.
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102 /* Scheduler include files. */
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103 #include "FreeRTOS.h"
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105 #include "semphr.h"
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107 /* Demo app include files. */
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108 #include "recmutex.h"
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110 /* Priorities assigned to the three tasks. recmuCONTROLLING_TASK_PRIORITY can
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111 be overridden by a definition in FreeRTOSConfig.h. */
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112 #ifndef recmuCONTROLLING_TASK_PRIORITY
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113 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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115 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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116 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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118 /* The recursive call depth. */
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119 #define recmuMAX_COUNT ( 10 )
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122 #define recmuSHORT_DELAY ( 20 / portTICK_RATE_MS )
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123 #define recmuNO_DELAY ( ( portTickType ) 0 )
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124 #define recmuFIVE_TICK_DELAY ( ( portTickType ) 5 )
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126 /* The three tasks as described at the top of this file. */
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127 static void prvRecursiveMutexControllingTask( void *pvParameters );
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128 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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129 static void prvRecursiveMutexPollingTask( void *pvParameters );
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131 /* The mutex used by the demo. */
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132 static xSemaphoreHandle xMutex;
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134 /* Variables used to detect and latch errors. */
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135 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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136 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles = 0, uxPollingCycles = 0;
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138 /* Handles of the two higher priority tasks, required so they can be resumed
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140 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
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142 /*-----------------------------------------------------------*/
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144 void vStartRecursiveMutexTasks( void )
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146 /* Just creates the mutex and the three tasks. */
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148 xMutex = xSemaphoreCreateRecursiveMutex();
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150 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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151 in use. The registry is provided as a means for kernel aware
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152 debuggers to locate mutex and has no purpose if a kernel aware debugger
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153 is not being used. The call to vQueueAddToRegistry() will be removed
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154 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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155 defined to be less than 1. */
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156 vQueueAddToRegistry( ( xQueueHandle ) xMutex, ( signed portCHAR * ) "Recursive_Mutex" );
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159 if( xMutex != NULL )
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161 xTaskCreate( prvRecursiveMutexControllingTask, ( signed portCHAR * ) "Rec1", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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162 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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163 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
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166 /*-----------------------------------------------------------*/
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168 static void prvRecursiveMutexControllingTask( void *pvParameters )
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170 unsigned portBASE_TYPE ux;
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172 /* Just to remove compiler warning. */
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173 ( void ) pvParameters;
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177 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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178 it. The first time through, the mutex will not have been used yet,
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179 subsequent times through, at this point the mutex will be held by the
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181 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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183 xErrorOccurred = pdTRUE;
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186 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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188 /* We should now be able to take the mutex as many times as
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191 The first time through the mutex will be immediately available, on
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192 subsequent times through the mutex will be held by the polling task
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193 at this point and this Take will cause the polling task to inherit
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194 the priority of this task. In this case the block time must be
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195 long enough to ensure the polling task will execute again before the
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196 block time expires. If the block time does expire then the error
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197 flag will be set here. */
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198 if( xSemaphoreTakeRecursive( xMutex, recmuFIVE_TICK_DELAY ) != pdPASS )
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200 xErrorOccurred = pdTRUE;
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203 /* Ensure the other task attempting to access the mutex (and the
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204 other demo tasks) are able to execute to ensure they either block
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205 (where a block time is specified) or return an error (where no
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206 block time is specified) as the mutex is held by this task. */
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207 vTaskDelay( recmuSHORT_DELAY );
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210 /* For each time we took the mutex, give it back. */
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211 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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213 /* Ensure the other task attempting to access the mutex (and the
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214 other demo tasks) are able to execute. */
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215 vTaskDelay( recmuSHORT_DELAY );
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217 /* We should now be able to give the mutex as many times as we
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218 took it. When the mutex is available again the Blocking task
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219 should be unblocked but not run because it has a lower priority
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220 than this task. The polling task should also not run at this point
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221 as it too has a lower priority than this task. */
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222 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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224 xErrorOccurred = pdTRUE;
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228 /* Having given it back the same number of times as it was taken, we
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229 should no longer be the mutex owner, so the next give should fail. */
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230 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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232 xErrorOccurred = pdTRUE;
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235 /* Keep count of the number of cycles this task has performed so a
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236 stall can be detected. */
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237 uxControllingCycles++;
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239 /* Suspend ourselves so the blocking task can execute. */
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240 xControllingIsSuspended = pdTRUE;
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241 vTaskSuspend( NULL );
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242 xControllingIsSuspended = pdFALSE;
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245 /*-----------------------------------------------------------*/
