委托会导致内存泄漏吗?GC.TotalMemory(true) 似乎表明了这一点 [英] Can delegates cause a memory leak? GC.TotalMemory(true) seems to indicate so

问题描述

代码

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) { }
}

输出

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

推荐答案

有趣的案例.这是解决方案:

Interesting case. Here is the solution:

组合委托是观察上纯粹的:看起来委托对外部来说是不可变的.但是在内部，正在修改现有的代表.出于性能原因，它们在某些条件下共享相同的 _invocationList(针对少数委托连接到同一事件的场景进行优化).不幸的是，simpleCombinedDelegate 的 _invocationList 引用了导致内存保持活动状态的 bigMgdResDelegate.

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.

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