Builds can now specify the attribute "isDeterministic = true" to tell
Hydra to build with build-repeat > 0. If there is a mismatch between
rounds, the step / build fails with a suitable status.
Maybe this should be a meta attribute, but that makes it invisible to
hydra-queue-runner, and it seems reasonable to make a claim of
mandatory determinism part of the derivation (since e.g. enabling this
flag should trigger a rebuild).
We now take into account the memory necessary for compressing the NAR
being exported to the binary cache, plus xz compression overhead.
Also, we now release the memory tokens for the NAR accessor *after*
releasing the NAR accessor. Previously the memory for the NAR accessor
might still be in use while another thread does an allocation, causing
the maximum to be exceeded temporarily.
Also, use notify_all instead of notify_one to wake up memory token
waiters. This is not very nice, but not every waiter is requesting the
same number of tokens, so some might be able to proceed.
This was a bad idea because pthread_cancel() is unsalvageable broken
in C++. Destructors are not allowed to throw exceptions (especially in
C++11), but pthread_cancel() can cause a __cxxabiv1::__forced_unwind
exception inside any destructor that invokes a cancellation
point. (This exception can be caught but *must* be rethrown.) So let's
just kill the builder process instead.
‘basicDrv.inputSrcs’ also contains the outputs of inputDrvs. These
don't necessarily exist in the local store, so copying them may cause
an exception. We should only copy the real inputSrcs.
The maximum output size per build step (as the sum of the NARs of each
output) can be set via hydra.conf, e.g.
max-output-size = 1000000000
The default is 2 GiB.
Also refactored the build error / status handling a bit.
When using a binary cache store, the queue runner receives NARs from
the build machines, compresses them, and uploads them to the
cache. However, keeping multiple large NARs in memory can cause the
queue runner to run out of memory. This can happen for instance when
it's processing multiple ISO images concurrently.
The fix is to use a TokenServer to prevent the builder threads to
store more than a certain total size of NARs concurrently (at the
moment, this is hard-coded at 4 GiB). Builder threads that cause the
limit to be exceeded will block until other threads have finished.
The 4 GiB limit does not include certain other allocations, such as
for xz compression or for FSAccessor::readFile(). But since these are
unlikely to be more than the size of the NARs and hydra.nixos.org has
32 GiB RAM, it should be fine.
It's easier for the Hydra provisioner to put host public keys in the
machines file than to separately manage the known_hosts file
(especially when the provisioner runs on a different machine).
This prevents a race where multiple threads see that machine X is
missing path P, and start sending it concurrently. Nix handles this
correctly, but it's still wasteful (especially for the case where P ==
GHC).
A more refined scheme would be to have per machine, per path locks.
Having a hundred threads doing I/O at the same time is bad on magnetic
disks because of the excessive disk seeks. So allow only 4 threads to
copy closures in parallel.
Aborted builds are now put back on the runnable queue and retried
after a certain time interval (currently 60 seconds for the first
retry, then tripled on each subsequent retry).
This removes the need for Nix's build-remote.pl.
Build logs are now written to $HYDRA_DATA/build-logs because
hydra-queue-runner doesn't have write permission to /nix/var/log.
