On 1/8/18 4:23 PM, Shawn Heisey wrote: > On 11/22/2017 5:00 PM, Phil Steitz wrote: >> If the problem is the evictor closing a connection and having that >> connection delivered to a client, the problem is almost certainly in >> pool. The thread-safety of the pool in this regard is engineered in >> DefaultPooledObject, which is the wrapper that pool manages and >> delivers to DBCP. When the evictor visits a PooledObject (in >> GenericObjectPool#evict) it tries to start the eviction test on the >> object by calling its startEvictionTest method. This method is >> synchronized on the DefaultPooledObject. Look at the code in that >> method. It checks to make sure that the object is in fact idle in >> the pool. The other half of the protection here is in >> GenericObjectPool#borrowObject, which is what PoolingDataSource >> calls to get a connection. That method tries to get a PooledObject >> from the pool and before handing it out (or validating it), it calls >> the PooledObject's allocate method. Look at the code for that in >> DefaultPooledObject. That method (also synchronized on the >> PooledObject) checks that the object is not under eviction and sets >> its state to allocated. That is the core sync protection that >> *should* make it impossible for the evictor to do anything to an >> object that has been handed out to a client. > I see the synchronization you're talking about here. It appears that > all of the critical methods in DefaultPooledObject are synchronized (on > the object). > > If you're absolutely certain that DefaultPooledObject is involved with > all of the implementation my code is using, it all looks pretty complete > to me.
Yes, the code you posted at the top of the thread uses a PoolableConnectionFactory as the object factory for the pool. You can see that PCF's makeObject returns a DefaultPooledObject, so that much is certain. > So I'm really curious as to why the connection is getting > closed. I have seen the problem only minutes after restarting my > program, so it seems unlikely that the server side is closing the > connection, since the timeout for that is 8 hours. I looked back at the initial stack trace and I noticed something that I had not noticed before. This line org.apache.commons.dbcp2.DelegatingConnection.createStatement(DelegatingConnection.java:262) means that checkOpen() succeeded. That, combined with your statement above that isClosed() returns true on a failed connection means that there might be concurrent access to the DelegatingConnections happening. It looks like the sequence might have been: thread 1: checkOpen - sees true thread 2: close the DelegatingConnection (there is no sync to prevent this) thread1 : createStatement - bang! thread1 : isClosed() returns true DBCP is not really safe to use that way - i.e., really the intended setup is that individual connection handles are not concurrently accessed by multiple threads. Is it possible something like this is going on? Note that what I am talking about here is two different threads holding references to the same connection handle - i.e., no trips back through the pool. Phil > > I did add the code a while back to test on create, borrow, return, and > while idle, but it turns out that I hadn't actually pulled it down to > the test server and recompiled. That is now done, so we'll see if that > makes any difference. > > If testing the connection on pool actions does make a difference, then > what is your speculation about what was happening when I ran into the > closed connection only minutes after restart, and would it be worthy of > an issue in Jira? The only theory I had was a race condition between > eviction and borrowing, but unless there's something amiss in how all > the object inheritance works out, it looks like that's probably not it. > Some kind of issue with the TCP stack in Linux (either on the machines > running my code or the MySQL server) is the only other idea I can think > of. Or maybe a hardware/firmware issue, since it's likely that at least > one of the NICs involved is doing TCP offload. I think that virtually > every NIC in our infrastructure has that feature and that Linux enables it. > > Thanks, > Shawn > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: user-unsubscr...@commons.apache.org > For additional commands, e-mail: user-h...@commons.apache.org > > --------------------------------------------------------------------- To unsubscribe, e-mail: user-unsubscr...@commons.apache.org For additional commands, e-mail: user-h...@commons.apache.org
