fix race condition in session init

Signed-off-by: Dhammika Pathirana <dhammika@gmail.com>

src/zmq_engine.cpp

@@ -40,6 +40,7 @@ zmq::zmq_engine_t::zmq_engine_t (fd_t fd_, const options_t &options_) :
     outsize (0),
     encoder (out_batch_size),
     inout (NULL),
+    ephemeral_inout (NULL),
     options (options_),
     plugged (false)
 {
@@ -57,8 +58,9 @@ void zmq::zmq_engine_t::plug (io_thread_t *io_thread_, i_inout *inout_)
 {
     zmq_assert (!plugged);
     plugged = true;
+    ephemeral_inout = NULL;
 
-    //  Conncet to session/init object.
+    //  Connect to session/init object.
     zmq_assert (!inout);
     zmq_assert (inout_);
     encoder.set_inout (inout_);
@@ -89,6 +91,7 @@ void zmq::zmq_engine_t::unplug ()
     //  Disconnect from init/session object.
     encoder.set_inout (NULL);
     decoder.set_inout (NULL);
+    ephemeral_inout = inout;
     inout = NULL;
 }
 
@@ -139,7 +142,13 @@ void zmq::zmq_engine_t::in_event ()
     }
 
     //  Flush all messages the decoder may have produced.
-    inout->flush ();
+    //  If IO handler has unplugged engine, flush transient IO handler.
+    if (unlikely (!plugged)) {
+        zmq_assert (ephemeral_inout);
+        ephemeral_inout->flush ();
+    } else {
+        inout->flush ();
+    }
 
     if (disconnection)
         error ();
@@ -152,7 +161,14 @@ void zmq::zmq_engine_t::out_event ()
 
         outpos = NULL;
         encoder.get_data (&outpos, &outsize);
-        
+
+        //  If IO handler has unplugged engine, flush transient IO handler.
+        if (unlikely (!plugged)) {
+            zmq_assert (ephemeral_inout);
+            ephemeral_inout->flush ();
+            return;
+        }
+
         //  If there is no data to send, stop polling for output.
         if (outsize == 0) {
             reset_pollout (handle);

src/zmq_engine.hpp

@@ -70,6 +70,9 @@ namespace zmq
 
         i_inout *inout;
 
+        //  Detached transient inout handler.
+        i_inout *ephemeral_inout;
+
         options_t options;
 
         bool plugged;

src/zmq_init.cpp

@@ -34,6 +34,7 @@ zmq::zmq_init_t::zmq_init_t (io_thread_t *io_thread_,
       socket_base_t *socket_, session_t *session_, fd_t fd_,
       const options_t &options_) :
     own_t (io_thread_, options_),
+    ephemeral_engine (NULL),
     sent (false),
     received (false),
     socket (socket_),
@@ -64,8 +65,7 @@ bool zmq::zmq_init_t::read (::zmq_msg_t *msg_)
         options.identity.size ());
     sent = true;
 
-    //  If initialisation is done, pass the engine to the session and
-    //  destroy the init object.
+    //  Try finalize initialization.
     finalise_initialisation ();
 
     return true;
@@ -92,6 +92,9 @@ bool zmq::zmq_init_t::write (::zmq_msg_t *msg_)
 
     received = true;
 
+    //  Try finalize initialization.
+    finalise_initialisation ();
+
     return true;
 }
 
@@ -101,9 +104,9 @@ void zmq::zmq_init_t::flush ()
     if (!received)
         return;
 
-    //  If initialisation is done, pass the engine to the session and
-    //  destroy the init object.
-    finalise_initialisation ();
+    //  Initialization is done, dispatch engine.
+    if (ephemeral_engine)
+        dispatch_engine ();
 }
 
 void zmq::zmq_init_t::detach ()
@@ -134,18 +137,31 @@ void zmq::zmq_init_t::process_unplug ()
 }
 
 void zmq::zmq_init_t::finalise_initialisation ()
+{
+     //  Unplug and prepare to dispatch engine.
+     if (sent && received) {
+        ephemeral_engine = engine;
+        engine = NULL;
+        ephemeral_engine->unplug ();
+        return;
+    }
+}
+
+void zmq::zmq_init_t::dispatch_engine ()
 {
     if (sent && received) {
 
+        //  Engine must be detached.
+        zmq_assert (!engine);
+        zmq_assert (ephemeral_engine);
+
         //  If we know what session we belong to, it's easy, just send the
         //  engine to that session and destroy the init object. Note that we
         //  know about the session only if this object is owned by it. Thus,
         //  lifetime of this object in contained in the lifetime of the session
         //  so the pointer cannot become invalid without notice.
         if (session) {
-            engine->unplug ();
-            send_attach (session, engine, peer_identity, true);
-            engine = NULL;
+            send_attach (session, ephemeral_engine, peer_identity, true);
             terminate ();
             return;
         }
@@ -165,9 +181,7 @@ void zmq::zmq_init_t::finalise_initialisation ()
             zmq_assert (session);
             session->inc_seqnum ();
             launch_sibling (session);
-            engine->unplug ();
-            send_attach (session, engine, peer_identity, false);
-            engine = NULL;
+            send_attach (session, ephemeral_engine, peer_identity, false);
             terminate ();
             return;
         }
@@ -178,9 +192,7 @@ void zmq::zmq_init_t::finalise_initialisation ()
         //  than by send_attach.
         session = socket->find_session (peer_identity);
         if (session) {
-            engine->unplug ();
-            send_attach (session, engine, peer_identity, false);
-            engine = NULL;
+            send_attach (session, ephemeral_engine, peer_identity, false);
             terminate ();
             return;
         }
@@ -194,9 +206,7 @@ void zmq::zmq_init_t::finalise_initialisation ()
         zmq_assert (session);
         session->inc_seqnum ();
         launch_sibling (session);
-        engine->unplug ();
-        send_attach (session, engine, peer_identity, false);
-        engine = NULL;
+        send_attach (session, ephemeral_engine, peer_identity, false);
         terminate ();
         return;
     }

src/zmq_init.hpp

@@ -44,6 +44,7 @@ namespace zmq
     private:
 
         void finalise_initialisation ();
+        void dispatch_engine ();
 
         //  i_inout interface implementation.
         bool read (::zmq_msg_t *msg_);
@@ -58,6 +59,9 @@ namespace zmq
         //  Associated wire-protocol engine.
         i_engine *engine;
 
+        //  Detached transient engine.
+        i_engine *ephemeral_engine;
+
         //  True if our own identity was already sent to the peer.
         bool sent;