How do I pull data from another thread or process (Android/Java)

Question

I know of concepts that allow inter-process communication. My program needs to launch a second thread. I know how to pass or "push" data from one thread to another from Java/Android, but I have not seen a lot of information regarding "pulling" data. The child thread needs to grab data on the parent thread every so often. How is this done?

Answer 1

Since threads share memory you can just use a thread safe data structure. Refer to java.util.concurrent for some. Everything in that package is designed for multi threaded situations.

In your case you might want to use a LinkedBlockingQueue. This way the parent thread can put things into the queue, and the child thread can grab it off whenever it likes. It also allows the child thread to block if the Queue is empty.

Answer 2

You may be confusing threads and data. Threads are lines of code execution which may operate on some data but they are not data themselves and they do not contain data. Data is contained in memory and threads are executed by CPU (or vm or whatever level you choose).

You access data in the same way whether it is done in threads or not. That is you use variables or object fields etc. But with threads you need to make sure that there are no race conditions which happen when threads concurrently access the same data.

To summarize, if you have an object that has some method executed by thread, you can still get data from this object in regular way as long as you make sure that only one thread does it at the same time.