Q: how the node know the binary name of Class A and UUID of client? So, node should send request to server? what I am thinking is a sever is responsible to distribute tasks.
As you rightly stated, when the driver sends tasks to the node, it also sends, as a part of the message header, the UUID of the client that submitted them. This UUID is then set onto the JPPF classloader. In fact, there will be a class loader instance for each client UUID.
Note that for the communication channel that handles the tasks, it is the server that sends a request to the node, and the node sends a response back.
Then, when deserializing or executing the task, the class loader will need to load some classes. The binary name of a class is computed from the class name (for instance "my.package.MyClass" is transformed into the resource name "my/package/MyClass.class"). When a class is loaded the first time by a class loader, it is its findClass()
method that is in charge of finding the class definition (in the classpath) and load it into the JVM (see the doc for the native method ClassLoader.defineClass()
). The JPPF class loader overrides the findClass() method so that the class definition is loaded from the client over the network, instead of in the node's local classpath. Thus, for the class loader channel, it is the node that sends the request, and the driver that sends the response back.
Some of this is explained in the Networking considerations
section of the JPPF Iverview.
Q:you mentioned class definition(byte code) what kind of form for loading the class definition? the byte stream reading from class files? if so, can I save the class definition on node side by using class files
Yes, we read the byte from the class file and send it over to the node. In theory it is possible to save the definition into a file on the node side, however we do not provide any API to do this, because this would interfere with the dynamic class reloading (if there is a new version of the class it will be loaded automatically). If you want the classes permanently on the node side, you have to deploy them manually.
Q: what a simple API call you hidden. could you show me some details
Using the JPPF APIs to submit a job, like JPPFClient.submit()
, will automatically trigger the class loading mechanism. For the details of how it is done, I invite to to look at the code of the classes in the package org.jppf.client
, and in particular how the classes JPPFClient
interact with each other. The code is accessible from our SVN repository at this location: http://jppf-project.svn.sourceforge.net/viewvc/jppf-project