Garbage Collection in .Net

Wenjin Xu

AgendaBasicsAllocationCollectionFinalizationGC ModeSample

BasicIdea

Automatic memory managementTerms

Domain, Heap, Generation 0, Generation 1, Generation 2, Large object heap

Heap

AllocationInitial

CLR reserve memory for small object heap and large object heap(16MB / 64MB)

newobjAllocate memory from heap

Generation Promotion

CollocationWhen

Generation 0 is fullCall GC.Collect()Low memory

HowAssume all objects are garbageMark following object are reachable:Static fieldsMethod parametersLocal variablesCPU registersStrong ReferencesCollect

Finalization

WhenGeneration 0 is fullCall GC.CollectLow memoryAppDomain unloadCLR is shutting down

Dispose

GC Mode

10

GC Mode

GC

Workstation Server

ConcurrentCollections

“Normal”Background GC

GC Mode - DefaultSingle processor should use default Mode

GC Mode – Concurrent GCIn background garbage collection, ephemeral generations (0 and 1) are collected as needed while the collection of generation 2 is in progress

GC Mode – Server ModeHigh priority threadGC together, so garbage collection is fasterServer garbage collection often has larger size segments

Pinned ObjectWhy do we need pinning

Interop with unmanaged codeHow objects get pinned

GCHandleType.PinnedAllowed by language syntax, eg. fixed in c#Args get pinned by the interop frame

Fragmentation problem

Domain MonitoringCan not disable after enableGlobalPerformance hunt (about <1%)Does not count memory from Marshal.AllocHGlobal

Memory LeakStrong ReferenceAllocate Memory by Marshal

Sample查看性能计数器使用对象池节省新建对象造成的 GC压力使用 VSTS检查内存分配情况WinDBG + sosDebug vs Release

ResourcePerformance Counter

http://msdn.microsoft.com/en-us/library/x2tyfybc.aspx

BookCLR via C# 3rd Edition

Source Codehttp://referencesource.microsoft.com/netframework.aspx

Thank you