On 11/12/15 16:28, Anders Björklund wrote:
Each invocation of ccache then connects to that socket and asks the
daemon to do the MD4 scan on its behalf. The daemon checks the mtime on
the file and serves the MD4 from its memory cache if nothing has
changed. The stat call could probably be optimized away if the cache is
very fresh (<1s?)

So basically something similar to the "sloppiness" file_stat_matches ?
Compare size/mtime/ctime, rather than rehashing the content of a file.

Yes, except that it *has* been checked this session. This is a significant difference when you try to share a cache between two machines, or two users, or just simply did some git foolery between builds.

Good point though: for a lone user doing nothing exciting, CCACHE_SLOPPINESS=file_stat_matches does nearly the same thing with considerably less effort.

You could, in principle, use this communication to limit how many
cache-miss compilations are permitted to run in parallel, and therefore
run "make -j" for maximum parallelism without fear of melting your memory.

Something like that is what I meant with a new "prefix" wrapper for cpp.
Similar to the current wrapper for cc, which does that with e.g. distcc.

Yes. You have to be careful with how many executables you have though: the dynamic linker is slooooow.

Unfortunately, I've moved on to other projects and don't have much time
to work on this stuff any more.

Thank you for your ideas. Will check the code out too if I get the time.
It seems that there are some opportunities left for faster manifest/cpp.

If you decide to go with the persistent background task approach, then there are a few ideas in there to pluck out, but the overall architecture had other goals, so maybe it's not that great a starting point. :-(

Good luck.


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