Copilot commented on code in PR #13898:
URL: https://github.com/apache/trafficserver/pull/13898#discussion_r4447725572
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src/iocore/net/UnixNetProcessor.cc:
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@@ -169,7 +177,7 @@ UnixNetProcessor::stop_accept()
SCOPED_MUTEX_LOCK(lock, naVecMutex, this_ethread());
for (auto *na : naVec) {
na->stop_accept();
- delete na;
+ na->retire();
Review Comment:
After cancellation, the dedicated accept thread can observe
`!is_listening()` and delete the original `NetAccept` before the stopping
thread finishes `stop_accept()` or calls `retire()`, causing a use-after-free.
`naVecMutex` does not protect the accept thread's deletion. Add an ownership
handoff that keeps the acceptor alive until the stopping thread finishes
accessing it, without waiting on the dedicated thread's lifetime-held mutex.
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src/iocore/net/UnixNetAccept.cc:
##########
@@ -85,6 +87,81 @@ count_client_connection(UnixNetVConnection *vc, bool exempt)
}
}
+/** Whether this acceptor should leave the connections queued on its listen
socket for now.
+ *
+ * True while the peak awake span has reached
+ * @c proxy.config.exec_thread.watchdog.timeout_refuse_ms, where the queued
connections cost nothing at
+ * all and the threads may yet catch up and serve them. Independent of the
accept queue shrink, which
+ * has its own threshold (see @c watchdog_apply_backlog) and lets the *kernel*
shed while ATS keeps
+ * accepting - a bounded queue only drains as fast as we call @c accept4,
which is what keeps inflow
+ * near the rate we can actually serve. Both can be in force at once, in which
case the queue is
+ * bounded and nothing is draining it.
+ *
+ * A listener marked @c f_watchdog_exempt is never subject to backpressure.
Those are the loopback
+ * companion listeners opened alongside each proxy port, so local connections
keep getting a
+ * truthful answer about the proxy however far behind the event threads are.
The volume of local
+ * connections is small against the inbound load that caused the saturation.
+ *
+ * @param[in] na The acceptor.
+ *
+ * @return true if the caller should not drain its listen socket on this pass.
+ */
+bool
+watchdog_should_refuse(NetAccept *na)
+{
+ return !na->opt.f_watchdog_exempt && Watchdog::accept_refuse();
Review Comment:
Existing local-only listeners, such as `ip-in=127.0.0.1`, `ip-in=::1`, and
Unix-domain proxy ports, get no companion and retain `f_watchdog_exempt=false`,
so overload shrinks their backlogs and stops accepting local health checks.
Exempt these listeners in both watchdog actions (`watchdog_should_refuse` here
and `watchdog_apply_backlog` at line 134) without changing the flag that also
controls per-thread listener topology.
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