Re: What is so bad aboud Thread.stop() ?
On 8/1/2013 11:00 AM, usvirtualobservatory@gmail.com wrote:
On Thursday, August 1, 2013 12:09:20 AM UTC-4, Kevin McMurtrie wrote:
...
The problem is that it causes an exception from code that can not throw
an exception. It corrupts the data in shared objects. Example:
if (thing == null)
throw new NullPointerException("thing must not be null");
data[++count]= thing;
This could be killed after incrementing 'count' but before assigning the
array element. Now you have a very illegal null element.
While it's clear that one cannot continue on naively after issuing a
Thread.stop(), the question I'm trying to understand is whether it's
feasible in some conditions to do so reasonably safely. E.g.,
suppose I don't look at any of the objects that are create/modified
in the stopped thread. They are all thrown away. Then the fact that
they are potentially in a damaged state need not be an issue -- they
will never be used again.
But is there any system level magic that precludes doing this
regardless of the care one takes? E.g., maybe there are lots of
internal globals in seemingly innocuous standard classes that get
corrupted that are impossible to avoid, or there's an unavoidable
chance that garbage collection will be broken, or ???
Or is it that in practice it's difficult to do this with sufficient
care, but is in principle achievable?
I think it is something like:
You can achieve what you want to do in two ways:
A) use Thread.stop
B) set a flag and let the thread do what it need to do to
terminate in a graceful manner
#A can be done safely in some cases and can not be done safely in
other cases. Even if it can be done safely, then it will require
significant analysis to get it right. And even if it gets done
right, then there is a high risk that that a bug will be introduced
during maintenance later, because the maintenance programmer do not
have the skill or the time to understand the subtleties of the
problem.
#B can always be done safely. It requires not much work. And
is relative maintenance friendly.
Easy choice in my opinion.
Arne