/interpreter/tags/at_build150307/src/edu/vub/at/actors/net/cmd/VMCommand.java

  1/**
  2 * AmbientTalk/2 Project
  3 * VMCommand.java created on 22-feb-2007 at 13:03:56
  4 * (c) Programming Technology Lab, 2006 - 2007
  5 * Authors: Tom Van Cutsem & Stijn Mostinckx
  6 * 
  7 * Permission is hereby granted, free of charge, to any person
  8 * obtaining a copy of this software and associated documentation
  9 * files (the "Software"), to deal in the Software without
 10 * restriction, including without limitation the rights to use,
 11 * copy, modify, merge, publish, distribute, sublicense, and/or
 12 * sell copies of the Software, and to permit persons to whom the
 13 * Software is furnished to do so, subject to the following
 14 * conditions:
 15 *
 16 * The above copyright notice and this permission notice shall be
 17 * included in all copies or substantial portions of the Software.
 18 *
 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 26 * OTHER DEALINGS IN THE SOFTWARE.
 27 */
 28package edu.vub.at.actors.net.cmd;
 29
 30import edu.vub.at.actors.natives.ELVirtualMachine;
 31import edu.vub.at.actors.net.Logging;
 32
 33import java.io.Serializable;
 34import java.util.Vector;
 35
 36import org.jgroups.Address;
 37import org.jgroups.Message;
 38import org.jgroups.SuspectedException;
 39import org.jgroups.TimeoutException;
 40import org.jgroups.blocks.GroupRequest;
 41import org.jgroups.blocks.MessageDispatcher;
 42
 43/**
 44 * VM Command objects are the message objects that AT/2 virtual machines send to one another.
 45 * They are control objects sent by one VM and received by another. The receiving VM
 46 * executes the VM Command object's uponReceiptBy method, which allows the command object to
 47 * encapsulate the reception code itself.
 48 * 
 49 * By convention, all VM Command classes are prefixed with CMD.
 50 *
 51 * @author tvcutsem
 52 */
 53public abstract class VMCommand implements Serializable {
 54	
 55	private final String description_;
 56	/** the default transmission timeout for JGroups synchronous message communication */
 57	public static final int _TRANSMISSION_TIMEOUT_ = 10000; // in milliseconds
 58	
 59	/**
 60	 * @param descr for debugging purposes
 61	 */
 62	public VMCommand(String descr) {
 63		description_ = descr;
 64	}
 65	
 66	public String toString() {
 67		return "VMCommand:"+description_;
 68	}
 69	
 70	/**
 71	 * To be overridden by subclasses to specify the behaviour to execute upon reception
 72	 * and execution of the command object at the recipient VM.
 73	 * 
 74	 * This code is still executed in a JGroups thread!
 75	 * 
 76	 * @param remoteHost the host at which the command arrived and is executed
 77	 * @param wrapper the JGroups message wrapper that was used to transport this command object
 78	 */
 79	public abstract Object uponReceiptBy(ELVirtualMachine remoteHost, Message wrapper) throws Exception;
 80	
 81	/**
 82	 * Sends this VM Command object asynchronously to the recipient VM.
 83	 */
 84	protected void sendAsyncUnicast(MessageDispatcher dispatcher, Address recipientVM) throws TimeoutException, SuspectedException {
 85		Logging.VirtualMachine_LOG.info("sending async unicast cmd: " + description_);
 86		// JGROUPS:castMessage(java.util.Vector dests, Message msg, int mode, long timeout)
 87		Vector recipients = new Vector(1);
 88		recipients.add(recipientVM);
 89		dispatcher.castMessage(
 90			recipients, // send to particular member
 91			// JGROUPS:Message.new(destination, source, Serializable)
 92			new Message(recipientVM, null, this),
 93			GroupRequest.GET_NONE, // asynchronous call, non-blocking
 94			0); // timeout is irrelevant
 95	}
 96	
 97	/**
 98	 * Sends this VM Command object asynchronously to all connected VMs.
 99	 */
100	protected void sendAsyncMulticast(MessageDispatcher dispatcher) throws TimeoutException, SuspectedException {
101		Logging.VirtualMachine_LOG.info("sending async multicast cmd: " + description_);
102		// JGROUPS:castMessage(java.util.Vector dests, Message msg, int mode, long timeout)
103		dispatcher.castMessage(
104			null, // send to all members
105			// JGROUPS:Message.new(destination, source, Serializable)
106			new Message(null, null, this),
107			GroupRequest.GET_NONE, // asynchronous call, non-blocking
108			0); // timeout is irrelevant
109	}
110	
111	/**
112	 * Sends this VM Command object synchronously to the recipient VM. The recipient's
113	 * address must be given, null is not allowed (i.e. broadcasting synchronously is not allowed)
114	 */
115	protected Object sendSynchronousUnicast(MessageDispatcher dispatcher, Address recipientVM) throws TimeoutException, SuspectedException {
116		Logging.VirtualMachine_LOG.info("sending sync unicast cmd: " + description_);
117		// send a discovery query message to the remote VM
118		// JGROUPS:MessageDispatcher.sendMessage(destination, message, mode, timeout)
119		return dispatcher.sendMessage(
120			// JGROUPS:Message.new(destination, source, Serializable)
121			new Message(recipientVM, null, this),
122			GroupRequest.GET_FIRST,
123			_TRANSMISSION_TIMEOUT_);
124	}
125	
126}