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Update task notification scheduler suspension usage (#982)
* Update task notification scheduler suspension Previously ulTaskGenericNotifyTake() and xTaskGenericNotifyWait() would suspend the scheduler while inside a critical section. This commit changes the order by wrapping the critical sections in a scheduler suspension block. This logic is more inuitive and allows the SMP scheduler suspension logic to be simplified. * tasks.c: Fix typo * Use a complete sentence in comment * Check portGET_CRITICAL_NESTING_COUNT when scheduler is running * Prevent potential NULL pointer access when scheduler is not running --------- Co-authored-by: Paul Bartell <pbartell@amazon.com> Co-authored-by: chinglee-iot <61685396+chinglee-iot@users.noreply.github.com> Co-authored-by: Ching-Hsin Lee <chinglee@amazon.com>
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Darian
GitHub
parent
57a5ed7f67
commit
7284d84dc8
185
tasks.c
185
tasks.c
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@ -3822,6 +3822,9 @@ void vTaskSuspendAll( void )
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if( xSchedulerRunning != pdFALSE )
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{
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/* This must never be called from inside a critical section. */
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configASSERT( portGET_CRITICAL_NESTING_COUNT() == 0 );
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/* Writes to uxSchedulerSuspended must be protected by both the task AND ISR locks.
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* We must disable interrupts before we grab the locks in the event that this task is
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* interrupted and switches context before incrementing uxSchedulerSuspended.
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@ -3839,8 +3842,6 @@ void vTaskSuspendAll( void )
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* purpose is to prevent altering the variable when fromISR APIs are readying
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* it. */
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if( uxSchedulerSuspended == 0U )
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{
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if( portGET_CRITICAL_NESTING_COUNT() == 0U )
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{
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prvCheckForRunStateChange();
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}
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@ -3848,11 +3849,6 @@ void vTaskSuspendAll( void )
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{
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mtCOVERAGE_TEST_MARKER();
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}
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}
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else
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{
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mtCOVERAGE_TEST_MARKER();
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}
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portGET_ISR_LOCK();
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@ -7676,14 +7672,22 @@ TickType_t uxTaskResetEventItemValue( void )
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TickType_t xTicksToWait )
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{
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uint32_t ulReturn;
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BaseType_t xAlreadyYielded;
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BaseType_t xAlreadyYielded, xShouldBlock = pdFALSE;
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traceENTER_ulTaskGenericNotifyTake( uxIndexToWaitOn, xClearCountOnExit, xTicksToWait );
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configASSERT( uxIndexToWaitOn < configTASK_NOTIFICATION_ARRAY_ENTRIES );
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/* We suspend the scheduler here as prvAddCurrentTaskToDelayedList is a
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* non-deterministic operation. */
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vTaskSuspendAll();
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{
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/* We MUST enter a critical section to atomically check if a notification
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* has occurred and set the flag to indicate that we are waiting for
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* a notification. If we do not do so, a notification sent from an ISR
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* will get lost. */
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taskENTER_CRITICAL();
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{
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/* Only block if the notification count is not already non-zero. */
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if( pxCurrentTCB->ulNotifiedValue[ uxIndexToWaitOn ] == 0UL )
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{
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@ -7692,53 +7696,7 @@ TickType_t uxTaskResetEventItemValue( void )
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if( xTicksToWait > ( TickType_t ) 0 )
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{
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traceTASK_NOTIFY_TAKE_BLOCK( uxIndexToWaitOn );
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/* We MUST suspend the scheduler before exiting the critical
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* section (i.e. before enabling interrupts).
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*
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* If we do not do so, a notification sent from an ISR, which
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* happens after exiting the critical section and before
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* suspending the scheduler, will get lost. The sequence of
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* events will be:
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* 1. Exit critical section.
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* 2. Interrupt - ISR calls xTaskNotifyFromISR which adds the
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* task to the Ready list.
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* 3. Suspend scheduler.
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* 4. prvAddCurrentTaskToDelayedList moves the task to the
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* delayed or suspended list.
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* 5. Resume scheduler does not touch the task (because it is
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* not on the pendingReady list), effectively losing the
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* notification from the ISR.
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*
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* The same does not happen when we suspend the scheduler before
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* exiting the critical section. The sequence of events in this
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* case will be:
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* 1. Suspend scheduler.
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* 2. Exit critical section.
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* 3. Interrupt - ISR calls xTaskNotifyFromISR which adds the
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* task to the pendingReady list as the scheduler is
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* suspended.
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* 4. prvAddCurrentTaskToDelayedList adds the task to delayed or
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* suspended list. Note that this operation does not nullify
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* the add to pendingReady list done in the above step because
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* a different list item, namely xEventListItem, is used for
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* adding the task to the pendingReady list. In other words,
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* the task still remains on the pendingReady list.
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* 5. Resume scheduler moves the task from pendingReady list to
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* the Ready list.
