fix: prevent deadlock on concurrent push and disconnect (2.13)#24214
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fix: prevent deadlock on concurrent push and disconnect (2.13)#24214
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The previous `AtomicBoolean` guard in `AtmospherePushConnection` closed only the disconnect-vs-disconnect race. A push thread that reads `disconnecting` as false before a concurrent `disconnect()` flips it can still proceed into `synchronized(lock)` behind the disconnect thread, which is itself blocked inside `resource.close()` waiting for the servlet container's HTTP session lock held by the push thread — a two-lock cycle. Move `resource.close()` out of the monitor: inside `synchronized(lock)` capture the resource into a local and call `connectionLost()` to transition the state, then release the monitor before invoking `close()` on the stashed reference. Add a matching re-check of `isConnected()` at the top of the `synchronized` block in `push()` so a push that waited for the monitor observes the late disconnect and defers via `PUSH_PENDING`/`RESPONSE_PENDING` instead of NPEing on the cleared resource. The `disconnecting` flag stays set until `close()` returns so subsequent pushes take the fast path and no new `disconnect()` re-enters while `close()` is still in flight. Related-to #24192
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mshabarov
approved these changes
Apr 30, 2026
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This ticket/PR has been released with Vaadin 14.14.3. |
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The previous
AtomicBooleanguard inAtmospherePushConnectionclosed only the disconnect-vs-disconnect race. A push thread that readsdisconnectingas false before a concurrentdisconnect()flips it can still proceed intosynchronized(lock)behind the disconnect thread, which is itself blocked insideresource.close()waiting for the servlet container's HTTP session lock held by the push thread — a two-lock cycle.Move
resource.close()out of the monitor: insidesynchronized(lock)capture the resource into a local and callconnectionLost()to transition the state, then release the monitor before invokingclose()on the stashed reference. Add a matching re-check ofisConnected()at the top of thesynchronizedblock inpush()so a push that waited for the monitor observes the late disconnect and defers viaPUSH_PENDING/RESPONSE_PENDINGinstead of NPEing on the cleared resource. Thedisconnectingflag stays set untilclose()returns so subsequent pushes take the fast path and no newdisconnect()re-enters whileclose()is still in flight.Related-to #24192