Java：许多线程中的XA事务传播

Question

How can I use a transaction manager (such as Bitronix , JBoss TS or Atomikos ) in a Java SE (not Java EE or Spring) to support the following use case:

Let's assume we have the following class:

public class Dao {

    public void updateDatabase(DB db) {
        connet to db
        run a sql
    }

}

and we create a Java Runnable from that, like the following:

public class MyRunnable extends Runnable {

    Dao dao;
    DB db;

    public MyRunnable(Dao dao, DB db) {
        this.dao=dao;
        this.db = db;
    }           

    public run() throws Exception {
        return dao.updateDatabase(db);
    }
}

Now in our Service layer, we have another class:

public class Service {

    public void updateDatabases() {

        BEGIN TRANSACTION;

        ExecutorService es = Executors.newFixedThreadPool(10);

        ExecutorCompletionService ecs = new ExecutorCompletionService(es);

        List<Future<T>> futures = new ArrayList<Future<T>>(n);

        Dao dao = new Dao();

        futures.add(ecs.submit(new MyRunnable(dao, new DB("db1")));
        futures.add(ecs.submit(new MyRunnable(dao, new DB("db2")));
        futures.add(ecs.submit(new MyRunnable(dao, new DB("db3")));

        for (int i = 0; i < n; ++i) {
            completionService.take().get();
        }

       END TRANSACTION;
    }

}

And the client can be a Servlet or any other multi-threaded environment:

public MyServlet extend HttpServlet {

    protected void service(final HttpServletRequest request, final HttpServletResponse response) throws IOException {

        Service service = new Service();

        service.updateDatabases();

    }

}

What would be the correct code for BEGIN TRANSACTION and END TRANSACTION parts? Is this even feasible? If not, what needs to be changed? The requirements is to keep the updateDatabases() method concurrent (since it will be accessing multiple databases at the same time) and transactional.

Answer 1

Seems like this can be done using Atomikos using SubTxThread

//first start a tx
TransactionManager tm = ...
tm.begin();

Waiter waiter = new Waiter();

//the code that calls the first EIS; defined by you
SubTxCode code1 = ...

//the associated thread
SubTxThread thread1 = new SubTxThread ( waiter , code1 );

//the code that calls the second EIS; defined by you
SubTxCode code2 = ...

//the associated thread
SubTxThread thread2 = new SubTxThread ( waiter , code2 );

//start each thread
thread1.start();

thread2.start();

//wait for completion of all calls
waiter.waitForAll();

//check result
if ( waiter.getAbortCount() == 0 ) {
    //no failures -> commit tx
    tm.commit();
} else {
    tm.rollback();
}

Answer 2

XA Specification mandates that all XA calls be executed in the same thread context. To elaborate on the reason for this its because the commit could be called before any of the transactional branches are even created in your threads.

if you are just interested in how to execute those three calls in a XA transaction in JBoss TS

First make sure your -ds.xml specifies your datasource as an <xa-datasource>

InitialContext ctx = new InitialContext(parms);
UserTransaction ut = (UserTransaction) ctx.lookup("java:comp/UserTransaction");

ut.begin();

//Some Transactional Code

ut.commit();

Keep in mind with the code above you would not be able to use the ExecutorService to parallelize the calls.

Side Note: I don't know a lot about it but JTS/OTS claims to allow multiple threads to share in a transaction. I think it does this by propagating transactional context similar to ws-coordination/ws-transaction and is supported by JBossTS. Could be a red herring, but if your not under a time crunch it might be worth researching.

Answer 3

How about you

1. BEGIN_TRANSATION: Connect to all 3 databases in your Service,
2. pass the Connection objects (instead of db object) to MyRunnable
3. END_TRANSACTION: invoke commit and close on all 3 connections in your Service