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C++ library series -- in the MFC multiple-thread environment, how to quit worker-thread safely which begins with AfxBeginThread

flagman — Sun, 11 Dec 2011 12:35:00 GMT

In the MFC environment, normally, thread should be launched with AfxBeginThread for taking usage of MFC multiple-thread mechanism; In such mechanism, those datastructures, such as AFX_MODULE_STATE, would be used by MFC framework to maintain related thread information. It runs well when threads, launched with AfxBeginThread, quit before the main thread, which is responsible for initializing C run-time, but if such main thread quit before any other thread launched by AfxBeginThread, the current application would crash.

Such crash comes from the _afxThreadData (CThreadSlotData* _afxThreadData, which is defined in AFXTLS.cpp as global data structure) has been destructed while the main thread quits and it will invoke related function to clean up global data structures, including _afxThreadData definitely.

Consequently, serious developer should prepare for such case (other worker thread quits before main thread).

The reasonable resolve for such issue, would ensure any other threads should quit before the main thread.

.h file

/////////////////////////////////////////////////////////////////////////////

// CSafeEnterLeaveThread thread

class CSafeEnterLeaveThread : public CWinThread

{

DECLARE_DYNCREATE(CSafeEnterLeaveThread)

protected:

CSafeEnterLeaveThread(); // protected constructor used by dynamic creation

// Attributes

public:

// Operations

public:

// Overrides

// ClassWizard generated virtual function overrides

//{{AFX_VIRTUAL(CSafeEnterLeaveThread)

public:

virtual BOOL InitInstance();

virtual int ExitInstance();

//}}AFX_VIRTUAL

// Implementation

protected:

virtual ~CSafeEnterLeaveThread();

// Generated message map functions

//{{AFX_MSG(CSafeEnterLeaveThread)

// NOTE - the ClassWizard will add and remove member functions here.

//}}AFX_MSG

DECLARE_MESSAGE_MAP()

};

.cpp file

/////////////////////////////////////////////////////////////////////////////

// CSafeEnterLeaveThread

IMPLEMENT_DYNCREATE(CSafeEnterLeaveThread, CWinThread)

CSafeEnterLeaveThread::CSafeEnterLeaveThread()

{

}

CSafeEnterLeaveThread::~CSafeEnterLeaveThread()

{

}

BOOL CSafeEnterLeaveThread::InitInstance()

{

// TODO: perform and per-thread initialization here

ASSERT(this->m_hThread);

CMainApp::RegisterMFCThread(this->m_hThread);

return TRUE;

}

int CSafeEnterLeaveThread::ExitInstance()

{

// TODO: perform any per-thread cleanup here

ASSERT(this->m_hThread);

CMainApp::UnRegisterMFCThread(this->m_hThread);

return CWinThread::ExitInstance();

}

BEGIN_MESSAGE_MAP(CSafeEnterLeaveThread, CWinThread)

//{{AFX_MSG_MAP(CSafeEnterLeaveThread)

// NOTE - the ClassWizard will add and remove mapping macros here.

//}}AFX_MSG_MAP

END_MESSAGE_MAP()

And in the CMainApp,

set g_ThreadHandleSet;

HANDLE g_ThreadHandleArray[MAXIMUM_WAIT_OBJECTS];

CCriticalSection g_csGlobalData;

void CAccgbApp::CheckAllOtherMFCThreadsLeave()

{

int count = g_ThreadHandleSet.size();

if (count == 0) return;

set::iterator it;

int idx = 0;

for (it = g_ThreadHandleSet.begin(); it != g_ThreadHandleSet.end() && idx < MAXIMUM_WAIT_OBJECTS; it++, idx++)

{

g_ThreadHandleArray[idx] = *it;

}

if (count > idx) count = idx;

::WaitForMultipleObjects(count, g_ThreadHandleArray, TRUE, INFINITE);

}

void CAccgbApp::CleanupGlobalData()

{

g_csGlobalData.Lock();

g_ThreadHandleSet.empty();

g_csGlobalData.Unlock();

}

BOOL CAccgbApp::RegisterMFCThread(HANDLE hThread)

