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package com.sun.grizzly.connectioncache.spi.transport;

import java.io.Closeable;

/** A concurrent connection cache for passively created connections (e.g.
 * from an acceptor).  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.  
 * 
 * 
 * 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.
 * 

 * Access is also provided to the cache configuration: maxParallelConnections,
 * highWaterMark, and numberToReclaim.  Currently these can only be set when
 * the cache is created.
 *
 * XXX We may wish to make the cache configuration dynamically configurable.
 * @param C  a connection
 */
public interface InboundConnectionCache extends ConnectionCache {
   /** Mark a connection as busy because a request is being processed
     * on the connection.  The connection may or may not be previously
     * known to the cache when this method is called.
     * Busy connections cannot be reclaimed.
     * This provides an early indication that a Connection is in use,
     * before we know how many responses still need to be sent on 
     * the Connection for this request.  This reduces the likelyhood 
     * of reclaiming a connection on which we are processing a request.
     * 

     * Note that this problem is inherent in a distributed system.
     * We could in any case reclaim a connection AFTER a client
     * has sent a request but BEFORE the request is received.
     * Note that AFTER and BEFORE refer to global time which does
     * not really exist in a distributed system (or at least we 
     * want to pretend it is not available).
     *
     * XXX Should we age out connections?  
     * This would require actual time stamps, rather than just an LRU queue.
     * @param conn  a connection
    */
    void requestReceived( C conn ) ;

    /** Indicate that request processing has been completed for a request
     * received on conn.  This indicates that a Connection that received
     * a request as indicated in a previous call to requestReceived has
     * completed request processing for that request.  Responses may still 
     * need to be sent.  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.
     * @param conn  a connection
     * @param numResponseExpected  number of connections in which a response is expected
     */
    void requestProcessed( C conn, int numResponseExpected ) ;

    /** Inform the cache that a response has been sent on a particular
     * connection.  
     * 
     * When a Connection is idle, and has no pending responses, it is
     * eligible for reclamation.
     * @param conn  a connection
     */
    void responseSent( C conn ) ;
}