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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, ( signed portCHAR * ) "Rec1", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
134 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
135 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
138 /*-----------------------------------------------------------*/
140 static void prvRecursiveMutexControllingTask( void *pvParameters )
142 unsigned portBASE_TYPE ux;
144 /* Just to remove compiler warning. */
\r
145 ( void ) pvParameters;
\r
149 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
151 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
153 xErrorOccurred = pdTRUE;
156 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
158 /* We should now be able to take the mutex as many times as
159 we like. A one tick delay is used so the polling task will
160 inherit our priority on all but the first cycle of this task.
161 If we did not block attempting to receive the mutex then no
162 priority inheritance would occur. */
163 if( xSemaphoreTakeRecursive( xMutex, recmuTWO_TICK_DELAY ) != pdPASS )
165 xErrorOccurred = pdTRUE;
168 /* Ensure the other task attempting to access the mutex (and the
169 other demo tasks) are able to execute. */
170 vTaskDelay( recmuSHORT_DELAY );
173 /* For each time we took the mutex, give it back. */
174 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
176 /* Ensure the other task attempting to access the mutex (and the
177 other demo tasks) are able to execute. */
178 vTaskDelay( recmuSHORT_DELAY );
180 /* We should now be able to give the mutex as many times as we
182 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
184 xErrorOccurred = pdTRUE;
188 /* Having given it back the same number of times as it was taken, we
189 should no longer be the mutex owner, so the next give sh ould fail. */
190 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
192 xErrorOccurred = pdTRUE;
195 /* Keep count of the number of cycles this task has performed so a
196 stall can be detected. */
197 uxControllingCycles++;
199 /* Suspend ourselves to the blocking task can execute. */
200 xControllingIsSuspended = pdTRUE;
201 vTaskSuspend( NULL );
202 xControllingIsSuspended = pdFALSE;
205 /*-----------------------------------------------------------*/
207 static void prvRecursiveMutexBlockingTask( void *pvParameters )
209 /* Just to remove compiler warning. */
\r
210 ( void ) pvParameters;
\r
214 /* Attempt to obtain the mutex. We should block until the
215 controlling task has given up the mutex, and not actually execute
216 past this call until the controlling task is suspended. */
217 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
219 if( xControllingIsSuspended != pdTRUE )
221 /* Did not expect to execute until the controlling task was
223 xErrorOccurred = pdTRUE;
227 /* Give the mutex back before suspending ourselves to allow
228 the polling task to obtain the mutex. */
229 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
231 xErrorOccurred = pdTRUE;
234 xBlockingIsSuspended = pdTRUE;
235 vTaskSuspend( NULL );
236 xBlockingIsSuspended = pdFALSE;
241 /* We should not leave the xSemaphoreTakeRecursive() function
242 until the mutex was obtained. */
243 xErrorOccurred = pdTRUE;
246 /* The controlling and blocking tasks should be in lock step. */
247 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
249 xErrorOccurred = pdTRUE;
252 /* Keep count of the number of cycles this task has performed so a
253 stall can be detected. */
257 /*-----------------------------------------------------------*/
259 static void prvRecursiveMutexPollingTask( void *pvParameters )
261 /* Just to remove compiler warning. */
262 ( void ) pvParameters;
266 /* Keep attempting to obtain the mutex. We should only obtain it when
267 the blocking task has suspended itself. */
268 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
270 /* Is the blocking task suspended? */
271 if( xBlockingIsSuspended != pdTRUE )
273 xErrorOccurred = pdTRUE;
277 /* Keep count of the number of cycles this task has performed so
278 a stall can be detected. */
281 /* We can resume the other tasks here even though they have a
282 higher priority than the polling task. When they execute they
283 will attempt to obtain the mutex but fail because the polling
284 task is still the mutex holder. The polling task (this task)
285 will then inherit the higher priority. */
286 vTaskResume( xBlockingTaskHandle );
287 vTaskResume( xControllingTaskHandle );
289 /* Release the mutex, disinheriting the higher priority again. */
290 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
292 xErrorOccurred = pdTRUE;
297 #if configUSE_PREEMPTION == 0
304 /*-----------------------------------------------------------*/
306 /* This is called to check that all the created tasks are still running. */
307 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
309 portBASE_TYPE xReturn;
310 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
312 /* Is the controlling task still cycling? */
313 if( uxLastControllingCycles == uxControllingCycles )
315 xErrorOccurred = pdTRUE;
319 uxLastControllingCycles = uxControllingCycles;
322 /* Is the blocking task still cycling? */
323 if( uxLastBlockingCycles == uxBlockingCycles )
325 xErrorOccurred = pdTRUE;
329 uxLastBlockingCycles = uxBlockingCycles;
332 /* Is the polling task still cycling? */
333 if( uxLastPollingCycles == uxPollingCycles )
335 xErrorOccurred = pdTRUE;
339 uxLastPollingCycles = uxPollingCycles;
342 if( xErrorOccurred == pdTRUE )