From: John Torjo (john.lists_at_[hidden])
Date: 2004-09-24 11:54:11
Peter Dimov wrote:
> John Torjo wrote:
>>I think there is a bug in your Interlocked* implementation of
>> shared_ptr (http://www.pdimov.com/cpp/shared_count_x86_exp2.hpp).
>>In atomic_read you have:
>>inline long atomic_read(long volatile const & value)
>> return value;
>>I don't believe this is thread-safe.
> On x86/IA32, I believe that it's as thread safe as you can get. Note that
> all count updates go through Interlocked* calls. On IA32, plain reads can
> only return a somewhat "surprising" value when interleaved with plain
> writes, and even then, the element of surprise is limited. ;-)
I kind of wonder.
Here's my test scenario, which I think is quite effective ;)
The main thread creates a window. Then it internally has a shared
pointer to it.
Other threads might want access to this window. Each other thread keeps
a weak_pointer to it.
Whenever a thread (other than main) wants to access this window, it will
query the weak_pointer. The weak_pointer needs to know the LATEST
reference count in order to know if the weak pointer is still valid.
Thus, atomic_read that simply returns the value is not enough.
-- John Torjo -- john_at_[hidden] Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ -- v1.4 - save_dlg - true binding of your data to UI controls! + easily add validation rules (win32gui/examples/smart_dlg)
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