[E-Lang] FW: Reasearch ideas in HDC

Ralph Hartley hartley@aic.nrl.navy.mil
Mon, 29 Jan 2001 08:49:01 -0500


Karp, Alan wrote:

>  > > IBM researchers, he said, are now trying to perfect software that 
> will identify
>  > > and repair the underlying coding errors that cause software aging.
> 
> The last paragraph is quite disturbing.  How many security holes do you
> think they'll introduce?  The good news is that they probably won't be
> fixing any E programs.


I assume they mean tools that bring problems to the attention of 
programers and then help fix the problems, not robots that automatically 
rewrite running machine code.

>>> "Aging" software
>>> 
>>> Lockups occur as often as weekly or monthly, Bradicich said, because
>>> otherwise
>>> sound software accumulates coding abnormalities that build up and drain
>>> memory
>>> in a process called "aging." If a computer isn't restarted to clear the
>>> erroneous instructions, the microprocessor eventually won't know 
>>> what to do
>>> next, and it freezes.
>> 
>> 
It looks to me that what they are trying to fix here are resource 
leaks.  As time goes on processes allocate memory but never free it, 
either  because they incorrectly no longer have a reference to it (C) or 
because  they do (java). The same thing happens on the scale of 
processes; a  process is started and hangs, waiting perhaps for some 
deadlock to  resolve, eventually a new request starts a new process for 
the same task  but the old one doesn't get killed.

How do E and EROS handle resource leaks? Persistence can make the  
problem much worse. In the quote it is implied that they treat the  
problem by rebooting the computer, which frees all (most) resources. If  
I understand correctly, in EROS this approach will not work at all,  
rebooting leaves the system in exactly the state it was in before.

How does E do manage memory? Does it rely on Java's garbage collection? 
If so, there is a problem because Java can leak memory quite badly (one 
reference to a high level object makes everything live forever).

What do you do when a system like EROS gets totally clogged by leaked  
resources? Don't say we will keep that from ever happening - it WILL 
happen.

Ralph Hartley