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OK, this is a major rework.
* tcp_server: connection threads are not detached anymore, the caller has
to clean them up. This was done so that the server can clean up the
threads cleanly.
* run_queue: simple refactoring, run_queue_entry is called just run now.
* server: worker threads are now killed when a run is assigned to a
worker.
* worker: the connection to server is no longer persistent. A worker
sends "new-worker", waits for a task, closes the connection, and when
it's done, sends the "complete" message and waits for a new task.
This is supposed to improve resilience, since the worker-server
connections don't have to be maintained while the worker is doing a CI
run.
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Previously, I had a stupid system where I would create a thread after
every accept(), and put worker descriptors in a queue. A special
"scheduler" thread would then pick them out, and give out jobs to
complete.
The problem was, of course, I couldn't conveniently poll job status from
workers. I thought about using poll(), but that turned out to be a
horribly complicated API. How do I deal with partial reads, for example?
I don't honestly know.
Then it hit me that I could just use the threads that handle accept()ed
connections as "worker threads", which would synchronously schedule jobs
and wait for them to complete. This solves every problem and removes the
need for a lot of inter-thread synchronization magic. It even works now,
holy crap! You can launch and terminate workers at will, and they will
pick up new jobs automatically.
As a side not, msg_recv_and_handle turned out to be too limiting and
complicated for me, so I got rid of that, and do normal
msg_recv/msg_send calls.
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This adds a basic "worker" program.
You can now do something like
./server &
./worker &
./client ci_run URL REV
and the server should pass a message to worker, after which it should
clone the repository at URL, checkout REV, and try to run the CI script.
It's extremely unfinished: I need to sort out the graceful shutdown, how
the server manages workers, etc.
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