bitbake: process: Clean up connection retry logic

Its possible for a connection to connect to the server as its shutting down
but before its removed the socket file. This patch:

a) Removes the socket file earlier to avoid connections.
b) Handles EOFError in initial connections gracefully. These occur if the
   socket is closed during the server shutdown.
c) Ensure duplicate events aren't shown on the console. This makes debugging
   these issues very very confusing.

With these changes the backtrace that was concerning users is hidden and the
server works as expected with a reconnect when it catches it in a bad state.

(Bitbake rev: f45196cf84669723382730944dddc7eaf50826f2)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/main.py

@@ -438,9 +438,10 @@ def setup_bitbake(configParams, configuration, extrafeatures=None):
                         return None, None
                     # we start a server with a given configuration
                     logger.info("Starting bitbake server...")
-                    server = bb.server.process.BitBakeServer(lock, sockname, configuration, featureset)
-                    # The server will handle any events already in the queue
+                    # Clear the event queue since we already displayed messages
                     bb.event.ui_queue = []
+                    server = bb.server.process.BitBakeServer(lock, sockname, configuration, featureset)
+
                 else:
                     logger.info("Reconnecting to bitbake server...")
                     if not os.path.exists(sockname):
@@ -448,7 +449,13 @@ def setup_bitbake(configParams, configuration, extrafeatures=None):
                         time.sleep(5)
                         raise bb.server.process.ProcessTimeout("Bitbake still shutting down as socket exists but no lock?")
                 if not configParams.server_only:
-                    server_connection = bb.server.process.connectProcessServer(sockname, featureset)
+                    try:
+                        server_connection = bb.server.process.connectProcessServer(sockname, featureset)
+                    except EOFError:
+                        # The server may have been shutting down but not closed the socket yet. If that happened,
+                        # ignore it.
+                        pass
+
                 if server_connection or configParams.server_only:
                     break
             except (Exception, bb.server.process.ProcessTimeout) as e:

bitbake/lib/bb/server/process.py

@@ -215,6 +215,10 @@ class ProcessServer(multiprocessing.Process):
             ready = self.idle_commands(.1, fds)
 
         print("Exiting")
+        # Remove the socket file so we don't get any more connections to avoid races
+        os.unlink(self.sockname)
+        self.sock.close()
+
         try: 
             self.cooker.shutdown(True)
         except:
@@ -222,10 +226,6 @@ class ProcessServer(multiprocessing.Process):
 
         self.cooker.post_serve()
 
-        # Remove the socket file so we don't get any more connections to avoid races
-        os.unlink(self.sockname)
-        self.sock.close()
-
         # Finally release the lockfile but warn about other processes holding it open
         lock = self.bitbake_lock
         lockfile = lock.name