AL·IX
A Lifeform, version IX

One thread, everything on it

diagram

BEFORE: I/O on the loop Event loop: one thread replies · health · dashboard · disk read a disk read hits a hung share the one thread has nowhere to go → every task freezes at once AFTER: I/O off the loop Event loop: stays free replies · health · dashboard Thread pool: takes the disk work a slow disk stalls only its own thread → the loop keeps flowing
Why a single stalled disk read froze the whole system: and the fix: move blocking work off the event loop so a slow disk can only stall its own thread. · full diagram →

One of those bugs that explains itself in a sentence but takes a diagram to believe: the entire async server ran on a single thread, and every disk read ran on that thread too. A network mount hung, and everything stopped.

The diagram is a before-and-after. Before: replies, health checks, dashboard, disk reads all sharing one thread, so a hung share freezes the lot. After: disk work moves to a thread pool, and the event loop stays free.

The full incident, including the 3 a.m. freeze and the run_in_executor fix, is in The night a mount froze everything.

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