[Scons-users] Fwd:Re: timing issues and protecting from them

[Gary Oberbrunner]

On Wed, Dec 9, 2015 at 3:43 PM, Tom Tanner <trtanner at btinternet.com> wrote:

> This is why I say - have any of the sources changed *while* I was building
> the target. This you check *after* the target has been built. So the
> database currently says
>
> a.hh - md5 MAH, time TAH
> a.cc - md5 MAC, time TAC
> b.hh - md5 MBH, time TBH
>
> then you execute the build actions to generate a.o
>
> then you check if any of a.hh, a.cc, b.hh have changed (on disk) from the
> values you currently have stored.
>
> And if they have, then you no longer have the right information
>

I just want to say this may be slow in some situations. You're going to
check every dependency of a.o transitively, right? So for the final targets
(or a big lib with lots of sources and/or headers), you're going to recheck
the timestamp for pretty much every file in the build. And then for the
next target that depends on that one, you're going to do all that again.
You're going to be touching the disk a whole lot, even if it's just stat()
calls. If the goal is "paranoid mode" and speed is unimportant, I could see
someone needing this. But I suspect it would slow our builds prohibitively,
especially a from-scratch build (because you do these checks after
executing a command).


-- 
Gary
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