Fixed deadlock in SMPPSession/AbstractSession close methods

[TomasAndersen]

I am using the jsmpp API to listen for incoming SMS messages on a socket connection.
In average this socket connection stopped every 24 hours. I could also make it stop by breaking the network connection between my server and the SMPP Gateway.

I turned out that it was a deadlock caused by the EnquireLinkSender thread waiting for the PDUReader thread and visa versa.

This pull request moves all cleanup code into the superclass (AbstractSession) and I have added a check for which thread is calling the close method.

After running with this patch the SMPP API is able to close properly without any deadlock.

I have added a watchdog in my code outside the SMPP API that reconnects the SMPP Session when this happens instead of making the jsmpp API handle this and restart itself.

[dpocock]

Hi Tomas, thanks for this contribution. I've merged your work here: opentelecoms-org/jsmpp@5da83c0

[04mahajan-98]

Hi @TomasAndersen.I am facing problem while calling session.close().I am using jsmpp 2.0.1 version That's why I have to override the close method and written the stopEnquireLinkSender() method to stop the enquire link sender thread.Below is the code to stop the thread:-
//////////////////////////////////////////////////

Field enquireLinkSenderField;
try {
enquireLinkSenderField = this.getClass().getSuperclass()
.getDeclaredField("enquireLinkSender");
enquireLinkSenderField.setAccessible(true);
Class noparams[] = {};
Object enquireLinkSenderThread = enquireLinkSenderField.get(this);
if (enquireLinkSenderThread != null && Thread.currentThread() != enquireLinkSenderThread ) {
LOGGER.info("Trying to stop enquirelink Sender thread.");
Method m = enquireLinkSenderThread.getClass().getMethod(
"isAlive", noparams);

			while ((Boolean) m.invoke(enquireLinkSenderThread, noparams)) {
				Method joinMethod = enquireLinkSenderThread.getClass()
						.getMethod("join", noparams);
				joinMethod.invoke(enquireLinkSenderThread, noparams);
									
				LOGGER.info(
						"Session {} is closed and enquireLinkSender stopped",
						this.getSessionId());
			}

		}

	}

But session got hanged sometimes when called session.close().And the I have to restart the server to connect to smpp again and again.What changes need to be done here so that It won't behave abnormal

[TomasAndersen]

Hi @04mahajan-98! As this is 8 years ago I am afraid I haven't any immediate answer to give you as I have forgotten a lot of this. At least not without spending time debugging and testing. Is there a reason for why you are sticking to the old version? I guess I would focus on upgrading the library to the latest version of the https://github.com/opentelecoms-org/jsmpp library instead and try it out. I hope there are not too many breaking changes to the API so the work of upgrading is too hard. I detected the error when debugging a project I stopped working on 6 years ago and opened a PR so I don't work on this project on a regular basis.