How to manage LocalConverter and when invoke ShutDown() method?

Question

I wrote some code using documents4j library to convert some documents from .docx to .pdf.

I followed the examples in the documentation and the convertion works perfectly using MS-Word, but I notice that after all conversions complete and methods return, the java application result still running and it seems not to exit.

If I explicitly close the converter using execute() and shutDown() methods instead of schedule(), the application exit, but I need this application run in concurrent mode, so I can't explicitly invoke shutDown() otherwise I cause MS-Word exits and breaks some still opened documents.

What is the best way to use the converter to achieve these objectives? Has LocalConverter got a method to check if there is a queue of documents to be converted? With this information I could invoke shutDown() only with an empty queue and instantiate a new LocalConverter on the next converting request.

Thanks in advance for your replies!

Dan

Answer 1

I am the maintainer of documents4j.

You are right, the LocalConverter does not currently await termination of the running conversions when it is shut down. I added a grace period that corresponds to the timeout for running conversions to finish which will be included in the next version of documents4j. I will release a new version once I have looked into a pending issue with escaping path in folders containing spaces.

In the mean time, I recommend you to implement something similar yourself. Every conversion emitts a Future. Simply collect all the futures in a Set and then call get on each future in a thread. If all futures have returned (i.e. all conversions are complete), it is safe to shut down the local converter:

IConverter converter = ...;
Set<Future<?>> futures = new HashSet<>();
for ( ... ) {
  futures.add(converter.from(...).to(...).schedule());
}
for (Future<?> future : futures) {
  future.get();
}
converter.shutDown();

The above is safe because all conversions are done concurrently but the main thread blocks until all futures have completed. Future::get blocks until its conversion has completed but returns immediately if a conversion already is complete. This way you make sure you do not reach shutDown before all conversions are complete.