[pca] multi-system download concurrency

[Dani Calloway]

I wish to use PCA to cache patches for a large number of (not
necessarily homogeneous) systems at once, all of which are behind a
firewall which does not allow access to the "outside".  So I currently
use PCA's excellent --from-file feature and run the --download one
system at a time.

I've noticed that there is a lot of idle time spent waiting on
SunSolve, or establishing connections, and so on. So doing each system
in sequence becomes a real time-waster. However, I can't use the
--threads feature of PCA since each system will require its own
invocation with a different --from-files argument.

So, the question is whether PCA is threadsafe. That is, can I fork off
four or five or ten instances at once without worrying that the patch
downloads will become corrupted, should more than one instance of PCA
attempt to download the same file at the same time?

Also, somewhat unrelated, should a patch become corrupt, is there a
mechanism for detecting that (GPG signature or SHA1 or similar)?

Thanks in advance.

--
Dani Calloway