51 lines
1.4 KiB
Java
51 lines
1.4 KiB
Java
//: concurrency/Pool.java
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// Using a Semaphore inside a Pool, to restrict
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// the number of tasks that can use a resource.
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import java.util.concurrent.*;
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import java.util.*;
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public class Pool<T> {
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private int size;
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private List<T> items = new ArrayList<>();
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private volatile boolean[] checkedOut;
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private Semaphore available;
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public Pool(Class<T> classObject, int size) {
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this.size = size;
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checkedOut = new boolean[size];
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available = new Semaphore(size, true);
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// Load pool with objects that can be checked out:
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for(int i = 0; i < size; ++i)
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try {
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// Assumes a default constructor:
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items.add(classObject.newInstance());
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} catch(Exception e) {
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throw new RuntimeException(e);
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}
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}
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public T checkOut() throws InterruptedException {
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available.acquire();
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return getItem();
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}
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public void checkIn(T x) {
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if(releaseItem(x))
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available.release();
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}
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private synchronized T getItem() {
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for(int i = 0; i < size; ++i)
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if(!checkedOut[i]) {
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checkedOut[i] = true;
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return items.get(i);
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}
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return null; // Semaphore prevents reaching here
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}
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private synchronized boolean releaseItem(T item) {
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int index = items.indexOf(item);
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if(index == -1) return false; // Not in the list
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if(checkedOut[index]) {
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checkedOut[index] = false;
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return true;
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}
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return false; // Wasn't checked out
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}
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} ///:~
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