[En-Nut-Discussion] RFC: Wait for Multiple Events

[Matthias Ringwald]

Hi all,
  I'd like to share with you a (I hope) clean & straight & easy  
solution to the problem,
that a thread has no easy way to wait for several events to happen  
without polling.

RFC: Wait for Multiple Events

It would be useful for a thread to wait on multiple events.
A straight forward way to implement this could be the introduction of
signals. A set of signals, e.g. 16, can be used similar as the  
current event queues.

For this to work, a mask of awaited (or triggering) signals need to  
be stored in the thread struct (+2 bytes) and to allow for signals to  
be sent without anyone waiting, the queue needs to also store a  
signal mask (signal queue size = pointer + signal mask = 4 bytes on  
AVR).

In the signal post function, the signal queue has to be searched for  
the first thread with a matching signal mask and set to runnable.

As this is in the order of threads, I would not use this within IRQs.  
But, if the signal queue contains an event queue at the first byte,  
NutEventPost|Broadcast can be directly called on a signal queue as  
well. In this case, the first or all threads in the queue will be  
awaken regardless of the signal settings. Hence NutEventPostIrq can  
also be used to wake up the first thread in a signal queue from an  
interrupt service handler.

New functions:
NutSignal[Post|Broadcast][async]( SignalQueue, signalNr);
NutSignalWait( SignalQueue, signalPattern);

Thanks for sharing your opinions on this,
Matthias