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From: Vivek Khera <vivek@khera.org>
Date: Wed, 17 May 2006 09:50:27 -0400
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Subject: Re: Is it safe to compile multiple ports at the same time ?
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On May 17, 2006, at 2:00 AM, Vasil Dimov wrote:

> Ofcourse if B depends also on Y it can fallback to building Y if it
> cannot gain exclusive lock on X.

If you do that, then you get a lock on Y, which may also happen to be  
a dependency of X, and now you have deadlock.

You also need to ensure that all ports specify dependencies in the  
same order (or at least take the locks in the same order) else you  
will deadlock at some point if you allow the port to take more than  
one lock at a time.