Merge #11849: [tests] Assert that only one NetworkThread exists

5c8ff26 [tests] Add NetworkThread assertions (John Newbery)
34e08b3 [tests] Fix network threading in functional tests (John Newbery)
74e64f2 [tests] Use network_thread_start() in tests. (John Newbery)
5fc6e71 [tests] Add network_thread_ utility functions. (John Newbery)

Pull request description:

  Add assert that only one NetworkThread exists at any time in functional tests, and fix cases where that wasn't true.

  fixes #11776

Tree-SHA512: fe5d1c59005f94bf66e11bb23ccf274b1cd9913741b56ea11dbcd21db4cc0b53b4413c0c4c16dbcd6ac611adad5e5cc2baaa39720598ce7b6393889945d06298

23 files changed, 96 insertions, 42 deletions

diff --git a/test/functional/README.md b/test/functional/README.md
index 193ca947bc..6be4d9cfab 100644
--- a/test/functional/README.md
+++ b/test/functional/README.md
@@ -68,7 +68,7 @@ contains the higher level logic for processing P2P payloads and connecting to
 the Bitcoin Core node application logic. For custom behaviour, subclass the
 P2PInterface object and override the callback methods.
 
-- Call `NetworkThread.start()` after all `P2PInterface` objects are created to
+- Call `network_thread_start()` after all `P2PInterface` objects are created to
 start the networking thread.  (Continue with the test logic in your existing
 thread.)
 
diff --git a/test/functional/assumevalid.py b/test/functional/assumevalid.py
index 13104f71bc..362b94e0d3 100755
--- a/test/functional/assumevalid.py
+++ b/test/functional/assumevalid.py
@@ -38,7 +38,8 @@ from test_framework.mininode import (CBlockHeader,
                                      CTransaction,
                                      CTxIn,
                                      CTxOut,
-                                     NetworkThread,
+                                     network_thread_join,
+                                     network_thread_start,
                                      P2PInterface,
                                      msg_block,
                                      msg_headers)
@@ -98,7 +99,7 @@ class AssumeValidTest(BitcoinTestFramework):
         # Connect to node0
         p2p0 = self.nodes[0].add_p2p_connection(BaseNode())
 
-        NetworkThread().start()  # Start up network handling in another thread
+        network_thread_start()
         self.nodes[0].p2p.wait_for_verack()
 
         # Build the blockchain
@@ -159,13 +160,22 @@ class AssumeValidTest(BitcoinTestFramework):
             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
diff --git a/test/functional/bip65-cltv-p2p.py b/test/functional/bip65-cltv-p2p.py
index 2af5eb275f..f4df879723 100755
--- a/test/functional/bip65-cltv-p2p.py
+++ b/test/functional/bip65-cltv-p2p.py
@@ -68,7 +68,7 @@ class BIP65Test(BitcoinTestFramework):
     def run_test(self):
         self.nodes[0].add_p2p_connection(P2PInterface())
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
 
         # wait_for_verack ensures that the P2P connection is fully up.
         self.nodes[0].p2p.wait_for_verack()
diff --git a/test/functional/bip68-112-113-p2p.py b/test/functional/bip68-112-113-p2p.py
index 7e6a4f4408..d3c7d8fc11 100755
--- a/test/functional/bip68-112-113-p2p.py
+++ b/test/functional/bip68-112-113-p2p.py
@@ -45,7 +45,7 @@ bip112tx_special - test negative argument to OP_CSV
 
 from test_framework.test_framework import ComparisonTestFramework
 from test_framework.util import *
-from test_framework.mininode import ToHex, CTransaction, NetworkThread
+from test_framework.mininode import ToHex, CTransaction, network_thread_start
 from test_framework.blocktools import create_coinbase, create_block
 from test_framework.comptool import TestInstance, TestManager
 from test_framework.script import *
@@ -100,7 +100,7 @@ class BIP68_112_113Test(ComparisonTestFramework):
     def run_test(self):
         test = TestManager(self, self.options.tmpdir)
         test.add_all_connections(self.nodes)
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         test.run()
 
     def send_generic_input_tx(self, node, coinbases):
diff --git a/test/functional/bip9-softforks.py b/test/functional/bip9-softforks.py
index ec4d1d9365..4cd6a177aa 100755
--- a/test/functional/bip9-softforks.py
+++ b/test/functional/bip9-softforks.py
@@ -22,7 +22,7 @@ import itertools
 
