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A fast and efficient image loading library for Android focused on smooth scrolling.

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package com.bumptech.glide.load.engine;

import android.os.Looper;
import android.os.MessageQueue;
import android.support.v4.util.Pools;
import android.util.Log;
import com.bumptech.glide.GlideContext;
import com.bumptech.glide.Priority;
import com.bumptech.glide.load.DataSource;
import com.bumptech.glide.load.Key;
import com.bumptech.glide.load.Options;
import com.bumptech.glide.load.Transformation;
import com.bumptech.glide.load.engine.cache.DiskCache;
import com.bumptech.glide.load.engine.cache.DiskCacheAdapter;
import com.bumptech.glide.load.engine.cache.MemoryCache;
import com.bumptech.glide.load.engine.executor.GlideExecutor;
import com.bumptech.glide.request.ResourceCallback;
import com.bumptech.glide.util.LogTime;
import com.bumptech.glide.util.Synthetic;
import com.bumptech.glide.util.Util;
import com.bumptech.glide.util.pool.FactoryPools;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;

/**
 * Responsible for starting loads and managing active and cached resources.
 */
public class Engine implements EngineJobListener,
    MemoryCache.ResourceRemovedListener,
    EngineResource.ResourceListener {
  private static final String TAG = "Engine";
  private static final int JOB_POOL_SIZE = 150;
  private final Map> jobs;
  private final EngineKeyFactory keyFactory;
  private final MemoryCache cache;
  private final EngineJobFactory engineJobFactory;
  private final Map>> activeResources;
  private final ResourceRecycler resourceRecycler;
  private final LazyDiskCacheProvider diskCacheProvider;
  private final DecodeJobFactory decodeJobFactory;

  // Lazily instantiate to avoid exceptions if Glide is initialized on a background thread. See
  // #295.
  private ReferenceQueue> resourceReferenceQueue;

  /**
   * Allows a request to indicate it no longer is interested in a given load.
   */
  public static class LoadStatus {
    private final EngineJob engineJob;
    private final ResourceCallback cb;

    public LoadStatus(ResourceCallback cb, EngineJob engineJob) {
      this.cb = cb;
      this.engineJob = engineJob;
    }

    public void cancel() {
      engineJob.removeCallback(cb);
    }
  }

  public Engine(MemoryCache memoryCache,
      DiskCache.Factory diskCacheFactory,
      GlideExecutor diskCacheExecutor,
      GlideExecutor sourceExecutor,
      GlideExecutor sourceUnlimitedExecutor) {
    this(memoryCache, diskCacheFactory, diskCacheExecutor, sourceExecutor, sourceUnlimitedExecutor,
        null, null, null, null, null, null);
  }

  // Visible for testing.
  Engine(MemoryCache cache,
      DiskCache.Factory diskCacheFactory,
      GlideExecutor diskCacheExecutor,
      GlideExecutor sourceExecutor,
      GlideExecutor sourceUnlimitedExecutor,
      Map> jobs,
      EngineKeyFactory keyFactory,
      Map>> activeResources,
      EngineJobFactory engineJobFactory,
      DecodeJobFactory decodeJobFactory,
      ResourceRecycler resourceRecycler) {
    this.cache = cache;
    this.diskCacheProvider = new LazyDiskCacheProvider(diskCacheFactory);

    if (activeResources == null) {
      activeResources = new HashMap<>();
    }
    this.activeResources = activeResources;

    if (keyFactory == null) {
      keyFactory = new EngineKeyFactory();
    }
    this.keyFactory = keyFactory;

    if (jobs == null) {
      jobs = new HashMap<>();
    }
    this.jobs = jobs;

    if (engineJobFactory == null) {
      engineJobFactory = new EngineJobFactory(diskCacheExecutor, sourceExecutor,
          sourceUnlimitedExecutor, this);
    }
    this.engineJobFactory = engineJobFactory;

    if (decodeJobFactory == null) {
      decodeJobFactory = new DecodeJobFactory(diskCacheProvider);
    }
    this.decodeJobFactory = decodeJobFactory;

    if (resourceRecycler == null) {
      resourceRecycler = new ResourceRecycler();
    }
    this.resourceRecycler = resourceRecycler;

    cache.setResourceRemovedListener(this);
  }

  /**
   * Starts a load for the given arguments. Must be called on the main thread.
   *
   * 
 The flow for any request is as follows: 
     
  • Check the memory cache and provide the
   * cached resource if present
    •  
  • Check the current put of actively used resources and return
   * the active resource if present
    •  
  • Check the current put of in progress loads and add the
   * cb to the in progress load if present
    •  
  • Start a new load
    •  
 

   *
   * 
 Active resources are those that have been provided to at least one request and have not yet
   * been released. Once all consumers of a resource have released that resource, the resource then
   * goes to cache. If the resource is ever returned to a new consumer from cache, it is re-added to
   * the active resources. If the resource is evicted from the cache, its resources are recycled and
   * re-used if possible and the resource is discarded. There is no strict requirement that
   * consumers release their resources so active resources are held weakly. 

