| 1 | package hub |
| 2 | |
| 3 | import ( |
| 4 | "testing" |
| 5 | "time" |
| 6 | ) |
| 7 | |
| 8 | // terminate runs with the hub's one lock held, and the stream's reader |
| 9 | // is not excluded by that lock: it drains the channel on its own |
| 10 | // goroutine, whenever it is scheduled. So a failed non-blocking send |
| 11 | // proves the buffer was full at that instant and nothing more, and the |
| 12 | // eviction that follows must not be a blocking receive — on an empty |
| 13 | // channel it would hold h.mu against every room in the process, waiting |
| 14 | // for an event that only h.mu's holder could send (Codex S2-4). |
| 15 | // |
| 16 | // The window is a few instructions wide, so this is a probabilistic |
| 17 | // test run many times rather than a single deterministic one. Against |
| 18 | // the unfixed code it hangs a few thousand rounds in, with and without |
| 19 | // -race; against the fixed code the whole run costs a quarter of a |
| 20 | // second (a second and a third under -race). A round that has not |
| 21 | // finished within the deadline is the deadlock, and the test says so |
| 22 | // rather than hanging the package. |
| 23 | func TestTerminateNeverBlocksOnAChannelTheReaderDrained(t *testing.T) { |
| 24 | const rounds = 50000 |
| 25 | for i := 0; i < rounds; i++ { |
| 26 | s := newSub() |
| 27 | for j := 0; j < subBuffer; j++ { |
| 28 | s.ch <- Message{Type: TypePeer} |
| 29 | } |
| 30 | // The reader: a stream handler, draining as fast as it is given |
| 31 | // events, exactly as serveStream does. |
| 32 | drained := make(chan struct{}) |
| 33 | go func() { |
| 34 | defer close(drained) |
| 35 | for range s.C() { |
| 36 | } |
| 37 | }() |
| 38 | done := make(chan struct{}) |
| 39 | go func() { |
| 40 | defer close(done) |
| 41 | s.terminate(Message{Type: TypeLost, Reason: ReasonRemoved}) |
| 42 | }() |
| 43 | select { |
| 44 | case <-done: |
| 45 | case <-time.After(5 * time.Second): |
| 46 | t.Fatalf("round %d: terminate blocked on a drained channel with the hub lock held", i) |
| 47 | } |
| 48 | <-drained |
| 49 | } |
| 50 | } |
| 51 | |
amadan