Play Framework 2.5.4 Async Hibernate operations

Question

How can you use Akka to perform an operation on the db using Hibernate and not block the web client?

UPDATE:

Turns out the error was caused by the dao.get() method. I changed the start() method to take an actual object and not the id from the database and now I get no error, but nothing is happening(it gets stuck on em.merge() as I previously said).

public CompletionStage<Result> start(SomeObject object) {
    ExecutionContext ec = Akka.system().dispatchers().lookup("akka.actor.db-context");
    return CompletableFuture.supplyAsync(() -> doStuff(object), play.libs.concurrent.HttpExecution.fromThread(ec))
            .thenApply(i -> ok("Got result: " + i));
}

---

OUTDATED:

If I try something like:

@Transactional
public CompletionStage<Result> start(Long id) {
    ExecutionContext ec = Akka.system().dispatchers().lookup("akka.actor.db-context");
    return CompletableFuture.supplyAsync(() -> doStuff(dao.get(id)), play.libs.concurrent.HttpExecution.fromThread(ec))
            .thenApply(i -> ok("Got result: " + i));
}

Where doStuff only performs an entityManager.merge(), I get:

[CompletionException: org.hibernate.SessionException: Session is closed!]

or

[CompletionException: java.lang.IllegalStateException: EntityManager is closed]

When I use the code below to start the process above:

@Transactional
public Result mainMethod() {
    List<SomeObject> allObjects= dao.getAll();
    int size = allObjects.size();
    for(int i = 0; i < size; i++) {
        start(allObjects.get(i).getId());
    }
    return ok("Started");
}

Then the newly created threads(actors) get into an infinite loop when trying a database operation.

Thanks!

Complete stack trace:

play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[CompletionException: org.hibernate.SessionException: Session is closed!]] at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:280) at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:206) at play.api.GlobalSettings$class.onError(GlobalSettings.scala:160) at play.api.DefaultGlobal$.onError(GlobalSettings.scala:188) at play.api.http.GlobalSettingsHttpErrorHandler.onServerError(HttpErrorHandler.scala:98) at play.core.server.netty.PlayRequestHandler$$anonfun$2$$anonfun$apply$1.applyOrElse(PlayRequestHandler.scala:100) at play.core.server.netty.PlayRequestHandler$$anonfun$2$$anonfun$apply$1.applyOrElse(PlayRequestHandler.scala:99) at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:344) at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:343) at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32) at play.api.libs.iteratee.Execution$trampoline$.executeScheduled(Execution.scala:109) at play.api.libs.iteratee.Execution$trampoline$.execute(Execution.scala:71) at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:40) at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:248) at scala.concurrent.Promise$class.complete(Promise.scala:55) at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:153) at scala.concurrent.java8.FuturesConvertersImpl$P.accept(FutureConvertersImpl.scala:94) at scala.concurrent.java8.FuturesConvertersImpl$P.accept(FutureConvertersImpl.scala:89) at java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:760) at java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:736) at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474) at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1595) at play.core.j.HttpExecutionContext$$anon$2.run(HttpExecutionContext.scala:56) at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:39) at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:405) at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) Caused by: java.util.concurrent.CompletionException: org.hibernate.SessionException: Session is closed! at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1592) ... 7 common frames omitted Caused by: org.hibernate.SessionException: Session is closed! at org.hibernate.internal.AbstractSessionImpl.errorIfClosed(AbstractSessionImpl.java:133) at org.hibernate.internal.SessionImpl.setCacheMode(SessionImpl.java:1455) at org.hibernate.jpa.spi.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:1144) at org.hibernate.jpa.spi.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:1068) at daos.dao.get(dao.java:45) at controllers.DemoController.lambda$start$0(DemoController.java:195) at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590) ... 7 common frames omitted

LE:

Tried with:

ExecutionContext ec = Akka.system().dispatchers().lookup("akka.actor.db-context");
return CompletableFuture.supplyAsync(() -> jpa.withTransaction("default", true, ()-> doStuff(dao.get(id))), play.libs.concurrent.HttpExecution.fromThread(ec))
                .thenApply(i -> ok("Got result: " + i));

And I get the same error.

Answer 1

I solved it by using what @asch suggested:

Controller:

    @Inject
    private JPAApi jpa;
    [...]
    return CompletableFuture.supplyAsync(() -> jpa.withTransaction("default", false, ()-> doStuff(objectDAO.get(id))), play.libs.concurrent.HttpExecution.fromThread(ec))
                .thenApply(i -> ok("Got result: " + i));

And in the doStuff method class:

    private static final JPAApi jpaApi = Play.current().injector().instanceOf(JPAApi.class);
    [...]
    jpaApi.withTransaction(() -> {
        EntityManager em = jpaApi.em();
        em.merge(object);
    });
    [...]

Answer 2

The @Transactional annotation is on the synchronous method. I guess you need a transaction inside the async block. You can use for jpa method withTransaction instead of the annotation. Its signature (from Play java api)

/**
 * Run a block of code in a JPA transaction.
 *
 * @param name The persistence unit name
 * @param readOnly Is the transaction read-only?
 * @param block Block of code to execute
 * @param <T> type of result
 * @return code execution result
 */
public <T> T withTransaction(String name, boolean readOnly, Supplier<T> block);

It should be something like this:

1. Inject JPAApi in the controller:

   @Inject
   JPAApi jpa;
   

2. Implement async executor with call to jpa:

    jpa.withTransaction("default", true, ()->doStuff(dao.get(id)), play.libs.concurrent.HttpExecution.fromThread(ec))
       .thenApply(i -> ok("Got result: " + i)));
   

   Note the second argument true in the call to withTransaction is for readOnly operation (in your case).

3. Change the DAO class to use injected JPAAPi as well.