LimitedCapacityList.java

package net.minecraft.launcher.process;

import java.lang.reflect.Array;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class LimitedCapacityList<T> {
    private final T[] items;
    private final Class<? extends T> clazz;
    private final ReadWriteLock locks = new ReentrantReadWriteLock();
    private int size;
    private int head;

    public LimitedCapacityList(Class<? extends T> clazz, int maxSize) {
        this.clazz = clazz;
        this.items = ((T[]) Array.newInstance(clazz, maxSize));
    }

    public T add(T value) {
        this.locks.writeLock().lock();

        this.items[this.head] = value;
        this.head = ((this.head + 1) % getMaxSize());
        if (this.size < getMaxSize()) this.size += 1;

        this.locks.writeLock().unlock();
        return value;
    }

    public int getSize() {
        this.locks.readLock().lock();
        int result = this.size;
        this.locks.readLock().unlock();
        return result;
    }

    public int getMaxSize() {
        this.locks.readLock().lock();
        int result = this.items.length;
        this.locks.readLock().unlock();
        return result;
    }

    public T[] getItems() {
        Object[] result = (Object[]) Array.newInstance(this.clazz, this.size);

        this.locks.readLock().lock();
        for (int i = 0; i < this.size; i++) {
            int pos = (this.head - this.size + i) % getMaxSize();
            if (pos < 0) pos += getMaxSize();
            result[i] = this.items[pos];
        }
        this.locks.readLock().unlock();

        return (T[]) result;
    }
}