I have been attempting to get transactional access to a node when inserting
key/value pairs into a node's map. However, no matter what I do this does not
work for me.
I have three VMs running on a multiprocessor box that each contain an instance
of a cache. All three VMs are reading the same cache configuration file. VMs
1 and 2 are running client code that is putting a key/value pair in a HashMap.
The key is the same, so by using transactions I would like for one of the
clients to successfully "put" the key/value pair, and I would like the other VM
to recognize that the value has already been "put". VMs 1 and 2 are started as
close as possible to the same time in order to ensure that transaction locking
is occurring.
The code for VMs 1 and 2 is as follows:
| _cache.startService();
|
| // Sleep to ensure that cache start is finished (does no good).
| System.out.println("Sleeping...");
| Thread.sleep(10000);
| System.out.println("Done sleeping.");
|
| UserTransaction tx =
| new DummyUserTransaction(DummyTransactionManager.getInstance());
|
| try
| {
| tx.begin();
|
| if (! _cache.exists("aom", "key"))
| {
| System.out.println("Inside if...");
|
| Object last = _cache.put("aom", "key", _value);
| tx.commit();
|
| if (last != null)
| {
| System.out.println("Last was not null...");
| System.out.println(last);
|
| // tx.rollback();
| }
| else
| {
| System.out.println("Last was null...");
| }
| }
| else
| {
| System.out.println("already exists");
| }
| }
| catch (Throwable t)
| {
| t.printStackTrace(System.out);
| }
|
The 3rd VM is just a "listener", but it does not implement the
TreeCacheListener interface. It just prints out the key/value pairs of the
node that the other VMs are working with so I can determine which VM won in the
race I am creating. It prints out these values once every 30 seconds.
I start the listener VM first, and put an arbitrary key/value pair into the
node that every VM is using in order to make sure the node already exists.
Then I start the other two VMs as close to simultaneously as possible.
All three VMs get timeout exceptions, and neither VM 1 nor VM 2 place anything
in the map (one of them does sometimes but it is auto-rolled back because of
the timeout exception). VM 3 appears to hang sometimes when it locks the cache
to update VM 1 / VM 2 because only a single "locking" message appears for state
transition rather than one for each of the other VMs, but this does not happen
every time.
This is the listener VM's timeout stacktrace log:
| 00:07:27,584 ERROR [TreeCacheAop] method invocation failed
| org.jboss.cache.lock.TimeoutException: lock could not be acquired after
15000 ms. Lock map ownership Read lock owners: []
| Write lock owner: <devns02:34215>:3
|
| at
org.jboss.cache.lock.IdentityLock.acquireWriteLock(IdentityLock.java:146)
| at org.jboss.cache.Node.acquireWriteLock(Node.java:422)
| at org.jboss.cache.Node.acquire(Node.java:388)
| at org.jboss.cache.TreeCache.findNode(TreeCache.java:3295)
| at org.jboss.cache.TreeCache._put(TreeCache.java:2341)
| at org.jboss.cache.aop.TreeCacheAop._put(TreeCacheAop.java:611)
| at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
| at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
| at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
| at java.lang.reflect.Method.invoke(Method.java:324)
| at org.jgroups.blocks.MethodCall.invoke(MethodCall.java:223)
| at org.jboss.cache.TreeCache.prepare(TreeCache.java:2736)
| at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
| at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
| at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
| at java.lang.reflect.Method.invoke(Method.java:324)
| at org.jgroups.blocks.MethodCall.invoke(MethodCall.java:223)
| at
org.jboss.cache.interceptors.CallInterceptor.invoke(CallInterceptor.java:14)
| at
org.jboss.cache.interceptors.Interceptor.invoke(Interceptor.java:39)
| at
org.jboss.cache.interceptors.ReplicationInterceptor.replicate(ReplicationInterceptor.java:144)
| at org.jboss.cache.TreeCache._replicate(TreeCache.java:2674)
| at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
| at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
| at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
| at java.lang.reflect.Method.invoke(Method.java:324)
| at org.jgroups.blocks.MethodCall.invoke(MethodCall.java:223)
| at org.jgroups.blocks.RpcDispatcher.handle(RpcDispatcher.java:220)
| at
org.jgroups.blocks.RequestCorrelator.handleRequest(RequestCorrelator.java:615)
| at
org.jgroups.blocks.RequestCorrelator.receiveMessage(RequestCorrelator.java:512)
| at
org.jgroups.blocks.RequestCorrelator.receive(RequestCorrelator.java:326)
| at
org.jgroups.blocks.MessageDispatcher$ProtocolAdapter.handleUp(MessageDispatcher.java:722)
| at
org.jgroups.blocks.MessageDispatcher$ProtocolAdapter.access$300(MessageDispatcher.java:554)
| at
org.jgroups.blocks.MessageDispatcher$1.run(MessageDispatcher.java:691)
| at java.lang.Thread.run(Thread.java:534)
| 00:07:27,588 ERROR [RpcDispatcher] failed invoking method
| org.jboss.cache.lock.TimeoutException: lock could not be acquired after
30000 ms. Lock map ownership Read lock owners: []
|
My question is why is this happening? The code above takes way less time to
execute than the configured 15 seconds for a timeout (I even tried it at a
higher value), and the 3rd VM should only have an issue if it is in one of its
"read" cycles (and I am making sure it is not).
The cache configuration sets the isolation level to SERIALIZABLE and the
replication method to REPL_SYNC.
Any help/other ideas would be readily accepted...
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