merge bitcoin#22817: Avoid race after connect_nodes

Due to stricter checks, we can no longer start masternodes in parallel,
as entities used to process `to_connection` checks are reused before the
previous check is completed, resulting in an exception. Since we're
now validating the establishment of a two-way connection, we have to do
it one at a time.

test/functional/test_framework/test_framework.py

@@ -692,18 +692,19 @@ def wait_for_node_exit(self, i, timeout):
         self.nodes[i].process.wait(timeout)
 
     def connect_nodes(self, a, b):
-        def connect_nodes_helper(from_connection, node_num):
-            ip_port = "127.0.0.1:" + str(p2p_port(node_num))
-            from_connection.addnode(ip_port, "onetry")
-            # poll until version handshake complete to avoid race conditions
-            # with transaction relaying
-            # See comments in net_processing:
-            # * Must have a version message before anything else
-            # * Must have a verack message before anything else
-            wait_until_helper(lambda: all(peer['version'] != 0 for peer in from_connection.getpeerinfo()))
-            wait_until_helper(lambda: all(peer['bytesrecv_per_msg'].pop('verack', 0) == 24 for peer in from_connection.getpeerinfo()))
-
-        connect_nodes_helper(self.nodes[a], b)
+        from_connection = self.nodes[a]
+        to_connection = self.nodes[b]
+        ip_port = "127.0.0.1:" + str(p2p_port(b))
+        from_connection.addnode(ip_port, "onetry")
+        # poll until version handshake complete to avoid race conditions
+        # with transaction relaying
+        # See comments in net_processing:
+        # * Must have a version message before anything else
+        # * Must have a verack message before anything else
+        wait_until_helper(lambda: all(peer['version'] != 0 for peer in from_connection.getpeerinfo()))
+        wait_until_helper(lambda: all(peer['version'] != 0 for peer in to_connection.getpeerinfo()))
+        wait_until_helper(lambda: all(peer['bytesrecv_per_msg'].pop('verack', 0) == 24 for peer in from_connection.getpeerinfo()))
+        wait_until_helper(lambda: all(peer['bytesrecv_per_msg'].pop('verack', 0) == 24 for peer in to_connection.getpeerinfo()))
 
     def disconnect_nodes(self, a, b):
         def disconnect_nodes_helper(from_connection, node_num):
@@ -1452,17 +1453,12 @@ def do_connect(idx):
             job.result()
         jobs.clear()
 
-        # connect nodes in parallel
-        for idx in range(0, self.mn_count):
-            jobs.append(executor.submit(do_connect, idx))
-
-        # wait for all nodes to connect
-        for job in jobs:
-            job.result()
-        jobs.clear()
-
         executor.shutdown()
 
+        # connect nodes
+        for idx in range(0, self.mn_count):
+            do_connect(idx)
+
     def start_masternode(self, mninfo, extra_args=None):
         args = ['-masternodeblsprivkey=%s' % mninfo.keyOperator] + self.extra_args[mninfo.nodeIdx]
         if extra_args is not None: