commit b93e61b8ab8067c1d00b8def777411791a2d6dc0
author jmmv <jmmv@google.com> Mon Apr 15 10:00:10 2019 -0700
committer Copybara-Service <copybara-worker@google.com> Mon Apr 15 10:02:17 2019 -0700
tree 3535b4f5ea6d004971e56898decd442744187340
parent 460843f02bb73baf57d1e3761e2987a45bbd87b9

Only wipe the whole sandbox base during the first build in a server.

During the lifetime of a Bazel server, assign unique identifiers to
each sandboxed action so that their symlink trees are guaranteed to be
disjoint as they are keyed on that identifier.  This was in theory
already happening... but it actually wasn't and there was no test to
validate this assumption.

With that done, there is no need to ensure that the sandbox base is clean
before a build -- unless we are the very first build of a server, in which
case we must ensure we don't clash with possible leftovers from a past
server.

Note that we already clean up each action's tree as soon as the action
completes, so the only thing we are trying to clean up here are stale
files that may be left if those individual deletions didn't work (e.g.
because there were still stray processes writing to the directories)
or if --sandbox_debug was in use.

This is a prerequisite before making deletions asynchronous for two
reasons: first, we don't want to delay build starts if old deletions are
still ongoing; and, second, we don't want to schedule too broad
deletions that could step over subsequent builds (i.e. we only want to
delete the contents of the *-sandbox directories, which contain one
subdirectory per action, and not the whole tree).

Lastly, add a test for this expected behavior (which is what actually
triggered the fix) and for the fact that we expect the identifiers to
be always different.

Partially addresses https://github.com/bazelbuild/bazel/issues/7527.

RELNOTES: None.
PiperOrigin-RevId: 243635557