{

if (hThread == NULL) return FALSE;

g_csGlobalData.Lock();

if (g_ThreadHandleSet.find(hThread) == g_ThreadHandleSet.end())

g_ThreadHandleSet.insert(hThread);

g_csGlobalData.Unlock();

return TRUE;

}

void CAccgbApp::UnRegisterMFCThread(HANDLE hThread)

{

if (hThread == NULL) return;

g_csGlobalData.Lock();

if (g_ThreadHandleSet.find(hThread) != g_ThreadHandleSet.end())

g_ThreadHandleSet.erase(hThread);

g_csGlobalData.Unlock();

}

flagman 2011-12-11 20:35 发表评论

操作�pȝ��怎么�Ҏ(gu��)��一个HWND句柄�Q�找到相应的代码

flagman — Mon, 04 Apr 2011 06:16:00 GMT

�?�?�?的大作中提到: �?/em>

: 比如我有一个CMyButton的类�Q�我现在有他的一个handle
: �~�译器怎么�Ҏ(gu��)��q�个句柄扑ֈ�CMyButton的代码的�Q?/em>

�?�?某某的大作中提到: �?br>: �q�个和OS/Compiler没关�p�，是库��L(f��ng)��作用
: 以从某个文章里看的，说MFC用了(ji��n)一个大map�Q�没验证�q?br>: 有本讲GDI的书里，用了(ji��n)WNDCLASS里的extra bytes来实现的�q�个映射

MFC的应用里�Q�每个MFC�U�程�Q�必��要使用MFC方式启动的线�E�）(j��)都维护有一个MFC object和HWND之间�?/p>
mapping�Q�整个MFC框架��是使用�q�个机制来实现应用��C++对象和系�l��原生�H�口内核对象之间的关联；

因�ؓ(f��)�q�个mapping是以�U�程为单位来�l�护的，每个�U�程间互不关联，所以，一个应用里对于涉及(qi��ng)UI�H�口�?/p>
��d��最好是都放在同一个线�E�里面，一般就是当前进�E�的�ȝ��E�，否则可能出现MFC object和HWND之间

兌��不上的问题，而且�q�样的问题还很隐蔽�?br>

至于WNDCLASS�l�构自带的extra bytes域，是以前缺乏应用框架的时代�Q��用Win32 API直接开发时�Q�让每个

�H�口�c�（�q�里的类�Q�不是C++ class的概念，而是Windows�pȝ��H�口定义时的一�U�数据结构）(j��)都能有个�?/p>
带一些额外的自定义数据的�I�间�Q�这个空间往往被用来存放与当前�H�口�cȝ��关的用户数据�Q�通常是指�?/p>
某个内存区域的指针，当程序操作这个属于这个窗口类的窗口时��可以根据这个附带的自定义数据（�?/p>
者指针）(j��)来操作对应的兌��自定义数据；很多后来出现的框�Ӟ��也都使用�?ji��n)这个extra bytes域，来存�?/p>
框架本��n的一些和�H�口�cȝ��兌��的数据结构。从目前��势看，直接使用WNDCLASS以及(qi��ng)extra bytes的可�?/p>
性是微乎其微�?ji��n)，但是如果要做好原生应用的开发，很多底层的实现细节最要还是要知道一下，以便�?/p>
优化�l�构和性能�Q�以�?qi��ng)出错时的调试处理；因��?f��)无论是Winform/WPF�Q�还是跨�q�_��的WTL/QT/WxWindows�{?/p>
�{�新型的机制或者框架、类库，只要是在Windows�q�_��上搭建的�Q�那都是��Z��前面说过的这套最基本也是

最核心(j��)的Win32 API基础之上�?/p>

flagman 2011-04-04 14:16 发表评论

C++ library�p�d�� -- static destructors in multiple threads

flagman — Tue, 08 Feb 2011 12:57:00 GMT

In VC++ 8.0, while code compiled with /clr or /clr:pure, static destructors sometimes would not being properly called before process exites in multiple threads.

CRT incorrectly set a lock at _global_unlock which resulted in such issue.

