Glide 缓存机制

Posted 2021-06-15 qianxiangs

Glide 缓存机制

@Nullable
private EngineResource<?> loadFromMemory(
    EngineKey key, boolean isMemoryCacheable, long startTime) {
  if (!isMemoryCacheable) {
    return null;
  }

  //从弱引用对象加载  图片加载过二次加载会从弱引用对象加载
  EngineResource<?> active = loadFromActiveResources(key);
  if (active != null) {
    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Loaded resource from active resources", startTime, key);
    }
    return active;
  }

  //退出app,在次进入,弱引用已被清理,从LurCached缓存加载
  EngineResource<?> cached = loadFromCache(key);
  if (cached != null) {
    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Loaded resource from cache", startTime, key);
    }
    return cached;
  }

  return null;
}

 

 Glide 在加载图片前会查询弱引用中是否有图片,如果有会直接加载,如果没有就会去找LruCached.

  synchronized (this) {
      //查找缓存
      memoryResource = loadFromMemory(key, isMemoryCacheable, startTime);

      if (memoryResource == null) {
        //缓存为空,查找磁盘缓存
        return waitForExistingOrStartNewJob(
            glideContext,
            model,
            signature,
            width,
            height,
            resourceClass,
            transcodeClass,
            priority,
            diskCacheStrategy,
            transformations,
            isTransformationRequired,
            isScaleOnlyOrNoTransform,
            options,
            isMemoryCacheable,
            useUnlimitedSourceExecutorPool,
            useAnimationPool,
            onlyRetrieveFromCache,
            cb,
            callbackExecutor,
            key,
            startTime);
      }
    }

    // Avoid calling back while holding the engine lock, doing so makes it easier for callers to
    // deadlock.
    cb.onResourceReady(memoryResource, DataSource.MEMORY_CACHE);
    return null;
  }

如果LruCached 也不存在,会查找磁盘缓存,如果磁盘缓存也没有才会进行网络请求,Glide 网络请求类HttpUrlFetcher 

 private <R> LoadStatus waitForExistingOrStartNewJob(
      GlideContext glideContext,
      Object model,
      Key signature,
      int width,
      int height,
      Class<?> resourceClass,
      Class<R> transcodeClass,
      Priority priority,
      DiskCacheStrategy diskCacheStrategy,
      Map<Class<?>, Transformation<?>> transformations,
      boolean isTransformationRequired,
      boolean isScaleOnlyOrNoTransform,
      Options options,
      boolean isMemoryCacheable,
      boolean useUnlimitedSourceExecutorPool,
      boolean useAnimationPool,
      boolean onlyRetrieveFromCache,
      ResourceCallback cb,
      Executor callbackExecutor,
      EngineKey key,
      long startTime) {

    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);
    }

    EngineJob<R> engineJob =
        engineJobFactory.build(
            key,
            isMemoryCacheable,
            useUnlimitedSourceExecutorPool,
            useAnimationPool,
            onlyRetrieveFromCache);

    DecodeJob<R> decodeJob =
        decodeJobFactory.build(
            glideContext,
            model,
            key,
            signature,
            width,
            height,
            resourceClass,
            transcodeClass,
            priority,
            diskCacheStrategy,
            transformations,
            isTransformationRequired,
            isScaleOnlyOrNoTransform,
            onlyRetrieveFromCache,
            options,
            engineJob);

    jobs.put(key, engineJob);

    engineJob.addCallback(cb, callbackExecutor);
    //读磁盘缓存
    engineJob.start(decodeJob);

    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Started new load", startTime, key);
    }
    return new LoadStatus(cb, engineJob);
  }

EngineJob 是一个线程对象,调用 strat 方法开启一个线程池，执行EngineJob线程的run 方法

class DecodeJob<R>
    implements DataFetcherGenerator.FetcherReadyCallback,
        Runnable,
        Comparable<DecodeJob<?>>,
        Poolable {

 

  public synchronized void start(DecodeJob<R> decodeJob) {
    this.decodeJob = decodeJob;
    GlideExecutor executor =
        decodeJob.willDecodeFromCache() ? diskCacheExecutor : getActiveSourceExecutor();
    //线程池
    executor.execute(decodeJob);
  }

　在run 方法中runWapped()方法　-->DecodeJob

@Override
  public void run() {
     ．．．．．．
    try {
      if (isCancelled) {
        notifyFailed();
        return;
      }
      runWrapped();
    } catch (CallbackException e) {
     
    } catch (Throwable t) {
     
      if (stage != Stage.ENCODE) {
        throwables.add(t);
        notifyFailed();
      }
  
    } finally {

      if (localFetcher != null) {
        localFetcher.cleanup();
      }
      GlideTrace.endSection();
    }
  }

