代表可以导致内存泄漏？ GC.TotalMemory（真）似乎表明这样 [英] Can delegates cause a memory leak? GC.TotalMemory(true) seems to indicate so

问题描述

代码

 使用系统; 
内部静态类测试
 {
私有静态无效的主要（）
 {
试
 {
 Console.WriteLine（{0， 10}：起点，GC.GetTotalMemory（真））; 
行动SimpleDelegate的= SimpleDelegate的; 
 Console.WriteLine（{0,10}：简单的委托创作，GC.GetTotalMemory（真））; 
行动simpleCombinedDelegate = SimpleDelegate的+ SimpleDelegate的+ SimpleDelegate的; 
 Console.WriteLine（{0,10}：简单的联合委托创作，GC.GetTotalMemory（真））; 
字节[] = bigManagedResource新的字节[亿]; 
 Console.WriteLine（{0,10}：大管理资源创建，GC.GetTotalMemory（真））; 
行动bigManagedResourceDelegate = bigManagedResource.BigManagedResourceDelegate; 
 Console.WriteLine（{0,10}：大托管资源的委托创作，GC.GetTotalMemory（真））; 
行动bigCombinedDelegate = simpleCombinedDelegate + bigManagedResourceDelegate; 
 Console.WriteLine（{0,10}：大联合委托创作，GC.GetTotalMemory（真））; 
 GC.KeepAlive（bigManagedResource）; 
 bigManagedResource = NULL; 
 GC.KeepAlive（bigManagedResourceDelegate）; 
 bigManagedResourceDelegate = NULL; 
 GC.KeepAlive（bigCombinedDelegate）; 
 bigCombinedDelegate = NULL; 
 Console.WriteLine（{0,10}：大托管资源，大管理的资源代表和大联合委托删除，但内存没有释放，GC.GetTotalMemory（真））; 
 GC.KeepAlive（simpleCombinedDelegate）; 
 simpleCombinedDelegate = NULL; 
 Console.WriteLine（{0,10}：简单组合委托删除，内存被释放，最后，GC.GetTotalMemory（真））; 
 GC.KeepAlive（SimpleDelegate的）; 
 SimpleDelegate的= NULL; 
 Console.WriteLine（{0,10}：简单的委托撤销，GC.GetTotalMemory（真））; 
} 
赶上（例外五）
 {
 Console.WriteLine（E）; 
} 
 Console.ReadKey（真）; 
} 
私有静态无效SimpleDelegate的（）{} 
私有静态无效BigManagedResourceDelegate（这byte []数组）{} 
} 
  

输出

  GC.TotalMemory（真）
 105776：起点
 191264：简单的委托创建
 191328：简单组合委托创建
 100191344：大管理资源创建
 100191780：大管理资源委派创建
 100191812：大联合委托创建
 100191780：大托管资源，大管理的资源代表和大联合委托删除，但内存没有释放
 191668：简单组合委托拆除，记忆中解脱出来，最后
 191636：简单的委托删除
  

解决方案

有趣的案例。这里是解决方案：

组合代表为观测上的纯：它看起来像代表是不可改变的外面。但内部，现有的代表正在修改即可。他们分享，在一定条件下，同样的 _invocationList 性能原因（这几个代表们迷上了同样的事件场景优化）。不幸的是， _invocationList 为 simpleCombinedDelegate 引用 bigMgdResDelegate 这导致内存来维持生命。

Code

using System;
internal static class Test
{
    private static void Main()
    {
        try
        {
            Console.WriteLine("{0,10}: Start point", GC.GetTotalMemory(true));
            Action simpleDelegate = SimpleDelegate;
            Console.WriteLine("{0,10}: Simple delegate created", GC.GetTotalMemory(true));
            Action simpleCombinedDelegate = simpleDelegate + simpleDelegate + simpleDelegate;
            Console.WriteLine("{0,10}: Simple combined delegate created", GC.GetTotalMemory(true));
            byte[] bigManagedResource = new byte[100000000];
            Console.WriteLine("{0,10}: Big managed resource created", GC.GetTotalMemory(true));
            Action bigManagedResourceDelegate = bigManagedResource.BigManagedResourceDelegate;
            Console.WriteLine("{0,10}: Big managed resource delegate created", GC.GetTotalMemory(true));
            Action bigCombinedDelegate = simpleCombinedDelegate + bigManagedResourceDelegate;
            Console.WriteLine("{0,10}: Big combined delegate created", GC.GetTotalMemory(true));
            GC.KeepAlive(bigManagedResource);
            bigManagedResource = null;
            GC.KeepAlive(bigManagedResourceDelegate);
            bigManagedResourceDelegate = null;
            GC.KeepAlive(bigCombinedDelegate);
            bigCombinedDelegate = null;
            Console.WriteLine("{0,10}: Big managed resource, big managed resource delegate and big combined delegate removed, but memory not freed", GC.GetTotalMemory(true));
            GC.KeepAlive(simpleCombinedDelegate);
            simpleCombinedDelegate = null;
            Console.WriteLine("{0,10}: Simple combined delegate removed, memory freed, at last", GC.GetTotalMemory(true));
            GC.KeepAlive(simpleDelegate);
            simpleDelegate = null;
            Console.WriteLine("{0,10}: Simple delegate removed", GC.GetTotalMemory(true));
        }
        catch (Exception e)
        {
            Console.WriteLine(e);
        }
        Console.ReadKey(true);
    }
    private static void SimpleDelegate() { }
    private static void BigManagedResourceDelegate(this byte[] array) { }
}

Output

GC.TotalMemory(true)
    105776: Start point
    191264: Simple delegate created
    191328: Simple combined delegate created
 100191344: Big managed resource created
 100191780: Big managed resource delegate created
 100191812: Big combined delegate created
 100191780: Big managed resource, big managed resource delegate and big combined delegate removed, but memory not freed
    191668: Simple combined delegate removed, memory freed, at last
    191636: Simple delegate removed

解决方案

Interesting case. Here is the solution:

Combining delegates is observationally pure: It looks like delegates are immutable to the outside. But internally, existing delegates are being modified. They share, under certain conditions, the same _invocationList for performance reasons (optimizing for the scenario that a few delegates are hooked up to the same event). Unfortunately, the _invocationList for the simpleCombinedDelegate references the bigMgdResDelegate which causes the memory to be kept alive.

这篇关于代表可以导致内存泄漏？ GC.TotalMemory（真）似乎表明这样的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！