COMP 310 Fall 2014	HW07: Remote task execution

Today's example has a "compute engine" (ICompute) on the server  which is served out as a remote object.   The client then sends a "compute task" (ITask) to the server for it to execute, returning the result to the client.   The key issue here is that the server does not know a priori what the client will have it do. 

Before starting this assignment, be sure that you can run the demo from Lab08, which includes configuring your computer for use with RMI.

This assignment, and all future assignments will use TCP ports in the ranges: 2001-2002 and 2099-2102.

References:

• Remote Method Invocation (RMI)
  • RMI connectivity issues

Obtaining and Runnning the demo

The code is available by setting the svn:externals property (under Team/Set Property) of your src folder to "provided https://svn.rice.edu/r/comp310/course/ComputeEngine/provided"

Be sure to set the working directory of both the client and server launch configurations to your the "bin" directory in your project.  
Also, set both the client and engine (server) launch configurations to be "shared" so that they will always be set correctlyu.
See the Eclipse Resources page for directions  

Ports that need to be opened (see the code for the values):

• In-bound on Server:
  • IRemoteTaskViewAdapter.BOUND_PORT_SERVER -- Used by IRemoteTaskViewAdapter sent from server to client to display back on server's view.
  • ICompute.BOUND_PORT-- The port the ComputeEngine is bound in the Registry.
  • IRMI_Defs.CLASS_SERVER_PORT_SERVER -- The class server the server uses.
  • IRMI_Defs.REGISTRY_PORT -- The port the Registry uses on the server.
• In-bound on Client:
  • IRemoteTaskViewAdapter.BOUND_PORT_CLIENT -- Used by IRemoteTaskViewAdapter sent from client to server to display back on client's view.
  • IRMI_Defs.CLASS_SERVER_PORT_CLIENT -- The class server the client uses.

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Features

• Via the remote ICompute interface, the server will execute any ITask implementation sent to it, returning its results in a type-safe manner.
• When a task arrives at the server, it's setTaskViewAdapter() method is called to attach it to the server's view, so that any status output from the task is displayed on the server's view.
• Not only are the tasks sent from the client to the server, but also, the ICompute interface provides a setTextAdapter() method enables the client to send a stub of a view adapter to the server so that the server can display information on the client's view plus that same method will return a stub of a view adapter that will enable the client to display information on the server's view.
• Object serialization:
  • Serializable interface tells the compiler that this object can be serialized, i.e. its data (not its code!) can be turned into a byte stream and sent over the network.
  • Code, if needed, is transmitted separately and automatically.   The client's java.rmi.server.codebase value is imbedded in the serialized byte stream.   The receiver's Java class loader will look at this value and find the class file server on the sender and then issue an http-type request to download the associated class file.
  • Note that the class file server does not have to be co-located with the serialized object's sender.   The class file server can be a separate machine altogether, e.g. a central class file repository.
  • transient fields are not serialized.
  • Optional readObject method in Pi2 and GetInfo is used for custom deserialization processes, here to reinitialize the transient taskView field.   The server will attach its own ITaskView adapter so the transmitted task can communicate to the server.
• IRMIUtils:
  • Has services for creating and/or locating the Registry for the client and server use, plus to obtain the local IP address in a consistent manner across multiple operating systems.
  • Has services to start and stop the RMI sub-system with minimal effort and maximum reliability.   
  • Abstracts and encapsulates the Registry obtainment process.
  • Uses techniques for composing lambdas to enable the methods to send multiple messages to multiple output targets.
  • Note:  There are some typos still running around where "IRMIUtils" (or its concrete implementation, RMIUtils) are still referred to by their old name,  "RegistryFactory"

Read the documentation!

Important concepts:

Stubs retrieved from remote Registries -- The ICompute stub that the client retrieves via the Registry delegates its calls back to its ComputeEngine implementation on the server.

Stubs sent and returned by stubs  (stubs as factories) -- IRemoteTaskViewAdapter stubs are both sent to the server via a method in the ICompute stub in the client as well as returned by the ICompute stub as a return value.  Thus a single stub can serve as a factory for all the other stubs that are needed, eliminating the need for multitudes of objects bound in the Registry--only a single factory needs to be bound.

Entire objects being serialized and sent via stubs -- the ITask objects are being completely serialized and sent over the network from the client to the server.  They are not sent as stubs.  

Automatic remote dynamic class loading of serialized objects -- If the server does not have the code for the concrete ITask sent to it, the RMI system settings that the client and server set up automatically cause the code for the task to be dynamically loaded from across the network, from the client's class server to the server.  Likewise, this is done for the stubs that are sent back and forth.

Requirements:

• Special note for teams where the members are running a mix of 32-bit and 64-bit Java computers:  You will need to use a special "svn:ignore" property to enable the different computers to separately and properly compile your code.   Please see the following directions on how to set the svn:ignore parameter to ignore the .classpath file.

You will need to create your OWN client package, including its controller, view and model.   You can start by simply copying the existing client package code to your own packages (be sure to rename the package internally!) and modifying from there.

You may NOT change any of the provided code -- you will receive a commit error if you do so!

• You are to create 3 new ITasks that can be sent across the network from a client to a remote server to be executed.
• You may copy and modify the given view client code (in your own packages) to accommodate your new tasks.   You should not need to modify the server code.
• You must be able to run both the client and the server on your and your partner's machines:
  • Connecting client to server on the same machine
  • CConnecting client to server on different machines (either way on your and your partner's machines).

Note that the provided.compute package contains all the interfaces that BOTH the client and the server need to talk to each other.

Testing

Testing RMI programs can be tricky.   You can easily be fooled into thinking that your code runs properly if you test insufficiently.   In particular, if both ends of your test contain all the code, the remote dynamic class loading will not be tested.  Here's a more complete test:

• Create a separate project with the unmodified demo code in it.   Run the demo code's server and test your client against it.
• Be sure to do the above test across different machines!   This will test all aspects of your code.

Most Common Errors

• Firewall ports not open
• Launch configurations not set properly -- working directory not set.
• Editing the provided code

Grading Guidelines

1. The tasks must return a value whose type is NOT BigDecimal.   The tasks should return at least 2 different types of results.   - 30 pts
2. The tasks' results should be displayed on the client.  - 15 pts
3. The task must display some sort of status message on the server when it is run.  - 15 pts
4. The task should run properly when both the client and server are on the same machine.  - 15 pts
5. The task should run properly when the client and server are on different machines.   Test this between your and your partner's machines! - 25 pts

Note that the above requirements mean that you cannot change anything in provided.compute package!

© 2014 by Stephen Wong