 在runWraoped()方法中分为三个swith 分别　INITIALIZE　SWITCH_TO_SOURCE_SERVICE　DECODE_DATA　默认走第一个INITIALIZE

/**
   * 读磁盘缓存
   */
  private void runWrapped() {
    switch (runReason) {
      case INITIALIZE:
        stage = getNextStage(Stage.INITIALIZE);
        currentGenerator = getNextGenerator();
        runGenerators();
        break;
      case SWITCH_TO_SOURCE_SERVICE:
        runGenerators();
        break;
      case DECODE_DATA:
        decodeFromRetrievedData();
        break;
      default:
        throw new IllegalStateException("Unrecognized run reason: " + runReason);
    }
  }

在第一个　INITIALIZE　方法中调用 runGenerators方法 　-->DecodeJob

 private void runGenerators() {
    currentThread = Thread.currentThread();
    startFetchTime = LogTime.getLogTime();
    boolean isStarted = false;
    while (!isCancelled
        && currentGenerator != null
                //currentGenerator.startNext()
        && !(isStarted = currentGenerator.startNext())) {
      stage = getNextStage(stage);
      currentGenerator = getNextGenerator();

      if (stage == Stage.SOURCE) {
        reschedule();
        return;
      }
    }
    // We've run out of stages and generators, give up.
    if ((stage == Stage.FINISHED || isCancelled) && !isStarted) {
      notifyFailed();
    }

    // Otherwise a generator started a new load and we expect to be called back in
    // onDataFetcherReady.
  }

在runGenerators　方法中调用currentGenerator.startNext()　这个currentGenerator　调的是　ResourceCacheGenerator　startNext　方法

public boolean startNext() {
　　//添加到LruCache中
    List<Key> sourceIds = helper.getCacheKeys();
    if (sourceIds.isEmpty()) {
      return false;
    }
    List<Class<?>> resourceClasses = helper.getRegisteredResourceClasses();
    if (resourceClasses.isEmpty()) {
      if (File.class.equals(helper.getTranscodeClass())) {
        return false;
      }
      throw new IllegalStateException(
          "Failed to find any load path from "
              + helper.getModelClass()
              + " to "
              + helper.getTranscodeClass());
    }
    while (modelLoaders == null || !hasNextModelLoader()) {
      resourceClassIndex++;
      if (resourceClassIndex >= resourceClasses.size()) {
        sourceIdIndex++;
        if (sourceIdIndex >= sourceIds.size()) {
          return false;
        }
        resourceClassIndex = 0;
      }

      Key sourceId = sourceIds.get(sourceIdIndex);
      Class<?> resourceClass = resourceClasses.get(resourceClassIndex);
      Transformation<?> transformation = helper.getTransformation(resourceClass);
      // PMD.AvoidInstantiatingObjectsInLoops Each iteration is comparatively expensive anyway,
      // we only run until the first one succeeds, the loop runs for only a limited
      // number of iterations on the order of 10-20 in the worst case.
      //key
      currentKey =
          new ResourceCacheKey( // NOPMD AvoidInstantiatingObjectsInLoops
              helper.getArrayPool(),
              sourceId,
              helper.getSignature(),
              helper.getWidth(),
              helper.getHeight(),
              transformation,
              resourceClass,
              helper.getOptions());
      cacheFile = helper.getDiskCache().get(currentKey);
      if (cacheFile != null) {
        sourceKey = sourceId;
        modelLoaders = helper.getModelLoaders(cacheFile);
        modelLoaderIndex = 0;
      }
    }

    loadData = null;
    boolean started = false;
    while (!started && hasNextModelLoader()) {
      ModelLoader<File, ?> modelLoader = modelLoaders.get(modelLoaderIndex++);
      loadData =
          modelLoader.buildLoadData(
              cacheFile, helper.getWidth(), helper.getHeight(), helper.getOptions());
      if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {
        started = true;
        loadData.fetcher.loadData(helper.getPriority(), this);
      }
    }

    return started;
  }

//添加到LruCache中　然后在创建存储key 通过　key 找到磁盘存储的文件 然后调用　 loadData.fetcher.loadData(helper.getPriority(), this);  　-->ByteBufferFileLoader

  @Override
    public void loadData(
        @NonNull Priority priority, @NonNull DataCallback<? super ByteBuffer> callback) {
      ByteBuffer result;
      try {
        result = ByteBufferUtil.fromFile(file);
      } catch (IOException e) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
          Log.d(TAG, "Failed to obtain ByteBuffer for file", e);
        }
        callback.onLoadFailed(e);
        return;
      }

      callback.onDataReady(result);
    }

然后调用onDataReady 　-->ResourceCacheGenerator

@Override
  public void onDataReady(Object data) {
    cb.onDataFetcherReady(
        sourceKey, data, loadData.fetcher, DataSource.RESOURCE_DISK_CACHE, currentKey);
  }

