Java Message passing among threads

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Im new to Java and have been stuck on an issue with respect to thread message passing. What i mean here is- I have 4 threads, one thread reads msg from network and based on type of msg passes on the msg to either parser thread or database thread . Database thread performs some operation and has to send msg back to the first network thread which puts it into socket. Similarly, the parser thread also performs some action and based on result either has to send msg back to network thread or database thread. Things i have tried-

  1. I have read about notify() wait() for thread communication which does not help in my case as i need one to one msg passing its not braodcast all
  2. I have read about concurrentqueues blockingqueues - Since this is not an ideal producer consumer problem where one thread is producing msgs and other threads reading from it- i cannot use this. Using this would be like i need to have 5 queues for each communication channel
network->db,
db->network,
parser->network,
parser->db

Is this efficient to go about?

In c++ i was using msging mechanism where i used to just post msg(windows msg) to corresponding thread's msg pool and that thread in its msging pool, would fetch it

Is there any mechanism like message passing in java which i could use?

message-queue multithreading java
1 Answers

one thread reads msg from network and based on type of msg passes on the msg to ...database thread. Database thread performs some operation and has to send msg back to the first network thread which puts it into socket.

You're making the "network" thread responsible to wait for messages from the network, and also, to wait for messages from the "database" thread. That's awkward. You may find it somewhere between mildly difficut and impossible to make that happen in a clean, satisfying way.

My personal opinion is that each long-lived thread in a multi-threaded program should wait for only one thing.

What is the reason for having the database thread "send msg back to the first network thread [to be put] into socket?" Why can't the database thread itself put the message into the socket?

If there's a good reason for the database not to send out the message, then why can't "put the message into the socket" be a task that your database thread submits to a thread pool?

I have read about notify() wait() for thread communication which does not help in my case

Would a BlockingQueue help?

I have read about concurrentqueues blockingqueues - Since this is not an ideal producer consumer problem where one thread is producing msgs and other threads reading from it- i cannot use this. Using this would be like i need to have 5 queues for each communication channel.

And? If adding more queues or more threads to a program makes the work that those threads do simpler or makes the explanation of what those queues are for easier to understand, would that be a Bad Thing?

Note about wait() and notify(). Those are low-level methods that are meant to be used in a very specific way to build higher-level mechanisms. I don't know whether the standard Java BlockingQueue implementations actually does use wait() and notify() but it would not be hard to implement a BlockingQueue that actually did use that mechanism. So, if BlockingQueue solves your problem, then that means wait() and notify() solve your problem. You just didn't see the solution.

In fact, I would be willing to bet that wait() and notify() can be used to solve any problem that requires one thread to wait for another. It's just a matter of seeing what else you need to build around them.

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