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Re: GNU make to consider files checksum

From: Harald Dunkel
Subject: Re: GNU make to consider files checksum
Date: Sat, 28 Nov 2009 09:39:49 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20091125 Thunderbird/3.0

I would say that this thread went a little bit out of focus.
Maybe it is allowed to add my $.02?

"Traditional" Make does a check like

        if timestamp(file1) > timestamp(file2) then
                rebuild file2 file1

The fundamental flaw in this is obvious: file1 can be replaced
anytime by another file with an older timestamp than file2. The
result is that file2 is not rebuilt, even though file1 has

As a workaround you have to touch file1 on checkout, _and_ you
have to be sure that no builds are running. Both restrictions can
become a huge problem when working with automatic builds in a
large team with several parallel development branches. You get
more builds than necessary (which implies more tests to be run),
and everybody has to spend more time in waiting.

Maybe you are used to these restrictions and don't consider it as
a problem, or maybe you are simply not affected, but IMHO this is
_highly_ painful.

Of course you can always make it "work somehow" without touching
Make. Surely I do not want you to drop the traditional timestamp
check. But an optional checksum feature as suggested by Giuseppe
would be a reasonable extension.

It doesn't have to be perfect, it just needs to be better.



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