 from test_framework.test_framework import ComparisonTestFramework
 from test_framework.util import *
-from test_framework.mininode import CTransaction, NetworkThread
+from test_framework.mininode import CTransaction, network_thread_start
 from test_framework.blocktools import create_coinbase, create_block
 from test_framework.comptool import TestInstance, TestManager
 from test_framework.script import CScript, OP_1NEGATE, OP_CHECKSEQUENCEVERIFY, OP_DROP
@@ -36,7 +36,7 @@ class BIP9SoftForksTest(ComparisonTestFramework):
     def run_test(self):
         self.test = TestManager(self, self.options.tmpdir)
         self.test.add_all_connections(self.nodes)
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         self.test.run()
 
     def create_transaction(self, node, coinbase, to_address, amount):
@@ -245,7 +245,7 @@ class BIP9SoftForksTest(ComparisonTestFramework):
         self.setup_chain()
         self.setup_network()
         self.test.add_all_connections(self.nodes)
-        NetworkThread().start()
+        network_thread_start()
         self.test.p2p_connections[0].wait_for_verack()
 
     def get_tests(self):
diff --git a/test/functional/bipdersig-p2p.py b/test/functional/bipdersig-p2p.py
index 7a3e565e2c..5d7b889e83 100755
--- a/test/functional/bipdersig-p2p.py
+++ b/test/functional/bipdersig-p2p.py
@@ -56,7 +56,7 @@ class BIP66Test(BitcoinTestFramework):
     def run_test(self):
         self.nodes[0].add_p2p_connection(P2PInterface())
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
 
         # wait_for_verack ensures that the P2P connection is fully up.
         self.nodes[0].p2p.wait_for_verack()
diff --git a/test/functional/example_test.py b/test/functional/example_test.py
index 35a6bd2673..12be685ecf 100755
--- a/test/functional/example_test.py
+++ b/test/functional/example_test.py
@@ -17,11 +17,12 @@ from collections import defaultdict
 from test_framework.blocktools import (create_block, create_coinbase)
 from test_framework.mininode import (
     CInv,
-    NetworkThread,
     P2PInterface,
     mininode_lock,
     msg_block,
     msg_getdata,
+    network_thread_join,
+    network_thread_start,
 )
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
@@ -131,12 +132,12 @@ class ExampleTest(BitcoinTestFramework):
     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
         # after the P2P connections have been created.
-        NetworkThread().start()
+        network_thread_start()
         # wait_for_verack ensures that the P2P connection is fully up.
         self.nodes[0].p2p.wait_for_verack()
 
@@ -188,7 +189,14 @@ class ExampleTest(BitcoinTestFramework):
         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")
diff --git a/test/functional/invalidblockrequest.py b/test/functional/invalidblockrequest.py
index 9f44b44927..a89d1d8ef2 100755
--- a/test/functional/invalidblockrequest.py
+++ b/test/functional/invalidblockrequest.py
@@ -15,6 +15,7 @@ from test_framework.test_framework import ComparisonTestFramework
 from test_framework.util import *
 from test_framework.comptool import TestManager, TestInstance, RejectResult
 from test_framework.blocktools import *
+from test_framework.mininode import network_thread_start
 import copy
 import time
 
@@ -32,7 +33,7 @@ class InvalidBlockRequestTest(ComparisonTestFramework):
         test.add_all_connections(self.nodes)
         self.tip = None
         self.block_time = None
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         test.run()
 
     def get_tests(self):
diff --git a/test/functional/invalidtxrequest.py b/test/functional/invalidtxrequest.py
index a22bd8f8cd..c60b0fce16 100755
--- a/test/functional/invalidtxrequest.py
+++ b/test/functional/invalidtxrequest.py
@@ -28,7 +28,7 @@ class InvalidTxRequestTest(ComparisonTestFramework):
         test.add_all_connections(self.nodes)
         self.tip = None
         self.block_time = None
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         test.run()
 
     def get_tests(self):
diff --git a/test/functional/maxuploadtarget.py b/test/functional/maxuploadtarget.py
index 5ef71c93cf..cf2e484d9f 100755
--- a/test/functional/maxuploadtarget.py
+++ b/test/functional/maxuploadtarget.py
@@ -57,7 +57,7 @@ class MaxUploadTest(BitcoinTestFramework):
         for _ in range(3):
             p2p_conns.append(self.nodes[0].add_p2p_connection(TestNode()))
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         for p2pc in p2p_conns:
             p2pc.wait_for_verack()
 
@@ -149,7 +149,7 @@ class MaxUploadTest(BitcoinTestFramework):
         # Reconnect to self.nodes[0]
         self.nodes[0].add_p2p_connection(TestNode())
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         self.nodes[0].p2p.wait_for_verack()
 
         #retrieve 20 blocks which should be enough to break the 1MB limit
diff --git a/test/functional/nulldummy.py b/test/functional/nulldummy.py
index 7bc7c168f4..9f9f2f90c0 100755
--- a/test/functional/nulldummy.py
+++ b/test/functional/nulldummy.py
@@ -15,7 +15,7 @@ Generate 427 more blocks.
 
