On 1/9/18 11:50 AM, Phil Steitz wrote: > 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.
I just noticed another thing in [pool] that might have something to do with this. It's probably best to investigate what I have in mind on the dev list. I will post a summary / ticket reference here if it turns out I this is a bug. Phil > > 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
