Question

我试图以以下方式构建一套:

    std::set<SomeType> mySet(aVector.begin(), aVector.end());

在大多数情况下,这一行文非常有效。 10%的时间里,我陷入了太长的境地(有时超过600毫秒!)。为什么会发生这种情况? 这些投入每次都非常相似(病媒大多是分类的)。任何想法?

Answer 1

我看到三种可能性:

限制令状软弱的。考虑到您的双重价值是否为/N,你正在打破这一假设(关于需要很长一段时间才能看到NaNs的一套假设)。
Occasionally your data isn t very sorted. Try always doing a std::sort on the vector first and see if the performance flattens out -- default construct the set then use the std::set::insert that takes two parameters, the first being a hint for what element to compare against first (if you can provide a good hint). That will let you build the set without resorting. If that fixes the spikes you know the initial sortedness of the data is the cause.
Your heap allocator occasionally does an operation that makes it take much longer than normal. It may be splitting or joining blocks to find free memory on the particular std::set() calls that are taking longer. You can try using an alternative allocator (if your program is multithreaded you might try Google s tcmalloc). You can rule this out if you have a profiler that shows time spent in the allocator, but most lack this feature. Another alternative would be to use a boost::intrusive_set, which will prevent the need for allocation when storing the items in the set.