Question

I have a method which takes a list and do some processing on it and it updates another global list. I need to run multiple instances of this method with different lists input in parallel.
Does multi-threading support this? If yes, how can i use it i.e.: what shall i put in the thread? Examples are highly appreciated.

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I am thinking of having a static list in the thread class which gets updated by the different instances of the thread while running (the list contains strings and counters, so the update is adding new strings or increasing the counters of existing ones).. i need to read whatever gets added to this global list every 10 seconds and print it.. is using static list suitable for this and how can i make it thread safe?

Answer 1

@purtip31 has a start for the parallel processing stuff.

I’m concerned about the results – you mention that you update a “global list”. If multiple threads at a time are trying to update that list at the same time there could be problems. A couple of options:

1. Make sure that list is properly thread safe. This may or may not be easy – depends on exactly what is getting changed.
2. Use ExecutorService, but with the invokeAll() method, which runs a bunch of Callables in parallel and waits till they are all done. Then you can go through all of the results and update them one at a time. No threading issues with the results. This means that your code will have to implement Callable instead of Runnable (not a big deal). I have a blog with an example here