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Simple is a high performance asynchronous HTTP server for Java
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/*
 * LeaseManager.java May 2004
 *
 * Copyright (C) 2004, Niall Gallagher 
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation.
 *
 * 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General 
 * Public License along with this library; if not, write to the 
 * Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
 * Boston, MA  02111-1307  USA
 */

package org.simpleframework.util.lease;

import java.util.concurrent.TimeUnit;

/**
 * The LeaseManager is used to issue a lease for a
 * named resource. This is effectively used to issue a request
 * for a keyed resource to be released when a lease has expired.
 * The use of a Lease simplifies the interface to
 * the notification and also enables other objects to manage the
 * lease without any knowledge of the resource it represents.
 *
 * @author Niall Gallagher
 */
public class LeaseManager implements LeaseProvider {
   
   /**
    * This is the controller used to handle lease operations.
    */
   private Controller handler;
   
   /**
    * Constructor for the LeaseManager object. This
    * instance is created using a specified notification handler.
    * The specified Cleaner will be notified when
    * the lease for a named resource expires, which will allow
    * the cleaner object to perform a clean up for that resource.
    *
    * @param cleaner the cleaner object receiving notifications
    */
   public LeaseManager(Cleaner cleaner) {
      this.handler = new Maintainer(cleaner);
   }
   
   /**
    * This method will issue a Lease object that
    * can be used to manage the release of a keyed resource. If
    * the lease duration expires before it is renewed then the 
    * notification is sent, typically to a Cleaner
    * implementation, to signify that the resource should be
    * recovered. The issued lease can also be canceled.
    * 
    * @param key this is the key for the leased resource 
    * @param duration this is the duration of the issued lease
    * @param unit this is the time unit to issue the lease with
    *
    * @return a lease that can be used to manage notification
    */
   public Lease lease(T key, long duration, TimeUnit unit) {
      Contract contract = new Entry(key, duration, unit);
      
      try {
         handler.issue(contract);
      } catch(Exception e) {        
         return null;
      }
      return new ContractLease(handler, contract);
   }

   /**
    * This is used to close the lease provider such that all of
    * the outstanding leases are canceled. This also ensures the
    * provider can no longer be used to issue new leases, such 
    * that further invocations of the lease method
    * will result in null leases. Once the provider has been 
    * closes all threads and other such resources are released.
    */ 
   public void close() {
      try {
        handler.close();              
      } catch(Exception e) {
        return;                
      }           
   }
}