Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem


Queue set and semaphore behavior question

Posted by rrrum on May 19, 2016


Suppose I have created queue set "xQueueSetTest" with one queue and semaphore. Then in a task I call

xActivatedMember = xQueueSelectFromSet( xQueueSetTest, portMAX_DELAY );

which will block the task. If semaphore is signaled from some other task, the task unblocks but in subsequent code I don't call

xSemaphoreTake( xActivatedMember, 0 );

If the task is executed again and arrives at xQueueSelectFromSet will it exit immediately since semaphore is still signaled?

Is my understanding correct or the behavior will be again blocked task?



Queue set and semaphore behavior question

Posted by rtel on May 19, 2016

No - the task will block again and that will be a logic error. If a task is blocked on a queue set and leaves the blocked state because an item was posted to a queue or semaphore in that set then the unblocked task MUST them remove the item from the queue or semaphore.

[ Back to the top ]    [ About FreeRTOS ]    [ Privacy ]    [ Sitemap ]    [ ]

Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

FreeRTOS v10.2.1 is available for immediate download. MIT licensed, includes 64-bit RISC-V, NXP Cortex-M33 demo & Nuvoton Cortex-M23 demo.

NXP tweet showing LPC5500 (ARMv8-M Cortex-M33) running FreeRTOS.

View a recording of the "OTA Update Security and Reliability" webinar, presented by TI and AWS.


FreeRTOS and other embedded software careers at AWS.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Cadence Tensilica Cortes

Espressif ESP32

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers





STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

OpenRTOS and SafeRTOS

Xilinx Microblaze and Zynq partner