Helfer Queue

Jan Burse, erstellt 15. Sep 2018
package matula.util.misc;
import matula.util.data.ListArray;
/**
* <p>This class provides a bounded queue. The advantage over the
* usual Java class ArrayBlockingQueue is that an empty bounded queue
* doesn't occupy much space even if it has a large capacity. The
* bounded queue is implemented by our class ListArray and a max
* field that indicates the capacity of the bounded queue:
* </p>
* <pre>
* +----------+-----------------+------------+
* | table[0] | ... | table[n-1] |
* +----------+-----------------+------------+
* < --------------- size = n -------------- >
* < ----------------------- max -------------------------- >
* </pre>
* <p>Putting and offering appends to the end of our class ListArray.
* Taking and polling removes from the start of our class ListArray.
* So the bounded queue works in a first-in first-out manner. Each
* operation is synchronized, whereby the bounded queue object itself
* is used for synchronization.
* </p>
* Warranty & Liability
* To the extent permitted by applicable law and unless explicitly
* otherwise agreed upon, XLOG Technologies GmbH makes no warranties
* regarding the provided information. XLOG Technologies GmbH assumes
* no liability that any problems might be solved with the information
* provided by XLOG Technologies GmbH.
* <p/>
* Rights & License
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* and patent rights in particular - are the sole property of XLOG
* Technologies GmbH. If the company was not the originator of some
* excerpts, XLOG Technologies GmbH has at least obtained the right to
* reproduce, change and translate the information.
* <p/>
* Reproduction is restricted to the whole unaltered document. Reproduction
* of the information is only allowed for non-commercial uses. Selling,
* giving away or letting of the execution of the library is prohibited.
* The library can be distributed as part of your applications and libraries
* for execution provided this comment remains unchanged.
* <p/>
* Restrictions
* Only to be distributed with programs that add significant and primary
* functionality to the library. Not to be distributed with additional
* software intended to replace any components of the library.
* <p/>
* Trademarks
* Jekejeke is a registered trademark of XLOG Technologies GmbH.
*/
public final class Queue extends AbstractPipe {
private final ListArray<Object> list;
private final int max;
/**
* <p>Create a queue.</p>
*
* @param m The maximum size, must be greater than zero.
*/
public Queue(int m) {
if (!(m > 0))
throw new IndexOutOfBoundsException("maxsize underflow");
list = new ListArray<Object>();
max = m;
}
/**
* <p>Post an object.</p>
* <p>Blocks if queue is full.</p>
*
* @param t The object, not null.
* @throws InterruptedException If the request was cancelled.
*/
public void put(Object t)
throws InterruptedException {
if (t == null)
throw new NullPointerException("null element");
synchronized (this) {
while (list.size() >= max)
this.wait();
list.add(t);
this.notifyAll();
}
}
/**
* <p>Post an object.</p>
* <p>Fails if queue is full.</p>
*
* @return True if object was posted, or false otherwise.
*/
public boolean offer(Object t) {
if (t == null)
throw new NullPointerException("null element");
synchronized (this) {
if (list.size() < max) {
list.add(t);
return true;
} else {
return false;
}
}
}
/**
* <p>Post an object or time-out.</p>
*
* @param t The object, not null.
* @param sleep The time-out.
* @return True if object was posted, or false otherwise.
*/
public boolean offer(Object t, long sleep)
throws InterruptedException {
if (t == null)
throw new NullPointerException("null element");
long when = System.currentTimeMillis() + sleep;
synchronized (this) {
while (list.size() >= max && sleep > 0) {
this.wait(sleep);
sleep = when - System.currentTimeMillis();
}
if (sleep > 0) {
list.add(t);
this.notifyAll();
return true;
} else {
return false;
}
}
}
/**
* <p>Take an object.</p>
* <p>Blocks if queue is empty.</p>
*
* @return The object, not null.
* @throws InterruptedException If the request was cancelled.
*/
public Object take()
throws InterruptedException {
synchronized (this) {
while (list.size() == 0)
this.wait();
Object t = list.get(0);
list.remove(0);
this.notifyAll();
return t;
}
}
/**
* <p>Take an object.</p>
* <p>Fails if queue is empty.</p>
*
* @return The object or null if no object was taken.
*/
public Object poll() {
synchronized (this) {
if (list.size() != 0) {
Object t = list.get(0);
list.remove(0);
return t;
} else {
return null;
}
}
}
/**
* <p>Take an object or time-out.</p>
*
* @param sleep The time-out.
* @return The object or null if no object was taken.
* @throws InterruptedException If the request was cancelled.
*/
public Object poll(long sleep)
throws InterruptedException {
long when = System.currentTimeMillis() + sleep;
synchronized (this) {
while (list.size() == 0 && sleep > 0) {
this.wait(sleep);
sleep = when - System.currentTimeMillis();
}
if (sleep > 0) {
Object t = list.get(0);
list.remove(0);
this.notifyAll();
return t;
} else {
return null;
}
}
}
}

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