Apache MINA 不删除未使用的数据

Question

I have a little problem about my MINA client.

I create only one connection to server, then the server sends some sort of data in every second periodically.

In short, client connects to the server; server sends back a string to the client and all those steps use the same opened connection (same client object and client handler).

But the problem is, I think, the old data is not collected by GC. The used heap is getting larger in seconds and never decreases. My messageReceived method is empty !

public void messageReceived(IoSession session, Object message) { }

Any idea?

Answer 1

VisualVM itself causes a lot of garbage. You can start an empty application and sleep the thread, enable VisualVM and watch the garbage start to collect. WITH NO CODE.

I am however, seeing a similar issue where mina is not retaining but generating long run items that are never garbage collected (unless you run a Full GC). This problem can cause an application with real memory of 4mb to show up as 80mb over an hour. It never gets collected.

I am about to build my own framework to wrap NIO because I could never keep a server online for long periods without restarts like this.

Answer 2

If it never decreases, enable -XX:+HeapDumpOnOutOfMemoryError and you will get a heap dump on an out of memory error.

The amount of memory used is not important, only how much is retained after a full GC. I suggest you run VisualVM and tirgger a full GC periodically and see how much free after this.

Answer 3

Here we are in 2023 with Apache Mina 2.2.1 and I ran into the same issue. Deployed software as a service and looked this morning to see it was using 9.6GB of memory after running for about a week!

I profiled it with VisualVM to find that the Objects being decoded were never being garbage collected: Turns out there's two fixes to this problem:

1. You have your IoSession set to use the read operation but you don't actually need it:

// Set this to false if you don't require ReadFuture!
session.getConfig().setUseReadOperation(false);

2. If you require asynchronous reading then you must call read on your session or it will cache all inbound messages until they are "read":

public void messageReceived(IoSession ioSession, Object message) { 
   ReadFuture future = ioSession.read();
        future.awaitUninterruptibly();
        future.getMessage();

}

In the Javadocs foundhere , under the read method, they state:

a ReadFuture which is notified when a new message is received, the connection is closed or an exception is caught. This operation is especially useful when you implement a client application. TODO: Describe here how we enable this feature. However, please note that this operation is disabled by default and throw IllegalStateException because all received events must be queued somewhere to support this operation, possibly leading to memory leak. This means you have to keep calling read() once you enabled this operation. To enable this operation, please call IoSessionConfig.setUseReadOperation(boolean) with true.