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*/
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vTaskSuspendAll();
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{
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taskEXIT_CRITICAL();
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prvAddCurrentTaskToDelayedList( xTicksToWait, pdTRUE );
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}
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xAlreadyYielded = xTaskResumeAll();
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if( xAlreadyYielded == pdFALSE )
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{
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taskYIELD_WITHIN_API();
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xShouldBlock = pdTRUE;
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}
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else
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{
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@ -7747,12 +7705,34 @@ TickType_t uxTaskResetEventItemValue( void )
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}
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else
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{
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taskEXIT_CRITICAL();
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mtCOVERAGE_TEST_MARKER();
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}
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}
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taskEXIT_CRITICAL();
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/* We are now out of the critical section but the scheduler is still
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* suspended, so we are safe to do non-deterministic operations such
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* as prvAddCurrentTaskToDelayedList. */
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if( xShouldBlock == pdTRUE )
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{
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traceTASK_NOTIFY_TAKE_BLOCK( uxIndexToWaitOn );
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prvAddCurrentTaskToDelayedList( xTicksToWait, pdTRUE );
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}
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else
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{
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taskEXIT_CRITICAL();
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mtCOVERAGE_TEST_MARKER();
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}
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}
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xAlreadyYielded = xTaskResumeAll();
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/* Force a reschedule if xTaskResumeAll has not already done so. */
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if( ( xShouldBlock == pdTRUE ) && ( xAlreadyYielded == pdFALSE ) )
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{
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taskYIELD_WITHIN_API();
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}
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else
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{
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mtCOVERAGE_TEST_MARKER();
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}
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taskENTER_CRITICAL();
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@ -7796,20 +7776,27 @@ TickType_t uxTaskResetEventItemValue( void )
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uint32_t * pulNotificationValue,
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TickType_t xTicksToWait )
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{
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BaseType_t xReturn, xAlreadyYielded;
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BaseType_t xReturn, xAlreadyYielded, xShouldBlock = pdFALSE;
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traceENTER_xTaskGenericNotifyWait( uxIndexToWaitOn, ulBitsToClearOnEntry, ulBitsToClearOnExit, pulNotificationValue, xTicksToWait );
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configASSERT( uxIndexToWaitOn < configTASK_NOTIFICATION_ARRAY_ENTRIES );
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/* We suspend the scheduler here as prvAddCurrentTaskToDelayedList is a
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* non-deterministic operation. */
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vTaskSuspendAll();
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{
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/* We MUST enter a critical section to atomically check and update the
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* task notification value. If we do not do so, a notification from
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* an ISR will get lost. */
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taskENTER_CRITICAL();
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{
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/* Only block if a notification is not already pending. */
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if( pxCurrentTCB->ucNotifyState[ uxIndexToWaitOn ] != taskNOTIFICATION_RECEIVED )
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{
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/* Clear bits in the task's notification value as bits may get
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* set by the notifying task or interrupt. This can be used to
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* clear the value to zero. */
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* set by the notifying task or interrupt. This can be used
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* to clear the value to zero. */
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pxCurrentTCB->ulNotifiedValue[ uxIndexToWaitOn ] &= ~ulBitsToClearOnEntry;
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/* Mark this task as waiting for a notification. */
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@ -7817,53 +7804,7 @@ TickType_t uxTaskResetEventItemValue( void )
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if( xTicksToWait > ( TickType_t ) 0 )
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{
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traceTASK_NOTIFY_WAIT_BLOCK( uxIndexToWaitOn );
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/* We MUST suspend the scheduler before exiting the critical
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* section (i.e. before enabling interrupts).
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*
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* If we do not do so, a notification sent from an ISR, which
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* happens after exiting the critical section and before
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* suspending the scheduler, will get lost. The sequence of
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* events will be:
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* 1. Exit critical section.
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* 2. Interrupt - ISR calls xTaskNotifyFromISR which adds the
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* task to the Ready list.
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* 3. Suspend scheduler.
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* 4. prvAddCurrentTaskToDelayedList moves the task to the
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* delayed or suspended list.
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* 5. Resume scheduler does not touch the task (because it is
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* not on the pendingReady list), effectively losing the
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* notification from the ISR.
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*
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* The same does not happen when we suspend the scheduler before
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* exiting the critical section. The sequence of events in this
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* case will be:
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* 1. Suspend scheduler.
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* 2. Exit critical section.
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* 3. Interrupt - ISR calls xTaskNotifyFromISR which adds the
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* task to the pendingReady list as the scheduler is
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* suspended.
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* 4. prvAddCurrentTaskToDelayedList adds the task to delayed or
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* suspended list. Note that this operation does not nullify
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* the add to pendingReady list done in the above step because
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* a different list item, namely xEventListItem, is used for
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* adding the task to the pendingReady list. In other words,
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* the task still remains on the pendingReady list.
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* 5. Resume scheduler moves the task from pendingReady list to
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* the Ready list.
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*/
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vTaskSuspendAll();
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{
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taskEXIT_CRITICAL();
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prvAddCurrentTaskToDelayedList( xTicksToWait, pdTRUE );
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}
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xAlreadyYielded = xTaskResumeAll();
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if( xAlreadyYielded == pdFALSE )
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{
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taskYIELD_WITHIN_API();
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xShouldBlock = pdTRUE;
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}
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else
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{
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@ -7872,12 +7813,34 @@ TickType_t uxTaskResetEventItemValue( void )
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}
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else
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{
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taskEXIT_CRITICAL();
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mtCOVERAGE_TEST_MARKER();
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}
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}
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taskEXIT_CRITICAL();
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/* We are now out of the critical section but the scheduler is still
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* suspended, so we are safe to do non-deterministic operations such
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* as prvAddCurrentTaskToDelayedList. */
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if( xShouldBlock == pdTRUE )
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{
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traceTASK_NOTIFY_WAIT_BLOCK( uxIndexToWaitOn );
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prvAddCurrentTaskToDelayedList( xTicksToWait, pdTRUE );
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}
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else
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{
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taskEXIT_CRITICAL();
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mtCOVERAGE_TEST_MARKER();
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}
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}
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xAlreadyYielded = xTaskResumeAll();
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/* Force a reschedule if xTaskResumeAll has not already done so. */
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if( ( xShouldBlock == pdTRUE ) && ( xAlreadyYielded == pdFALSE ) )
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{
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taskYIELD_WITHIN_API();
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}
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else
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{
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mtCOVERAGE_TEST_MARKER();
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}
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taskENTER_CRITICAL();
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