Remove pending_servers, self.interfaces is now the complete set of

interfaces we have created.

Existing code has the concept of pending servers, where a connection
thread is started but has not sent a connection notification, and
and interfaces which have received the notification.

This separation caused a couple of minor bugs, and given the cleaner
semantics of unifying the two I don't think the separation is beneficial.
The bugs:

1) When stopping the network, we only stopped the connected interface
threads, not the pending ones.  This would leave Python hanging
on exit if we don't make them daemon threads.

2) start_interface() did not check pending servers before starting
a new thread.  Some of its callers did, but not all, so it was
possible to initiate two threads to one server and "lose" one thread.

Apart form fixing the above two issues, unification causes one more
change in semantics: we are now willing to switch to a connection
that is pending (we don't switch to failed interfaces). I don't
think that is a problem: if it times out we'll just switch
again when we receive the disconnect notification, and previously the
fact that an interface was in the interaces dictionary wasn't a
guarantee the connection was good anyway: we might not have processed
a pending disconnection notification.

lib/network.py

@@ -153,7 +153,6 @@ class Network(util.DaemonThread):
 
         self.irc_servers = {} # returned by interface (list from irc)
         self.recent_servers = self.read_recent_servers()
-        self.pending_servers = set()
 
         self.banner = ''
         self.heights = {}
@@ -173,7 +172,9 @@ class Network(util.DaemonThread):
         # retry times
         self.server_retry_time = time.time()
         self.nodes_retry_time = time.time()
-        # kick off the network
+        # kick off the network.  interface is the main server we are currently
+        # communicating with.  interfaces is the set of servers we are connecting
+        # to or have an ongoing connection with
         self.interface = None
         self.interfaces = {}
         self.start_network(deserialize_server(self.default_server)[2],
@@ -279,11 +280,11 @@ class Network(util.DaemonThread):
             if server == self.default_server:
                 self.set_status('connecting')
             i = interface.Interface(server, self.queue, self.config)
-            self.pending_servers.add(server)
+            self.interfaces[i.server] = i
             i.start()
 
     def start_random_interface(self):
-        exclude_set = self.disconnected_servers.union(self.pending_servers).union(set(self.interfaces))
+        exclude_set = self.disconnected_servers.union(set(self.interfaces))
         server = pick_random_server(self.get_servers(), self.protocol, exclude_set)
         if server:
             self.start_interface(server)
@@ -319,7 +320,6 @@ class Network(util.DaemonThread):
         self.start_interfaces()
 
     def stop_network(self):
-        # FIXME: this forgets to handle pending servers...
         self.print_error("stopping network")
         for i in self.interfaces.values():
             i.stop()
@@ -352,18 +352,21 @@ class Network(util.DaemonThread):
                 self.switch_to_random_interface()
 
     def switch_to_interface(self, server):
-        '''Switch to server as our interface.  If not already connected, start a
-        connection - we will switch on receipt of the connection notification'''
+        '''Switch to server as our interface.  If no connection exists nor
+        being opened, start a thread to connect.  The actual switch will
+        happen on receipt of the connection notification.  Do nothing
+        if server already is our interface.'''
         self.default_server = server
         if server in self.interfaces:
-            self.print_error("switching to", server)
-            # stop any current interface in order to terminate subscriptions
-            self.stop_interface()
-            self.interface = self.interfaces[server]
-            self.send_subscriptions()
-            self.set_status('connected')
-            self.notify('updated')
-        elif server not in self.pending_servers:
+            if self.interface != self.interfaces[server]:
+                self.print_error("switching to", server)
+                # stop any current interface in order to terminate subscriptions
+                self.stop_interface()
+                self.interface = self.interfaces[server]
+                self.send_subscriptions()
+                self.set_status('connected')
+                self.notify('updated')
+        else:
             self.print_error("starting %s; will switch once connected" % server)
             self.start_interface(server)
 
@@ -387,11 +390,7 @@ class Network(util.DaemonThread):
 
     def process_if_notification(self, i):
         '''Handle interface addition and removal through notifications'''
-        if i.server in self.pending_servers:
-            self.pending_servers.remove(i.server)
-
         if i.is_connected():
-            self.interfaces[i.server] = i
             self.add_recent_server(i)
             i.send_request({'method':'blockchain.headers.subscribe','params':[]})
             if i.server == self.default_server:
@@ -472,7 +471,7 @@ class Network(util.DaemonThread):
     def check_interfaces(self):
         now = time.time()
         # nodes
-        if len(self.interfaces) + len(self.pending_servers) < self.num_server:
+        if len(self.interfaces) < self.num_server:
             self.start_random_interface()
             if now - self.nodes_retry_time > NODES_RETRY_INTERVAL:
                 self.print_error('network: retrying connections')