Hi, Thanks for the observation! It's true that setConsumed should only be called once per kernel entry, and it's not obvious just from the code snippets to observe that this is true.
However, the semantics of YieldTo mean that both of these code paths cannot be executed in the same kernel entry. If return_now is true, this means that the current thread will be switched to and sc->scYieldFrom should be NULL (as the YieldTo call has completed). This is usually the case if the calling thread YieldTo a lower priority thread, or a thread that is not runnable. On the other hand if return_now is false, the YieldTo resulted in the thread being YieldedTo being switched to, so we return the result of the YieldTo on a different kernel entry (when we run the thread that called YieldTo again). With this context, take a look at the if block here: https://github.com/seL4/seL4/blob/master/src/object/schedcontext.c#L191 Where you can see that we only set sc->scYieldFrom when we also set return_now to false. Glad to see someone looking at the MCS kernel. Anna. Confidentiality Note:This email is intended only for the person or entity to which it is addressed and may contain information that is privileged, confidential or otherwise protected from disclosure. Unauthorized use, dissemination, distribution or copying of this email or the information herein by anyone other than the intended recipient is strictly prohibited. If you have received this email in error, please notify the sender immediately and destroy the original message, any attachments thereto and all copies. _______________________________________________ Devel mailing list Devel@sel4.systems https://sel4.systems/lists/listinfo/devel
