We are using a rather complex SVN structure for our software projects with many externals. Since checkout of externals is rather slow, it happens regularly to us, that a commit is performed to the repository, while the checkout is still running. Unfortunately this causes the externals to be checked out with different (head) revisions - resulting into a "mixed source" warning of our build script later.

Is there any way check out a SVN project with a consistent head revision for all externals?
Is it possible to let the SVN plugin repeat a checkout when a "mixed source" condition is detected?