IPC between Tasks

Hi,

I'm planning on building a small example of a producer/consumer build
on top of L4Re. From the documentation I know about the shared memory
inteface which will help to pass information from the producer to the
consumer but I am a bit clueless on how I notify the consumer that
there is something new to read. The semaphore is only to be used in
between threads so there is no way to use them for IPC between Tasks?!
Is there another possibility to make this work other than to use
polling?

regards Tobi