jpl

Class QueryInProgressException

java.lang.Object

java.lang.Throwable

java.lang.Exception

java.lang.RuntimeException

jpl.JPLException

jpl.QueryInProgressException

All Implemented Interfaces:

Serializable

public final class QueryInProgressException
extends JPLException

An exception of this type is thrown if a Query is made while another Query is in progress, for example, if the JPL programmer has negglected to close a query by exhausting all solutions or by failing to rweind() a Query, or in multi-threaded situations.

To prevent this kind of exception from being thrown, first make absolutely sure that all Queries are being closed properly, either by exhausting all solutions in a Query (i.e., hasMoreSolutions() returns false), or by explicitly calling rewind(). If your program involves multi-threading, make sure you obtain the lock from the Query object before entering a hasMoreSolutions()/nextSolution loop:

 Query query = // get a query somehow
 synchronized ( jpl.Query.lock() ){
     while ( query.hasMoreElements() ){
          Hashtable solution = query.nextSolution();
          // process solution...
     }
 }
 

Note: In most situations such care is not necessary, since the Query.query(), Query,oneSolution(), and Query.allSolutions() methods are thread-safe. However, users may have reason to use the hasMoreSolutions() and nextSolutions() methods, which, while synchronized, do allow Queries to be opened between calls to these methods.

If you catch this Exception, you can usese the query() accessor to obtain a reference to the Query that is in progress.

Copyright (C) 1998 Fred Dushin

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library Public License for more details.

Version:

$Revision: 1.1.1.1 $

Author:

Fred Dushin

See Also:

Serialized Form

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	QueryInProgressException(Query query)

Method Summary

Modifier and Type	Method and Description
Query	query()

Methods inherited from class java.lang.Throwable

addSuppressed, fillInStackTrace, getCause, getLocalizedMessage, getMessage, getStackTrace, getSuppressed, initCause, printStackTrace, printStackTrace, printStackTrace, setStackTrace, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

QueryInProgressException

protected QueryInProgressException(Query query)

Method Detail

query

public final Query query()

Returns:

a reference to the Query that is in progress