richard_damon wrote on Sunday, January 24, 2016:
First, xqueuesend and xquesendtoback are aliases for the same function. So the difference you are looking at is the difference between a non-fromisr function and a fromisr function. The major difference between them is that the non-ISR version give you the option to block the task for awhile for the operation to complete if needed, while the ISR versions do not (you DON’T want to delay an ISR execution) but instead give you a flag to let you decide if you need to run the scheduler.
A second internal difference is the way critical sections are implemented. The non-ISR versions use slightly simpler code knowing they aren’t in an interrupt context.