bitbake: process: Rewrite multiple connection handling

If the bitbake server recieved multiple connections, it currently closes
ones it can't handle (while its dealing with another). This is rather
antisocial behaviour which causes clients to quickly run through their
retries and abort.

Instead, queue any other connections until the current one is closed. This
way the client can decide when it wants to stop waiting for the server. If the
client is gone by the time we handle it, we handle that gracefully.

This also fixes a number of bugs in the connection handling where connections
which did drop early were badly handled causing tracebacks in the logs.

Also, handle queue incomming connections in a loop to ensure that the main
client handling doesn't starve that piece of the system.

This code was stress tested by running 50 connection attempts in parallel at
once, ensuring the code correctly handled them.

(Bitbake rev: 220193dc38c4e78cb7cf36132a3a5b499a35bc8a)

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

bitbake/lib/bb/server/process.py

@@ -130,6 +130,7 @@ class ProcessServer(multiprocessing.Process):
         bb.utils.set_process_name("Cooker")
 
         ready = []
+        newconnections = []
 
         self.controllersock = False
         fds = [self.sock]
@@ -138,37 +139,48 @@ class ProcessServer(multiprocessing.Process):
         print("Entering server connection loop")
 
         def disconnect_client(self, fds):
-            if not self.haveui:
-                return
             print("Disconnecting Client")
-            fds.remove(self.controllersock)
-            fds.remove(self.command_channel)
-            bb.event.unregister_UIHhandler(self.event_handle, True)
-            self.command_channel_reply.writer.close()
-            self.event_writer.writer.close()
-            del self.event_writer
-            self.controllersock.close()
-            self.controllersock = False
-            self.haveui = False
-            self.lastui = time.time()
-            self.cooker.clientComplete()
-            if self.timeout is None:
+            if self.controllersock:
+                fds.remove(self.controllersock)
+                self.controllersock.close()
+                self.controllersock = False
+            if self.haveui:
+                fds.remove(self.command_channel)
+                bb.event.unregister_UIHhandler(self.event_handle, True)
+                self.command_channel_reply.writer.close()
+                self.event_writer.writer.close()
+                self.command_channel.close()
+                self.command_channel = False
+                del self.event_writer
+                self.lastui = time.time()
+                self.cooker.clientComplete()
+                self.haveui = False
+            ready = select.select(fds,[],[],0)[0]
+            if newconnections:
+                print("Starting new client")
+                conn = newconnections.pop(-1)
+                fds.append(conn)
+                self.controllersock = conn
+            elif self.timeout is None and not ready:
                 print("No timeout, exiting.")
                 self.quit = True
 
         while not self.quit:
             if self.sock in ready:
-                self.controllersock, address = self.sock.accept()
-                if self.haveui:
-                    print("Dropping connection attempt as we have a UI %s" % (str(ready)))
-                    self.controllersock.close()
-                else:
-                    print("Accepting %s" % (str(ready)))
-                    fds.append(self.controllersock)
+                while select.select([self.sock],[],[],0)[0]:
+                    controllersock, address = self.sock.accept()
+                    if self.controllersock:
+                        print("Queuing %s (%s)" % (str(ready), str(newconnections)))
+                        newconnections.append(controllersock)
+                    else:
+                        print("Accepting %s (%s)" % (str(ready), str(newconnections)))
+                        self.controllersock = controllersock
+                        fds.append(controllersock)
             if self.controllersock in ready:
                 try:
-                    print("Connecting Client")
+                    print("Processing Client")
                     ui_fds = recvfds(self.controllersock, 3)
+                    print("Connecting Client")
 
                     # Where to write events to
                     writer = ConnectionWriter(ui_fds[0])