solver/src/main/java/android/support/constraint/solver/Pools.java

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.support.constraint.solver;

/**
 * Helper class for crating pools of objects. An example use looks like this:
 * <pre>
 * public class MyPooledClass {
 *
 *     private static final SimplePool<MyPooledClass> sPool =
 *             new SimplePool<MyPooledClass>(10);
 *
 *     public static MyPooledClass obtain() {
 *         MyPooledClass instance = sPool.acquire();
 *         return (instance != null) ? instance : new MyPooledClass();
 *     }
 *
 *     public void recycle() {
 *          // Clear state if needed.
 *          sPool.release(this);
 *     }
 *
 *     . . .
 * }
 * </pre>
 */
final class Pools {
    private static final boolean DEBUG = false;

    /**
     * Interface for managing a pool of objects.
     *
     * @param <T> The pooled type.
     */
    interface Pool<T> {

        /**
         * @return An instance from the pool if such, null otherwise.
         */
        T acquire();

        /**
         * Release an instance to the pool.
         *
         * @param instance The instance to release.
         * @return Whether the instance was put in the pool.
         *
         * @throws IllegalStateException If the instance is already in the pool.
         */
        boolean release(T instance);

        /**
         * Try releasing all instances at the same time
         *
         * @param variables the variables to release
         * @param count the number of variables to release
         */
        void releaseAll(T[] variables, int count);
    }

    private Pools() {
        /* do nothing - hiding constructor */
    }

    /**
     * Simple (non-synchronized) pool of objects.
     *
     * @param <T> The pooled type.
     */
    static class SimplePool<T> implements Pool<T> {
        private final Object[] mPool;

        private int mPoolSize;

        /**
         * Creates a new instance.
         *
         * @param maxPoolSize The max pool size.
         *
         * @throws IllegalArgumentException If the max pool size is less than zero.
         */
        SimplePool(int maxPoolSize) {
            if (maxPoolSize <= 0) {
                throw new IllegalArgumentException("The max pool size must be > 0");
            }
            mPool = new Object[maxPoolSize];
        }

        @Override
        @SuppressWarnings("unchecked")
        public T acquire() {
            if (mPoolSize > 0) {
                final int lastPooledIndex = mPoolSize - 1;
                T instance = (T) mPool[lastPooledIndex];
                mPool[lastPooledIndex] = null;
                mPoolSize--;
                return instance;
            }
            return null;
        }

        @Override
        public boolean release(T instance) {
            if (DEBUG) {
                if (isInPool(instance)) {
                    throw new IllegalStateException("Already in the pool!");
                }
            }
            if (mPoolSize < mPool.length) {
                mPool[mPoolSize] = instance;
                mPoolSize++;
                return true;
            }
            return false;
        }

        @Override
        public void releaseAll(T[] variables, int count) {
            if (count > variables.length) {
                count = variables.length;
            }
            for (int i = 0; i < count; i++) {
                T instance = variables[i];
                if (DEBUG) {
                    if (isInPool(instance)) {
                        throw new IllegalStateException("Already in the pool!");
                    }
                }
                if (mPoolSize < mPool.length) {
                    mPool[mPoolSize] = instance;
                    mPoolSize++;
                }
            }
        }

        private boolean isInPool(T instance) {
            for (int i = 0; i < mPoolSize; i++) {
                if (mPool[i] == instance) {
                    return true;
                }
            }
            return false;
        }
    }

}