7708bf12cd
The write gate was one mutex the writer held across every synchronous transport poll, and close_conn took that same mutex before reclaiming a connection's owners. Under a transport that accepts a byte per poll the writer re-acquired it hundreds of times while teardown queued behind it, so teardown could be starved for a whole frame and the delivery completed just before its owner was reclaimed. bus-v1 section 9 puts release and route-health control out of reach of telemetry starvation; tests/sol_rereview_regressions.rs's poll-gate regression failed 6 release runs out of 6 alone, and about one debug run in five. The gate now separates "teardown has begun" from "a poll is in progress": a mutex plus a condvar. begin_close sets closing once without waiting, then waits for the poll already in progress and records whether it left a frame half written. The writer brackets each poll with enter_poll (refused once closing) and leave_poll(bytes) instead of holding a lock across it, so teardown's window is one poll rather than a frame, and no byte follows it. close_conn no longer holds the gate across reclamation. Every item is pub(crate): no public signature changed. The regression test no longer synchronises with a sleep. The shutdown thread announces itself on a channel, and what follows is structural: teardown cannot pass the gate until the held poll returns, which only release() allows. Its delivery is 50 KB now, which a writer resuming a byte per poll cannot finish inside the window, so the test observes the ordering instead of a coin toss and asserts the two legal shapes of the stream: cut short with nothing appended, or never begun with exactly the closing notices following. |
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