Re: protected type interrupts

["Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>]

REH wrote:
> 
> I don't understand.  How can a procedure within a protected object
> modify data internal to the object in a thread-safe way without the
> potentially blocking effect of enforcing mutual exclusion?  If one task
> is "using" the object, and another calls one of the object's
> procedures, would the second task not be blocked until the first one
> exits the object?  

In the terms of the ARM, mutual exclusion is not considered potentially 
blocking. Only waiting for data synchronization is potentially blocking. 
Since protected actions are supposed to be short and quick, and cannot 
perform potentially blocking operations, mutual exclusion cannot delay a 
task for very long. On the other hand, waiting for an entry barrier to 
become true can take forever.

Many external actions, such as I/O, are also considered potentially 
blocking.

-- 
Jeff Carter
"Now go away or I shall taunt you a second time."
Monty Python & the Holy Grail
07