The problem is basically unsolvable if you want to satisfy these two conditions:
(1) the low-prio thread must finish writing into the data structure so the data is always valid when read by the hi-prio thread.
(2) the hi-prio thread may not be blocked by the the lo-prio thread
In other words, if you demand that the data structure is always fully valid, you MUST allow the low-prio thread to finish the write operation.
Therefore, you must give up one of the two. Since high priority is high priority, I assume you can accept that the data sttructure is not always up-to-date when you use it in te hi-prio thread.
You could therefor do this:
in the lo-prio thread:
Code:
set semaphore
write the data structure
unset semaphore
in the hi-prio thread
Code:
if semaphore is set
{
do not use the data structure
or use the old data
}
else
{
use the data from the data structure
}
It can be benefical if you make a copy of the data structure in your hi-prio thread so you have the old data when you cannot access it.
The important point here is that semaphore operations are atomic, and write operations can not be interrupted. It is never invalid, and you don't have to mutex the access to a semaphore.
jlinkels
avoid hipri thread waiting on lowpri
