Re: STL container read thread-safety.

"Jim Langston" <>
Fri, 4 Apr 2008 11:16:25 -0700
<kguJj.20$_71.13@newsfe02.lga> wrote:

I know that the overall thread safety of STL containers is not
guaranteed. However, if I have an std::vector<int> or an
std::list<int>, and multiple threads are reading them but nothing is
writing them, do I still need to synchronize access to them? By
"reading" I mean iterating through with const_iterators, and also
copying them to other containers with the assignment operator.

What I mean is, am I guaranteed that, say, I don't know, obtaining a
const_iterator via std::list<int>::begin() isn't doing any internal
housekeeping or anything that would potentially make it not thread-

What about set and map?

If "nothing is writing them" is indeeed true, you *should* be okay most of
the time. However, how can you be 100% sure that something won't write to
it somewhere? Somehow you need to get the entries into the container for
your threads to read. If something is writing to a container while
something else is reading it, bad things happen.

It is much eaiser to wrap the container in a thread safe class then to make
sure your code doesn't write to a container when something is reading it.

Jim Langston

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