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From "J.J. Larrea" <...@panix.com>
Subject Re: Renewing IndexSearcher on index change.
Date Tue, 04 Oct 2005 17:17:16 GMT
At 6:39 PM +0200 10/4/05, Olivier Jaquemet wrote:
>In every case I think I will use this to prevent any problem but why nobody uses finalize
methods? is it somehow bad to try to close things correctly that way?

Because they are not run under "brutal termination" conditions.  For that you need to add
a shutdown hook to the Java runtime.  A shutdown hook will run if the runtime process receives
a signal eg. SIGHUP which on Unix occurs if the controlling terminal "hangs up", etc. It won't
get run on a SIGKILL, but nothing will.  It also runs if you get an OutOfMemoryException or
similar problem in the runtime, though there is no guarantee the hook code e.g. close() won't
also fail in that case.

For example, my indexing code looks something like this:

    final IndexWriter writer = ...
   
    Thread shutdown = new Thread() {
        public void run() {
	    if(writer != null) {
		// feebly try to prevent concurrent reentry problems
		IndexWriter w = writer;
		w = null;
                try {
                    w.close();
                } catch(Exception ex) {
                    logger.error("Closing", ex);
                }
            }
        }
    };
    Runtime.getRuntime().addShutdownHook(shutdown);

    // do indexing here
    doit(writer, ...);

    // no abnormal termination
    // just exit and the shutdown hook will run

In a multi-threaded context, one might need to add synchronization to prevent concurrent entry
from causing problems.

I'm not sure whether this relates to the IndexSearcher problem you're trying to solve, but
it is certainly useful when indexing.

- J.J.

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