[Queue Set API]

 QueueSetMemberHandle_t xQueueSelectFromSet
                             QueueSetHandle_t xQueueSet,
                             const TickType_t xTicksToWait

configUSE_QUEUE_SETS must be set to 1 in FreeRTOSConfig.h for the xQueueSelectFromSet() API function to be available.

xQueueSelectFromSet() selects from the members of a queue set a queue or semaphore that either contains data (in the case of a queue) or is available to take (in the case of a semaphore). xQueueSelectFromSet() effectively allows a task to block (pend) on a read operation on all the queues and semaphores in a queue set simultaneously.


  • There are simpler alternatives to using queue sets. See the Blocking on Multiple Objects page for more information.

  • Blocking on a queue set that contains a mutex will not cause the mutex holder to inherit the priority of the blocked task.

  • A receive (in the case of a queue) or take (in the case of a semaphore) operation must not be performed on a member of a queue set unless a call to xQueueSelectFromSet() has first returned a handle to that set member.

xQueueSet   The queue set on which the task will (potentially) block.
xTicksToWait   The maximum time, in ticks, that the calling task will remain in the Blocked state (with other tasks executing) to wait for a member of the queue set to be ready for a successful queue read or semaphore take operation.
xQueueSelectFromSet() will return the handle of a queue (cast to a QueueSetMemberHandle_t type) contained in the queue set that contains data, or the handle of a semaphore (cast to a QueueSetMemberHandle_t type) contained in the queue set that is available, or NULL if no such queue or semaphore exists before before the specified block time expires.
Example usage:

See the example on the xQueueCreateSet() documentation page.

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