LruArrayPool.java

package com.bumptech.glide.load.engine.bitmap_recycle;

import android.support.annotation.Nullable;
import android.support.annotation.VisibleForTesting;
import android.util.Log;
import com.bumptech.glide.util.Preconditions;
import com.bumptech.glide.util.Synthetic;
import java.util.HashMap;
import java.util.Map;
import java.util.NavigableMap;
import java.util.TreeMap;

/**
 * A fixed size Array Pool that evicts arrays using an LRU strategy to keep the pool under
 * the maximum byte size.
 */
public final class LruArrayPool implements ArrayPool {
  // 4MB.
  static final int DEFAULT_SIZE = 4 * 1024 * 1024;

  /**
   * The maximum number of times larger an int array may be to be than a requested size to eligible
   * to be returned from the pool.
   */
  private static final int MAX_OVER_SIZE_MULTIPLE = 8;
  /** Used to calculate the maximum % of the total pool size a single byte array may consume. */
  private static final int SINGLE_ARRAY_MAX_SIZE_DIVISOR = 2;

  private final GroupedLinkedMap<Key, Object> groupedMap = new GroupedLinkedMap<>();
  private final KeyPool keyPool = new KeyPool();
  private final Map<Class<?>, NavigableMap<Integer, Integer>> sortedSizes = new HashMap<>();
  private final Map<Class<?>, ArrayAdapterInterface<?>> adapters = new HashMap<>();
  private final int maxSize;
  private int currentSize;

  @VisibleForTesting
  public LruArrayPool() {
    maxSize = DEFAULT_SIZE;
  }

  /**
   * Constructor for a new pool.
   *
   * @param maxSize The maximum size in integers of the pool.
   */
  public LruArrayPool(int maxSize) {
    this.maxSize = maxSize;
  }

  @Override
  public synchronized <T> void put(T array, Class<T> arrayClass) {
    ArrayAdapterInterface<T> arrayAdapter = getAdapterFromType(arrayClass);
    int size = arrayAdapter.getArrayLength(array);
    int arrayBytes = size * arrayAdapter.getElementSizeInBytes();
    if (!isSmallEnoughForReuse(arrayBytes)) {
      return;
    }
    Key key = keyPool.get(size, arrayClass);

    groupedMap.put(key, array);
    NavigableMap<Integer, Integer> sizes = getSizesForAdapter(arrayClass);
    Integer current = sizes.get(key.size);
    sizes.put(key.size, current == null ? 1 : current + 1);
    currentSize += arrayBytes;
    evict();
  }

  @Override
  public <T> T get(int size, Class<T> arrayClass) {
    ArrayAdapterInterface<T> arrayAdapter = getAdapterFromType(arrayClass);
    T result;
    synchronized (this) {
      Integer possibleSize = getSizesForAdapter(arrayClass).ceilingKey(size);
      final Key key;
      if (mayFillRequest(size, possibleSize)) {
        key = keyPool.get(possibleSize, arrayClass);
      } else {
        key = keyPool.get(size, arrayClass);
      }

      result = getArrayForKey(key);
      if (result != null) {
        currentSize -= arrayAdapter.getArrayLength(result) * arrayAdapter.getElementSizeInBytes();
        decrementArrayOfSize(arrayAdapter.getArrayLength(result), arrayClass);
      }
    }

    if (result == null) {
      if (Log.isLoggable(arrayAdapter.getTag(), Log.VERBOSE)) {
        Log.v(arrayAdapter.getTag(), "Allocated " + size + " bytes");
      }
      result = arrayAdapter.newArray(size);
    }
    return result;
  }

  @SuppressWarnings("unchecked")
  @Nullable
  private <T> T getArrayForKey(Key key) {
    return (T) groupedMap.get(key);
  }

  private boolean isSmallEnoughForReuse(int byteSize) {
    return byteSize <= maxSize / SINGLE_ARRAY_MAX_SIZE_DIVISOR;
  }

  private boolean mayFillRequest(int requestedSize, Integer actualSize) {
    return actualSize != null
        && (isNoMoreThanHalfFull() || actualSize <= (MAX_OVER_SIZE_MULTIPLE * requestedSize));
  }

  private boolean isNoMoreThanHalfFull() {
    return currentSize == 0 || (maxSize / currentSize >= 2);
  }

