[cmake-developers] CMake daemon for user tools

[Daniel Pfeifer]

On Wed, Jan 20, 2016 at 10:03 PM, Stephen Kelly <steveire at gmail.com> wrote:
> Milian Wolff wrote:
>
>>> I'm concerned that the memory usage of a daemon implementing the proposed
>>> capabilities may be too large to be practical (at least without a major
>>> redesign of certain structures that tend to duplicate substrings, or
>>> some kind of out-of-core approach).
>>
>> This sounds like optimizations to that daemon will benefit CMake.
>
> FYI I merged a reduce-allocations branch to next for testing. It came from
> Milian here:
>
>  https://github.com/steveire/CMake/pull/1

Very nice! It is impressive what kind of an impact a simple 'const&'
can have. Also, nice work identifying the hotspots.

> Milian also mentioned the possibility of using something like a sqlite
> database (probably what you meant by out-of-core above) for definitions for
> querying by the daemon.
>
> I also mentioned some possibile optimization possibilities, such as removing
> the closure of definitions created for all directories. I wrote a branch
> which does that some months ago, but it resulted in a slow down. I'll see if
> I can rebase the commit to master and push it to github, together with a
> patch for avoiding computing the hash multiple times in cmDefinitions.

What do you think about string interning? I started a cmString class
[2] that stores short strings inplace and puts long strings into a
pool. Copies never allocate extra memory and equality comparison is
always O(1).
In addition to `operator<` (which is lexicographical) there is a O(1)
comparison that can be used where lexicographical ordering is not
required (ie. for lookup tables).

[1] https://en.wikipedia.org/wiki/String_interning
[2] https://github.com/purpleKarrot/CMake/commits/string-pool

cheers, Daniel