cluster/zeromq: Call DoTerminate() in destructor

Normal life-cycle is that Terminate() / DoTerminate() is called
by zeek-setup code. If that doesn't happen, shutdown and join
threads during destructor.

try { } catch (...) suggested by Benjamin.

src/cluster/backend/zeromq/ZeroMQ.cc

@@ -66,6 +66,16 @@ ZeroMQBackend::ZeroMQBackend(std::unique_ptr<EventSerializer> es, std::unique_pt
     main_inproc = zmq::socket_t(ctx, zmq::socket_type::pair);
 }
 
+ZeroMQBackend::~ZeroMQBackend() {
+    try {
+        // DoTerminate is idempotent.
+        DoTerminate();
+    } catch ( ... ) {
+        // This should never happen.
+        abort();
+    }
+}
+
 void ZeroMQBackend::DoInitPostScript() {
     ThreadedBackend::DoInitPostScript();
 
@@ -109,6 +119,7 @@ void ZeroMQBackend::DoTerminate() {
     if ( proxy_thread ) {
         ZEROMQ_DEBUG("Shutting down proxy thread");
         proxy_thread->Shutdown();
+        proxy_thread.reset();
     }
 
     ZEROMQ_DEBUG("Terminated");

src/cluster/backend/zeromq/ZeroMQ.h

@@ -20,6 +20,11 @@ public:
     ZeroMQBackend(std::unique_ptr<EventSerializer> es, std::unique_ptr<LogSerializer> ls,
                   std::unique_ptr<detail::EventHandlingStrategy> ehs);
 
+    /**
+     * Destructor.
+     */
+    ~ZeroMQBackend();
+
     /**
      * Spawns a thread running zmq_proxy() for the configured XPUB/XSUB listen
      * sockets. Only one node in a cluster should do this.