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From: Jacob Rhoden <jrhoden@unimelb.edu.au>
To: java-user@lucene.apache.org
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Subject: Re: Wrapping IndexSearcher so that it is safe?
Date: Thu, 12 Nov 2009 11:33:08 +1100
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The source code for SearcherManager is even downloadable for free:
    http://www.manning.com/hatcher3/LIAsourcecode.zip

The example source code does some things that is beyond my level of  
understanding
of lucene. ie:
1) To me it looks like an IndexSearcher never gets closed.
2) I don't understand what happens if the indexreader is reopened  
while a thread
     in the middle of a search using an indexsearcher.

So I am going for something a bit simpler:

If a thread wants to use the "SafeIndexSearcher", it first calls  
retain() and then calls
release() when its done.

If a thread wants to close the "SafeIndexSearcher" , the close is  
deferred until all threads
have called release():


public class SafeIndexSearcher {

	private boolean finish = false;
	private int retainCount = 0;
	private IndexSearcher searcher;

	public SafeIndexSearcher(IndexSearcher searcher) {
		this.searcher = searcher;
	}

	public TopDocs search(Query query, int limit) throws IOException {
		TopDocs result = searcher.search(query, limit);
		return result;
	}

	public Document doc(int doc) throws CorruptIndexException,  
IOException {
		return searcher.doc(doc);
	}

	public synchronized void close() {
		finish = true;
	}

	public synchronized SafeIndexSearcher retain() throws IOException {
		if(finish)
			throw new IOException("SafeIndexSearcher used after close has been  
called.");
		retainCount++;
		return this;
	}

	public synchronized SafeIndexSearcher release() {
		retainCount--;
		if(finish && retainCount==0)
			try {
				searcher.close();
			} catch (IOException e) {
				System.err.println("IndexSearcher.close() unexpected error: " +  
e.getMessage());
			}
		return this;
	}

}

On 12/11/2009, at 9:53 AM, Erick Erickson wrote:

> If you want to spend a few bucks, here's part of a reply to a similar
> question
> from Mike McCandless a day or so ago....
>
> <<<
> You can get the book here http://www.manning.com/hatcher3 (NOTE: I'm
> one of the authors!).
>
> Chapter 11 in the book has a class called SearcherManager, that
> handles the details of reopen/closing the IndexReader while queries
> are still in flight, that might be useful here.
>>>>
>
> The book is Lucene In Action II. Manning has an "early access program"
> (MEAP) that lets you get a PDF version. That class is considerably  
> more
> extensive and handles the edge cases as I remember it....
>
> Best
> Erick
>
>
> On Wed, Nov 11, 2009 at 5:41 PM, Jacob Rhoden  
> <jrhoden@unimelb.edu.au>wrote:
>
>> I knew I would have overlooked something, thanks for the help!
>>
>> On 12/11/2009, at 9:21 AM, Uwe Schindler wrote:
>>
>> ....simply do not catch and rethrow the IOException, instead put  
>> release
>>> in a
>>>
>>> finally block and let the IOException automatically go upwards.
>>>
>>>                this.retain();
>>>>               try {
>>>>                       TopDocs result = searcher.search(query,  
>>>> limit);
>>>>                       return result;
>>>>               } finally {
>>>>                       this.release();
>>>>               }
>>>>
>>>
>>> Less code more secure and effective :-)
>>>
>>
>>
>> ____________________________________
>> Information Technology Services,
>> The University of Melbourne
>>
>> Email: jrhoden@unimelb.edu.au
>> Phone: +61 3 8344 2884
>> Mobile: +61 4 1095 7575
>>
>>
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>>

____________________________________
Information Technology Services,
The University of Melbourne

Email: jrhoden@unimelb.edu.au
Phone: +61 3 8344 2884
Mobile: +61 4 1095 7575


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