Re: Best way to halt Java process?

From:
"Mike Schilling" <mscottschilling@hotmail.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 12 Jun 2010 01:07:42 -0700
Message-ID:
<huvf8h$tni$1@news.eternal-september.org>
"ClassCastException" <zjkg3d9gj56@gmail.invalid> wrote in message
news:huuvm3$c4e$1@news.eternal-september.org...

On Thu, 10 Jun 2010 22:55:59 -0700, Mike Schilling wrote:

"ClassCastException" <zjkg3d9gj56@gmail.invalid> wrote in message
news:husivb$hsb$3@news.eternal-september.org...

On Thu, 10 Jun 2010 20:38:23 -0700, Mike Schilling wrote:

"ClassCastException" <zjkg3d9gj56@gmail.invalid> wrote in message
news:hus9o8$g1n$6@news.eternal-september.org...

On Thu, 10 Jun 2010 19:54:51 -0700, Mike Schilling wrote:

"ClassCastException" <zjkg3d9gj56@gmail.invalid> wrote in message
news:hus76c$g1n$2@news.eternal-september.org...

I think the usual situation will be that a) you don't catch Error
and b) servlet containers etc. run servlets etc. in separate
threads and deal with it gracefully if any of these threads abends.
If you have multiple threads, provide some interrupt mechanism that
can be triggered.


A servlet container will handle each request in a separate thread,
and direct that thread to the servlet that should handle it. One
request's thread erroring horribly doesn't prevent further requests
from being processed by that same servlet. Preventing any further
processing would require some management operation that disables the
servlet, or more likely its containing web application.


Euuww. That means you need to tell the servlet container to
unregister you, or else set a public static mutable error flag that
makes all subsequent instances prompt-fail, or something. Global
variables. Ick!

Does the servlet<->container API/protocol/whatever not include an
explicit way for a servlet to signal a fatal error to the container?
Let alone to perform just-once initialization, prior to handling
requests, which can fail?


Yeah, that you can do. There's an init() method, and if it throws an
exception the servlet is never enabled (at least, in containers I know
of. Not sure if that's part of the spec.)


Ah, then Todd should probably be doing these checks in the init()
method and throwing an exception if they fail.

But even without that, there's no need for anything but a private
field used by the (single) instance of the servlet class. Multiple
threads -- single instance.


Global variables by any other name ... *sigh*


A private instance field is a global variable?


Not normally, but in this case it's sort-of one in disguise.


It represents the state of the object (the servlet), which is what instance
fields are supposed to do. This works quite well for intermittent
problems, say losing the connection to an underlying DBMS. The servlet can
retry the connection every N seconds, while rejecting all requests that come
while it's down. For unrecoverable initialization failures, throwing an
exception from init() makes more sense.

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