JAVA-BASED REAL-TIME PROGRAMMING

3. Multi-Threaded Programming
decouple the execution, that is, to make object interaction asynchronous but
still based on the methods at hand. Hence, the normal case is to hide the
mailbox as an attribute inside the object. There is a subclass of Thread that
provides that feature, namely class se.lth.cs.realtime.JThread.
The featured Java Thread class – JThread
To support the most common case that the mailbox in terms of an RTEventBuffer
is handled locally within the receiving thread, and encapsulated by the methods
of that thread, class se.lth.cs.realtime.JThread contains the following
(see volatile on Page 72):
public class JThread extends java.lang.Thread {
/** The event inbut buffer. */
protected volatile RTEventBuffer mailbox;
}
/**
* Put the time -stamped event in the input buffer of this thread.
* If the buffer is full , the caller is blocked.
*/
public RTEvent putEvent(RTEvent ev) {
mailbox.doPost(ev); // Subclasses may use tryPost.
return null; // Subclasses may return resulting event.
}
// etc. etc.
The J in JThread is to stress the fact that this type of thread still is a (concurrent)
Java thread (that is, not specified to be real time as will be the case
in following chapters).
To simplify programming in the case that the same thing should be repeated
over and over again, there is a default run method that calls perform
according to the following:
public void run() {
while (!isInterrupted ()) {
perform();
}
}
When implementing the thread behavior, in run or perform, the the doFetch
and tryFetch methods are useful, like is this exemplifying perform method:
class MyEventProcessor extends JThread {
public void perform() {
serverObject.process(mailbox.doFetch ());
}
}
In addition to the methods of the base class Thread as shown on Page 55, this
means that the class JThread provides the following simple to implement but
convenient methods:
RTEvent putEvent(RTEvent ev) // Generic event input
void terminate() // Interrupt and join
static void sleepUntil(long wakeUpTime) // Sleep until that absolute time
void perform() // Override to define cyclic work
96 2012-08-29 16:05