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1: /* LeaseRenewingTask.java -- The task to renew the lease. 2: Copyright (C) 2006 Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: 39: package gnu.java.rmi.dgc; 40: 41: import gnu.java.rmi.server.UnicastRef; 42: 43: import java.lang.ref.WeakReference; 44: import java.rmi.dgc.Lease; 45: import java.util.Iterator; 46: import java.util.LinkedList; 47: import java.util.Timer; 48: import java.util.TimerTask; 49: import java.util.WeakHashMap; 50: 51: /** 52: * The task to renew the lease to some object reference. The UnicastRef 53: * being renewed is stored as a weak reference. So the presence of the 54: * sheduled task does not prevent it from being garbage collected. If the 55: * reference has not been garbage collected, the task is resheduled after 56: * the lease is renewed. 57: * 58: * @author Audrius Meskauskas (Audriusa@Bioinformatics.org) 59: */ 60: public class LeaseRenewingTask 61: { 62: /** 63: * The sheduled timer task to call the renew() method. 64: */ 65: class LeaseTimerTask extends TimerTask 66: { 67: public void run() 68: { 69: renew(); 70: } 71: } 72: 73: /** 74: * The default requested lease duration time (one minute by default). 75: */ 76: public static long REQUEST_LEASE_DURATION = 60000; 77: 78: /** 79: * The reference to the UnicastRef that must renew its lease until not 80: * garbage collected. The different members of this list may point to the 81: * different instances of the UnicastRef's, but these references are 82: * pointing to the same remote object (they .equals() returns 83: * true when comparing with each other). Using LinkedList to make 84: * frequent deletions from the middle easy. 85: */ 86: LinkedList ref = new LinkedList(); 87: 88: /** 89: * The granted (or supposed) lease. 90: */ 91: Lease lease = new Lease(null, REQUEST_LEASE_DURATION); 92: 93: /** 94: * The timer, shared by all lease renewing tasks. The same instance is also 95: * used for the reference protector discarding in DGCImpl. 96: */ 97: static Timer timer = new Timer(true); 98: 99: /** 100: * Maps the UnicastRef to its renewing task. 101: */ 102: static WeakHashMap existingTasks = new WeakHashMap(); 103: 104: /** 105: * Creates the lease renewing task that renews the lease of the given 106: * UnicastRef until it is not collected. This constructor requests the lease 107: * value from the server and schedules the lease renewal action. 108: * 109: * @param renewIt the reference that must be renewed. 110: */ 111: public LeaseRenewingTask(UnicastRef renewIt) 112: { 113: lease = notifyDGC(renewIt); 114: if (lease != null) 115: { 116: schedule(lease); 117: ref.add(new WeakReference(renewIt)); 118: } 119: } 120: 121: /** 122: * Schedule periodic leases for the given UnicastRef reference. 123: * 124: * @param renewIt the reference, for that the leases must be scheduled. 125: */ 126: public static void scheduleLeases(UnicastRef renewIt) 127: { 128: // No need to schedule leases for null. 129: if (renewIt == null) 130: return; 131: try { 132: synchronized (existingTasks) 133: { 134: // Check maybe the task for refreshing this remote object already 135: // exists. 136: LeaseRenewingTask task = (LeaseRenewingTask) existingTasks.get(renewIt); 137: 138: if (task != null) 139: { 140: // Extend the reference list only. The scheduling must be 141: // alredy done with the previous lease. 142: synchronized (task.ref) 143: { 144: task.ref.add(new WeakReference(renewIt)); 145: } 146: } 147: else 148: existingTasks.put(renewIt, new LeaseRenewingTask(renewIt)); 149: } 150: } 151: catch (Exception ex) 152: { 153: InternalError ierr = new InternalError("Lease for "+renewIt); 154: ierr.initCause(ex); 155: throw ierr; 156: } 157: } 158: 159: /** 160: * Shedule the renewing call, taking into consideration that the following 161: * lease was granted. 162: * 163: * @param lease the lease that was granted. 164: */ 165: public void schedule(Lease lease) 166: { 167: long value = lease.getValue(); 168: 169: // Shedule a 10 % earlier because some time is needed for the message 170: // to reach the server. 171: long reduced = (value * 90)/100; 172: if (reduced == 0) 173: reduced = value; 174: 175: timer.schedule(new LeaseTimerTask(), reduced); 176: } 177: 178: /** 179: * Renew the lease. 180: */ 181: public void renew() 182: { 183: Object renewIt = null; 184: // Iterate throw the list of associated references. If all are 185: // discarded, there is no need to renew. 186: synchronized (ref) 187: { 188: Iterator iter = ref.iterator(); 189: WeakReference w; 190: while (iter.hasNext() && renewIt == null) 191: { 192: w = (WeakReference) iter.next(); 193: renewIt = w.get(); 194: if (renewIt == null) 195: // Discard the weak reference if its target has been garbage 196: // collected. 197: iter.remove(); 198: } 199: } 200: 201: if (renewIt!=null) 202: { 203: Lease lease = notifyDGC( (UnicastRef) renewIt); 204: 205: // Schedule the next renewing session. 206: if (lease!=null) 207: schedule(lease); 208: } 209: { 210: // All references collected - discard this entry. 211: } 212: } 213: 214: /** 215: * Notify DGC that we still hold this reference. 216: * 217: * @param renewIt the reference we still have (must not be null). 218: */ 219: public Lease notifyDGC(UnicastRef renewIt) 220: { 221: try 222: { 223: return renewIt.notifyDGC(lease); 224: } 225: catch (Exception e) 226: { 227: // Failed to notify. 228: // TODO Take some relevant action in the case if we failed 229: // to notify the remote object owner. 230: return null; 231: } 232: } 233: 234: }