NanoHttpd leaking threads

Question

Does anyone encountered the issue with NanoHttpd leaking threads?

The thing is the library creates a new thread for each incoming request and while I see response for those requests the internal thread that was running requests processing is never finished. That leads to that it has eventually several hundreds of leaked threads and app crash.

My code is pretty much basic and straightforward. I just sublclass NanoHTTPD and override serve() method.

I've debugged the lib itself and it loops in the following code forever in NanoHTTPD class:

while (!finalAccept.isClosed()) {        
    session.execute();
}

Any suggestions?

Update: Turned out that this is and edge case that is connected to the client app that makes requests to my app where http server is launched. When I make requests from Chrome or with curl it doesn't leak any threads.

Answer 1

I believe this leak is caused by your client not closing the socket. NanoHttpd uses a timeout of 5s on read and only stops the serving thread when the socket has been closed on client side :

Line 190 :

} catch (Exception e) {
    // When the socket is closed by the client, we throw our own SocketException
    // to break the "keep alive" loop above.
    if (!(e instanceof SocketException && "NanoHttpd Shutdown".equals(e.getMessage()))) {
        e.printStackTrace();
    }

}

Line 863 :

if (read == -1) {
    // socket was been closed
    safeClose(inputStream);
    safeClose(outputStream);
    throw new SocketException("NanoHttpd Shutdown");
}

I would suggest checking if your client correctly closes the connection and maybe write your own AsyncRunner implementation instead of the DefaultAsyncRunner provided by NanoHttpd, in order to limit the number of threads. You could also implement, on top of that, a mechanism to stop threads serving for more than x sec (30s would be a good start imo).