prestonbane/src/engine/pooling/ObjectPool.java

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//      Magicbane Emulator Project © 2013 - 2022
//                www.magicbane.com


package engine.pooling;

import org.pmw.tinylog.Logger;

import java.util.ArrayList;

public abstract class ObjectPool<T> {
    protected final static int DEFAULT_SIZE = 1000;

    // Simple + quick list
    private final ArrayList<T> pool;

    /**
     * Once the ArrayList fills to <b>threshold</b>, subsequent .put() calls
     * result in the object being thrown away. Default is 75% of supplied
     * <b>size</b>.
     */
    private int threshold;

    /**
     * Constructor that allows the caller to specify initial array size and
     * percent of prefill.
     *
     * @param size - initial size for the containing array (pool)
     */
    public ObjectPool(int size) {
        if (size == 0) {
            size = DEFAULT_SIZE;
        }

        threshold = (int) (0.75 * size);

        this.pool = new ArrayList<>(size);

    }

    /**
     * Default Constructor that uses default initial Array size and percent
     * prefill values
     */
    public ObjectPool() {
        this(DEFAULT_SIZE);
    }

    /**
     * Forces pool to add <i>numberOfObjects</i> to the pool. This may cause
     * internal ArrayList to resize.
     *
     * @param numberOfObjects
     */
    public void fill(int numberOfObjects) {
        for (int i = 0; i < numberOfObjects; ++i)
            this.makeAndAdd();
    }

    /**
     * Forces subclasses to implement factory routine for object creation.
     */
    protected abstract T makeNewObject();

    /**
     * Forces subclasses to implement a way to reset object to a reusable state.
     */
    protected abstract void resetObject(T obj);

    /**
     * Generic Get routine. If the pool is empty, then one (or more) of T type
     * objects will be created. If more than one T is created, then they will be
     * put into the pool. One T will always be created and returned.
     */
    public T get() {
        synchronized (pool) {
            //Logger.debug("Objectpool.get().  Pool size before get: " + pool.size());
            if (pool.size() > 0) {
                return pool.remove(0);
            }
        }

        this.handlePoolExhaustion();

        T obj = this.makeNewObject();

        if (obj == null) {
            Logger.error("Pooling failure: Object creation failed.");
        }
        return obj;
    }

    protected void handlePoolExhaustion() {
        Logger.debug("Pool exhausted, making more objects.");

        // If none exist, make (and pool) a few
        // Dont sync the loop, let the makeNewObject()
        // call return before locking the pool object
        for (int i = 0; i < 5; ++i)
            this.makeAndAdd();

    }

    /**
     * Generic put routine. If the current pool size is below threshold, this
     * object will be pooled, otherwise it will be NULL'ed and scheduled for
     * Garbage Collection
     *
     * @param obj
     */
    public void put(T obj) {
        synchronized (pool) {
            if (pool.size() >= this.threshold) {
                //Logger.debug("Objectpool.put() rejected.  Pool size: " + pool.size());
                return;
            }
            //Logger.debug("Objectpool.put().  Pool size: " + pool.size());
            this.resetObject(obj);
            this.pool.add(obj);
        }
    }

    /**
     * Helper method. Attempts to create and add a new <i>T</i> object. If this
     * fails, an error is logged.
     */
    protected final void makeAndAdd() {
        T obj = this.makeNewObject();
        if (obj == null) {
            Logger.error("Pooling failure: Object creation failed.");
        } else {
            this.put(obj);
        }
    }

    /**
     * @return the current size of the pool, not the maximum capacity of the
     * Array holding the pool.
     */
    public final int getPoolSize() {
        synchronized (this.pool) {
            return this.pool.size();
        }
    }

    /**
     * Culls the pool and removes half of the stored objects. Removed objects
     * are NULL'ed and scheduled form Garbage Collection.
     *
     * @return the number of Objects removed from the pool.
     */
    public int cullHalf() {
        int full, half;
        synchronized (this.pool) {
            full = this.pool.size();
            if (full < 1) {
                return full;
            }

            half = (full / 2);

            for (int i = 0; i < (full / 2); ++i) {
                T obj = this.get();
                obj = null; // Null out for GC
            }
        }
        return half;
    }

    /**
     * @return the threshold
     */
    public final int getThreshold() {
        return threshold;
    }

    /**
     * @param threshold the threshold to set
     */
    public void setThreshold(int threshold) {
        if (threshold < 0)
            return;

        this.threshold = threshold;
    }

}