 然后调用　onDataFetcherReady -->DecodeJob

public void onDataFetcherReady(
      Key sourceKey, Object data, DataFetcher<?> fetcher, DataSource dataSource, Key attemptedKey) {
    this.currentSourceKey = sourceKey;
    this.currentData = data;
    this.currentFetcher = fetcher;
    this.currentDataSource = dataSource;
    this.currentAttemptingKey = attemptedKey;
    if (Thread.currentThread() != currentThread) {
      runReason = RunReason.DECODE_DATA;
      callback.reschedule(this);
    } else {
      GlideTrace.beginSection("DecodeJob.decodeFromRetrievedData");
      try {
         //转码
        decodeFromRetrievedData();
      } finally {
        GlideTrace.endSection();
      }
    }
  }

然后调用　 decodeFromRetrievedData();  -->DecodeJob

  private void decodeFromRetrievedData() {
    if (Log.isLoggable(TAG, Log.VERBOSE)) {
      logWithTimeAndKey(
          "Retrieved data",
          startFetchTime,
          "data: "
              + currentData
              + ", cache key: "
              + currentSourceKey
              + ", fetcher: "
              + currentFetcher);
    }
    Resource<R> resource = null;
    try {
      resource = decodeFromData(currentFetcher, currentData, currentDataSource);
    } catch (GlideException e) {
      e.setLoggingDetails(currentAttemptingKey, currentDataSource);
      throwables.add(e);
    }
    if (resource != null) {
      notifyEncodeAndRelease(resource, currentDataSource);
    } else {
      runGenerators();
    }
  }

 然后调用　decodeFromData　解码到　Resource　Resource　不等于空调用　notifyEncodeAndRelease  -->DecodeJob

 private void notifyEncodeAndRelease(Resource<R> resource, DataSource dataSource) {
    if (resource instanceof Initializable) {
      ((Initializable) resource).initialize();
    }

    Resource<R> result = resource;
    LockedResource<R> lockedResource = null;
    if (deferredEncodeManager.hasResourceToEncode()) {
      lockedResource = LockedResource.obtain(resource);
      result = lockedResource;
    }
    //写入弱引用
    notifyComplete(result, dataSource);

    stage = Stage.ENCODE;
    try {
      //写入磁盘
      if (deferredEncodeManager.hasResourceToEncode()) {
        deferredEncodeManager.encode(diskCacheProvider, options);
      }
    } finally {
      if (lockedResource != null) {
        lockedResource.unlock();
      }
    }
    // Call onEncodeComplete outside the finally block so that it's not called if the encode process
    // throws.
    onEncodeComplete();
  }

然后调用 notifyComplete　-->DecodeJob 

 private void notifyComplete(Resource<R> resource, DataSource dataSource) {
    setNotifiedOrThrow();
    callback.onResourceReady(resource, dataSource);
  }

 然后调用 onResourceReady　--> EngineJob

 @Override
  public void onResourceReady(Resource<R> resource, DataSource dataSource) {
    synchronized (this) {
      this.resource = resource;
      this.dataSource = dataSource;
    }
    notifyCallbacksOfResult();
  }

 然后调用 notifyCallbacksOfResult- -> EngineJob 

  @Synthetic
  void notifyCallbacksOfResult() {
    ResourceCallbacksAndExecutors copy;
    Key localKey;
    EngineResource<?> localResource;
    synchronized (this) {
      stateVerifier.throwIfRecycled();
      if (isCancelled) {
        // TODO: Seems like we might as well put this in the memory cache instead of just recycling
        // it since we've gotten this far...
        resource.recycle();
        release();
        return;
      } else if (cbs.isEmpty()) {
        throw new IllegalStateException("Received a resource without any callbacks to notify");
      } else if (hasResource) {
        throw new IllegalStateException("Already have resource");
      }
      engineResource = engineResourceFactory.build(resource, isCacheable, key, resourceListener);
      // Hold on to resource for duration of our callbacks below so we don't recycle it in the
      // middle of notifying if it synchronously released by one of the callbacks. Acquire it under
      // a lock here so that any newly added callback that executes before the next locked section
      // below can't recycle the resource before we call the callbacks.
      hasResource = true;
      copy = cbs.copy();
      incrementPendingCallbacks(copy.size() + 1);

      localKey = key;
      localResource = engineResource;
    }

    //保存弱引用
    engineJobListener.onEngineJobComplete(this, localKey, localResource);

    for (final ResourceCallbackAndExecutor entry : copy) {
        //CallResourceReady 线程run方法
      entry.executor.execute(new CallResourceReady(entry.cb));
    }
    decrementPendingCallbacks();
  }