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247 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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249 /* Just to remove compiler warning. */
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250 ( void ) pvParameters;
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254 /* This task will run while the controlling task is blocked, and the
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255 controlling task will block only once it has the mutex - therefore
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256 this call should block until the controlling task has given up the
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257 mutex, and not actually execute past this call until the controlling
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258 task is suspended. portMAX_DELAY - 1 is used instead of portMAX_DELAY
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259 to ensure the task's state is reported as Blocked and not Suspended in
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260 a later call to configASSERT() (within the polling task). */
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261 if( xSemaphoreTakeRecursive( xMutex, ( portMAX_DELAY - 1 ) ) == pdPASS )
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263 if( xControllingIsSuspended != pdTRUE )
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265 /* Did not expect to execute until the controlling task was
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267 xErrorOccurred = pdTRUE;
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271 /* Give the mutex back before suspending ourselves to allow
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272 the polling task to obtain the mutex. */
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273 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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275 xErrorOccurred = pdTRUE;
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278 xBlockingIsSuspended = pdTRUE;
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279 vTaskSuspend( NULL );
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280 xBlockingIsSuspended = pdFALSE;
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285 /* We should not leave the xSemaphoreTakeRecursive() function
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286 until the mutex was obtained. */
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287 xErrorOccurred = pdTRUE;
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290 /* The controlling and blocking tasks should be in lock step. */
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291 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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293 xErrorOccurred = pdTRUE;
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296 /* Keep count of the number of cycles this task has performed so a
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297 stall can be detected. */
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298 uxBlockingCycles++;
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301 /*-----------------------------------------------------------*/
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303 static void prvRecursiveMutexPollingTask( void *pvParameters )
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305 /* Just to remove compiler warning. */
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306 ( void ) pvParameters;
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310 /* Keep attempting to obtain the mutex. We should only obtain it when
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311 the blocking task has suspended itself, which in turn should only
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312 happen when the controlling task is also suspended. */
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313 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
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315 #if( INCLUDE_eTaskGetState == 1 )
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317 configASSERT( eTaskGetState( xControllingTaskHandle ) == eSuspended );
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318 configASSERT( eTaskGetState( xBlockingTaskHandle ) == eSuspended );
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320 #endif /* INCLUDE_eTaskGetState */
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322 /* Is the blocking task suspended? */
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323 if( ( xBlockingIsSuspended != pdTRUE ) || ( xControllingIsSuspended != pdTRUE ) )
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325 xErrorOccurred = pdTRUE;
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329 /* Keep count of the number of cycles this task has performed
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330 so a stall can be detected. */
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333 /* We can resume the other tasks here even though they have a
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334 higher priority than the polling task. When they execute they
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335 will attempt to obtain the mutex but fail because the polling
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336 task is still the mutex holder. The polling task (this task)
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337 will then inherit the higher priority. The Blocking task will
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338 block indefinitely when it attempts to obtain the mutex, the
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339 Controlling task will only block for a fixed period and an
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340 error will be latched if the polling task has not returned the
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341 mutex by the time this fixed period has expired. */
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342 vTaskResume( xBlockingTaskHandle );
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343 vTaskResume( xControllingTaskHandle );
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345 /* The other two tasks should now have executed and no longer
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347 if( ( xBlockingIsSuspended == pdTRUE ) || ( xControllingIsSuspended == pdTRUE ) )
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349 xErrorOccurred = pdTRUE;
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352 #if( INCLUDE_uxTaskPriorityGet == 1 )
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354 /* Check priority inherited. */
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355 configASSERT( uxTaskPriorityGet( NULL ) == recmuCONTROLLING_TASK_PRIORITY );
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357 #endif /* INCLUDE_uxTaskPriorityGet */
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359 #if( INCLUDE_eTaskGetState == 1 )
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361 configASSERT( eTaskGetState( xControllingTaskHandle ) == eBlocked );
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362 configASSERT( eTaskGetState( xBlockingTaskHandle ) == eBlocked );
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364 #endif /* INCLUDE_eTaskGetState */
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366 /* Release the mutex, disinheriting the higher priority again. */
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367 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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369 xErrorOccurred = pdTRUE;
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372 #if( INCLUDE_uxTaskPriorityGet == 1 )
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374 /* Check priority disinherited. */
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375 configASSERT( uxTaskPriorityGet( NULL ) == recmuPOLLING_TASK_PRIORITY );
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377 #endif /* INCLUDE_uxTaskPriorityGet */
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381 #if configUSE_PREEMPTION == 0
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388 /*-----------------------------------------------------------*/
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390 /* This is called to check that all the created tasks are still running. */
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391 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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393 portBASE_TYPE xReturn;
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394 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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396 /* Is the controlling task still cycling? */
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397 if( uxLastControllingCycles == uxControllingCycles )
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399 xErrorOccurred = pdTRUE;
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403 uxLastControllingCycles = uxControllingCycles;
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406 /* Is the blocking task still cycling? */
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407 if( uxLastBlockingCycles == uxBlockingCycles )
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409 xErrorOccurred = pdTRUE;
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413 uxLastBlockingCycles = uxBlockingCycles;
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416 /* Is the polling task still cycling? */
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417 if( uxLastPollingCycles == uxPollingCycles )
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419 xErrorOccurred = pdTRUE;
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423 uxLastPollingCycles = uxPollingCycles;
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426 if( xErrorOccurred == pdTRUE )
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