java - Hibernate, Multithreading and CascadeType.ALL -

in multithreaded environment,

this works

box box = new box("b"); toy t1 = box.addnewtoy("t1"); toy t2 = box.addnewtoy("t2"); synchronized (em) {     em.gettransaction().begin();     em.persist(t1);     em.gettransaction().commit(); } synchronized (em) {     em.gettransaction().begin();     em.persist(t2);     em.gettransaction().commit(); } 

but doesn't

box box = new box("b"); toy t1 = box.addnewtoy("t1"); synchronized (em) {     em.gettransaction().begin();     em.persist(t1);     em.gettransaction().commit(); } toy t2 = box.addnewtoy("t2"); synchronized (em) {     em.gettransaction().begin();     em.persist(t2);     em.gettransaction().commit(); } 

i errors like: "object references unsaved transient instance", "a different object same identifier value associated session"

any ideas?

here minimal maven project reproduces problem: http://www.2shared.com/file/bglmj6ao/example.html

details

java version "1.7.0_17", hibernate 4.2.3.final, ubuntu 11.04 natty, sqlite

class toy {     @manytomany(mappedby="toys",fetch = fetchtype.lazy, cascade = cascadetype.all)     public list<box> getboxes() { return boxes; }      public void setboxes(list<box> boxes) { this.boxes = boxes; } }  class box {     @manytomany(fetch = fetchtype.lazy, cascade = cascadetype.all)     public list<toy> gettoys() { return toys; }      public void settoys(list<toy> toys) { this.toys = toys; }      public toy addnewtoy(string name) {         toy toy = new toy();         toy.setname(name);         toy.boxes.add(this);         toys.add(toy);         return toy;     } } 

a entitymanagerfactory expensive-to-create, threadsafe object intended shared application threads. created once, on application startup.

an entitymanager inexpensive, non-threadsafe object should used once, single business process, single unit of work, , discarded. ...

see: http://docs.jboss.org/hibernate/entitymanager/3.6/reference/en/html_single/#transactions-basics

i'm not sure you're doing if you're using same static entitymanager multiple threads that's problem.

the entitymanagerfactory thread-safe object want share, should create new entitymanager each request/unit of work being performed.