Instead of hard-coding the use of the "org.osbuild.linux" runner,
use the new `osbuild.pipeline.detect_host_runner` function to
dynamically detect the runner for the host system. That should fix
the tests on RHEL systems, where python3 is by default not present
and even if it is manually installed, is an indirection via
alternatives (i.e. a link to /etc/alternatives), which must be
explicitly configured in the build root container for the host.
Change the API endpoint to prevent retrieving monitor-output from a
running instance. Instead, we require the caller to exit the API context
before querying the monitor-output. This guarantees that the api-thread
was synchronously taken down and scheduled any outstanding events.
This fixes an issue where a side-channel notifies us of a buildroot
exit, but the api-thread has not yet returned from epoll, and thus might
not have dispatched pending I/O events, yet. If we instead wait for the
thread to exit, we have a synchronous shutdown and know that all
*ordered* kernel events must have been handled.
In particular, imagine a build-root program running (like `echo` in the
test_monitor unittest) which writes data to the stdout-pipe and then
immediately exits. The syscall-order guarantees that the data is written
to the pipe before the SIGCHLD is sent (or wait(2) returns). However, we
retrieve the SIGCHLD from our main-thread usually (p.join() in our test,
and BuildRoot() in our main code), while the pipe-reading is done from
an API thread. Therefore, we might end up handling the SIGCHLD first
(just imagine a single-threaded CPU that schedules the main task before
the thread). To avoid this race, we can simply synchronize with the
api-thread. Since we already have this synchronization as part of the
api-thread takedown, it is as simple as stopping the api-thread before
continuing with operations.
Lastly, if a write operation to a pipe was issued, we are guaranteed
that a SIGCHLD synchronization across processes is ordered correctly.
Furthermore, the python event-loop also guarantees that stopping an
event-loop will necessarily dispatch all outstanding events. A read is
guaranteed to be outstanding in our race-scenario, so the read will be
dispatched. The only possible problem is `_output_ready()` only
dispatching a maximum of 4096 bytes. This might need to be fixed
separately. A comment is left in place.
Rely on the ability of `BaseAPI` to auto-generate socket addresses
when no one was provided. The `BuildRoot` does not rely on the
sockets being created in the `BuildRoot.api` directory anymore and
will instead bind-mount each individual socket address to the well
known location via the `BaseAPI.endpoint` identifier.
Convert all API providers to take the `socket_address` as an
optional keyword argument.
Split out the part of `api.API` that is responsible for providing
the server infrastructure for the API; i.e. setting up the server
and the corresponding context manager and asynchronous event
handling. This leaves `API` itself which just the implementation
of the high level protocol and makes the API-server part re-usable.
NB: pylint, for some reason, confuses `API` and `BaseAPI`, like in
`test_monitor`. Annotate that accordingly.
Create a new monitor that records all the invocations of the
monitoring (virtual) functions and use that to check that when
running (i.e. building) a pipeline all of them are executed
the excepted number of times (and with the correct arguments).
Add a basic test that will set up an 'API' endpoint, then spawn a
child process that uses that 'API' endpoint to setup its stdio in
very much the same way as runners do. This is used to verify that
the API itself works properly as well as the new LogMonitor class
by comparing the inputs and outputs.
