NioSocketConnector leaks the last open NioSocketSession after close
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Key: DIRMINA-827
URL: https://issues.apache.org/jira/browse/DIRMINA-827
Project: MINA
Issue Type: Bug
Components: Core
Affects Versions: 2.0.2
Environment: Windows 7/Solaris SPARC/Solaris x86
Java versions 6u18 & 6u24
Reporter: Matt Yates
Priority: Critical
My company's program uses MINA makes multiple (usually) simultaneous
connections to various other machines, while reusing the same
NioSocketConnector for each new connection. For better or worse, we store
various objects in the IoSession's attributes, which we expect to get released
on close, however, said session remains in memory until either a new connection
is made or the connector is disposed. After writing the simplest Connector
program I could (I have several servers available on my network, so I did not
write a matching Acceptor), and performing some profiling and debugging, I was
able to confirm the leak and identify the issue.
Below is my Connector test program
{code}
public class MinaMain {
private static final Logger LOGGER =
LoggerFactory.getLogger(MinaMain.class);
public static void main(String[] args) throws InterruptedException {
LOGGER.trace("Waiting for YourKit to start");
Thread.sleep(15000);
NioSocketConnector connector = new NioSocketConnector();
connector.setHandler(new IoHandlerAdapter());
closeSession(getConnectedSession(connector));
// LOGGER.info("Creating and closing 5 sessions in series");
//
// for (int x = 0; x < 5; x++) {
// IoSession session = getConnectedSession(connector);
//
// if (session == null) {
// continue;
// }
//
// closeSession(session);
// }
//
// LOGGER.info("Creating 5 sessions and then closing 5 sessions");
// IoSession[] sessions = new IoSession[5];
//
// for (int x = 0; x < 5; x++) {
// sessions[x] = getConnectedSession(connector);
// }
//
// for (int x = 0; x < 5; x++) {
// IoSession session = sessions[x];
//
// if (session != null) {
// closeSession(session);
// sessions[x] = null;
// }
// }
LOGGER.info("Test complete. Sleeping for 60s");
Thread.sleep(60000);
}
private static IoSession getConnectedSession(IoConnector connector) throws
InterruptedException {
IoSession session = null;
try {
ConnectFuture future = connector.connect(new
InetSocketAddress("134.64.37.183", 11109));
future.addListener(new IoFutureListener<ConnectFuture>() {
@Override
public void operationComplete(ConnectFuture future) {
LOGGER.debug("Connection completed callback for session " +
future.getSession().getId());
}
});
future.awaitUninterruptibly();
LOGGER.debug("Connection created for session " +
future.getSession().getId());
session = future.getSession();
Thread.sleep(15000);
}
catch (Exception e) {
LOGGER.error("Failed to connect", e);
}
return session;
}
private static void closeSession(IoSession session) throws
InterruptedException {
try {
CloseFuture closeFuture = session.getCloseFuture();
closeFuture.addListener(new IoFutureListener<CloseFuture>() {
@Override
public void operationComplete(CloseFuture future) {
LOGGER.debug("Session closed callback for session " +
future.getSession().getId());
}
});
LOGGER.debug("Attempting to close session " + session.getId());
session.close(false);
LOGGER.debug("IoSession.close(false) returned. Awaiting
uninterruptibily for session " + session.getId());
closeFuture.awaitUninterruptibly();
LOGGER.debug("Close completed for session " + session.getId());
}
catch (Exception e) {
LOGGER.error("Failed to close session " + session.getId());
session.close(true);
}
Thread.sleep(15000);
}
}
{/code}
Attached is the hprof file of my program, taken after the program has run
(during the 60 second sleep at the end) and a screen shot of the GC Root of the
leaked NioSocketSession.
After a couple days of debugging, I've identified why this is happening. Below
is a snippet from the AbstractPollingIoConnector.Connector thread
{code}private class Connector implements Runnable {
public void run() {
int nHandles = 0;
while (selectable) {
try {
// the timeout for select shall be smaller of the connect
// timeout or 1 second...
int timeout = (int)Math.min(getConnectTimeoutMillis(),
1000L);
int selected = select(timeout);
nHandles += registerNew();
if (selected > 0) {
nHandles -= processConnections(selectedHandles());
}
processTimedOutSessions(allHandles());
nHandles -= cancelKeys();
if (nHandles == 0) {
synchronized (lock) {
if (connectQueue.isEmpty()) {
connector = null;
break;
}
}
}
}
...
{/code}
When IoSession.close(boolean) is called, the above Connector thread cancels the
SelectionKey associated with the session, which reduces the number of handles
from 1 to 0. Immediately afterwards, the thread stops executing because there
are no handles and nothing in the connetQueue, however, the previously
cancelled key is still in the Selector because its cancelledKeys Set is not
processed until the next call to select(int)
Calling dispose on the IoConnector restarts the Connector thread, which calls
Selector.select(int), at which time, the Selector cleans out its canclledKeys.
Creating a new connection causes the same thing to happen, because the new
session also recreates the AbstractPollingIoConnector.Connector thread, as
there is a new handle to be processed.
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