In CLR-mixed mode, during the inialization of static local object, CRT would call _atexit_m(_CPVFV func) in msilexit.cpp to register a special __clrcall callback function which would be called back to destroy such static object when the current AppDomain quited.

In the multithread environment, _atexit_helper which was invoked by _atexit_m, could register such callbace function successfully because it had been guarded by __global_lock() and __global_unlock(). But in the same environment, the _atexit_m would fail to assign the correct value to __onexitbegin_m and __onexitend_m.

__onexitbegin_m and __onexitend_m were shared by the different threads; It's the key point of such issue. For example, the following statements,

__onexitbegin_m = (_CPVFV *)_encode_pointer(onexitbegin_m);
__onexitend_m = (_CPVFV *)_encode_pointer(onexitend_m);

should also guarded by __global_lock() and __global_unlock() or other syn primitives.

__global_lock();
__onexitbegin_m = (_CPVFV *)_encode_pointer(onexitbegin_m);
__onexitend_m = (_CPVFV *)_encode_pointer(onexitend_m);
__global_unlock();

extern "C" int __clrcall _atexit_m(_CPVFV func)
{
MANAGED_ASSERT(AppDomain::CurrentDomain->IsDefaultAppDomain(), "This fuction must be called in the default domain");

__global_lock();
_CPVFV* onexitbegin_m = (_CPVFV*)_decode_pointer(__onexitbegin_m);
_CPVFV* onexitend_m = (_CPVFV*)_decode_pointer(__onexitend_m);
__global_unlock();

int retval = _atexit_helper((_CPVFV)_encode_pointer(func), &__exit_list_size, &onexitend_m, &onexitbegin_m);

__global_lock();
__onexitbegin_m = (_CPVFV*)_encode_pointer(onexitbegin_m);
__onexitend_m = (_CPVFV*)_encode_pointer(onexitend_m);
__global_unlock();

return retval;
}

flagman 2011-02-08 20:57 发表评论

C++ library�p�d�� -- STL实现中的ODR “one-definition-rule�?for types

flagman — Sun, 19 Dec 2010 03:09:00 GMT

Linking issue
- While different modules (.obj) using istreambuf_iterator/ostreambuf_iterator, compiled with different options on HID/no-HID and SCL/no-SCL, these modules could not be linked successfully;

The error comes directly from the CLR when a type has multiple definitions that are not consistent based upon the ODR, one-definition-rule for types. And, the linker itself isn't involved.

For example, with one module compile with /D_SECURE_SCL=0, while another is compiled with _SECURE_SCL=1;

At first, it's found that with _SECURE_SCL, the only thing that could be different as following,

#if _SECURE_SCL
typedef _Range_checked_iterator_tag _Checked_iterator_category;
#endif

But, actually, it's not the typedef that changed the layout the these iterators (istreambuf_iterator/ostreambuf_iterator), and further they don't really use the extra pointer that _SECURE_SCL adds.

Finally, it's found the root cause is that, these iterators, istreambuf_iterator/ostreambuf_iterator had been moved from to , and their ultimate base class had been changed from _Iterator_base_secure to _Iterator_base. And, the layout of _Iterator_base would be different between HID and no-HID, and between SCL and no-SCL. It is the cause where the issue comes from.

What we can learn from such issue,
These iterators really shouldn't derive from either _Iterator_base_secure or _Iterator_base, because these classes contain data members (pointers) which are entirely unused. It would result in unnecessary bloat and extra work being performed in ctor/dtor etc.

Introduce a new class, _Iterator_base_universal, which is defined identically regardless of HID/no-HID and SCL/no-SCL. It would contains the three internal typedefs that all standard iterators need to have, and nothing else. And _Iterator_base (in all of its variants) and _Iterator_base_secure now should derive from _Iterator_base_universal to get these typedefs.

