fix(vrtManager): a request whose read of other hosts fails counts on its host again

other_hosts counted the request on its own host again only when the
block ended normally: a quota check that raised left the request
counted on the other host while it went on with its own. The count is
now restored however the block ends.

vrtManager/connection.py

@@ -147,9 +147,11 @@ def other_hosts():
     then goes on with the host it used before, through the objects it kept:
     the request counts on that host again after the block (HOST_REQUESTS)."""
     held = getattr(_request, "held", None)
-    yield
-    if held is not None:
-        _count_on(held)
+    try:
+        yield
+    finally:
+        if held is not None:
+            _count_on(held)
 
 
 request_started.connect(_request_started, dispatch_uid="vrtManager.connection.request_started")

vrtManager/tests/test_connection.py

@@ -1,5 +1,6 @@
 """Reachability probe and connections that do not block each other."""
 
+import contextlib
 import os
 import socket
 import threading
@@ -296,11 +297,19 @@ class HostRequestsTestCase(unittest.TestCase):
         self.assertEqual(self.request("h") + self.request("h"), [])
 
     def test_a_request_back_from_other_hosts_counts_on_its_own_again(self):
+        self.back_from_other_hosts(fails=False)
+
+    def test_a_request_back_from_other_hosts_that_failed_counts_on_its_own_again(self):
+        self.back_from_other_hosts(fails=True)
+
+    def back_from_other_hosts(self, fails):
         def run():
             request_started.send(sender=None)
             self.manager.get_connection("h", "u", "p", CONN_TCP)
-            with connection.other_hosts():
+            with contextlib.suppress(RuntimeError), connection.other_hosts():
                 self.manager.get_connection("g", "u", "p", CONN_TCP)
+                if fails:
+                    raise RuntimeError("the other host's read failed")
             back.set()
             self.done.wait(5)
             request_finished.send(sender=None)