   *
   * @param width  The target width in pixels of the desired resource.
   * @param height The target height in pixels of the desired resource.
   * @param cb     The callback that will be called when the load completes.
   */
  public  LoadStatus load(
      GlideContext glideContext,
      Object model,
      Key signature,
      int width,
      int height,
      Class resourceClass,
      Class transcodeClass,
      Priority priority,
      DiskCacheStrategy diskCacheStrategy,
      Map, Transformation> transformations,
      boolean isTransformationRequired,
      Options options,
      boolean isMemoryCacheable,
      boolean useUnlimitedSourceExecutorPool,
      boolean onlyRetrieveFromCache,
      ResourceCallback cb) {
    Util.assertMainThread();
    long startTime = LogTime.getLogTime();

    EngineKey key = keyFactory.buildKey(model, signature, width, height, transformations,
        resourceClass, transcodeClass, options);

    EngineResource cached = loadFromCache(key, isMemoryCacheable);
    if (cached != null) {
      cb.onResourceReady(cached, DataSource.MEMORY_CACHE);
      if (Log.isLoggable(TAG, Log.VERBOSE)) {
        logWithTimeAndKey("Loaded resource from cache", startTime, key);
      }
      return null;
    }

    EngineResource active = loadFromActiveResources(key, isMemoryCacheable);
    if (active != null) {
      cb.onResourceReady(active, DataSource.MEMORY_CACHE);
      if (Log.isLoggable(TAG, Log.VERBOSE)) {
        logWithTimeAndKey("Loaded resource from active resources", startTime, key);
      }
      return null;
    }

    EngineJob current = jobs.get(key);
    if (current != null) {
      current.addCallback(cb);
      if (Log.isLoggable(TAG, Log.VERBOSE)) {
        logWithTimeAndKey("Added to existing load", startTime, key);
      }
      return new LoadStatus(cb, current);
    }

    EngineJob engineJob = engineJobFactory.build(key, isMemoryCacheable,
        useUnlimitedSourceExecutorPool);
    DecodeJob decodeJob = decodeJobFactory.build(
        glideContext,
        model,
        key,
        signature,
        width,
        height,
        resourceClass,
        transcodeClass,
        priority,
        diskCacheStrategy,
        transformations,
        isTransformationRequired,
        onlyRetrieveFromCache,
        options,
        engineJob);
    jobs.put(key, engineJob);
    engineJob.addCallback(cb);
    engineJob.start(decodeJob);

    if (Log.isLoggable(TAG, Log.VERBOSE)) {
      logWithTimeAndKey("Started new load", startTime, key);
    }
    return new LoadStatus(cb, engineJob);
  }

  private static void logWithTimeAndKey(String log, long startTime, Key key) {
    Log.v(TAG, log + " in " + LogTime.getElapsedMillis(startTime) + "ms, key: " + key);
  }

  private EngineResource loadFromActiveResources(Key key, boolean isMemoryCacheable) {
    if (!isMemoryCacheable) {
      return null;
    }

    EngineResource active = null;
    WeakReference> activeRef = activeResources.get(key);
    if (activeRef != null) {
      active = activeRef.get();
      if (active != null) {
        active.acquire();
      } else {
        activeResources.remove(key);
      }
    }

    return active;
  }

  private EngineResource loadFromCache(Key key, boolean isMemoryCacheable) {
    if (!isMemoryCacheable) {
      return null;
    }

    EngineResource cached = getEngineResourceFromCache(key);
    if (cached != null) {
      cached.acquire();
      activeResources.put(key, new ResourceWeakReference(key, cached, getReferenceQueue()));
    }
    return cached;
  }

  @SuppressWarnings("unchecked")
  private EngineResource getEngineResourceFromCache(Key key) {
    Resource cached = cache.remove(key);

    final EngineResource result;
    if (cached == null) {
      result = null;
    } else if (cached instanceof EngineResource) {
      // Save an object allocation if we've cached an EngineResource (the typical case).
      result = (EngineResource) cached;
    } else {
      result = new EngineResource<>(cached, true /*isMemoryCacheable*/);
    }
    return result;
  }

  public void release(Resource resource) {
    Util.assertMainThread();
    if (resource instanceof EngineResource) {
      ((EngineResource) resource).release();
    } else {
      throw new IllegalArgumentException("Cannot release anything but an EngineResource");
    }
  }

  @SuppressWarnings("unchecked")
  @Override
  public void onEngineJobComplete(Key key, EngineResource resource) {
    Util.assertMainThread();
    // A null resource indicates that the load failed, usually due to an exception.
    if (resource != null) {
      resource.setResourceListener(key, this);

      if (resource.isCacheable()) {
        activeResources.put(key, new ResourceWeakReference(key, resource, getReferenceQueue()));
      }
    }
    // TODO: should this check that the engine job is still current?
    jobs.remove(key);
  }

  @Override
  public void onEngineJobCancelled(EngineJob engineJob, Key key) {
    Util.assertMainThread();
    EngineJob current = jobs.get(key);
    if (engineJob.equals(current)) {
      jobs.remove(key);
    }
  }

  @Override
  public void onResourceRemoved(final Resource resource) {
    Util.assertMainThread();
    resourceRecycler.recycle(resource);
  }

