package net.jcip.examples;
import java.util.concurrent.*;
import net.jcip.annotations.*;
/**
* BoundedBuffer
*
* Bounded buffer using \Semaphore
*
* @author Brian Goetz and Tim Peierls
*/
@ThreadSafe
public class SemaphoreBoundedBuffer {
private final Semaphore availableItems, availableSpaces;
@GuardedBy("this") private final E[] items;
@GuardedBy("this") private int putPosition = 0, takePosition = 0;
public SemaphoreBoundedBuffer(int capacity) {
if (capacity <= 0)
throw new IllegalArgumentException();
availableItems = new Semaphore(0);
availableSpaces = new Semaphore(capacity);
items = (E[]) new Object[capacity];
}
public boolean isEmpty() {
return availableItems.availablePermits() == 0;
}
public boolean isFull() {
return availableSpaces.availablePermits() == 0;
}
public void put(E x) throws InterruptedException {
availableSpaces.acquire();
doInsert(x);
availableItems.release();
}
public E take() throws InterruptedException {
availableItems.acquire();
E item = doExtract();
availableSpaces.release();
return item;
}
private synchronized void doInsert(E x) {
int i = putPosition;
items[i] = x;
putPosition = (++i == items.length) ? 0 : i;
}
private synchronized E doExtract() {
int i = takePosition;
E x = items[i];
items[i] = null;
takePosition = (++i == items.length) ? 0 : i;
return x;
}
}