It won't likely do much regarding file handling as code is currently still
using `boost::asio::posix::stream_descriptor` or Boost.Beast's file
handling (which uses blocking I/O). I suppose one needs to use the new file
API described here under "Asio 1.22.0 / Boost 1.78":
https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/history.html
* Aquire the mutex before setting `m_exclusivelyOwned = false`; otherwise
it might be set after `lock()` has checked it but before `lock()` has
entered `wait()` leading to a deadlock
* Check state again after `wait()` because it may also be unblocked
"spuriously" so it isn't guaranteed that the state will have actually
changed after unblocking
* Do HTTP head request first when loading database from mirror to avoid
downloading the full database all the time
* Use the last modification date of the local database file because with
the persistent storage even local database reloads became a bit expensive
When `repo-add` fails but files could be copied before refusing to override
is actually very annoying because one has to delete the files before
restarting the build task.
* Record full path for the deletion of orphaned signatures
* Test for the existence of the signature symlink itself and not the target
because the symlink target (in the any directory) might not exist anymore
but the symlink should be removed in any case
Otherwise all other attempts to acquire named locks are blocked. It should
be ok because references are not invalidated when inserting/accessing
elements of an `std::unique_map`. When cleaning locks up elements are
erased, though. Hence an additional cleanup lock is required to prevent
acquiring a named lock which has already been cleaned up.
This recently failed because the cuda package exceeded the max. body size.
I suppose it makes generally sense to be able to exclude packages as I
don't need that package anyways.
Usually this doesn't make sense because we want to build all packages which
were determined in the previous prepare action. When specifying the
packages again in the conduct build action we'd skip packages which are
pulled into the build as dependencies which is normally not desired.