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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��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��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��作用
: 以从某个文章里看的，说MFC用了一个大map�Q�没验证�q?br>: 有本讲GDI的书里，用了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�）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�ؓ�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）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）来操作对应的兌��自定义数据；很多后来出现的框�Ӟ��也都使用了这个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extra bytes的可�?/p>
性是微乎其微了，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�以及出错时的调试处理；因�ؓ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

�?某某提到: �?br>: 一般说COM复杂�Q�首先是名词太多�Q�其�ơ是��Z��ATL的实现比较难�?br>: �q��ƈ不是COM本��n复杂�Q�而是C++已经落后于时代了。所以ATL看�v来才会像天书一�?/em>

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不过从另一个角度看�Q�COM已经很容易了�Q?br>a) COM规范已把要达致这些目标的�pȝ��Q�所必须提供的接口和�Ҏ��抽象了出来�Q�只不过��Z��表达�q�些抽象的概念而新造的术语名词有些陌生和突兀�Q�如果让遇到�怼�问题的每一个设计和开发�h员都自己来做抽象�Q�未必会生成更好的方案；

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首先COM的规范的��是复杂的，为啥�Q�第一点已�l�说了，��是��Z��要抽象出跨边界和对象透明的组件技术；.net表象上看比较“��单容�?#8221;�Q�风��g��q�设计和开发�h员，实际上复杂事务和实现�l�节都被划分到CLR那个层面上去实现了；�ȝ��一下CLR的开源实现SSCLI�Q�你会发玎ͼ�整个虚拟机��^台的实现�Q�大量运用了COM的思想和机�Ӟ��是一个巨型系�l��^台��的COM server�Q?/p>
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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

关于�E�序设计语言本��n的设计有许多有趣的话题，比如�Q��ؓ何C++中的�c�L��员函数没有采用类似Java中的“全虚”设计�Q?br>
1) 从语�a�本��n设计上看�Q?br>效率定然是c++当初设计时考虑的重点之一�Q��D个例子，��Z��节省不必要的VTable开销�Q�ATL用template技术静态�{换来模拟动态绑定以支持COM�Ҏ��的实现�Q�和C的兼容，��VTable角度看，问题不大�Q�因为后者可以用函数指针数组来模拟；

2) 再从大多数应用中常见的类�l�承体系上看�Q?br>除了整个�l�承体系所�l�一开攑և�来的接口集（也就是由虚函数所�l�成�Q�，在��承体�pȝ��每个层面另外会有大量的其他辅助成员函敎ͼ�其数量通常比虚函数多的多）�Q�这些成员函数完全没必要设计成虚函数�Q?/p>
3) 从其他语�a�看，
即��较新的虚拟机语言C#(Java��是较老的虚拟��a�),反而定义了比C++更�ؓ严格更�ؓ昑ּ�的成员方法实现或覆盖或重载或新徏的规则；�q�是非常重要的对C++以及Java设计思想的反思�?/p>
4) 从语�a�的适用场合看，
我们现在的讨论，�l�大多数情况下带有一个非帔R��要的默认前提�Q�那��是在用��h��模式下使用C++�Q�如果放宽这个约束，在内核模式下使用C++�Q�那情况又完全不同了�?br>引用下面�q�个文档的观点，http://www.microsoft.com/china/whdc/driver/kernel/KMcode.mspx
首先�Q�用��h��下非常廉�h几乎不用考虑的资源，在内�怸�是非常昂�늚��Q�比如内核堆栈一般就3个page�Q?/p>
在内�怸�能分��?paging)时必��M��证将被执行的所有代码和数据必须有效的驻留在物理内存中，如果�q�时需要多�ȝ��几张虚表以及虚表指针那还是显得非常昂�늚��Q�同时编译器��函数�Q�模板等生成代码的方式，让开发�h员很隄��定要执行一个函数所需要的所有代码的所在位�|�，因此也无法直接控制用于安�|�这些代码的节（个�h认�ؓ可能通过progma segment/datasegment/codesegment对于代码和数据进行集中控�Ӟ��Q�因此在需要这些代码时�Q�可能已�l�被page out了；

所有涉及类层次�l�构�Q�模板，异常�{�等�q�样的一些语�a��l�构在内核态中都可能是不安全的�Q�最好是把类的��用限定�ؓPOD�c�，回到我们的主题虚函数�Q�也��是说内核态下�c�设计中没有虚函数�?/p>

flagman 2010-12-13 08:57 发表评论