  @Override
  public void onResourceReleased(Key cacheKey, EngineResource resource) {
    Util.assertMainThread();
    activeResources.remove(cacheKey);
    if (resource.isCacheable()) {
      cache.put(cacheKey, resource);
    } else {
      resourceRecycler.recycle(resource);
    }
  }

  public void clearDiskCache() {
    diskCacheProvider.getDiskCache().clear();
  }

  private ReferenceQueue> getReferenceQueue() {
    if (resourceReferenceQueue == null) {
      resourceReferenceQueue = new ReferenceQueue<>();
      MessageQueue queue = Looper.myQueue();
      queue.addIdleHandler(new RefQueueIdleHandler(activeResources, resourceReferenceQueue));
    }
    return resourceReferenceQueue;
  }

  private static class LazyDiskCacheProvider implements DecodeJob.DiskCacheProvider {

    private final DiskCache.Factory factory;
    private volatile DiskCache diskCache;

    public LazyDiskCacheProvider(DiskCache.Factory factory) {
      this.factory = factory;
    }

    @Override
    public DiskCache getDiskCache() {
      if (diskCache == null) {
        synchronized (this) {
          if (diskCache == null) {
            diskCache = factory.build();
          }
          if (diskCache == null) {
            diskCache = new DiskCacheAdapter();
          }
        }
      }
      return diskCache;
    }
  }

  private static class ResourceWeakReference extends WeakReference> {
    @Synthetic final Key key;

    public ResourceWeakReference(Key key, EngineResource r,
        ReferenceQueue> q) {
      super(r, q);
      this.key = key;
    }
  }

  // Responsible for cleaning up the active resource map by remove weak references that have been
  // cleared.
  private static class RefQueueIdleHandler implements MessageQueue.IdleHandler {
    private final Map>> activeResources;
    private final ReferenceQueue> queue;

    public RefQueueIdleHandler(Map>> activeResources,
        ReferenceQueue> queue) {
      this.activeResources = activeResources;
      this.queue = queue;
    }

    @Override
    public boolean queueIdle() {
      ResourceWeakReference ref = (ResourceWeakReference) queue.poll();
      if (ref != null) {
        activeResources.remove(ref.key);
      }

      return true;
    }
  }

  // Visible for testing.
  static class DecodeJobFactory {
    @Synthetic final DecodeJob.DiskCacheProvider diskCacheProvider;
    @Synthetic final Pools.Pool> pool = FactoryPools.simple(JOB_POOL_SIZE,
        new FactoryPools.Factory>() {
          @Override
          public DecodeJob create() {
            return new DecodeJob(diskCacheProvider, pool);
          }
        });
    private int creationOrder;

    DecodeJobFactory(DecodeJob.DiskCacheProvider diskCacheProvider) {
      this.diskCacheProvider = diskCacheProvider;
    }

    @SuppressWarnings("unchecked")
     DecodeJob build(GlideContext glideContext,
        Object model,
        EngineKey loadKey,
        Key signature,
        int width,
        int height,
        Class resourceClass,
        Class transcodeClass,
        Priority priority,
        DiskCacheStrategy diskCacheStrategy,
        Map, Transformation> transformations,
        boolean isTransformationRequired,
        boolean onlyRetrieveFromCache,
        Options options,
        DecodeJob.Callback callback) {
      DecodeJob result = (DecodeJob) pool.acquire();
      return result.init(
          glideContext,
          model,
          loadKey,
          signature,
          width,
          height,
          resourceClass,
          transcodeClass,
          priority,
          diskCacheStrategy,
          transformations,
          isTransformationRequired,
          onlyRetrieveFromCache,
          options,
          callback,
          creationOrder++);
    }
  }

  // Visible for testing.
  static class EngineJobFactory {
    @Synthetic final GlideExecutor diskCacheExecutor;
    @Synthetic final GlideExecutor sourceExecutor;
    @Synthetic final GlideExecutor sourceUnlimitedExecutor;
    @Synthetic final EngineJobListener listener;
    @Synthetic final Pools.Pool> pool = FactoryPools.simple(JOB_POOL_SIZE,
        new FactoryPools.Factory>() {
          @Override
          public EngineJob create() {
            return new EngineJob(diskCacheExecutor, sourceExecutor, sourceUnlimitedExecutor,
                listener, pool);
          }
        });

    EngineJobFactory(GlideExecutor diskCacheExecutor, GlideExecutor sourceExecutor,
        GlideExecutor sourceUnlimitedExecutor, EngineJobListener listener) {
      this.diskCacheExecutor = diskCacheExecutor;
      this.sourceExecutor = sourceExecutor;
      this.sourceUnlimitedExecutor = sourceUnlimitedExecutor;
      this.listener = listener;
    }

    @SuppressWarnings("unchecked")
     EngineJob build(Key key, boolean isMemoryCacheable,
        boolean useUnlimitedSourceGeneratorPool) {
      EngineJob result = (EngineJob) pool.acquire();
      return result.init(key, isMemoryCacheable, useUnlimitedSourceGeneratorPool);
    }
  }
}
    

    

    

            

    

            



    
    






    
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