[Scons-users] Decider which checks md5 checksums unexpectedly detecting changed/invalid ones

[Tom Tanner (BLOOMBERG/ LONDON)]

Replying to myself again:

The problem appears to be to do with copying something from the cache: If you copy a file from the cache, the timestamp can go backwards rather than forwards. So the '(time.time() - mtime) > max_drift' test can spuriously return true (especially if max_drift is quite low because you have a stable clock over your network, as recommended by the 'GoFastButton' on the wiki).

I am at a bit of a loss here, as what the wiki seems to say (only cache the signature if) and what the code seem to do (use the cached signature if) appear to be rather different.

The option appears to be to either (1) set the max_drift to negative or (2) to force the sig to be recalculated after a build in the built() function in Node/__init__.py. You certainly need to do the later if you've got the max drift set to 0, or you'll get wrong builds. But I'm not sure what get_max_drift_csig is actually meant to be doing.

Help would be appreciated as I want my build to be both fast an accurate.
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