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51 The tasks defined on this page demonstrate the use of recursive mutexes.
53 For recursive mutex functionality the created mutex should be created using
54 xSemaphoreCreateRecursiveMutex(), then be manipulated
55 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
58 This demo creates three tasks all of which access the same recursive mutex:
60 prvRecursiveMutexControllingTask() has the highest priority so executes
61 first and grabs the mutex. It then performs some recursive accesses -
62 between each of which it sleeps for a short period to let the lower
63 priority tasks execute. When it has completed its demo functionality
64 it gives the mutex back before suspending itself.
66 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
67 a blocking 'take'. The blocking task has a lower priority than the
68 controlling task so by the time it executes the mutex has already been
69 taken by the controlling task, causing the blocking task to block. It
70 does not unblock until the controlling task has given the mutex back,
71 and it does not actually run until the controlling task has suspended
72 itself (due to the relative priorities). When it eventually does obtain
73 the mutex all it does is give the mutex back prior to also suspending
74 itself. At this point both the controlling task and the blocking task are
77 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
78 a tight loop attempting to obtain the mutex with a non-blocking call. As
79 the lowest priority task it will not successfully obtain the mutex until
80 both the controlling and blocking tasks are suspended. Once it eventually
81 does obtain the mutex it first unsuspends both the controlling task and
82 blocking task prior to giving the mutex back - resulting in the polling
83 task temporarily inheriting the controlling tasks priority.
86 /* Scheduler include files. */
91 /* Demo app include files. */
94 /* Priorities assigned to the three tasks. */
95 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
96 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
97 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
99 /* The recursive call depth. */
100 #define recmuMAX_COUNT ( 10 )
103 #define recmuSHORT_DELAY ( 20 / portTICK_RATE_MS )
104 #define recmuNO_DELAY ( ( portTickType ) 0 )
105 #define recmuTWO_TICK_DELAY ( ( portTickType ) 2 )
107 /* The three tasks as described at the top of this file. */
108 static void prvRecursiveMutexControllingTask( void *pvParameters );
109 static void prvRecursiveMutexBlockingTask( void *pvParameters );
110 static void prvRecursiveMutexPollingTask( void *pvParameters );
112 /* The mutex used by the demo. */
113 static xSemaphoreHandle xMutex;
115 /* Variables used to detect and latch errors. */
116 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
117 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles, uxPollingCycles = 0;
119 /* Handles of the two higher priority tasks, required so they can be resumed
121 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
123 /*-----------------------------------------------------------*/
125 void vStartRecursiveMutexTasks( void )
127 /* Just creates the mutex and the three tasks. */
129 xMutex = xSemaphoreCreateRecursiveMutex();
133 xTaskCreate( prvRecursiveMutexControllingTask, "Rec1", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
134 xTaskCreate( prvRecursiveMutexBlockingTask, "Rec2", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
135 xTaskCreate( prvRecursiveMutexPollingTask, "Rec3", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
138 /*-----------------------------------------------------------*/
140 static void prvRecursiveMutexControllingTask( void *pvParameters )
142 unsigned portBASE_TYPE ux;
146 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
148 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
150 xErrorOccurred = pdTRUE;
153 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
155 /* We should now be able to take the mutex as many times as
156 we like. A one tick delay is used so the polling task will
157 inherit our priority on all but the first cycle of this task.
158 If we did not block attempting to receive the mutex then no
159 priority inheritance would occur. */
160 if( xSemaphoreTakeRecursive( xMutex, recmuTWO_TICK_DELAY ) != pdPASS )
162 xErrorOccurred = pdTRUE;
165 /* Ensure the other task attempting to access the mutex (and the
166 other demo tasks) are able to execute. */
167 vTaskDelay( recmuSHORT_DELAY );
170 /* For each time we took the mutex, give it back. */
171 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
173 /* Ensure the other task attempting to access the mutex (and the
174 other demo tasks) are able to execute. */
175 vTaskDelay( recmuSHORT_DELAY );
177 /* We should now be able to give the mutex as many times as we
179 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
181 xErrorOccurred = pdTRUE;
185 /* Having given it back the same number of times as it was taken, we
186 should no longer be the mutex owner, so the next give sh ould fail. */
187 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
189 xErrorOccurred = pdTRUE;
192 /* Keep count of the number of cycles this task has performed so a
193 stall can be detected. */
194 uxControllingCycles++;
196 /* Suspend ourselves to the blocking task can execute. */
197 xControllingIsSuspended = pdTRUE;
198 vTaskSuspend( NULL );
199 xControllingIsSuspended = pdFALSE;
202 /*-----------------------------------------------------------*/
204 static void prvRecursiveMutexBlockingTask( void *pvParameters )
208 /* Attempt to obtain the mutex. We should block until the
209 controlling task has given up the mutex, and not actually execute
210 past this call until the controlling task is suspended. */
211 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
213 if( xControllingIsSuspended != pdTRUE )
215 /* Did not expect to execute until the controlling task was
217 xErrorOccurred = pdTRUE;
221 /* Give the mutex back before suspending ourselves to allow
222 the polling task to obtain the mutex. */
223 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
225 xErrorOccurred = pdTRUE;
228 xBlockingIsSuspended = pdTRUE;
229 vTaskSuspend( NULL );
230 xBlockingIsSuspended = pdFALSE;
235 /* We should not leave the xSemaphoreTakeRecursive() function
236 until the mutex was obtained. */
237 xErrorOccurred = pdTRUE;
240 /* The controlling and blocking tasks should be in lock step. */
241 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
243 xErrorOccurred = pdTRUE;
246 /* Keep count of the number of cycles this task has performed so a
247 stall can be detected. */
251 /*-----------------------------------------------------------*/
253 static void prvRecursiveMutexPollingTask( void *pvParameters )
257 /* Keep attempting to obtain the mutex. We should only obtain it when
258 the blocking task has suspended itself. */
259 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
261 /* Is the blocking task suspended? */
262 if( xBlockingIsSuspended != pdTRUE )
264 xErrorOccurred = pdTRUE;
268 /* Keep count of the number of cycles this task has performed so
269 a stall can be detected. */
272 /* We can resume the other tasks here even though they have a
273 higher priority than the polling task. When they execute they
274 will attempt to obtain the mutex but fail because the polling
275 task is still the mutex holder. The polling task (this task)
276 will then inherit the higher priority. */
277 vTaskResume( xBlockingTaskHandle );
278 vTaskResume( xControllingTaskHandle );
280 /* Release the mutex, disinheriting the higher priority again. */
281 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
283 xErrorOccurred = pdTRUE;
288 #if configUSE_PREEMPTION == 0
295 /*-----------------------------------------------------------*/
297 /* This is called to check that all the created tasks are still running. */
298 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
300 portBASE_TYPE xReturn;
301 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
303 /* Is the controlling task still cycling? */
304 if( uxLastControllingCycles == uxControllingCycles )
306 xErrorOccurred = pdTRUE;
310 uxLastControllingCycles = uxControllingCycles;
313 /* Is the blocking task still cycling? */
314 if( uxLastBlockingCycles == uxBlockingCycles )
316 xErrorOccurred = pdTRUE;
320 uxLastBlockingCycles = uxBlockingCycles;
323 /* Is the polling task still cycling? */
324 if( uxLastPollingCycles == uxPollingCycles )
326 xErrorOccurred = pdTRUE;
330 uxLastPollingCycles = uxPollingCycles;
333 if( xErrorOccurred == pdTRUE )