public <R> LoadStatus load(...) {
    long startTime = VERBOSE_IS_LOGGABLE ? LogTime.getLogTime() : 0;
    EngineKey key =
        keyFactory.buildKey(
            model,
            signature,
            width,
            height,
            transformations,
            resourceClass,
            transcodeClass,
            options);
    EngineResource<?> memoryResource;
    synchronized (this) {
      memoryResource = loadFromMemory(key, isMemoryCacheable, startTime);
      if (memoryResource == null) {
        return waitForExistingOrStartNewJob(...);
      }
    }
    // Avoid calling back while holding the engine lock, doing so makes it easier for callers to
    // deadlock.
    cb.onResourceReady(
        memoryResource, DataSource.MEMORY_CACHE, /* isLoadedFromAlternateCacheKey= */ false);
    return null;
  }

private <R> LoadStatus waitForExistingOrStartNewJob(...) {
    //通过添加和删除加载的回调并通知来管理加载的类
    //加载完成时回调。
    //咱都没数据肯定没加载完成，这个不管。急着往下看
    EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
    if (current != null) {
      current.addCallback(cb, callbackExecutor);
      if (VERBOSE_IS_LOGGABLE) {
        logWithTimeAndKey("Added to existing load", startTime, key);
      }
      return new LoadStatus(cb, current);
    }
    //同上，接着向下看
    EngineJob<R> engineJob =
        engineJobFactory.build(
            key,
            isMemoryCacheable,
            useUnlimitedSourceExecutorPool,
            useAnimationPool,
            onlyRetrieveFromCache);
    //负责从缓存数据或原始源解码资源的类，看着像，咱看看DecodeJob
    //应用转换和代码转换。
    DecodeJob<R> decodeJob =
        decodeJobFactory.build(
            ...
            engineJob);
    jobs.put(key, engineJob);
    engineJob.addCallback(cb, callbackExecutor);
    engineJob.start(decodeJob);
    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Started new load", startTime, key);
    }
    return new LoadStatus(cb, engineJob);
  }

class DecodeJob<R>
    implements DataFetcherGenerator.FetcherReadyCallback,
        Runnable,
        Comparable<DecodeJob<?>>,
        Poolable {
  }
  ...
  //构造方法有个DiskCacheProvider看着跟磁盘缓存有关咱进去瞅瞅
  DecodeJob(DiskCacheProvider diskCacheProvider, Pools.Pool<DecodeJob<?>> pool) {
    this.diskCacheProvider = diskCacheProvider;
    this.pool = pool;
  }
  ...

/** 用于向磁盘缓存写入数据和从磁盘缓存读取数据的接口 */
public interface DiskCache {
  /** 用于创建磁盘缓存的接口 */
  interface Factory {
    /** 250 MB of cache. */
    int DEFAULT_DISK_CACHE_SIZE = 250 * 1024 * 1024;
    String DEFAULT_DISK_CACHE_DIR = "image_manager_disk_cache";
    /** 返回新的磁盘缓存，如果无法创建磁盘缓存，则返回{@code null}*/
    @Nullable
    DiskCache build();
  }
  /** 向磁盘缓存中的密钥实际写入数据的接口 */
  interface Writer {
  /**
  *将数据写入文件
  *如果写入操作应中止，则返回false。
  *@param file写入程序应写入的文件。
  */
    boolean write(@NonNull File file);
  }
  /**
   *获取给定键处的值的缓存。
   */
  @Nullable
  File get(Key key);
  /**
  *@param key要写入的密钥。
  *@param writer一个接口，该接口将在给定密钥输出流的情况下写入数据。
   */
  void put(Key key, Writer writer);
  /**
   * 从缓存中删除键和值。.
   */
  @SuppressWarnings("unused")
  void delete(Key key);
  /** Clear the cache. */
  void clear();
}

/** An LRU in memory cache for {@link com.bumptech.glide.load.engine.Resource}s. */
public class LruResourceCache extends LruCache<Key, Resource<?>> implements MemoryCache {
  private ResourceRemovedListener listener;
  /**
  *LruResourceCache的构造函数。
  *@param size内存缓存可以使用的最大字节大小。
  */
  public LruResourceCache(long size) {
    super(size);
  }
  @Override
  public void setResourceRemovedListener(@NonNull ResourceRemovedListener listener) {
    this.listener = listener;
  }
  @Override
  protected void onItemEvicted(@NonNull Key key, @Nullable Resource<?> item) {
    if (listener != null && item != null) {
      listener.onResourceRemoved(item);
    }
  }
  @Override
  protected int getSize(@Nullable Resource<?> item) {
    if (item == null) {
      return super.getSize(null);
    } else {
      return item.getSize();
    }
  }
  @SuppressLint("InlinedApi")
  @Override
  public void trimMemory(int level) {
    if (level >= android.content.ComponentCallbacks2.TRIM_MEMORY_BACKGROUND) {
     //正在输入缓存的后台应用程序列表
    //退出我们的整个Bitmap缓存
      clearMemory();
    } else if (level >= android.content.ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN
        || level == android.content.ComponentCallbacks2.TRIM_MEMORY_RUNNING_CRITICAL) {
      // The app's UI is no longer visible, or app is in the foreground but system is running
      // critically low on memory
      // Evict oldest half of our bitmap cache
      trimToSize(getMaxSize() / 2);
    }
  }
}

Map<T,Y> cache = new LinkedHashMap<>(100,0.75f, true):