at line 349 and line 474 in queue.c , there is the same code below:

if( prvUnlockQueue( pxQueue ) )
{
if( !xTaskResumeAll() )
{
taskYIELD();
}
}
else
{
xTaskResumeAll();
}

But i think in these code if prvUnlockQueue( pxQueue ) return pdTRUE then xTaskResumeAll() must return pdTRUE( if scheduler is not locket nested) , so it's meaningless to do taskYIELD(). So these code can be changed to:

prvUnlockQueue( pxQueue ) ;
xTaskResumeAll();

This is the most complex part of the code. Everything is geared at ensuring interrupts are disabled for the shortest possible period.

You might be right in your comment - with the scheduler suspended unlocking the queue can only move items to the pending ready list - where they will be removed by xTaskResumeAll().

I know there was a lot of thought that went into this code sequence. It was originally as per or similar to your suggestion. This one will take a bit of digging time for me to find why the change was made. It will be good to look again at this in detail. Out of interest I will run a few black box style tests to see if they ever fail with the change.

In any case the optimisation saving would be minimal - with a couple of tests being removed.

Regards.