simple/simple-common/src/main/java/org/simpleframework/common/lease/LeaseManager.java

/*
 * LeaseManager.java May 2004
 *
 * Copyright (C) 2004, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 
 * implied. See the License for the specific language governing 
 * permissions and limitations under the License.
 */

package org.simpleframework.common.lease;

import java.util.concurrent.TimeUnit;

/**
 * The <code>LeaseManager</code> 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 <code>Lease</code> 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<T> implements LeaseProvider<T> {
   
   /**
    * This is the controller used to handle lease operations.
    */
   private ContractController<T> handler;
   
   /**
    * Constructor for the <code>LeaseManager</code> object. This
    * instance is created using a specified notification handler.
    * The specified <code>Cleaner</code> 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<T> cleaner) {
      this.handler = new ContractMaintainer<T>(cleaner);
   }
   
   /**
    * This method will issue a <code>Lease</code> 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 <code>Cleaner</code>
    * 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<T> lease(T key, long duration, TimeUnit unit) {
      Contract<T> contract = new Expiration<T>(key, duration, unit);
      
      try {
         handler.issue(contract);
      } catch(Exception e) {        
         throw new LeaseException("Could not issue lease", e);
      }
      return new ContractLease<T>(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 <code>lease</code> 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;                
      }           
   }
}