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import *
-from test_framework.mininode import CTransaction, NetworkThread
+from test_framework.mininode import CTransaction, network_thread_start
 from test_framework.blocktools import create_coinbase, create_block, add_witness_commitment
 from test_framework.script import CScript
 from io import BytesIO
@@ -50,7 +50,7 @@ class NULLDUMMYTest(BitcoinTestFramework):
         self.wit_address = self.nodes[0].addwitnessaddress(self.address)
         self.wit_ms_address = self.nodes[0].addwitnessaddress(self.ms_address)
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         self.coinbase_blocks = self.nodes[0].generate(2) # Block 2
         coinbase_txid = []
         for i in self.coinbase_blocks:
diff --git a/test/functional/p2p-acceptblock.py b/test/functional/p2p-acceptblock.py
index d9d7c24416..bb204322ed 100755
--- a/test/functional/p2p-acceptblock.py
+++ b/test/functional/p2p-acceptblock.py
@@ -83,7 +83,7 @@ class AcceptBlockTest(BitcoinTestFramework):
         # min_work_node connects to node1 (whitelisted)
         min_work_node = self.nodes[1].add_p2p_connection(P2PInterface())
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
 
         # Test logic begins here
         test_node.wait_for_verack()
@@ -207,9 +207,13 @@ class AcceptBlockTest(BitcoinTestFramework):
         # 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()
@@ -294,7 +298,7 @@ class AcceptBlockTest(BitcoinTestFramework):
             self.nodes[0].disconnect_p2ps()
             test_node = self.nodes[0].add_p2p_connection(P2PInterface())
 
-            NetworkThread().start() # Start up network handling in another thread
+            network_thread_start()
             test_node.wait_for_verack()
 
         # We should have failed reorg and switched back to 290 (but have block 291)
diff --git a/test/functional/p2p-compactblocks.py b/test/functional/p2p-compactblocks.py
index c43744328c..1e763df2a4 100755
--- a/test/functional/p2p-compactblocks.py
+++ b/test/functional/p2p-compactblocks.py
@@ -792,7 +792,7 @@ class CompactBlocksTest(BitcoinTestFramework):
         self.segwit_node = self.nodes[1].add_p2p_connection(TestNode(), services=NODE_NETWORK|NODE_WITNESS)
         self.old_node = self.nodes[1].add_p2p_connection(TestNode(), services=NODE_NETWORK)
 
-        NetworkThread().start()  # Start up network handling in another thread
+        network_thread_start()
 
         self.test_node.wait_for_verack()
 
diff --git a/test/functional/p2p-feefilter.py b/test/functional/p2p-feefilter.py
index ac55336e3d..ff4bed0efd 100755
--- a/test/functional/p2p-feefilter.py
+++ b/test/functional/p2p-feefilter.py
@@ -49,7 +49,7 @@ class FeeFilterTest(BitcoinTestFramework):
 
         # Setup the p2p connections and start up the network thread.
         self.nodes[0].add_p2p_connection(TestNode())
-        NetworkThread().start()
+        network_thread_start()
         self.nodes[0].p2p.wait_for_verack()
 
         # Test that invs are received for all txs at feerate of 20 sat/byte
diff --git a/test/functional/p2p-fingerprint.py b/test/functional/p2p-fingerprint.py
index 209c789f22..93ef73e25e 100755
--- a/test/functional/p2p-fingerprint.py
+++ b/test/functional/p2p-fingerprint.py
@@ -13,12 +13,12 @@ import time
 from test_framework.blocktools import (create_block, create_coinbase)
 from test_framework.mininode import (
     CInv,
-    NetworkThread,
     P2PInterface,
     msg_headers,
     msg_block,
     msg_getdata,
     msg_getheaders,
+    network_thread_start,
     wait_until,
 )
 from test_framework.test_framework import BitcoinTestFramework
@@ -77,7 +77,7 @@ class P2PFingerprintTest(BitcoinTestFramework):
     def run_test(self):
         node0 = self.nodes[0].add_p2p_connection(P2PInterface())
 
