为什么 fresco 选择不在 android 5.0 或更高版本的 ashmem 中放置位图答案

【问题标题】：Why fresco chose not put bitmap in ashmem on android 5.0 or higher为什么 fresco 选择不在 android 5.0 或更高版本的 ashmem 中放置位图
【发布时间】：2016-03-20 22:10:29
【问题描述】：

正如 git hub 上的 Fresco 项目所说：“在 Android 4.x 及更低版本中，Fresco 将图像放在 Android 内存的一个特殊区域中。这可以让您的应用程序运行得更快 - 并且更少地遭受可怕的 OutOfMemoryError。”

从this 回答，我知道它使用 ashmem 来放置位图。

我的问题是：为什么 fresco 不将位图放在 android 5.0 或更高版本的 ashmem 中？ Android 是否会更改某些系统功能并将其禁用？

【问题讨论】：

什么是ashmem？

标签： android memory-management bitmap fresco

【解决方案1】：

是的，Google 在 Android 5.0 中禁用了可清除位图。

【讨论】：

【解决方案2】：

  you can see here

https://android.googlesource.com/platform/frameworks/base/+/android-cts-7.1_r2/graphics/java/android/graphics/BitmapFactory.java

 /**
     * @deprecated As of {@link android.os.Build.VERSION_CODES#LOLLIPOP}, this is
     * ignored.
     *
     * In {@link android.os.Build.VERSION_CODES#KITKAT} and below, if this
     * is set to true, then the resulting bitmap will allocate its
     * pixels such that they can be purged if the system needs to reclaim
     * memory. In that instance, when the pixels need to be accessed again
     * (e.g. the bitmap is drawn, getPixels() is called), they will be
     * automatically re-decoded.
     *
     * <p>For the re-decode to happen, the bitmap must have access to the
     * encoded data, either by sharing a reference to the input
     * or by making a copy of it. This distinction is controlled by
     * inInputShareable. If this is true, then the bitmap may keep a shallow
     * reference to the input. If this is false, then the bitmap will
     * explicitly make a copy of the input data, and keep that. Even if
     * sharing is allowed, the implementation may still decide to make a
     * deep copy of the input data.</p>
     *
     * <p>While inPurgeable can help avoid big Dalvik heap allocations (from
     * API level 11 onward), it sacrifices performance predictability since any
     * image that the view system tries to draw may incur a decode delay which
     * can lead to dropped frames. Therefore, most apps should avoid using
     * inPurgeable to allow for a fast and fluid UI. To minimize Dalvik heap
     * allocations use the {@link #inBitmap} flag instead.</p>
     *
     * <p class="note"><strong>Note:</strong> This flag is ignored when used
     * with {@link #decodeResource(Resources, int,
     * android.graphics.BitmapFactory.Options)} or {@link #decodeFile(String,
     * android.graphics.BitmapFactory.Options)}.</p>
     */
    @Deprecated
    public boolean inPurgeable;

【讨论】：

【解决方案3】：

在Fresco documentation 他们提到：

Android 5.0 及更高版本比早期版本的内存管理有了很大改进，因此将位图缓存留在 Java 堆上更安全。

【讨论】：