Fresco

解码器

• Android 8.0及以上使用系统的，bitmap数据保存在native
• Android 5.0~Android8.0 使用系统的，bitmap数据保存在java堆好
• Android 4.4 也保存在了java堆上，但是使用了pool减少内存的分配
• Android 2.3-Android 4.4 Bitmap缓存位于匿名共享内存,Android中操作匿名共享内存对应的类是MemoryFile，将bitmap的数据拷贝到memoryFile中，然后用file descriptor 解析图片

// com.facebook.imagepipeline.platform.java
public static PlatformDecoder buildPlatformDecoder(
      PoolFactory poolFactory, boolean gingerbreadDecoderEnabled) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
      int maxNumThreads = poolFactory.getFlexByteArrayPoolMaxNumThreads();
      return new OreoDecoder(
          poolFactory.getBitmapPool(), maxNumThreads, new Pools.SynchronizedPool<>(maxNumThreads));
    } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      int maxNumThreads = poolFactory.getFlexByteArrayPoolMaxNumThreads();
      return new ArtDecoder(
          poolFactory.getBitmapPool(), maxNumThreads, new Pools.SynchronizedPool<>(maxNumThreads));
    } else {
      if (gingerbreadDecoderEnabled && Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {
        return new GingerbreadPurgeableDecoder();
      } else {
        return new KitKatPurgeableDecoder(poolFactory.getFlexByteArrayPool());
      }
    }
  }