I've written a unit test which seems to demonstrate that the Repeatable Read
semantics are not being followed for PojoCache under 1.4.0.BETA2. Even though
the test uses DummyTransactionManager, I understand that the locking semantics
should still be correct.
In summary, I create two threads, each with their own PojoCache instance, but
in the same cluster. The 1st thread reads a value from the cache within a
transaction, the 2nd thread then writes a new value under that FQN, and the 1st
thread then re-reads the value (within the original transaction), and gets a
non-repeatable read, i.e. the value as written by thread 2.
When I read the source code for PojoCache, I see that explicit locks are
acquired for a putObject() or removeObject(), but not for getObject().
Is this a flaw, or am I mis-understanding the applicability of isolation level
within this context? It doesn't seem to follow ACID semantics.
Anyway, here's the test case, plus the cache config file:
| package test;
|
| import java.io.InputStream;
| import java.util.concurrent.Callable;
| import java.util.concurrent.CountDownLatch;
| import java.util.concurrent.ExecutorService;
| import java.util.concurrent.Executors;
|
| import junit.framework.TestCase;
|
| import org.apache.commons.logging.Log;
| import org.apache.commons.logging.LogFactory;
| import org.jboss.cache.PropertyConfigurator;
| import org.jboss.cache.aop.PojoCache;
|
| public class RepeatableReadTest extends TestCase {
|
| private final CountDownLatch startSignal = new CountDownLatch(1);
| private final CountDownLatch doneSignal = new CountDownLatch(2);
|
| private final CountDownLatch signalA = new CountDownLatch(1);
| private final CountDownLatch signalB = new CountDownLatch(1);
|
| private final ExecutorService executor =
Executors.newCachedThreadPool();
|
| @Override
| protected void tearDown() throws Exception {
| executor.shutdownNow();
| }
|
| public void test() throws Exception {
| Log log = LogFactory.getLog(getClass());
|
| log.info("Creating and starting worker threads");
| executor.submit(new Worker1());
| executor.submit(new Worker2());
|
| log.info("Seeding cache with initial value for /test");
| PojoCache cache = createCache();
| cache.putObject("/test", "value1");
|
| startSignal.countDown();
| doneSignal.await();
| }
|
| class Worker1 implements Callable {
| private final PojoCache cache = createCache();
| private Log log = LogFactory.getLog(getClass());
|
| public Object call() throws Exception {
| startSignal.await();
|
| log.info("Beginning new tx and reading value");
| cache.getTransactionManager().begin();
| log.info("Cache contains value for /test : " +
cache.getObject("/test"));
|
| log.info("Sending signal to thread 2");
| signalA.countDown();
|
| log.info("Waiting for signal from thread 2");
| signalB.await();
|
| log.info("Cache contains value for /test : " +
cache.getObject("/test"));
|
| log.info("Done");
| doneSignal.countDown();
|
| return null;
| }
| }
|
| class Worker2 implements Callable {
| private final PojoCache cache = createCache();
| private Log log = LogFactory.getLog(getClass());
|
| public Object call() throws Exception {
| startSignal.await();
|
| log.info("Waiting for signal from thread 1");
| signalA.await();
|
| log.info("Starting new tx and writing new value for
/test");
| cache.getTransactionManager().begin();
| cache.putObject("/test", "value2");
|
| log.info("Committing");
| cache.getTransactionManager().commit();
|
| log.info("Sending signal to thread 1");
| signalB.countDown();
|
| log.info("Done");
| doneSignal.countDown();
|
| return null;
| }
| }
|
| private PojoCache createCache() throws RuntimeException {
| try {
| PojoCache cache = new PojoCache();
| InputStream configStream =
getClass().getResourceAsStream("cache-service.xml");
| new PropertyConfigurator().configure(cache,
configStream);
|
| cache.setClusterName(getName());
|
| cache.start();
| return cache;
| } catch (Exception ex) {
| throw new RuntimeException(ex);
| }
| }
| }
|
And now the config:
| <?xml version="1.0" encoding="UTF-8"?>
|
| <!-- =====================================================================
-->
| <!--
-->
| <!-- Sample TreeCache Service Configuration
-->
| <!--
-->
| <!-- =====================================================================
