Null references (oh no, not again!)

[Sean Kelly]

Denis Koroskin wrote:
> On Wed, 04 Mar 2009 13:55:57 +0300, Walter Bright 
> <newshound1 at digitalmars.com> wrote:
>>
>> If software is in your flight critical systems, the way one proceeds 
>> is to *assume skynet takes it over* and will attempt to do everything 
>> possible to crash the airplane.
> 
> Assume you got a null-derefence under Linux. How are you going to 
> recover from it? You can't catch the NullPointerException, so your 
> program will fail and bring down the whole system *anyway*.

Every process is monitored and backed-up by one or more other processes, 
thus the system is resilient through preemptive failover to back-up 
systems.  It's also common for monitor processes to run every operation 
in parallel through more than one equivalent sub-process and compare 
results.  If a discrepancy occurs, either a failover is triggered or the 
"correct" result is determined by consensus.   In every case though, 
attempting in-process error recovery in mission-critical code is a bad idea.