Re: Delete a list item from a separate thread safe?

"Doug Harrison [MVP]" <>
Mon, 28 Apr 2008 22:54:23 -0500
On Mon, 28 Apr 2008 19:49:26 +0100, "Stephen Howe"
<stephenPOINThoweATtns-globalPOINTcom> wrote:

Sure. But I take it for granted that any list modifying action in one thread
is protected by a critical section so that other threads have to wait.

There's not much I take for granted when talking to others about
multithreaded programming. IME, talking about "obvious" things often hits
on things the other person hasn't thought about or understood incorrectly.
This was a rather subtle question; just because an iterator remains "valid"
doesn't mean it remains "usable" in the absence of something the OP didn't
mention, namely, synchronization. For all we know, he may have devised some
hinky way of ensuring that the iterator isn't modified while another thread
is adding to the list, yet when he goes on to use the iterator, he has no
memory visibility guarantee. Oops. The program might work fine on a
uniprocessor system and even x86 multiprocessor, but fail subtly and
intermittently on weakly ordered multiprocessor systems.

Doug Harrison
Visual C++ MVP

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