packages/SystemUI/src/com/android/systemui/recents/model/TaskKeyLruCache.java

/*
 * Copyright (C) 2014 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 com.android.systemui.recents.model;

import android.util.Log;
import android.util.LruCache;
import android.util.SparseArray;

import java.io.PrintWriter;
import java.util.ArrayList;

/**
 * A mapping of {@link Task.TaskKey} to value, with additional LRU functionality where the least
 * recently referenced key/values will be evicted as more values than the given cache size are
 * inserted.
 *
 * In addition, this also allows the caller to invalidate cached values for keys that have since
 * changed.
 */
public class TaskKeyLruCache<V> {

    public interface EvictionCallback {
        public void onEntryEvicted(Task.TaskKey key);
    }

    private static final String TAG = "TaskKeyLruCache";

    private final SparseArray<Task.TaskKey> mKeys = new SparseArray<>();
    private final LruCache<Integer, V> mCache;
    private final EvictionCallback mEvictionCallback;

    public TaskKeyLruCache(int cacheSize) {
        this(cacheSize, null);
    }

    public TaskKeyLruCache(int cacheSize, EvictionCallback evictionCallback) {
        mEvictionCallback = evictionCallback;
        mCache = new LruCache<Integer, V>(cacheSize) {

            @Override
            protected void entryRemoved(boolean evicted, Integer taskId, V oldV, V newV) {
                if (mEvictionCallback != null) {
                    mEvictionCallback.onEntryEvicted(mKeys.get(taskId));
                }
                mKeys.remove(taskId);
            }
        };
    }

    /**
     * Gets a specific entry in the cache with the specified key, regardless of whether the cached
     * value is valid or not.
     */
    final V get(Task.TaskKey key) {
        return mCache.get(key.id);
    }

    /**
     * Returns the value only if the key is valid (has not been updated since the last time it was
     * in the cache)
     */
    final V getAndInvalidateIfModified(Task.TaskKey key) {
        Task.TaskKey lastKey = mKeys.get(key.id);
        if (lastKey != null) {
            if ((lastKey.stackId != key.stackId) ||
                    (lastKey.lastActiveTime != key.lastActiveTime)) {
                // The task has updated (been made active since the last time it was put into the
                // LRU cache) or the stack id for the task has changed, invalidate that cache item
                remove(key);
                return null;
            }
        }
        // Either the task does not exist in the cache, or the last active time is the same as
        // the key specified, so return what is in the cache
        return mCache.get(key.id);
    }

    /** Puts an entry in the cache for a specific key. */
    final void put(Task.TaskKey key, V value) {
        if (key == null || value == null) {
            Log.e(TAG, "Unexpected null key or value: " + key + ", " + value);
            return;
        }
        mKeys.put(key.id, key);
        mCache.put(key.id, value);
    }

    /** Removes a cache entry for a specific key. */
    final void remove(Task.TaskKey key) {
        // Remove the key after the cache value because we need it to make the callback
        mCache.remove(key.id);
        mKeys.remove(key.id);
    }

    /** Removes all the entries in the cache. */
    final void evictAll() {
        mCache.evictAll();
        mKeys.clear();
    }

    /** Trims the cache to a specific size */
    final void trimToSize(int cacheSize) {
        mCache.trimToSize(cacheSize);
    }

    public void dump(String prefix, PrintWriter writer) {
        String innerPrefix = prefix + "  ";

        writer.print(prefix); writer.print(TAG);
        writer.print(" numEntries="); writer.print(mKeys.size());
        writer.println();
        int keyCount = mKeys.size();
        for (int i = 0; i < keyCount; i++) {
            writer.print(innerPrefix); writer.println(mKeys.get(mKeys.keyAt(i)));
        }
    }
}