c# – 重型WPF控件如何以确定的方式使用一个空闲内存？

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525" x:Name="window" MouseMove="window_MouseMove">
</Window>

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {
        private class HeavyObject : UserControl
        {
            private byte[] x = new byte[750000000];

            public HeavyObject()
            {
                for (int i = 0; i++ < 99999999; ) { } // just so we can follow visually in Process Explorer
                Content = "Peekaboo!"; // change Content to el cheapo re-trigger MouseMove
            }
        }

        public MainWindow()
        {
            InitializeComponent();

            //Works 1:
            //while (true)
            //{
            //    window.Content = null;
            //    window.Content = new HeavyObject();
            //}
        }

        private void window_MouseMove(object sender,MouseEventArgs e)
        {
            if (window.Content == null)
            {
                GC.Collect();
                GC.WaitForPendingFinalizers();
                // Works 2:
                //new HeavyObject();
                //window.Content = "Peekaboo!"; // change Content to el cheapo re-trigger MouseMove
                //return;
                window.Content = new HeavyObject();
            }
            else
            {
                window.Content = null;
            }
        }
    }
}

好吧,我想我可能知道这里发生了什么.拿一小撮盐虽然……

我稍微修改了你的代码.

XAML

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" x:Name="window" MouseDown="window_MouseDown">
</Window>

代码背后

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {
        private class HeavyObject : UserControl
        {
            private byte[] x = new byte[750000000];

            public HeavyObject()
            {
                for (int i = 0; i < 750000000; i++ )
                {                    
                    unchecked
                    {
                        x[i] = (byte)i;       
                    }
                }

                // Release optimisation will not compile the array
                // unless you initialize and use it. 
                Content = "Loadss a memory!! " + x[1] + x[1000]; 
            }
        }

        const string msg = " ... nulled the HeavyObject ...";

        public MainWindow()
        {
            InitializeComponent();
            window.Content = msg;
        }

        private void window_MouseDown(object sender,MouseEventArgs e)
        {
            if (window.Content.Equals(msg))
            {
                window.Content = new HeavyObject();
            }
            else
            {
                window.Content = msg;
            }
        }
    }
}

现在运行它并单击窗口.我修改了代码,不使用GC.Collect()并在mousedown上设置内存.我正在发布模式下编译并在没有附加调试器的情况下运行.

在窗口上慢慢单击.

第一次点击,你看到内存使用量增加了750MBytes.随后的点击切换消息之间..取消重物..并加载内存！只要你慢慢点击.分配和释放内存时会有轻微的延迟.内存使用量不应超过750MBytes,但是当重对象被清空时它也不会减少.这是设计为GC Large Object Heap is lazy and collects large object memory when new large object memory is needed.从MSDN：

If I don’t have enough free space to accommodate the large object allocation requests,I will first attempt to acquire more segments from the OS. If that fails,then I will trigger a generation 2 garbage collection in hope of freeing up some space.

单击窗口上的快速

大约20次点击.怎么了？在我的PC上,内存使用量没有增加,但主窗口现在不再更新消息了.它冻结了.我没有内存不足异常,我的系统的整体内存使用率保持不变.

在Window上使用MouseMove强调系统

现在,通过更改此Xaml,将MouseDown替换为MouseMove事件(根据您的问题代码)：

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" x:Name="window" MouseMove="window_MouseDown">
</Window>

我可以将鼠标移动它很长一段时间但最终它会抛出一个OutofMemoryException.强制异常的一个好方法是多次移动然后尝试最大化窗口.

理论

好的,这就是我的理论.由于您的UI线程在消息循环事件(MouseMove)内创建和删除内存时运行平稳,因此垃圾收集器无法跟上.大对象堆上的垃圾收集在when memory is needed完成.它也是一项昂贵的任务,因此尽可能不经常执行.

当在MouseMove中执行时,我们在快速单击开/关/开/关时注意到的滞后变得更加明显.如果要分配另一个大对象,根据该MSDN文章,GC将尝试收集(如果内存不可用)或将开始使用磁盘.

System Is in Low Memory Situation: This happens when I receive the high memory notification from the OS. If I think doing a generation 2 GC will be productive,I will trigger one.

现在这部分很有意思,我猜这里,但是

Finally,as of right now,the LOH is not compacted as a part of collection,but that is an implementation detail that should not be relied on. So to make sure something is not moved by the GC,always pin it. Now take your newfound LOH knowledge and go take control of the heap.

因此,如果大对象堆未被压缩,并且您在紧密循环中请求多个大对象,那么即使理论上应该有足够的内存,集合是否可能导致碎片最终导致OutOfMemoryException？

解决方案

让我们释放一下UI线程让GC室呼吸.将分配代码包装在异步Dispatcher调用中并使用低优先级,例如SystemIdle.这样它只会在UI线程空闲时分配内存.

private void window_MouseDown(object sender,MouseEventArgs e)
    {
        Dispatcher.BeginInvoke((ThreadStart)delegate()
            {
                if (window.Content.Equals(msg))
                {
                    window.Content = new HeavyObject();
                }
                else
                {
                    window.Content = msg;
                }
            },DispatcherPriority.ApplicationIdle);
    }

使用这个我可以在整个表单上跳过鼠标指针,它永远不会抛出OutOfMemoryException.无论是真正的工作还是“修复”了我不知道的问题,但它值得测试.

结论

>请注意,此大小的对象将在大对象堆上分配
>如果没有足够的可用空间,LOH分配会触发GC
>在GC循环期间LOH没有被压缩,因此可能发生碎片,导致OutOfMemoryException,尽管理论上存在足够的内存
>理想情况下,重复使用大型对象,不要重新分配.如果那是不可能的：

>在后台线程中对您的大对象进行分组,以便从UI线程中解耦>要允许GC室呼吸,请使用Dispatcher解除分配,直到应用程序空闲