Allow new states slowly even when queue full (fixes Axel Beckert lockup)

src/network/networktransport.cc

@@ -45,6 +45,7 @@ Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState
   : connection( desired_ip, desired_port ),
     sender( &connection, initial_state ),
     received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) ),
+    receiver_quench_timer( 0 ),
     last_receiver_state( initial_remote ),
     fragments(),
     verbose( false )
@@ -58,6 +59,7 @@ Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState
   : connection( key_str, ip, port ),
     sender( &connection, initial_state ),
     received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) ),
+    receiver_quench_timer( 0 ),
     last_receiver_state( initial_remote ),
     fragments(),
     verbose( false )
@@ -116,11 +118,16 @@ void Transport<MyState, RemoteState>::recv( void )
     process_throwaway_until( inst.throwaway_num() );
 
     if ( received_states.size() > 1024 ) { /* limit on state queue */
+      uint64_t now = timestamp();
+      if ( now < receiver_quench_timer ) { /* deny letting state grow further */
 	if ( verbose ) {
 	  fprintf( stderr, "[%u] Receiver queue full, discarding %d (malicious sender or long-unidirectional connectivity?)\n",
 		   (unsigned int)(timestamp() % 100000), (int)inst.new_num() );
 	}
 	return;
+      } else {
+	receiver_quench_timer = now + 15000;
+      }
     }
 
     /* apply diff to reference state */

src/network/networktransport.h

@@ -60,6 +60,7 @@ namespace Network {
 
     /* simple receiver */
     list< TimestampedState<RemoteState> > received_states;
+    uint64_t receiver_quench_timer;
     RemoteState last_receiver_state; /* the state we were in when user last queried state */
     FragmentAssembly fragments;
     bool verbose;