RemoteCache & RemoteCacheServerFactory setting RMISocketFactory
---------------------------------------------------------------
Key: JCS-41
URL: https://issues.apache.org/jira/browse/JCS-41
Project: JCS
Issue Type: Improvement
Components: RMI Remote Cache
Affects Versions: jcs-1.3, jcs-1.4-dev
Environment: All
Reporter: Niall Gallagher
Assignee: Aaron Smuts
Classes...
org.apache.jcs.auxiliary.remote.RemoteCache
and
org.apache.jcs.auxiliary.remote.server.RemoteCacheServerFactory
.. both try to set a timeout on RMI connections between the remote cache server
and client machines using the following code to install a timeout-enabled
socket factory which the RMI subsystem subsequently uses...
RMISocketFactory.setSocketFactory( new RMISocketFactory() {
public Socket createSocket( String host, int port ) throws
IOException {
Socket socket = new Socket( host, port );
socket.setSoTimeout( DEFAULT_RMI_SOCKET_FACTORY_TIMEOUT_MS );
socket.setSoLinger( false, 0 );
return socket;
}
public ServerSocket createServerSocket( int port ) throws
IOException {
return new ServerSocket( port );
}
});
The socket factory code above applies a "read timeout" to RMI sockets such that
if a connection is already established and subsequently stalls or a machine
goes offline, the timeout will break the connection as intended. The code does
not apply a "connect timeout" however, which means that if an attempt is made
to establish a new connection to a machine which is offline, the socket
connection attempt will stall for an infinite amount of time (such is the
default connect timeout), and therefore the thread opening the connection will
stall permanently in the JVM.
This is not a bug in JCS code, it was a limitation in JDK3 in that you could
not AFAIK set a connection timeout on a socket.
As of JDK4, there is a socket.connect(address, timeout) method, so this issue
can be fixed.
Here's the required replacement code:
RMISocketFactory.setSocketFactory( new RMISocketFactory() {
public Socket createSocket( String host, int port ) throws
IOException {
Socket socket = new Socket();
socket.setSoTimeout(timeoutMillis);
socket.setSoLinger( false, 0 );
socket.connect(new InetSocketAddress(host, port),
timeoutMillis);
return socket;
}
public ServerSocket createServerSocket( int port ) throws
IOException {
return new ServerSocket( port );
}
});
This was an issue for us recently. We fixed it by installing the
RMISocketFactory above in the JVM before initializing JCS. We have tested and
confirmed that this code works well with JCS, it times out reads same as before
and it now times out new connection attempts too.
How about including this in the next version of JCS?
By the way I read some JCS mailing list archives from last time socket timeouts
were discussed. Not sure if this will be helpful to anyone... but we found that
if an RMI client and server were running on the same subnet, timeouts were not
required and each machine detected that the other was offline immediately.
Cross-subnet through our router however, timeouts became important as attempts
to connect to an offline machine resulted in JCS threads hanging whilst trying
to connect.
We are not sure, but we suspect that this is related to our firewall blocking
required ICMP "host not reachable" packets between subnets, causing different
behaviour depending on the network setup. The replacement code above allows our
machines in both subnets to recover when a machine is offline, previously they
just stalled.
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