fix(forge): monitor beam rewriting worker process #370
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This was referenced Feb 10, 2026
Replace bare spawn with spawn_monitor in Beams.apply_to_all/2.
If the worker process crashed, the parent would hang forever
waiting for :progress messages that would never arrive.
Propagate the monitor ref through block_until_done and raise on
{:DOWN, ...} so crashes surface immediately. Demonitor on normal
completion.
QuinnWilton
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This is part of a set of 4 PRs that arose out of some static analysis tooling I'm working on:
That means that these aren't crashes or issues that I've observed in practice, however based on my reading of the code, they do represent issues worth addressing.
Problem:
Beams.apply_to_all/2spawns its worker process using a barespawn/1, and then blocks inblock_until_done/3until it receives a:progressmessage from it. If the worker crashes, this message will never arrive, and the caller will block indefinitely.Solution
Replace
spawn/1withspawn_monitor/1, and add areceiveclause inblock_until_done/3to handle the worker unexpectedly terminating before a:progressmessage is sent, so that we're able to immediately raise instead of blocking forever.In the successful case, the monitor is flushed to avoid
:DOWNmessages building up and causing a mailbox leak.