On Tue, Jan 20, 2009 at 3:46 AM, Paul Rubin <"http://phr.cx"@nospam.invalid> wrote: > s...@pobox.com writes: >> Carl, I'm quite unfamiliar with Boost and am not a C++ person, so may have >> read what you saw but not recognized it in the C++ punctuation soup. I >> couldn't find what you referred to. Can you provide a URL? > > http://www.boost.org/doc/libs/1_37_0/libs/smart_ptr/shared_ptr.htm#ThreadSafety
I think you are misreading that. It says that multiple assignments to different copies of a share_ptr in different threads are fine. This is the important bit because copies of the same pointer share the same reference count, and assignments and resets will decrement that ref count. They say they don't handle mutations of the *same* pointer in different threads, which is a different issue. The programmer is responsible for synchronizing access to the pointer, and the pointed to object, but not the ref count. This may be not be obvious if you don't use shared_ptr a lot. You also mentioned in an earlier post that most processors don't support automic increments... I'm hesitant to dispute you here because this is outside of my field of expertise. However, a quick google search for "x86 atomic increment" comes up with this: XADD http://www.codemaestro.com/reviews/8 http://siyobik.info/index.php?module=x86&id=159 Again, I'm not an assembly guru, but his sounds like exactly what you'd want. It gains exclusive access to system memory in a multi-processor environtment without leaving user space. Thus XADD is an atomic increment/decrement. It would be educational if someone more famliar with x86 than me could speak to the performance merits of this on modern multicore machines. -- http://mail.python.org/mailman/listinfo/python-list
