[e-lang] GridLock

[Kevin Reid]

On Feb 1, 2007, at 2:01, Dr. Pierre Vignéras wrote:

> I have some questions concerning GridLock (mentionned in Event-Loop
> Concurrency http://www.erights.org/elib/concurrency/event-loop.html).
...
> Are GridLocks E related? I mean do we found GridLocks in a traditional
> thread-based concurrent OO Application?  (I guess yes, and so they  
> are not E related).

A program with a gridlock bug has at least one buffer and a procedure  
for emptying it which fills some buffer (not necessarily the same one).

Note that a buffer does not necessarily hold just bits: for example,  
if a program starts threads which end up waiting for some condition  
before proceeding, the collection of waiting threads constitutes a  
buffer.

> Are GridLocks deterministics? (I guess no)

They're deterministic if the available space of the particular buffer  
is deterministic and every process which fills it is deterministic.

> In the case of a gridlock, can we recover from it at runtime (For  
> example, by increasing the buffer space and restarting something  
> (request or thread, ...))?
>
> How to prevent gridlocks?

By designing a program so that parts of it which empty buffers can  
make progress without additional buffer space.

-- 
Kevin Reid                            <http://homepage.mac.com/kpreid/>