  @SuppressWarnings("WeakerAccess")
  @Synthetic
  synchronized void incrementPendingCallbacks(int count) {
    Preconditions.checkArgument(isDone(), "Not yet complete!");
    if (pendingCallbacks.getAndAdd(count) == 0 && engineResource != null) {
      engineResource.acquire();
    }
  }

executor 线程池调用 CallResourceReady　线程run方法　-->CallResourceReady

  private class CallResourceReady implements Runnable {

    private final ResourceCallback cb;

    CallResourceReady(ResourceCallback cb) {
      this.cb = cb;
    }

    @Override
    public void run() {
      // Make sure we always acquire the request lock, then the EngineJob lock to avoid deadlock
      // (b/136032534).
      synchronized (cb.getLock()) {
        synchronized (EngineJob.this) {
          if (cbs.contains(cb)) {
            // Acquire for this particular callback.
            engineResource.acquire();
            callCallbackOnResourceReady(cb);
            removeCallback(cb);
          }
          decrementPendingCallbacks();
        }
      }
    }
  }

然后调用　callCallbackOnResourceReady  - -> EngineJob 

  @SuppressWarnings("WeakerAccess")
  @Synthetic
  @GuardedBy("this")
  void callCallbackOnResourceReady(ResourceCallback cb) {
    try {
      // This is overly broad, some Glide code is actually called here, but it's much
      // simpler to encapsulate here than to do so at the actual call point in the
      // Request implementation.
      cb.onResourceReady(engineResource, dataSource);
    } catch (Throwable t) {
      throw new CallbackException(t);
    }
  }

 然后调用　onResourceReady　-->SingleRequest

  @Override
  public void onResourceReady(Resource<?> resource, DataSource dataSource) {
    stateVerifier.throwIfRecycled();
    Resource<?> toRelease = null;
    try {
      synchronized (requestLock) {
        loadStatus = null;
        if (resource == null) {
         
          onLoadFailed(exception);
          return;
        }

        Object received = resource.get();
        if (received == null || !transcodeClass.isAssignableFrom(received.getClass())) {
          toRelease = resource;
          this.resource = null;
         
          onLoadFailed(exception);
          return;
        }

        if (!canSetResource()) {
          toRelease = resource;
          this.resource = null;
          // We can't put the status to complete before asking canSetResource().
          status = Status.COMPLETE;
          return;
        }

        onResourceReady((Resource<R>) resource, (R) received, dataSource);
      }
    } finally {
      if (toRelease != null) {
        engine.release(toRelease);
      }
    }
  }

 然后调用　onResourceReady　-->SingleRequest 

  @GuardedBy("requestLock")
  private void onResourceReady(Resource<R> resource, R result, DataSource dataSource) {
    // We must call isFirstReadyResource before setting status.
    boolean isFirstResource = isFirstReadyResource();
    status = Status.COMPLETE;
    this.resource = resource;

    if (glideContext.getLogLevel() <= Log.DEBUG) {
      
    }

    isCallingCallbacks = true;
    try {
      boolean anyListenerHandledUpdatingTarget = false;
      if (requestListeners != null) {
        for (RequestListener<R> listener : requestListeners) {
          anyListenerHandledUpdatingTarget |=
              listener.onResourceReady(result, model, target, dataSource, isFirstResource);
        }
      }
      anyListenerHandledUpdatingTarget |=
          targetListener != null
              && targetListener.onResourceReady(result, model, target, dataSource, isFirstResource);

      if (!anyListenerHandledUpdatingTarget) {
        Transition<? super R> animation = animationFactory.build(dataSource, isFirstResource);
        target.onResourceReady(result, animation);
      }
    } finally {
      isCallingCallbacks = false;
    }

    notifyLoadSuccess();
  }

     target　为 ImageViewTarget

　target.onResourceReady(result, animation); 　--> ImageViewTarget

  @Override
  public void onResourceReady(@NonNull Z resource, @Nullable Transition<? super Z> transition) {
    if (transition == null || !transition.transition(resource, this)) {
      setResourceInternal(resource);
    } else {
      maybeUpdateAnimatable(resource);
    }
  }

然后调用　setResourceInternal --> ImageViewTarget

 private void setResourceInternal(@Nullable Z resource) {
    // Order matters here. Set the resource first to make sure that the Drawable has a valid and
    // non-null Callback before starting it.
    setResource(resource);
    maybeUpdateAnimatable(resource);
  }

 @Override
  protected void setResource(@Nullable Drawable resource) {
    Log.d(TAG, "setResource: -----"+resource);
    view.setImageDrawable(resource);
  }

这就是图片加载的整体流程，首先Glide会查询弱引用，如果弱引用没有，会查找LruCached,如果LruCached也没有会查找DiskLruCache　磁盘缓存，如果磁盘缓存也没有，才会进行网络请求，请求到数据会同步到弱引用，LruCached，DiskLruCache，这就是整体策略，这还要注意，如果磁盘缓存有图片，就不会网络请求，会同步到弱引用和LruCache 中.