编译原理-全动态内存管理

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1、Chapter7DynamicMemoryParameterPassingMechanismsInstructorJianhuiYueSoftwareCollege@SCUcompilerscu@21cn.comLimitationsofStack-BasedEnvironmentIfareferencetoalocalvariableinaprocedurecanbereturnedtothecaller,theresultwillbedanglingreference.Whentheprocedu

2、reisexited,theactivationrecordwillbedeallocatedfromthestack.addr=dangle()causesaddrtopointtoanunsafelocation.SuchprogramiserroneousinC.(Nocompilerwillgiveanerrormessage)int*dangle(){intx;return&x;}LimitationsofStack-BasedEnvironment(cont)Cprohibitslocal

3、procedures.Functionalprogramminglanguages(LISP,ML)FunctionsmustbeabletobelocallydefinedPassedasparametersReturnedasresults.Stack-basedruntimeenvironmentisinadequatefortheselanguages.FullyDynamicEnvironmentItcandeallocateactivationrecordsonlywhenallrefer

4、encestothemhavedisappeared.Activationrecordscanbedynamicallyfreedatarbitrarytimesduringexecution.Fullydynamicenvironmentismorecomplicated.Trackingthereferencesduringexecution.Findinganddeallocatinginaccessibleareasofmemoryatarbitrarytimesduringexecution

5、(garbagecollection).ActivationRecordsThebasicstructureofanactivationrecordremainsthesame:Spaceforparametersandlocalvariables.Controlandaccesslinks.Theexitedactivationrecordremainsinmemory,tobedeallocatedatsomelatertime.Theentireadditionalcomplexitycanbe

6、encapsulatedinamemorymanagerthatreplacestheruntimestackoperationswithmoregeneralallocationanddeallocationroutines.Object-OrientedLanguagesOOlanguagesrequirespecialmechanismsintheruntimeenvironmenttoimplementtheiraddedfeatures:ObjectsMethodsInheritanceDy

7、namicbindingOOlanguagesvaryintheirrequirementsfortheruntimeenvironment:C++retainsthestack-basedenvironmentofC,noautomaticdynamicmemorymanagementSmalltalkrequiresfullydynamicenvironmentsimilartoLISPImplementationofObjectsKeepacompletedescriptionoftheclas

8、sstructureinmemoryduringexecution.Maintaintheinheritancebythesuperclasspointers.Keeppointerstoallmethods.Eachobjectkeeps:FieldsforinstancevariablesApointertoitsdefiningclassAllmethods(localandinherited)arefoundthroughit.Instancev