Kr_Shubham's blog

Unexpected Time taken.
By Kr_Shubham, 3 years ago, In English

This code is taking around 1300 ms. (size of set shouldn't exceed more than 1 at any time, Since I am inserting same element every time)

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But , After commenting the s.erase(), it just took 15 ms.

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Can anyone please explain the reason behind this? Thanks in advance :)

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3 years ago, # |
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my guess is that the compiler sees that the set isn't actually used for anything, so it's optimized out

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    3 years ago, # ^ |
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    Can we somehow avoid these optimizations? It was the only one moment in my life when I thought to use keyword volatile. But after I did that, code refused to compile, and I don't understand why. Would be glad if someone explained why it is happening.

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      3 years ago, # ^ |
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      Actually compiler gives errors on erase and insert functions, so I suspect existing versions of these function doesn't implemented for volatile case. So it's tempting me to think maybe there is no optimization at all?

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3 years ago, # |
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I think it has to do with memory allocation (e.g., malloc(..)), which is quite an expensive operation.

Without erasing, only the first insertion causes allocation (RB-tree nodes and all), and subsequent insertions only require reads (if the operations are not optimized away). On the other hand, with erasing, every inserting invokes memory allocation. And 7 million times is a lot!

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