diff -r 038108a9811c -r 042ed354b9eb mercurial/commandserver.py
--- a/mercurial/commandserver.py	Thu Dec 13 23:20:28 2018 -0800
+++ b/mercurial/commandserver.py	Wed Oct 31 22:19:03 2018 +0900
@@ -506,12 +506,19 @@
             raise error.Abort(_('no socket path specified with --address'))
         self._servicehandler = handler or unixservicehandler(ui)
         self._sock = None
+        self._mainipc = None
+        self._workeripc = None
         self._oldsigchldhandler = None
         self._workerpids = set()  # updated by signal handler; do not iterate
         self._socketunlinked = None
 
     def init(self):
         self._sock = socket.socket(socket.AF_UNIX)
+        # IPC channel from many workers to one main process; this is actually
+        # a uni-directional pipe, but is backed by a DGRAM socket so each
+        # message can be easily separated.
+        o = socket.socketpair(socket.AF_UNIX, socket.SOCK_DGRAM)
+        self._mainipc, self._workeripc = o
         self._servicehandler.bindsocket(self._sock, self.address)
         if util.safehasattr(procutil, 'unblocksignal'):
             procutil.unblocksignal(signal.SIGCHLD)
@@ -527,6 +534,8 @@
     def _cleanup(self):
         signal.signal(signal.SIGCHLD, self._oldsigchldhandler)
         self._sock.close()
+        self._mainipc.close()
+        self._workeripc.close()
         self._unlinksocket()
         # don't kill child processes as they have active clients, just wait
         self._reapworkers(0)
@@ -543,6 +552,8 @@
         selector = selectors.DefaultSelector()
         selector.register(self._sock, selectors.EVENT_READ,
                           self._acceptnewconnection)
+        selector.register(self._mainipc, selectors.EVENT_READ,
+                          self._handlemainipc)
         while True:
             if not exiting and h.shouldexit():
                 # clients can no longer connect() to the domain socket, so
@@ -592,8 +603,10 @@
             try:
                 selector.close()
                 sock.close()
+                self._mainipc.close()
                 self._runworker(conn)
                 conn.close()
+                self._workeripc.close()
                 os._exit(0)
             except:  # never return, hence no re-raises
                 try:
@@ -601,6 +614,17 @@
                 finally:
                     os._exit(255)
 
+    def _handlemainipc(self, sock, selector):
+        """Process messages sent from a worker"""
+        try:
+            path = sock.recv(32768)  # large enough to receive path
+        except socket.error as inst:
+            if inst.args[0] == errno.EINTR:
+                return
+            raise
+
+        self.ui.log(b'cmdserver', b'repository: %s\n', path)
+
     def _sigchldhandler(self, signal, frame):
         self._reapworkers(os.WNOHANG)
 
@@ -628,6 +652,22 @@
         h = self._servicehandler
         try:
             _serverequest(self.ui, self.repo, conn, h.createcmdserver,
-                          prereposetups=None)  # TODO: pass in hook functions
+                          prereposetups=[self._reposetup])
         finally:
             gc.collect()  # trigger __del__ since worker process uses os._exit
+
+    def _reposetup(self, ui, repo):
+        if not repo.local():
+            return
+
+        class unixcmdserverrepo(repo.__class__):
+            def close(self):
+                super(unixcmdserverrepo, self).close()
+                try:
+                    self._cmdserveripc.send(self.root)
+                except socket.error:
+                    self.ui.log(b'cmdserver',
+                                b'failed to send repo root to master\n')
+
+        repo.__class__ = unixcmdserverrepo
+        repo._cmdserveripc = self._workeripc