running multiple emerges concurrently == problem??

[ptheborg]

I've searched the man pages for an answer, but couldn't find any.

So my question is:
Is it a problem to run lets say in vc1 an emerge vorbis-tools and in vc2 an emerge apache mod_php mod_ssl??
Of course emerge will merge all the programs, but when both emerge processes are finished at exactly the same time, aren't they both trying to update the same system file or whatever??

I've found myself doing this most of the time when emerging, because after starting an emerge, I think hey, I want that program too....BUT I have not run into trouble YET....
But is there a (little) chance things go wrong???
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[Naan Yaar]

According to this thread:
https://forums.gentoo.org/viewtopic.php?t=7212
a developer believes that it can cause problems.

[ptheborg]

hmm, but he's saying that running emerge -f and emerge at the same time could cause problems.....but is this the same as two normal emerges???
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[Naan Yaar]

emerge -f just fetches the package. This is a subset of fetching and building it, which a plain "emerge" will do.

[ptheborg]

so this means running emerge -f and emerge at the same time is something different.
emerge -f fetches the packages but does not compile it, the other emerge process is compiling the packages being fetched by the first process....of course this can lead to troubles....

but emerge 1 and emerge 2, emerge both different packages, this means fetching, compiling and installing.

(oh wait, I see where it can go wrong, if two packages depend on the same package and this package need to be emerge too, both emerge instances will emerge this package?? or am I wrong?)
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[Naan Yaar]

"emerge -f" is basically one of the beginning steps of an emerge. If this is unsafe, according to the developer, I imagine two parallel emerges would be too. I cannot really see how "emerge -f" can screw up things when done in parallel with an emerge, but I would definitely defer to a developer's knowledge of emerge .

Anyway, if all you are looking for is compile speed-ups, why don't you set MAKE_OPTS to "-j3" or "-j4", etc., to parallelize make?

[ptheborg]

OK OK, you've won, I will never run parallel emerges anymore, too dangerous

But of course an emerge -f and an emerge on a different package (than the emerge -f) couldn't go wrong. But if it's about the same packages.....the emerge may be faster than the file download.......
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[Naan Yaar]

As I said, I really cannot see how a parallel fetch (emerge -f/ebuild fetch) of something unrelated can hurt and the "Tips and Tricks" forum suggests that people have tried it safely... I have a cable connection, so it is not too much of a plus anyway

[rac]

It does seem that a lockfile such as the one that Debian's dpkg uses might be prudent to protect against two simultaneous merge stages, if it is indeed such a dangerous activity, although I can't really see it rising to the level of "bug". At least not "urgent enough to file bug".
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[ptheborg]

ah......but ehm, I think I'll just stick with running one emerge at the same time.....

Naan Yaar has scared me too much with his reference to that thread with "the developer's" opinion
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[puddpunk]

i think most of the problem is when the two emerges try do access a cetain file, or write to a certain file, that they will be denied access, or data will be overwritten. You probebly wont end up corrupting...much...but its safer to stack up merges.