-->
|
| <server>
|
| <!--
==================================================================== -->
| <!-- Defines TreeCache configuration
-->
| <!--
==================================================================== -->
|
| <mbean code="org.jboss.cache.aop.PojoCache"
| name="test:service=PojoCache">
|
| <depends>jboss:service=Naming</depends>
| <depends>jboss:service=TransactionManager</depends>
|
| <!--
| Configure the TransactionManager
| -->
| <attribute
name="TransactionManagerLookupClass">org.jboss.cache.GenericTransactionManagerLookup</attribute>
|
| <!--
| Isolation level : SERIALIZABLE
| REPEATABLE_READ (default)
| READ_COMMITTED
| READ_UNCOMMITTED
| NONE
| -->
| <attribute name="IsolationLevel">REPEATABLE_READ</attribute>
|
| <!--
| Valid modes are LOCAL
| REPL_ASYNC
| REPL_SYNC
| INVALIDATION_ASYNC
| INVALIDATION_SYNC
| -->
| <attribute name="CacheMode">REPL_SYNC</attribute>
|
| <!--
| Just used for async repl: use a replication queue
| -->
| <attribute name="UseReplQueue">false</attribute>
|
| <!--
| Replication interval for replication queue (in ms)
| -->
| <attribute name="ReplQueueInterval">0</attribute>
|
| <!--
| Max number of elements which trigger replication
| -->
| <attribute name="ReplQueueMaxElements">0</attribute>
|
| <!-- Name of cluster. Needs to be the same for all clusters, in
order
| to find each other
| -->
| <attribute name="ClusterName">TestCache</attribute>
|
| <!-- JGroups protocol stack properties. Can also be a URL,
| e.g. file:/home/bela/default.xml
| <attribute name="ClusterProperties"></attribute>
| -->
|
| <attribute name="ClusterConfig">
| <config>
| <!-- UDP: if you have a multihomed machine,
| set the bind_addr attribute to the appropriate NIC IP
address, e.g bind_addr="192.168.0.2"
| -->
| <!-- UDP: On Windows machines, because of the media sense
feature
| being broken with multicast (even after disabling media
sense)
| set the loopback attribute to true -->
| <UDP mcast_addr="228.1.2.3" mcast_port="48866"
| ip_ttl="64" ip_mcast="true"
| mcast_send_buf_size="150000" mcast_recv_buf_size="80000"
| ucast_send_buf_size="150000" ucast_recv_buf_size="80000"
| loopback="false"/>
| <PING timeout="2000" num_initial_members="3"
| up_thread="false" down_thread="false"/>
| <MERGE2 min_interval="10000" max_interval="20000"/>
| <!-- <FD shun="true" up_thread="true"
down_thread="true" />-->
| <FD_SOCK/>
| <VERIFY_SUSPECT timeout="1500"
| up_thread="false" down_thread="false"/>
| <pbcast.NAKACK gc_lag="50"
retransmit_timeout="600,1200,2400,4800"
| max_xmit_size="8192" up_thread="false"
down_thread="false"/>
| <UNICAST timeout="600,1200,2400" window_size="100"
min_threshold="10"
| down_thread="false"/>
| <pbcast.STABLE desired_avg_gossip="20000"
| up_thread="false" down_thread="false"/>
| <FRAG frag_size="8192"
| down_thread="false" up_thread="false"/>
| <pbcast.GMS join_timeout="5000" join_retry_timeout="2000"
| shun="true" print_local_addr="true"/>
| <pbcast.STATE_TRANSFER up_thread="true" down_thread="true"/>
| </config>
| </attribute>
|
|
| <!--
| Whether or not to fetch state on joining a cluster
| NOTE this used to be called FetchStateOnStartup and has been
renamed to be more descriptive.
| -->
| <attribute name="FetchInMemoryState">true</attribute>
|
| <!--
| The max amount of time (in milliseconds) we wait until the
| initial state (ie. the contents of the cache) are retrieved from
| existing members in a clustered environment
| -->
| <attribute name="InitialStateRetrievalTimeout">15000</attribute>
|
| <!--
| Number of milliseconds to wait until all responses for a
| synchronous call have been received.
| -->
| <attribute name="SyncReplTimeout">15000</attribute>
|
| <!-- Max number of milliseconds to wait for a lock acquisition -->
| <attribute name="LockAcquisitionTimeout">10000</attribute>
|
| <!-- Name of the eviction policy class. -->
| <attribute name="EvictionPolicyClass"></attribute>
|
| <!--
| Indicate whether to use region based marshalling or not. Set this
to true if you are running under a scoped
| class loader, e.g., inside an application server. Default is
"false".
| -->
| <attribute name="UseRegionBasedMarshalling">true</attribute>
| </mbean>
| </server>
|
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