package com.bigdata.bop.engine;
import java.lang.ref.WeakReference;
/**
* Class pairs together the immutable deadline associated with a query and the
* {@link AbstractRunningQuery}. The natural ordering places instances of this
* class into ascending deadline order. The deadline is simply the timestamp at
* which the query deadline is expired. Therefore, the instances are simply
* ordered by the time when their deadline will expire. The queries that will
* expire soonest are first, those that can run longer come later. This ordering
* is used for a priority queue.
*
* @see <a href="https://sourceforge.net/apps/trac/bigdata/ticket/772"> Query
* timeout only checked at operator start/stop. </a>
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
*/
class QueryDeadline implements Comparable<QueryDeadline> {
/**
* The deadline for this query (in nanoseconds).
*/
final long deadlineNanos;
/**
* A reference to the query.
* <p>
* Note: A {@link WeakReference} is used to avoid having the deadline queue
* pin the {@link AbstractRunningQuery} objects.
*/
private final WeakReference<AbstractRunningQuery> queryRef;
/**
*
* @param deadlineNanos
* The deadline for this query (in nanoseconds).
* @param query
* The query.
*/
public QueryDeadline(final long deadlineNanos, final AbstractRunningQuery query) {
this.deadlineNanos = deadlineNanos;
this.queryRef = new WeakReference<AbstractRunningQuery>(query);
}
/**
* Comparator orders the queries based on increasing deadline. The query
* with the soonest deadline will be ordered first. The query with the
* greatest deadline will be ordered last. Queries that do not have an
* explicit deadline are assigned a deadline of {@link Long#MAX_VALUE} and
* will be ordered last.
* <p>
* Note: A natural order based on deadline was added to support timely
* termination of compute bound queries that exceed their deadline.
*
* @see <a href="https://sourceforge.net/apps/trac/bigdata/ticket/772">
* Query timeout only checked at operator start/stop. </a>
*/
@Override
public int compareTo(final QueryDeadline o) {
final long d0 = this.deadlineNanos;
final long d1 = o.deadlineNanos;
if (d0 < d1)
return -1;
if (d0 > d1)
return 1;
return 0;
}
/**
* Check the deadline on the query. If the query is not terminated and the
* deadline has expired, then the query is terminated as a side-effect.
*
* @param nowNanosIsIgnored
* A current timestamp.
*
* @return <code>null</code> if the query is terminated and
* <code>this</code> if the query is not terminated.
*/
QueryDeadline checkDeadline(final long nowNanosIsIgnored) {
final AbstractRunningQuery q = queryRef.get();
if (q == null) {
/*
* The weak reference to the query has been cleared. This query is
* known to be terminated.
*/
return null;
}
// Check the deadline.
q.checkDeadline();
if (q.isDone()) {
// Query is terminated.
return null;
}
// Query is running and deadline is not expired.
return this;
}
}