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How would one synchronize one real-time thread with a normal thread in Java? Take for example a real-time thread that calculates some temperatures and the GUI thread that has to collect those numbers and show them on some controls.
The implementation of the real-time library shouldn't matter as it should follow the specifications.
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Within a process or program, we can run multiple threads concurrently to improve the performance. Threads, unlike heavyweight process, are lightweight and run inside a single process – they share the same address space, the resources allocated and the environment of that process.
Real-time threads are schedulable objects and, therefore, can have associated release, scheduling, memory and processing group parameters. A real-time thread can also have its memory area set.
Barriers. Barriers are a synchronization mechanism that can be used to coordinate multiple threads working in parallel. A barrier allows each thread to wait until all cooperating threads have reached the same point, and then continue executing from there.
If you declare any method as synchronized, it is known as synchronized method. Synchronized method is used to lock an object for any shared resource. When a thread invokes a synchronized method, it automatically acquires the lock for that object and releases it when the thread completes its task.
You're going to need two things. You want your real-time thread to get priority, and preferably have it driven by a timer so you get (nearly) periodic measurements. Then, you're going to want a resource that can be used to communicate the values. That can either be a simple monitor, with a critical section so the timer thread can write into it, or it could be -- and very probably would be better as -- a FIFO, so that the GUI thread can eat up values whenever it has cycles.
In Java, the GUI (at least in Swing and similar) is already running a separate thread for UI interactions, so you're big issue is to set up your measurement thread. Have a look at Runnables.
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To use real-time threads you need Real Time Java on real time operating system. http://java.sun.com/javase/technologies/realtime/index.jsp
However if you have a thread which is latency sensitive, I suggest you;
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Since others have brought up RTSJ, I'll comment that synchronization between real-time and non-real-time code has a number of solutions. RTSJ provides wait-free queues for such communication. It is also possible to build upon these or other queues and make use of RTSJ's AsyncEvent and AsyncEventHandler abstractions to manage the communication. This is appropriate for situations where you really, truly have a need for deterministic behavior for the "real-time" thread.
If you can accept best-effort behavior (try really hard to hit your deadlines, but the world doesn't fall apart if you miss) I suggest building carefully on the executor framework provided by the Java concurrency utilities. A careful selection of task boundaries, a suitable queuing policy (here, "suitable" would depend on more detail about your application than you've given), and threadpool policy will get what you need.
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