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Subject: Re: [boost] [Block Pointer] Benchmarks
From: Glen Fernandes (glen.fernandes_at_[hidden])
Date: 2016-03-13 13:28:24

On Sun, Mar 13, 2016 at 1:02 PM, Phil Bouchard wrote:
> Thanks for your help.
> So block_ptr<> wouldn't be a drop-in replacement for shared_ptr<> but an
> add-on for:
> - complex containers,
> - neural networks,
> - C# / Java / Javascript engines,
> - etc.

No problem. Also renaming the thread to reflect the current benchmarks
(since it doesn't appear that block_ptr is faster than shared_ptr
where creation is involved).

1. Gathering these benchmarks is always useful, even if block_ptr was
not designed to be a drop-in replacement for share_ptr. So you had the
right idea, even if the execution needed some work. It's important to
get the execution correct, though, otherwise the results are not
meaningful - which is where I (and I believe Rob, also) was trying to
steer you.

2. Looking at the numbers you obtained after modifying my benchmark
example, they are close enough that at least you could say "Using
block_ptr over shared_ptr won't be a significant performance loss":

> unique_ptr (new): 47.7686
> unique_ptr (make_unique): 46.8545
> shared_ptr (new): 77.8261
> shared_ptr (make_shared): 50.8072
> shared_ptr (allocate_shared_noinit): 33.021
> block_ptr (new): 69.6554

3. There are more benchmarks beyond just creation (though creation is
likely the most meaningfully expensive one). Copying overhead might be
one: I haven't looked at what is involved in copying a block_ptr, but
some work happens when you copy a shared_ptr.

4. shared_ptr by way of allocate_shared allows creation to not involve
'new' expressions, or even a call to '::operator new(std::size_t)' at

i.e. For those C++ projects that have a requirement for all dynamic
allocation in their project to involve some stateful custom allocator
instances of some stateful custom allocator type, they can still use
shared_ptr (with allocate_shared). Is this possible with block_ptr?

I hope to take a look at the block_ptr motivation, design, and
implementation when I have some time next week. The title of the
thread caught my attention; "X is 600% faster than Y" always has a
high excitement potential.


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