WCTwait chain traveral.docx

WCTwait chain traveral.docx

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WCTwaitchaintraveral

WaitChainTraversal（WCT）enablesdebuggerstodiagnoseapplicationhangsanddeadlocks.Awaitchainisanalternatingsequenceofthreadsandsynchronizationobjects;eachthreadwaitsfortheobjectthatfollowsit,whichisownedbythesubsequentthreadinthechain.

Athreadwaitsforasynchronizationobjectfromthetimeitrequestsituntilithasacquiredit.Alockisownedbyathreadfromthetimethethreadacquiresit,untilitreleasesit.Lockownershipisequivalenttothelockwaitingforthethreadtoreleaseit.Therefore,ifthread1waitsforalockthatisownedbythread2,thisisthesameassayingthatthread1waitsforthread2.WCTcurrentlysupportsthefollowingsynchronizationprimitives:

∙ALPC

∙COM

∙Criticalsections

∙Mutexes

∙SendMessage

∙Waitoperationsonprocessesandthreads

Toretrievethewaitchainforoneormorethreads,createaWCTsessionusingtheOpenThreadWaitChainSessionandGetThreadWaitChainfunctions.WCTsessionsarerepresentedbyahandleoftypeHWCT.Sessionscanbeeithersynchronousorasynchronousinnature.Synchronoussessionswillblockthecallingthreaduntilawaitchainhasbeenretrieved.Synchronoussessionscannotbecanceled.AsynchronoussessionsdonotblockthecallingthreadandcanbecanceledbytheapplicationusingtheCloseThreadWaitChainSessionfunction.ResultsfromasynchronousoperationsaremadeavailablethroughaWaitChainCallbackcallbackfunctionprovidedbytheapplication.

Forasynchronoussessions,thecallercanspecifyapointertoacontextdatastructurethroughGetThreadWaitChain.Thesamepointerispassedtothecallbackfunction.Thiscontextdatastructureisuser-definedandopaquetoWCT.ItcanbeusedbytheapplicationtocommunicatecontextbetweenaWCTqueryandacallbackfunction.Acommonapproachistopassaneventhandlethroughthisstructure;whenthecallbackisexecuted,itsignalsthiseventandinformssomemonitoringthreadthatthequeryhasbeencompleted.

Relatedtopics

UsingWCT

WCTReference

ThefollowingsamplecodedemonstratestheuseofthewaitchaintraversalAPI.Itenumeratesallthreadsinthesystemandprintsthewaitchainforeachthread.

Toenumerateallthreadsinthesystem,runthesamplewithnoparameters.Toenumerateonlythethreadsfromaspecifiedprocess,runthesampleandpasstheprocessidentifierasaparameter.Thesampleperformsthefollowingsteps:

1.CallstheRegisterWaitChainCOMCallbackfunctiontoregistertheCOMcallbackfunctions.

2.CallstheOpenThreadWaitChainSessionfunctiontocreatethewaitchainsession.

3.CallstheAdjustTokenPrivilegesfunctiontoenabletheSE_DEBUG_NAMEprivilege.

4.CallstheEnumProcessesandCreateToolhelp32Snapshotfunctionstoenumeratethespecifiedthreads.

5.CallstheGetThreadWaitChaintoretrieveanarrayofWAITCHAIN_NODE_INFOstructuresthatcontainthenodesofthewaitchain.

6.Printsinformationfromthewaitchain.

7.CallstheCloseThreadWaitChainSessionfunctiontocleanupthewaitchain.

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//Copyright（C）Microsoft.Allrightsreserved.

/*

*SamplecodefortheWaitChainTraversal（WCT）API.

*

*Thisprogramenumeratesallthreadsinthesystemandprintsthe

*waitchainforeachofthem.Itshouldberunfromanelevated

*commandprompttogetresultsforservices.

*

*/

#ifndefUNICODE

#defineUNICODE

#endif

#include

#include

#include

#include

#include

#include

#include

#pragmacomment（lib,"Psapi.lib"）

#pragmacomment（lib,"Advapi32.lib"）

typedefstruct_STR_ARRAY

{

CHARDesc[32];

}STR_ARRAY;

//Human-readablenamesforthedifferentsynchronizationtypes.

STR_ARRAYSTR_OBJECT_TYPE[]=

{

{"CriticalSection"},

{"SendMessage"},

{"Mutex"},

{"Alpc"},

{"Com"},

{"ThreadWait"},

{"ProcWait"},

{"Thread"},

{"ComActivation"},

{"Unknown"},

{"Max"}

};

//GlobalvariabletostoretheWCTsessionhandle

HWCTg_WctHandle=NULL;

//GlobalvariabletostoreOLE32.DLLmodulehandle.

HMODULEg_Ole32Hnd=NULL;

//

//Functionprototypes

//

void

PrintWaitChain（

__inDWORDThreadId

）;

BOOL

GrantDebugPrivilege（）

/*++

RoutineDescription:

Enablesthedebugprivilege（SE_DEBUG_NAME）forthisprocess.

Thisisnecessaryifwewanttoretrievewaitchainsforprocesses

notownedbythecurrentuser.

Arguments:

None.

ReturnValue:

TRUEifthisprivilegecouldbeenabled;FALSEotherwise.

--*/

{

BOOLfSuccess=FALSE;

HANDLETokenHandle=NULL;

TOKEN_PRIVILEGESTokenPrivileges;

if（!

OpenProcessToken（GetCurrentProcess（）,

TOKEN_ADJUST_PRIVILEGES|TOKEN_QUERY,

&TokenHandle））

{

printf（"Couldnotgettheprocesstoken"）;

gotoCleanup;

}

TokenPrivileges.PrivilegeCount=1;

if（!

LookupPrivilegeValue（NULL,

SE_DEBUG_NAME,

&TokenPrivileges.Privileges[0].Luid））

{

p