3.7. Resource sharing

When the same transactional resource is used to interleave multiple transactions, the application server must ensure that only one transaction is enlisted with the resource at any given time. To initiate the transaction commit process, the transaction manager is allowed to use any of the resource objects connected to the same resource manager instance. The resource object used for the two-phase commit protocol does not need to have been involved with the transaction being completed.

The resource adapter must be able to handle multiple threads invoking the XAResource methods concurrently for transaction commit processing. This is illustrated in Example 3.1, “Resource sharing example”.

Example 3.1. Resource sharing example

XAResource xares = r1.getXAResource();

xares.start(xid1); // associate xid1 to the connection

..
xares.end(xid1); // disassociate xid1 to the connection
..
xares.start(xid2); // associate xid2 to the connection
..
// While the connection is associated with xid2,
// the TM starts the commit process for xid1
status = xares.prepare(xid1);
..
xares.commit(xid1, false);

A transactional resource r1. Global transaction xid1 is started and ended with r1. Then a different global transaction xid2 is associated with r1. Meanwhile, the transaction manager may start the two phase commit process for xid1 using r1 or any other transactional resource connected to the same resource manager. The resource adapter needs to allow the commit process to be executed while the resource is currently associated with a different global transaction.