Glide 源码解析 之 线程池

GlideBuilder 中 线程池的初始化

  @NonNull
  Glide build(@NonNull Context context) {
    if (sourceExecutor == null) {
      sourceExecutor = GlideExecutor.newSourceExecutor();
    }

    if (diskCacheExecutor == null) {
      diskCacheExecutor = GlideExecutor.newDiskCacheExecutor();
    }

    if (animationExecutor == null) {
      animationExecutor = GlideExecutor.newAnimationExecutor();
    }
    //..
  }

从下面具体实现代码可以看到:
DiskCacheExecutor 的 corePoolSize 和 maximumPoolSize 均为 1；
SourceExecutor 的 corePoolSize 和 maximumPoolSize 均为 根据cpu processor数量计算得到的bestThreadCount；
AnimationExecutor 的 corePoolSize = 0 ， maximumPoolSize = bestThreadCount >= 4 ? 2 : 1；

GlideExecutor

  private static final int DEFAULT_DISK_CACHE_EXECUTOR_THREADS = 1;
  
  public static int calculateBestThreadCount() {
    if (bestThreadCount == 0) {
      bestThreadCount =
          Math.min(MAXIMUM_AUTOMATIC_THREAD_COUNT, RuntimeCompat.availableProcessors());
    }
    return bestThreadCount;
  }
  
  /**
   * Returns a new fixed thread pool with the default thread count returned from
   * {@link #calculateBestThreadCount()}, the {@link #DEFAULT_DISK_CACHE_EXECUTOR_NAME} thread name
   * prefix, and the
   * {@link com.bumptech.glide.load.engine.executor.GlideExecutor.UncaughtThrowableStrategy#DEFAULT}
   * uncaught throwable strategy.
   *
   * <p>Disk cache executors do not allow network operations on their threads.
   */
  public static GlideExecutor newDiskCacheExecutor() {
    return newDiskCacheExecutor(
        DEFAULT_DISK_CACHE_EXECUTOR_THREADS,
        DEFAULT_DISK_CACHE_EXECUTOR_NAME,
        UncaughtThrowableStrategy.DEFAULT);
  }
  
  public static GlideExecutor newDiskCacheExecutor(
      int threadCount, String name, UncaughtThrowableStrategy uncaughtThrowableStrategy) {
    return new GlideExecutor(
        new ThreadPoolExecutor(
            threadCount /* corePoolSize */,
            threadCount /* maximumPoolSize */,
            0 /* keepAliveTime */,
            TimeUnit.MILLISECONDS,
            new PriorityBlockingQueue<Runnable>(),
            new DefaultThreadFactory(name, uncaughtThrowableStrategy, true)));
  }
  
  /**
   * Returns a new fixed thread pool with the default thread count returned from
   * {@link #calculateBestThreadCount()}, the {@link #DEFAULT_SOURCE_EXECUTOR_NAME} thread name
   * prefix, and the
   * {@link com.bumptech.glide.load.engine.executor.GlideExecutor.UncaughtThrowableStrategy#DEFAULT}
   * uncaught throwable strategy.
   *
   * <p>Source executors allow network operations on their threads.
   */
  public static GlideExecutor newSourceExecutor() {
    return newSourceExecutor(
        calculateBestThreadCount(),
        DEFAULT_SOURCE_EXECUTOR_NAME,
        UncaughtThrowableStrategy.DEFAULT);
  }
  
  public static GlideExecutor newSourceExecutor(
      int threadCount, String name, UncaughtThrowableStrategy uncaughtThrowableStrategy) {
    return new GlideExecutor(
        new ThreadPoolExecutor(
            threadCount /* corePoolSize */,
            threadCount /* maximumPoolSize */,
            0 /* keepAliveTime */,
            TimeUnit.MILLISECONDS,
            new PriorityBlockingQueue<Runnable>(),
            new DefaultThreadFactory(name, uncaughtThrowableStrategy, false)));
  }
  
  /**
   * Returns a new cached thread pool that defaults to either one or two threads depending on the
   * number of available cores to use when loading frames of animations.
   */
  public static GlideExecutor newAnimationExecutor() {
    int bestThreadCount = calculateBestThreadCount();
    // We don't want to add a ton of threads running animations in parallel with our source and
    // disk cache executors. Doing so adds unnecessary CPU load and can also dramatically increase
    // our maximum memory usage. Typically one thread is sufficient here, but for higher end devices
    // with more cores, two threads can provide better performance if lots of GIFs are showing at
    // once.
    int maximumPoolSize = bestThreadCount >= 4 ? 2 : 1;

    return newAnimationExecutor(maximumPoolSize, UncaughtThrowableStrategy.DEFAULT);
  }
  
  public static GlideExecutor newAnimationExecutor(
      int threadCount, UncaughtThrowableStrategy uncaughtThrowableStrategy) {
     return new GlideExecutor(
        new ThreadPoolExecutor(
            0 /* corePoolSize */,
            threadCount,
            KEEP_ALIVE_TIME_MS,
            TimeUnit.MILLISECONDS,
            new PriorityBlockingQueue<Runnable>(),
            new DefaultThreadFactory(
                ANIMATION_EXECUTOR_NAME,
                uncaughtThrowableStrategy,
                true)));
  }

EngineJob 对线程池的调度

  public void start(DecodeJob<R> decodeJob) {
    this.decodeJob = decodeJob;
    GlideExecutor executor = decodeJob.willDecodeFromCache()
        ? diskCacheExecutor
        : getActiveSourceExecutor();
    executor.execute(decodeJob);
  }
  
  private GlideExecutor getActiveSourceExecutor() {
    return useUnlimitedSourceGeneratorPool
        ? sourceUnlimitedExecutor : (useAnimationPool ? animationExecutor : sourceExecutor);
  }