Now, when an iterator wants these typedefs, but not the data members of _Iterator_base and _Iterator_base_secure, it could derive from _Iterator_base_universal. And istreambuf_iterator and ostreambuf_iterator are now as small as possible, and keep identical representations or layout across HID/no-HID, SCL/no-SCL.

flagman 2010-12-19 11:09 发表评论

flagman — Sun, 19 Dec 2010 03:04:00 GMT

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flagman 2010-12-19 11:04 发表评论

flagman — Mon, 13 Dec 2010 01:02:00 GMT

Fusion is one of the most importants features among ones in the runtime implementation of CLI.

In the fusion, or any other components or modules, how to retrieve the execution engine instance and how to generate such engine?

UtilExecutionEngine, implemented as COM object, support Queryinterface/AddRef/Release, and exposed via interface IExecutionEngine.

With SELF_NO_HOST defined,
BYTE g_ExecutionEngineInstance[sizeof(UtilExecutionEngine)];
g_ExecutionEngineInstance would be the singleton instance of current execution engine,

otherwise, without SELF_NO_HOST, the 'sscoree' dll would be loaded and try to get the exported function, which is named 'IEE' from such dll. Here, it is the well-known shim, in .net CLR, such module is named 'mscoree'. Further, if 'IEE' could not be found in such dll, system would try to locate another exported function, named 'LoadLibraryShim', and use such function to load the 'mscorwks' module, and try to locate the 'IEE' exportd functionin it.

It's very obvious that Rotor has implemented its own execution engine, but it also gives or make space for implementation of execution engine from 3rd party. Here, .net CLR is a good candidate definitely, Rotor might load the mscorwks.dll module for its usage.

PAL, PALAPI, for example, HeapAlloc, one famous WIN32 API, has been implemented as one PALAPI (defined in Heap.c), to make it possible that the CLI/Rotor be ported smoothly to other OS, such freebsd/mac os.

CRT routines are also reimplemented, such as memcpy, it has been implemented as GCSafeMemCpy

There're many macros in fuctions, such as SCAN_IGNORE_FAULT/STATIC_CONTRACT_NOTHROW/STATIC_CONTRACT_NOTRIGGER, they are for static analysis tool to scan, analyse and figour out the potential issues in code.

From view point of the execution model by CLI, the act of compiling (including JIT) high-level type descriptions would be separated from the act of turning these type descriptions into processor-specific code and memory structures.

And such executino model, in other word, the well-known 'managed execution', would defer the loading, verification and compilation of components until runtime really needs; At the same time, the type-loading is the key trigger that causes CLI's tool chain to be engaged at runtime. Deferred compilation(lead to JIT)/linking/loading would get better portability to different target platform and be ready for version change; The whole deferred process would driven by well-defined metadata and policy, and it would be very robust for building a virtual execution environment;

At the top of such CLI tool chain, fusion is reponsible for not only finding and binding related assemblies, which are via assembly reference defined in assembly, fusion also takes another important role, loader, and its part of functionality is implemented in PEAssembly, ClassLoader classes. For example, ClassLoader::LoadTypeHandleForTypeKey.

For types in virtual execution environment of CLI, rotor defines four kinds of elements for internal conducting,
ELEMENT_TYPE_CLASS for ordinary classes and generic instantiations(including value types);
ELEMENT_TYPE_ARRAY AND ELEMENT_TYPE_SZARRAY for array types
ELEMENT_TYPE_PRT and ELEMENT_TYPE_BYREF for pointer types
ELEMENT_TYPE_FNPTR for function pointer types

every type would be assigned unique ulong-typed token, and such token would be used to look up in m_TypeDefToMethodTableMap (Linear mapping from TypeDef token to MethodTable *)which is maintained by current module; If there it is, the pointer to method table of such type would be retrieved, or it would look up in the loader module, where the method table should exist in while it's JIT loaded, not launched from NGEN image;

And all the unresolved typed would be maintained in a hash table, PendingTypeLoadTable; Types and only those types that are needed, such as dependencies, including parent types, are loaded in runtime, such type is fully loaded and ready for further execution, and other unresolved types would be kept in the previous hash table.

flagman 2010-12-13 09:02 发表评论

flagman — Mon, 13 Dec 2010 00:57:00 GMT

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flagman 2010-12-13 08:57 发表评论