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From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-03-27 13:44:39

Howard Hinnant wrote:

> New use case:
> vector<thread> v;
> ... fill with threads ...
> for (auto i = v.begin(), e = v.end(); i != e; ++i)
> if (i_feel_like_it)
> i->detach();
> ...
> // need new thread now, go look for a detached one and use it
> auto i = v.begin();
> for (auto e = v.end(); i != e; ++i)
> if (i->is_detached()) // N2184 spells this i->get_id() ==
> thread::id()
> break;
> if (i != v.end())
> *i = std::thread(f); // recycle detached thread
> else
> v.push_back(std::thread(f));

I was thinking of something along these lines, but it still seems contrived
to me. There is no reason to reuse an std::thread _object_ because you gain
no efficiency from that (as opposed to reusing a thread).

So I'd use something like:

> for (auto i = v.begin(), e = v.end(); i != e; ++i)
> if (i_feel_like_it)
> i->detach();

and then just add new threads with push_back... If I'm not interested in *i,
I see no reason to keep it in the vector - if I use v.size() as an
indication of the number of my active threads, this would skew the results.

There's also:

for (auto i = v.begin(), e = v.end(); i != e; ++i)
    if( i->try_join() )

(ignoring invalidation for the purposes of the pseudocode :-) )

which is useful if I want to keep an eye on 'my' threads but need v.size()
to not include dead ones. In this case, I can decide whether a detached
thread still counts against 'mine' by leaving or not leaving it in v after

In a less forgiving model such as N2178, the original example is just

erase_if( v, feel_like_it_predicate );

since it has an implicit detach, although I admit that cancel on destroy is
useful in other scenarios and have no strong preference for one over the

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