Java APIs

RMI is concurrent Rabi,

it will make the threads automatically. If parts of your called implementation are not threadsafe, you should synchronize the critical regions. In general it is poor form to synchronize the remote method itself. (It can too easily lead to long backlogs at best, and deadlocks at worst)

John

ok thanks Cajo, I suspected it was from looking at the Bind code statement as you have to type new i just wanted confirmation. In terms of critical regions such as a common buffer store of data and a published file of data these would be best served as a seperate class, is that one way of doing it?

Yes, a separate class is certainly a valid technique to accomplish this.

More simply might be to have remoted methods call synchronizied non-remote methods of the same class, to perform the non-thread safe operations.

[url https://cajo.dev.java.net/index.html]John

Hi,

well cajo can you explain to me in a example what u mean by
- have remoted methods call synchronizied non-remote methods of the same class, to perform the non-thread safe operations.

Thanks.
Clement

No problem Clement,

Let's suppose you have this implementation for a remotely accessible object:

public class Foo ... {
   public void bar(...); { // this is a remotely callable method

      // do some non-critical, i.e. threadsafe stuff ...

      if (condition) // perhaps based on a condition, or not
         baz(...);   // this is a cricial section

      // maybe do some final non-critical stuff ...

   }
   protected synchronized void baz(...) { // this is not remotely callable
      // it doesn't really need to be protected, but looks better that way
      // do the critical, i.e. non-threadsafe operations here ...
   }
}

Hope this makes sense.

Hi John,

Hmm, I just want to confirm with you if my understanding is correct.
I am doing some kind of booking system.
I am doing the implementation in RMI.

First i have a client to login and this properbly will be handled by the ConnectionManager and then it will keep track of all clients (regardless of whether it is a user / adminstrator).
Then if the client wants to book a ticket, all the bookings will be handled by the BookingManager.

That means the client will be in the non-critical section unless the BookingManager assigns a key to the client to access the critical section. So in this case there will be only one client doing the booking, am i right?

But what i dun understand is how threads can be used in this case.
Can you enlighten me?
Thanks.

Clement

Hello Clement,

When you expose an object for remote access, the underlying RMI framework will each calling client its own thread automatically. If you synchronize the exposed method(s), only one client will be allowed in at a time, this can create large backlogs, and even connection rejects, in a busy system.

In most objects, very little of its code is really not threadsafe. A booking in your case, would not be threadsafe, i.e. you don't want two clients to get the identical booking, whereas the booking manager, generally would be threadsafe. Generally speaking, the more agressively you minimize your critical regions, the better the overall system performance, under high loading.

John