calling .clear() or .erase() on c++ std::multimap sometimes causes freeze (100% cpu)

Question

We are using a multimap for quick value/index lookups, declared like this

typedef double Numerical;
std::multimap<Numerical, Int32> SortableRowIndex;

And we fill it up with pairs, using

SortableRowIndex.insert(std::pair<Numerical, Int32>(GetSortable(i), i));

The function GetSortable() always returns a double. And this works fine. Iterating through the values works fine too. But then comes the weird part... sometimes when we try to clear the data...

SortableRowIndex.clear();

... it goes into some kind of loop and stalls/races, hogging the used core of the CPU at 100%.

The clear method seems to be inherited from xtree (system file) and there are only a coupld of rows inside it:

    void clear() _NOEXCEPT
        {   // erase all
 #if _ITERATOR_DEBUG_LEVEL == 2
        this->_Orphan_ptr(*this, 0);
 #endif /* _ITERATOR_DEBUG_LEVEL == 2 */

        _Erase(_Root());
        _Root() = this->_Myhead;
        _Lmost() = this->_Myhead;
        _Rmost() = this->_Myhead;
        this->_Mysize = 0;
        }

For some reason, my Visual Studio 2013 won't let me step into this method when debugging... and I can't, for the life of me figure out what the problem is!

Any help will be ridiculously appreciated!

this http://stackoverflow.com/questions/8096817/is-nan-a-valid-key-value-for-associative-containers can be related — Slava, Nov 18 '15 at 14:06
Oh, thanks for the link... I don't think there should be any NaNs in there, but I'll write some code to verify it! Thanks. — Linus Särnhult, Nov 18 '15 at 14:18
I did a std::isnan() check on all the keys going in, and none returned true. I am also able to insert new keys and iterate over the data. — Linus Särnhult, Nov 18 '15 at 15:53
I'm considering trying the multimap in boost... maybe it behaves differently? — Linus Särnhult, Nov 18 '15 at 15:54
I'll try to create an example, but the data I'm inserting is around 1.7 million pairs.... btw this works: auto it = SortableRowIndex.begin(); while (it != SortableRowIndex.end()) it = SortableRowIndex.erase(it); but is REALLY slow! — Linus Särnhult, Nov 18 '15 at 16:48

score 3 · Answer 1 · answered Nov 19 '15 at 12:16

As it turns out, it's not really stalling, but clearing a multimap through Visual Studio's debugger is REALLY SLOW. I noticed that the memory was getting released slooowly and let it run for a couple of minutes and then it was finally done. Running the application outside of Visual Studio made the .clear() calls drop down to < 1s, even for millions of pairs.

So, heads up if you are clearing huge multimaps while running in debug mode in visual studio. It's sloooooow.

Appearently Release mode is just as slow if you launch it trough Visual Studio's debugger. — Linus Särnhult, Nov 19 '15 at 12:17

calling .clear() or .erase() on c++ std::multimap sometimes causes freeze (100% cpu)

1 Answers1