从线程内部调用时，Spring数据存储库查找方法挂起

Question

I want to call a find method from a repository and somehow it is blocking the thread and never returns.

We use spring data to create repositories.

I have a test case with this code:

Thread t = new Thread(() -> {
    repository.findById(1); // this line blocks the thread
}
t.start();
t.join();

The repository implementation is standard, it works correctly when called from the main thread.

I noticed that spring uses a thread local that contains the current open session. So I tried to bind a new session in the new thread with this code:

EntityManager em = entityManagerFactory.createEntityManager();
EntityManagerHolder emHolder = new EntityManagerHolder(em);
TransactionSynchronizationManager.bindResource(entityManagerFactory, emHolder);

But it didn't work, the repository call still blocks.

So I tried to use the newly created EntityManager to find a record from the database using the TransactionTemplate like so:

TransactionTemplate template = new TransactionTemplate(transactionManager);
template.execute((TransactionCallback<Object>) status ->
                emHolder.getEntityManager().find(User.class, updated.getId()));

But it did't work either, the find method blocks the thread as well.

Do you know what a may be doing wrong? Or is it a bug?

Answer 1

I found the problem.

We were using hsqldb as embedded database in tests and that was the problem.

It hangs when we try to run a select query from a thread. I think it can't handle multiple connections properly, but I didn't go deep into that.

I just changed the database to h2 and it worked.