Hi,

I've committed the attached patch which simplifies the implementation of 
sidutil::blocking_component. The use of two mutex/condition variable 
pairs for synchronizing the parent and child threads was unnecessary 
and, if you look at the existing code, you will see that they were 
always locked/unlocked/blocked in unison. The implementation now uses a 
single mutex/condition variable pair.

The patch also adds checking that a return from pthread_cond_wait was 
not spontaneous and makes the control_status member volatile for this 
purpose.

Tested extensively using the MeP port which is the only committed port 
using this class.

Dave