Merge #14958: qa: Remove race between connecting and shutdown on separate connections

4412a59bfe qa: Remove race between connecting and shutdown on separate connections (João Barbosa)

Pull request description:

  Fixes the error https://github.com/bitcoin/bitcoin/pull/14670#issuecomment-447255352 reported by @ken2812221.

  There is a race between RPC stop and another concurrent call in the test framework. The connection must be established and the command `waitfornewblock` running before calling `stop`.

  See also https://github.com/bitcoin/bitcoin/pull/14670#issuecomment-447304513.

Tree-SHA512: 77feb8628d3b9c025ec0cf83565d4d6680cad4fb182fc93a65df8b573f3e799ba4c44e06d9001dd8a375ca0b1ee17f10e66c3902b6256d0ae2acbc64539185d7

test/functional/feature_shutdown.py

@@ -5,7 +5,7 @@
 """Test bitcoind shutdown."""
 
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal, get_rpc_proxy
+from test_framework.util import assert_equal, get_rpc_proxy, wait_until
 from threading import Thread
 
 def test_long_call(node):
@@ -20,8 +20,14 @@ class ShutdownTest(BitcoinTestFramework):
 
     def run_test(self):
         node = get_rpc_proxy(self.nodes[0].url, 1, timeout=600, coveragedir=self.nodes[0].coverage_dir)
+        # Force connection establishment by executing a dummy command.
+        node.getblockcount()
         Thread(target=test_long_call, args=(node,)).start()
-        # wait 1 second to ensure event loop waits for current connections to close
+        # Wait until the server is executing the above `waitfornewblock`.
+        wait_until(lambda: len(self.nodes[0].getrpcinfo()['active_commands']) == 2)
+        # Wait 1 second after requesting shutdown but not before the `stop` call
+        # finishes. This is to ensure event loop waits for current connections
+        # to close.
         self.stop_node(0, wait=1000)
 
 if __name__ == '__main__':