Re: Selective commit

[Álvaro Martínez]

Hi, I'm running some issues on this one. I now create a new child data context on every situation. But I'm always getting the same deadlock. I can't figure out how to fix this from my own code. I've googled other people who also had a similar problem, but didn't help. This is the explanation from jConsole: Name: Timer-0 State: BLOCKED on [EMAIL PROTECTED] owned by: Timer-4 Total blocked: 3  Total waited: 68 Stack trace: org.apache.cayenne.event.DispatchQueue.dispatchEvent(DispatchQueue.java:54) org.apache.cayenne.event.EventManager.dispatchEvent(EventManager.java:336) org.apache.cayenne.event.EventManager.postEvent(EventManager.java:307) org.apache.cayenne.access.DataContext.fireDataChannelChanged(DataContext.java:1704) org.apache.cayenne.access.DataContextMergeHandler.graphFlushed(DataContextMergeHandler.java:114) sun.reflect.GeneratedMethodAccessor65.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) java.lang.reflect.Method.invoke(Method.java:597) org.apache.cayenne.util.Invocation.fire(Invocation.java:204) org.apache.cayenne.event.EventManager$Dispatch.fire(EventManager.java:397) org.apache.cayenne.event.DispatchQueue.dispatchEvent(DispatchQueue.java:162) org.apache.cayenne.event.DispatchQueue.dispatchEvent(DispatchQueue.java:58)    - locked [EMAIL PROTECTED] org.apache.cayenne.event.EventManager.dispatchEvent(EventManager.java:336) org.apache.cayenne.event.EventManager.postEvent(EventManager.java:307) org.apache.cayenne.access.DataContext.fireDataChannelCommitted(DataContext.java:1680) org.apache.cayenne.access.DataContext.flushToParent(DataContext.java:1247)    - locked [EMAIL PROTECTED] org.apache.cayenne.access.DataContext.onContextFlush(DataContext.java:1192) org.apache.cayenne.access.DataContext.onSync(DataContext.java:1167) org.apache.cayenne.access.DataContext.flushToParent(DataContext.java:1234)    - locked [EMAIL PROTECTED] org.apache.cayenne.access.DataContext.commitChanges(DataContext.java:1138) com.ptb.confignode.ConfigNode.newConfigGenerated(ConfigNode.java:711)    - locked [EMAIL PROTECTED] com.ptb.confignode.tasks.GenerateNewDistribution.run(GenerateNewDistribution.java:162) java.util.TimerThread.mainLoop(Timer.java:512) java.util.TimerThread.run(Timer.java:462) Name: Timer-4 State: BLOCKED on [EMAIL PROTECTED] owned by: Timer-0 Total blocked: 20  Total waited: 799 Stack trace: org.apache.cayenne.access.DataContextMergeHandler.graphChanged(DataContextMergeHandler.java:99) sun.reflect.GeneratedMethodAccessor69.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) java.lang.reflect.Method.invoke(Method.java:597) org.apache.cayenne.util.Invocation.fire(Invocation.java:204) org.apache.cayenne.event.EventManager$Dispatch.fire(EventManager.java:397) org.apache.cayenne.event.DispatchQueue.dispatchEvent(DispatchQueue.java:162) org.apache.cayenne.event.DispatchQueue.dispatchEvent(DispatchQueue.java:58)    - locked [EMAIL PROTECTED] org.apache.cayenne.event.EventManager.dispatchEvent(EventManager.java:336) org.apache.cayenne.event.EventManager.postEvent(EventManager.java:307) org.apache.cayenne.access.DataContext.fireDataChannelChanged(DataContext.java:1704) org.apache.cayenne.access.DataContext.onContextFlush(DataContext.java:1189) org.apache.cayenne.access.DataContext.onSync(DataContext.java:1167) org.apache.cayenne.access.DataContext.flushToParent(DataContext.java:1234)    - locked [EMAIL PROTECTED] org.apache.cayenne.access.DataContext.commitChanges(DataContext.java:1138) com.ptb.commons.db.services.StatsServices.addForClient(StatsServices.java:42) com.ptb.backendnode.tasks.DataMgrStatsCalculation.run(DataMgrStatsCalculation.java:78) java.util.TimerThread.mainLoop(Timer.java:512) java.util.TimerThread.run(Timer.java:462) Thanks! Michael Gentry escribió: Hi Álvaro, Creating a DataContext is a fairly cheap operation. I would suggest creating them as you need them and not try to optimize this operation at this point. If you run into bottlenecks in the future, then maybe look at other options, but there is a good chance that creating extra DataContexts will not be the source of a performance problem. /dev/mrg On Jan 7, 2008 10:30 AM, Álvaro Martínez <[EMAIL PROTECTED]> wrote: Thanks, Andrus and Philip The threads I'm talking about are created from many sources and for different reasons. Not of all them are triggered in response to "something". There are also watchers, periodic tasks... So I can't map data contexts to some particular condition. So then I have to create one data context per operation (that means a set of actions). Is this expensive? We are developing a heavy loaded cluster of servers, so it's important. Thanks again! Andrus Adamchik escribió: Hi Álvaro, It is hard to give a precise advice on multithreading without knowing the nature of your application. So here is a few general notes: * DataContext instance is your isolated area for making in-memory changes to objects that will all be committed at once. So consider using multiple contexts as appropriate. Cayenne docs recommend various common patterns, such as DataContext per session (i.e. each user has a dedicated context), DataContext per request, or DataContext per application (in a read-only app). You can also devise your own approach, if none of the above fit your needs. All you need to know here is that multiple threads *reading* from a shared DataContext is ok, but multiple threads *writing* to a shared DataContext is not ok. * In a rare case if you really need multiple threads to work off of the same context, consider using a dedicated nested DataContext for each atomic object modifications. Andrus On Jan 7, 2008, at 2:44 PM, Álvaro Martínez wrote: Hi, I've been working for a while with Cayenne but never realized I had a problem... until I got a weird exception. The fact is that I had been using context.newObject() and context.commitChanges() to create new rows in the database. But my application works with many threads, so global commits can (and in fact do) interrupt normal creation of objects. Thread A and Thread B are creating objects and filling their fields, but then B commits all and A throws a validation exception because mandatory fields are missing. How could I commit only one object? Thanks, Álvaro from Spain (Push the button Inc.)