[tests] Fix network threading in functional tests

assumevalid.py, example_test.py and p2p-acceptblocks.py add
p2p_connections after the NetworkThread has been started. This isn't
permitted. Fix test to restart the network thread when adding new
connections.

p2p-leaktest.py had a potential race condition if the NetworkThread
hadn't terminated by the time we tried to restart it.

test/functional/assumevalid.py

@@ -38,10 +38,11 @@
                                      CTransaction,
                                      CTxIn,
                                      CTxOut,
+                                     network_thread_join,
+                                     network_thread_start,
                                      P2PInterface,
                                      msg_block,
-                                     msg_headers,
-                                     network_thread_start)
+                                     msg_headers)
 from test_framework.script import (CScript, OP_TRUE)
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal
@@ -159,13 +160,22 @@ def run_test(self):
             self.block_time += 1
             height += 1
 
+        # We're adding new connections so terminate the network thread
+        self.nodes[0].disconnect_p2ps()
+        network_thread_join()
+
         # Start node1 and node2 with assumevalid so they accept a block with a bad signature.
         self.start_node(1, extra_args=["-assumevalid=" + hex(block102.sha256)])
-        p2p1 = self.nodes[1].add_p2p_connection(BaseNode())
-        p2p1.wait_for_verack()
-
         self.start_node(2, extra_args=["-assumevalid=" + hex(block102.sha256)])
+
+        p2p0 = self.nodes[0].add_p2p_connection(BaseNode())
+        p2p1 = self.nodes[1].add_p2p_connection(BaseNode())
         p2p2 = self.nodes[2].add_p2p_connection(BaseNode())
+
+        network_thread_start()
+
+        p2p0.wait_for_verack()
+        p2p1.wait_for_verack()
         p2p2.wait_for_verack()
 
         # send header lists to all three nodes

test/functional/example_test.py

@@ -21,6 +21,7 @@
     mininode_lock,
     msg_block,
     msg_getdata,
+    network_thread_join,
     network_thread_start,
 )
 from test_framework.test_framework import BitcoinTestFramework
@@ -131,7 +132,7 @@ def custom_method(self):
     def run_test(self):
         """Main test logic"""
 
-        # Create a P2P connection to one of the nodes
+        # Create P2P connections to two of the nodes
         self.nodes[0].add_p2p_connection(BaseNode())
 
         # Start up network handling in another thread. This needs to be called
@@ -188,7 +189,14 @@ def run_test(self):
         connect_nodes(self.nodes[1], 2)
 
         self.log.info("Add P2P connection to node2")
+        # We can't add additional P2P connections once the network thread has started. Disconnect the connection
+        # to node0, wait for the network thread to terminate, then connect to node2. This is specific to
+        # the current implementation of the network thread and may be improved in future.
+        self.nodes[0].disconnect_p2ps()
+        network_thread_join()
+
         self.nodes[2].add_p2p_connection(BaseNode())
+        network_thread_start()
         self.nodes[2].p2p.wait_for_verack()
 
         self.log.info("Wait for node2 reach current tip. Test that it has propagated all the blocks to us")

test/functional/p2p-acceptblock.py

@@ -207,9 +207,13 @@ def run_test(self):
         # disconnect/reconnect first
 
         self.nodes[0].disconnect_p2ps()
-        test_node = self.nodes[0].add_p2p_connection(P2PInterface())
+        self.nodes[1].disconnect_p2ps()
+        network_thread_join()
 
+        test_node = self.nodes[0].add_p2p_connection(P2PInterface())
+        network_thread_start()
         test_node.wait_for_verack()
+
         test_node.send_message(msg_block(block_h1f))
 
         test_node.sync_with_ping()

test/functional/p2p-leaktests.py

@@ -126,8 +126,9 @@ def run_test(self):
 
         self.nodes[0].disconnect_p2ps()
 
-        # Wait until all connections are closed
+        # Wait until all connections are closed and the network thread has terminated
         wait_until(lambda: len(self.nodes[0].getpeerinfo()) == 0)
+        network_thread_join()
 
         # Make sure no unexpected messages came in
         assert(no_version_bannode.unexpected_msg == False)