If a step is cancelled just as its builder step is starting,
doBuildStep() will return sRetry. This causes builder() to make the
step runnable again, since the queue monitor may have added new builds
referencing it. The idea is that if the latter condition is not true,
the step's reference count will drop to zero and it will be
deleted. However, if the dispatcher thread sees and locks the step
before the reference count can drop to zero in the builder thread, the
dispatcher thread will start a new builder thread for the step. Thus
the step can be kept alive for an indefinite amount of time.
The fix is for State::builder() to use a weak pointer to the step, to
ensure that the step's reference count can drop to zero *before* it's
added to the runnable queue.
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.
It was hitting
assert(reservation.unique());
Since we do want the machine reservation to be released before calling
wakeDispatcher(), let's use a different object for keeping track of
active steps.
We now kill active build steps when there are no more referring
builds. This is useful e.g. for preventing cancelled multi-hour TPC-H
benchmark runs from hogging build machines.
If two active steps of the same build failed, then the first would be
marked as "failed", but the second would end up as "orphaned", causing
it to be marked as "aborted" later on. Now it's correctly marked as
"failed".
These are build steps that remain "busy" in the database even though
they have finished, because they couldn't be updated (e.g. due to a
PostgreSQL connection problem). To prevent them from showing up as
busy in the "Machine status" page, we now periodically purge them.
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.
This removes the "busy", "locker" and "logfile" columns, which are no
longer used by the queue runner. The "Running builds" page now only
shows builds that have an active build step.
"hydra-queue-runner --status" now prints how many runnable and running
build steps exist for each machine type. This allows additional
machines to be provisioned based on the Hydra load.
