In Lucene, how can I find out if the IndexSearcher or IndexWriter is being used in another thread or not?
Lucene documentation states that single instances of IndexSearcher and IndexWriter should be used for each index in the whole application, and across all threads. Also, writes to an index will not be visible until the index is re-opened.

So, I'm trying to follow these guides, in a multi-threaded setup. (a few threads writing, multiple user threads searching). I don't want to re-open the index on every change, rather, I want to keep searcher instance not older than a certain amount of time (say, like 20 seconds). 

A central component is responsible to open index readers and writers, and keep the single instance and synchronize the threads. I keep track of the last time the IndexSearcher has been accessed by any user thread, and the time it became dirty. If anyone needs to access it after 20 seconds has passed from the change, I want to close the searcher and re-open it.

The problem is that I'm not sure of the previously requests for the searcher (made by other threads) has finished yet, so that I can close the IndexSearcher. It means that if I close and re-open the single IndexSearcher instance that is shared among all threads, there might be a search going on concurrently in some other thread.

To make the matter worse, here's what can happen theoretically: there can be multiple searches being performed at the same time all the time. (suppose you have thousands of users running searches on the same index). The single IndexSearcher instance may never become free so that it can be closed. Ideally, I want to create another IndexSearcher and direct new requests to it (while the old one is still open and running the searches already requested before). When the searches running on the old instance are complete, I want to close it.

What is the best way to synchronize multiple users of the IndexSearcher (or IndexWriter) for calling the close() method? Does Lucene provide any features / facilities for this, or it should be done totally by the user code (like counting the threads using a searcher, and increase / decrease the count each time it is used)?

Are there any recommendation / ideas about the above mentioned design?
In Lucene, how can I find out if the IndexSearcher or IndexWriter is being used in another thread or not?
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Lucene documentation states that single instances of IndexSearcher and IndexWriter should be used for each index in the whole application, and across all threads. Also, writes to an index will not be visible until the index is re-opened.

So, I'm trying to follow these guides, in a multi-threaded setup. (a few threads writing, multiple user threads searching). I don't want to re-open the index on every change, rather, I want to keep searcher instance not older than a certain amount of time (say, like 20 seconds). 

A central component is responsible to open index readers and writers, and keep the single instance and synchronize the threads. I keep track of the last time the IndexSearcher has been accessed by any user thread, and the time it became dirty. If anyone needs to access it after 20 seconds has passed from the change, I want to close the searcher and re-open it.

The problem is that I'm not sure of the previously requests for the searcher (made by other threads) has finished yet, so that I can close the IndexSearcher. It means that if I close and re-open the single IndexSearcher instance that is shared among all threads, there might be a search going on concurrently in some other thread.

To make the matter worse, here's what can happen theoretically: there can be multiple searches being performed at the same time all the time. (suppose you have thousands of users running searches on the same index). The single IndexSearcher instance may never become free so that it can be closed. Ideally, I want to create another IndexSearcher and direct new requests to it (while the old one is still open and running the searches already requested before). When the searches running on the old instance are complete, I want to close it.

What is the best way to synchronize multiple users of the IndexSearcher (or IndexWriter) for calling the close() method? Does Lucene provide any features / facilities for this, or it should be done totally by the user code (like counting the threads using a searcher, and increase / decrease the count each time it is used)?

Are there any recommendation / ideas about the above mentioned design?