  @Override
  public synchronized void clearMemory() {
    evictToSize(0);
  }

  @Override
  public synchronized void trimMemory(int level) {
    if (level >= android.content.ComponentCallbacks2.TRIM_MEMORY_BACKGROUND) {
      clearMemory();
    } else if (level >= android.content.ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN) {
      evictToSize(maxSize / 2);
    }
  }

  private void evict() {
    evictToSize(maxSize);
  }

  private void evictToSize(int size) {
    while (currentSize > size) {
      Object evicted = groupedMap.removeLast();
      Preconditions.checkNotNull(evicted);
      ArrayAdapterInterface<Object> arrayAdapter = getAdapterFromObject(evicted);
      currentSize -= arrayAdapter.getArrayLength(evicted) * arrayAdapter.getElementSizeInBytes();
      decrementArrayOfSize(arrayAdapter.getArrayLength(evicted), evicted.getClass());
      if (Log.isLoggable(arrayAdapter.getTag(), Log.VERBOSE)) {
        Log.v(arrayAdapter.getTag(), "evicted: " + arrayAdapter.getArrayLength(evicted));
      }
    }
  }

  private void decrementArrayOfSize(int size, Class<?> arrayClass) {
    NavigableMap<Integer, Integer> sizes = getSizesForAdapter(arrayClass);
    Integer current = sizes.get(size);
    if (current == null) {
      throw new NullPointerException(
          "Tried to decrement empty size" + ", size: " + size + ", this: " + this);
    }
    if (current == 1) {
      sizes.remove(size);
    } else {
      sizes.put(size, current - 1);
    }
  }

  private NavigableMap<Integer, Integer> getSizesForAdapter(Class<?> arrayClass) {
    NavigableMap<Integer, Integer> sizes = sortedSizes.get(arrayClass);
    if (sizes == null) {
      sizes = new TreeMap<>();
      sortedSizes.put(arrayClass, sizes);
    }
    return sizes;
  }

  @SuppressWarnings("unchecked")
  private <T> ArrayAdapterInterface<T> getAdapterFromObject(T object) {
    return (ArrayAdapterInterface<T>) getAdapterFromType(object.getClass());
  }

  @SuppressWarnings("unchecked")
  private <T> ArrayAdapterInterface<T> getAdapterFromType(Class<T> arrayPoolClass) {
    ArrayAdapterInterface<?> adapter = adapters.get(arrayPoolClass);
    if (adapter == null) {
      if (arrayPoolClass.equals(int[].class)) {
        adapter = new IntegerArrayAdapter();
      } else if (arrayPoolClass.equals(byte[].class)) {
        adapter = new ByteArrayAdapter();
      } else {
          throw new IllegalArgumentException("No array pool found for: "
              + arrayPoolClass.getSimpleName());
      }
      adapters.put(arrayPoolClass, adapter);
    }
    return (ArrayAdapterInterface<T>) adapter;
  }

  // VisibleForTesting
  int getCurrentSize() {
    int currentSize = 0;
    for (Class<?> type : sortedSizes.keySet()) {
      for (Integer size : sortedSizes.get(type).keySet()) {
        ArrayAdapterInterface<?> adapter = getAdapterFromType(type);
        currentSize += size * sortedSizes.get(type).get(size) * adapter.getElementSizeInBytes();
      }
    }
    return currentSize;
  }

  private static final class KeyPool extends BaseKeyPool<Key> {

    @Synthetic
    KeyPool() { }

    Key get(int size, Class<?> arrayClass) {
      Key result = get();
      result.init(size, arrayClass);
      return result;
    }

    @Override
    protected Key create() {
      return new Key(this);
    }
  }

  private static final class Key implements Poolable {
    private final KeyPool pool;
    @Synthetic int size;
    private Class<?> arrayClass;

    Key(KeyPool pool) {
      this.pool = pool;
    }

    void init(int length, Class<?> arrayClass) {
      this.size = length;
      this.arrayClass = arrayClass;
    }

    @Override
    public boolean equals(Object o) {
      if (o instanceof Key) {
        Key other = (Key) o;
        return size == other.size && arrayClass == other.arrayClass;
      }
      return false;
    }

    @Override
    public String toString() {
      return "Key{" + "size=" + size + "array=" + arrayClass + '}';
    }

    @Override
    public void offer() {
      pool.offer(this);
    }

    @Override
    public int hashCode() {
      int result = size;
      result = 31 * result + (arrayClass != null ? arrayClass.hashCode() : 0);
      return result;
    }
  }
}