C++ library系列 -- static destructors in multiple threads

  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;
}

posted on 2011-02-08 20:57 flagman 阅读(2053) 评论(0)  编辑 收藏 引用 所属分类: C++并发和并行 concurrency & parallelism


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