Re: std::deque Thread Saftey Situtation

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 1 Sep 2008 13:32:27 -0700 (PDT)

Message-ID:

<ec4e807a-0d01-4ece-b828-62e178cf693b@m45g2000hsb.googlegroups.com>

On Sep 1, 11:45 am, zaim...@zaimoni.com wrote:

On Sep 1, 2:34 am, NvrBst <nvr...@gmail.com> wrote:

No - you are not correct. Imagine a situation where the
pushing thread pushes the object to the dequeue and then
increases the counter. However, the size get written
through the cache whereas the object stays (partly) in the
cache. Now the reader will see that there is an object in
the dequeue, but in reality it was never written to a
location that allows the other thread to see it (it is on
another core), so it reads rubbish where the object should
be.

I don't quite understand what you say ("on another core"
part), but I'm pretty sure it is safe. The pop'ing thread
is only taking the first element, and the push'ing thread is
appending to the end.

It's absolutely safe only if the std::deque has been specially
implemented so that each member function has "enough"
synchronization.

I don't think that that's possible, given the interface.

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