-        NetworkThread().start()
+        network_thread_start()
         node0.wait_for_verack()
 
         # Set node time to 60 days ago
diff --git a/test/functional/p2p-fullblocktest.py b/test/functional/p2p-fullblocktest.py
index f19b845a32..010dbdccad 100755
--- a/test/functional/p2p-fullblocktest.py
+++ b/test/functional/p2p-fullblocktest.py
@@ -18,6 +18,7 @@ from test_framework.blocktools import *
 import time
 from test_framework.key import CECKey
 from test_framework.script import *
+from test_framework.mininode import network_thread_start
 import struct
 
 class PreviousSpendableOutput():
@@ -68,7 +69,7 @@ class FullBlockTest(ComparisonTestFramework):
     def run_test(self):
         self.test = TestManager(self, self.options.tmpdir)
         self.test.add_all_connections(self.nodes)
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
         self.test.run()
 
     def add_transactions_to_block(self, block, tx_list):
diff --git a/test/functional/p2p-leaktests.py b/test/functional/p2p-leaktests.py
index b469a9a47a..ce4e6e9144 100755
--- a/test/functional/p2p-leaktests.py
+++ b/test/functional/p2p-leaktests.py
@@ -103,7 +103,7 @@ class P2PLeakTest(BitcoinTestFramework):
         unsupported_service_bit5_node = self.nodes[0].add_p2p_connection(CLazyNode(), services=NODE_NETWORK|NODE_UNSUPPORTED_SERVICE_BIT_5)
         unsupported_service_bit7_node = self.nodes[0].add_p2p_connection(CLazyNode(), services=NODE_NETWORK|NODE_UNSUPPORTED_SERVICE_BIT_7)
 
-        NetworkThread().start()  # Start up network handling in another thread
+        network_thread_start()
 
         wait_until(lambda: no_version_bannode.ever_connected, timeout=10, lock=mininode_lock)
         wait_until(lambda: no_version_idlenode.ever_connected, timeout=10, lock=mininode_lock)
@@ -126,8 +126,9 @@ class P2PLeakTest(BitcoinTestFramework):
 
         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)
@@ -142,7 +143,8 @@ class P2PLeakTest(BitcoinTestFramework):
         allowed_service_bit5_node = self.nodes[0].add_p2p_connection(P2PInterface(), services=NODE_NETWORK|NODE_UNSUPPORTED_SERVICE_BIT_5)
         allowed_service_bit7_node = self.nodes[0].add_p2p_connection(P2PInterface(), services=NODE_NETWORK|NODE_UNSUPPORTED_SERVICE_BIT_7)
 
-        NetworkThread().start()  # Network thread stopped when all previous P2PInterfaces disconnected. Restart it
+        # Network thread stopped when all previous P2PInterfaces disconnected. Restart it
+        network_thread_start()
 
         wait_until(lambda: allowed_service_bit5_node.message_count["verack"], lock=mininode_lock)
         wait_until(lambda: allowed_service_bit7_node.message_count["verack"], lock=mininode_lock)
diff --git a/test/functional/p2p-mempool.py b/test/functional/p2p-mempool.py
index d24dbac51d..168f9f685a 100755
--- a/test/functional/p2p-mempool.py
+++ b/test/functional/p2p-mempool.py
@@ -21,7 +21,7 @@ class P2PMempoolTests(BitcoinTestFramework):
     def run_test(self):
         # Add a p2p connection
         self.nodes[0].add_p2p_connection(P2PInterface())
-        NetworkThread().start()
+        network_thread_start()
         self.nodes[0].p2p.wait_for_verack()
 
         #request mempool
diff --git a/test/functional/p2p-segwit.py b/test/functional/p2p-segwit.py
index a240d79013..a06601c38e 100755
--- a/test/functional/p2p-segwit.py
+++ b/test/functional/p2p-segwit.py
@@ -1882,7 +1882,7 @@ class SegWitTest(BitcoinTestFramework):
         # self.std_node is for testing node1 (fRequireStandard=true)
         self.std_node = self.nodes[1].add_p2p_connection(TestNode(), services=NODE_NETWORK|NODE_WITNESS)
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
 
