Question

I’m trying to exclude two reading threads from read the same record via hibernate. My SSCCE is as above, but both threads can read the object, while i was expecting that Thread-2 will throw an Exception.

The Store class is my one to create Sessions easily.

I’m testing now with HSQLDB, maybe there is no locking available ?

Update Did what Augusto propose, but still the same. Thread-2 should throw an Exception (?)

        new Thread(new Runnable() { // Thread-1

            @Override
            public void run() {
                Session ses = Store.$.ses();
                Object x = ses.load(Client.class, 1l,
                        new LockOptions(LockMode.PESSIMISTIC_WRITE));
                System.err.println("T1 :"+(x==null));
                try {
                    Thread.sleep(10000);
                } catch (InterruptedException ex) {
                }
                ses.close();
            }
        }).start();

        Thread.yield();

        new Thread(new Runnable() { // Thread-2

            @Override
            public void run() {
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException ex) {
                }
                Session ses = Store.$.ses();
                Object x = ses.load(Client.class, 1L,
                        new LockOptions(LockMode.PESSIMISTIC_WRITE).setTimeOut(1));
                System.err.println("T2 :"+(x==null));
                ses.close();
            }
        }).start();

---

Output:

T1: false
t2: false

Answer 1

LockMode.Read is a shared lock, so all the reads with that lock mode will be able to read from the same source without blocking.

I think that what you want is an exclusive lock, which uses the LockMode.PESSIMISTIC_WRITE. And HSQLDB supports this type of lock (docs)

I would also add Thread.yield() between the two threads, to allow the first one to actually start, otherwise the 2nd thread might start before the 1st one you defined.

---

I don’t think HSQLDB has a lock timeout, and thus throw an exception when a thread is waiting for a lock for more a given amount of time. What you’ll see is that the ses.load in T2 will always happen after the ses.close from t1.

If you have a mysql database at hand, you can update the configuration with innodb_lock_wait_timeout = 2 which will cause the DB to throw a lock timeout after 2 seconds.