WCTwait chain traveral.docx

1、WCTwait chain traveralWait Chain Traversal (WCT) enables debuggers to diagnose application hangs and deadlocks. A wait chain is an alternating sequence of threads and synchronization objects; each thread waits for the object that follows it, which is owned by the subsequent thread in the chain.A thr

2、ead waits for a synchronization object from the time it requests it until it has acquired it. A lock is owned by a thread from the time the thread acquires it, until it releases it. Lock ownership is equivalent to the lock waiting for the thread to release it. Therefore, if thread 1 waits for a lock

3、 that is owned by thread 2, this is the same as saying that thread 1 waits for thread 2. WCT currently supports the following synchronization primitives: ALPC COM Critical sections Mutexes SendMessage Wait operations on processes and threadsTo retrieve the wait chain for one or more threads, create

4、a WCT session using the OpenThreadWaitChainSession and GetThreadWaitChain functions. WCT sessions are represented by a handle of type HWCT. Sessions can be either synchronous or asynchronous in nature. Synchronous sessions will block the calling thread until a wait chain has been retrieved. Synchron

5、ous sessions cannot be canceled. Asynchronous sessions do not block the calling thread and can be canceled by the application using the CloseThreadWaitChainSession function. Results from asynchronous operations are made available through a WaitChainCallback callback function provided by the applicat

6、ion.For asynchronous sessions, the caller can specify a pointer to a context data structure through GetThreadWaitChain. The same pointer is passed to the callback function. This context data structure is user-defined and opaque to WCT. It can be used by the application to communicate context between

7、 a WCT query and a callback function. A common approach is to pass an event handle through this structure; when the callback is executed, it signals this event and informs some monitoring thread that the query has been completed.Related topicsUsing WCTWCT ReferenceThe following sample code demonstra

8、tes the use of the wait chain traversal API. It enumerates all threads in the system and prints the wait chain for each thread.To enumerate all threads in the system, run the sample with no parameters. To enumerate only the threads from a specified process, run the sample and pass the process identi

9、fier as a parameter. The sample performs the following steps:1. Calls the RegisterWaitChainCOMCallback function to register the COM callback functions.2. Calls the OpenThreadWaitChainSession function to create the wait chain session.3. Calls the AdjustTokenPrivileges function to enable the SE_DEBUG_

10、NAME privilege.4. Calls the EnumProcesses and CreateToolhelp32Snapshot functions to enumerate the specified threads.5. Calls the GetThreadWaitChain to retrieve an array of WAITCHAIN_NODE_INFO structures that contain the nodes of the wait chain.6. Prints information from the wait chain.7. Calls the C

11、loseThreadWaitChainSession function to clean up the wait chain.Copy/ Copyright (C) Microsoft. All rights reserved./* * Sample code for the Wait Chain Traversal (WCT) API. * * This program enumerates all threads in the system and prints the * wait chain for each of them. It should be run from an elev

12、ated * command prompt to get results for services. * */#ifndef UNICODE #define UNICODE#endif#include #include #include #include #include #include #include #pragma comment(lib, Psapi.lib)#pragma comment(lib, Advapi32.lib)typedef struct _STR_ARRAY CHAR Desc32; STR_ARRAY;/ Human-readable names for the

13、different synchronization types.STR_ARRAY STR_OBJECT_TYPE = CriticalSection, SendMessage, Mutex, Alpc, Com, ThreadWait, ProcWait, Thread, ComActivation, Unknown, Max;/ Global variable to store the WCT session handleHWCT g_WctHandle = NULL;/ Global variable to store OLE32.DLL module handle.HMODULE g_

14、Ole32Hnd = NULL;/ Function prototypes/voidPrintWaitChain ( _in DWORD ThreadId );BOOLGrantDebugPrivilege ( )/*+Routine Description: Enables the debug privilege (SE_DEBUG_NAME) for this process. This is necessary if we want to retrieve wait chains for processes not owned by the current user.Arguments:

15、 None.Return Value: TRUE if this privilege could be enabled; FALSE otherwise.-*/ BOOL fSuccess = FALSE; HANDLE TokenHandle = NULL; TOKEN_PRIVILEGES TokenPrivileges; if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, &TokenHandle) printf(Could not get the process token); goto Cleanup; TokenPrivileges.PrivilegeCount = 1; if (!LookupPrivilegeValue(NULL, SE_DEBUG_NAME, &TokenPrivileges.Privileges0.Luid) p