         # Keep a place to store utxo's that can be used in later tests
         self.utxo = []
diff --git a/test/functional/p2p-timeouts.py b/test/functional/p2p-timeouts.py
index b2f3a861cf..984a3c8b90 100755
--- a/test/functional/p2p-timeouts.py
+++ b/test/functional/p2p-timeouts.py
@@ -43,7 +43,7 @@ class TimeoutsTest(BitcoinTestFramework):
         no_version_node = self.nodes[0].add_p2p_connection(TestNode(), send_version=False)
         no_send_node = self.nodes[0].add_p2p_connection(TestNode(), send_version=False)
 
-        NetworkThread().start()  # Start up network handling in another thread
+        network_thread_start()
 
         sleep(1)
 
diff --git a/test/functional/p2p-versionbits-warning.py b/test/functional/p2p-versionbits-warning.py
index be137381d0..d29d43ebed 100755
--- a/test/functional/p2p-versionbits-warning.py
+++ b/test/functional/p2p-versionbits-warning.py
@@ -66,7 +66,7 @@ class VersionBitsWarningTest(BitcoinTestFramework):
         # Setup the p2p connection and start up the network thread.
         self.nodes[0].add_p2p_connection(TestNode())
 
-        NetworkThread().start() # Start up network handling in another thread
+        network_thread_start()
 
         # Test logic begins here
         self.nodes[0].p2p.wait_for_verack()
diff --git a/test/functional/sendheaders.py b/test/functional/sendheaders.py
index 99b7f6b99e..256227f721 100755
--- a/test/functional/sendheaders.py
+++ b/test/functional/sendheaders.py
@@ -90,7 +90,7 @@ from test_framework.mininode import (
     CBlockHeader,
     CInv,
     NODE_WITNESS,
-    NetworkThread,
+    network_thread_start,
     P2PInterface,
     mininode_lock,
     msg_block,
@@ -238,7 +238,7 @@ class SendHeadersTest(BitcoinTestFramework):
         # will occur outside of direct fetching
         test_node = self.nodes[0].add_p2p_connection(BaseNode(), services=NODE_WITNESS)
 
-        NetworkThread().start()  # Start up network handling in another thread
+        network_thread_start()
 
         # Test logic begins here
         inv_node.wait_for_verack()
diff --git a/test/functional/test_framework/mininode.py b/test/functional/test_framework/mininode.py
index 9e92a70da1..724d418099 100755
--- a/test/functional/test_framework/mininode.py
+++ b/test/functional/test_framework/mininode.py
@@ -18,7 +18,7 @@ import logging
 import socket
 import struct
 import sys
-from threading import RLock, Thread
+import threading
 
 from test_framework.messages import *
 from test_framework.util import wait_until
@@ -69,6 +69,10 @@ class P2PConnection(asyncore.dispatcher):
     sub-classed and the on_message() callback overridden."""
 
     def __init__(self):
+        # All P2PConnections must be created before starting the NetworkThread.
+        # assert that the network thread is not running.
+        assert not network_thread_running()
+
         super().__init__(map=mininode_socket_map)
 
     def peer_connect(self, dstaddr, dstport, net="regtest"):
@@ -397,9 +401,12 @@ mininode_socket_map = dict()
 # and whenever adding anything to the send buffer (in send_message()).  This
 # lock should be acquired in the thread running the test logic to synchronize
 # access to any data shared with the P2PInterface or P2PConnection.
-mininode_lock = RLock()
+mininode_lock = threading.RLock()
+
+class NetworkThread(threading.Thread):
+    def __init__(self):
+        super().__init__(name="NetworkThread")
 
-class NetworkThread(Thread):
     def run(self):
         while mininode_socket_map:
             # We check for whether to disconnect outside of the asyncore
@@ -412,3 +419,24 @@ class NetworkThread(Thread):
             [obj.handle_close() for obj in disconnected]
             asyncore.loop(0.1, use_poll=True, map=mininode_socket_map, count=1)
         logger.debug("Network thread closing")
+
+def network_thread_start():
+    """Start the network thread."""
+    # Only one network thread may run at a time
+    assert not network_thread_running()
+
+    NetworkThread().start()
+
+def network_thread_running():
+    """Return whether the network thread is running."""
+    return any([thread.name == "NetworkThread" for thread in threading.enumerate()])
+
+def network_thread_join(timeout=10):
+    """Wait timeout seconds for the network thread to terminate.
+
+    Throw if the network thread doesn't terminate in timeout seconds."""
+    network_threads = [thread for thread in threading.enumerate() if thread.name == "NetworkThread"]
+    assert len(network_threads) <= 1
+    for thread in network_threads:
+        thread.join(timeout)
+        assert not thread.is_alive()