Status: New
Owner: ----
New issue 739 by h...@anthologique.net: Guice-persist: Injection of
EntityManager outside a UnitOfWork can lead to never closed EntityManagers
http://code.google.com/p/google-guice/issues/detail?id=739
Form the commit rb7a02b02d81c (Jul 7, 2011), in JpaPersistService.java
which is a Provider<EntityManager>, in the get() method, we can see that if
we don't already have an EntityManager stored in the thread local variable,
we call the begin() method. This method will create a new EntityManager,
and store it in the thread local variable.
So, if we follow the documentation in the wiki (page "Using JPA",
section "Using the EntityManager inside transactions"), for each thread,
for every other action needing an EntityManager, the same instance will
always be returned, and this EntityManager will never be closed.
This can lead to broken threads, as if for any reason the EntityManager can
no longer be used (connection closed, etc.), there is no way to replace it.
Note that this issue doesn't happen if the injection of EntityManager is
done inside an opened UnitOfWork or inside a method annotated with
@Transactional. In these cases, the EntityManager is already created, and
will be destroyed at the end of the transaction, or on UnitOfWork close.
While taking a look at the get() method of JpaPersistService, we can also
see that there is a strange precondition test. As said, if the
EntityManager doesn't exist, it's created. Juste after that, we check if we
have an EntityManager. If we don't have any, we throw this error
message: "Requested EntityManager outside work unit.". Sounds like a bug,
we should either remove the Precondition test, or remove the begin() call
if the EntityManager doesn't exist.
So, my suggestion would be either to fix the get() method, or change the
documentation to tell about this potential issue, and suggest the injection
of Provider<EntityManager> in every cases.
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