Yep the only problem is that users of the API will have to manually move
objects between DataContexts, so they will have to know what to do.
I spend this whole day to rewrite the API and pass a datacontext for
every call.
So I let developers manage their datacontexts.
thanks.
Mike Kienenberger wrote:
> Why not create a new DataContext when you need to do write operations?
>
> On 3/25/08, Laurent Marchal <lmarcha..maeur.com> wrote:
>
>> Hi all !
>>
>> I spent some time searching documentation about the thread-safety status
>> of DataContext, i found some answers on this mailing list but i would
>> like to know some details :
>>
>> I have a big application (Eclipse RCP based) which monitors a database,
>> so i have to poll the database each 10 seconds.
>> To be simple i have a single DataContext in my App in :
>> Session->getDataContext() and i created an API that look like
>>
>> public static List<User> getAll()
>> {
>> SelectQuery q = new SelectQuery(User.class);
>> try {
>> return (List<User>)Session.getDataContext().performQuery(q);
>> } catch(CayenneRuntimeException e {
>> //manage exception
>> }
>> }
>>
>> So everywhere the API use a single DataContext no bound to a thread.
>>
>> Naturally to be reactive the application fetch the data from the
>> database in a background thread (actually there is one background thread
>> for each view in the application), and what i've seen is that read
>> operations are thread-safe within a DataContext so i don't care and all
>> threads use the API and so the same DataContext.
>>
>> Here comes the complex part : I need this single DataContext to have a
>> good cache in my app, and because the application is 90% visualization
>> and only 10% modifications, so i just had to find a thread-safe
>> workaround for writing data.
>> I tried some solutions :
>> - Bind a DC per thread is not a good solution because all my fetching is
>> in background threads so the main Session DC (in the UI thread) is never
>> updated.
>> - I have tried to create a childDataContext bound to the current thread
>> for writing, but i had some strange behaviors, and i don't know if the
>> flushToParent() is thread safe ?
>>
>> So i would like to know if the new LifecycleListener can be used to
>> "lock" the DataContext while writing, to have a single thread-safe R/W
>> DataContext like :
>>
>> dataContext.getEntityResolver().getCallbackRegistry().addDefaultListener(new
>> LifecycleListener(){
>>
>> Lock lock = new ReentrantLock();
>>
>> public void postPersist(Object entity) {
>> lock.unlock();
>> }
>> public void postRemove(Object entity) {
>> lock.unlock();
>> }
>> public void postUpdate(Object entity) {
>> lock.unlock();
>> }
>> public void prePersist(Object entity) {
>> lock.lock();
>> }
>> public void preRemove(Object entity) {
>> lock.lock();
>> }
>> public void preUpdate(Object entity) {
>> lock.lock();
>> }
>> });
>>
>> Do you think it can be a good solution ?
>>
>> Thanks.
>>
>>
>> Laurent Marchal.
>>
>>
>
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