com.sun.xml.ws.transport.tcp.connectioncache.spi.transport.OutboundConnectionCache Maven / Gradle / Ivy

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/*
 * Copyright (c) 1997, 2021 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0, which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package com.sun.xml.ws.transport.tcp.connectioncache.spi.transport;

import java.io.IOException ;

/** A concurrent mostly non-blocking connection cache.  Here a Connection is an
 * abstraction of a Socket or SocketChannel: basically some sort of resource
 * that is expensive to acquire, and can be re-used freely.  The cache
 * maintains a loose upper bound on the number of cached connections, and
 * reclaims connections as needed.
 * 
 * This cache places minimal requirements on the Connections that it contains:
 * 

 * A Connection must implement a close() method.  This is called when idle
 * connections are reclaimed.
 * 
A Connection must be usable as a HashMap key.
 * 
There must be a ContactInfo class that is used to create Connection
 * instances.  The ContactInfo class must support a create() method that
 * returns a Connection.
 * 
The ContactInfo must be usable as a HashMap key.
 * 
All instances created from a ContactInfo are equal; that is, any request
 * sent to a particular ContactInfo can used an instance created from that
 * ContactInfo.  For example, in the CORBA case, IP host and port is not always
 * sufficient: we may also need the Codeset type that indicates how Strings are
 * encoded.  Basically, protocols (like GIOP) that bind session state to a
 * Connection may need more than transport information in the ContactInfo.
 * 
 * 
 * Some simple methods are provided for monitoring the state of the cache:
 * numbers of busy and idle connections, and the total number of connections in
 * the cache.
 */
public interface OutboundConnectionCache
    extends ConnectionCache {
    /** Configured maximum number of connections supported per ContactInfo.
     */
    int maxParallelConnections() ;

    /** Determine whether a new connection could be created by the
     * ConnectionCache or not.
     */
    boolean canCreateNewConnection( ContactInfo cinfo ) ;

    /** Return a Connection corresponding to the given ContactInfo.
     * This works as follows:
     * 

     * Call the finder.  If it returns non-null, use that connection;
     * (Note that this may be a new connection, created in the finder)
     * 
otherwise, Use an idle connection, if one is available;
     * 
otherwise, create a new connection, if not too many connections are
     * open;
     * 
otherwise, use a busy connection.
     * 
     * Note that creating a new connection requires EITHER:
     * 
     * there is no existing connection for the ContactInfo
     * 
 OR the total number of connections in the cache is less than the
     * HighWaterMark and the number of connections for this ContactInfo
     * is less than MaxParallelConnections.
     * 
     * We will always return a
     * Connection for a get call UNLESS we have no existing connection and
     * an attempt to create a new connection fails.  In this case, the
     * IOException thrown by ContactInfo.create is propagated out of this
     * method.
     * 
     * It is possible that the cache contains connections that no longer connect
     * to their destination.  In this case, it is the responsibility of the
     * client of the cache to close the broken connection as they are detected.
     * Connection reclamation may also handle the cleanup, but note that a
     * broken connection with pending responses will never be reclaimed.
     * 

     * Note that the idle and busy connection collections that are
     * passed to the finder are unmodifiable collections.  They have iterators
     * that return connections in LRU order, with the least recently used
     * connection first.  This is done to aid a finder that wishes to consider
     * load balancing in its determination of an appropriate connection.
     * 

     */
    C get( ContactInfo cinfo, ConnectionFinder finder
	) throws IOException ;

    /** Behaves the same as {@code get( ContactInfo, ConnectionFinder )}
     * except that no connection finder is provided, so that step is
     * ignored.
     */
    C get( ContactInfo cinfo ) throws IOException ;

    /** Release a Connection previously obtained from get.  Connections that
     * have been released as many times as they have been returned by
     * get are idle; otherwise a Connection is busy.  Some number of
     * responses (usually 0 or 1) may be expected ON THE SAME CONNECTION
     * even for an idle connection.  We maintain a count of the number of
     * outstanding responses we expect for protocols that return the response
     * on the same connection on which the request was received.  This is
     * necessary to prevent reclamation of a Connection that is idle, but
     * still needed to send responses to old requests.
     */
    void release( C conn, int numResponseExpected ) ;

    /** Inform the cache that a response has been received on a particular
     * connection.  This must also be called in the event that no response
     * is received, but the client times out waiting for a response, and
     * decides to abandon the request.
     * 
     * When a Connection is idle, and has no pending responses, it is
     * eligible for reclamation.
     */
    void responseReceived( C conn ) ;
}