Fix pinger cache bug and add test.

Testing Done:
Added a unit test that shows pinger will return UNREACHABLE on a netloc that should pass if the netloc has been used previously with a faster timeout.

Changed global_pinger_memo to take into account the timeout and number of tries, and the global_pinger_memo test now passes.

CI is running: https://travis-ci.org/pantsbuild/pants/builds/85163916

Bugs closed: 1766

Reviewed at https://rbcommons.com/s/twitter/r/2948/

src/python/pants/cache/pinger.py

@@ -13,7 +13,7 @@
 from pants.util.contextutil import Timer
 
 
-_global_pinger_memo = {}  # netloc -> rt time in secs.
+_global_pinger_memo = {}  # (netloc, timeout, tries) -> rt time in secs.
 
 
 class Pinger(object):
@@ -28,12 +28,18 @@ def __init__(self, timeout, tries):
   def ping(self, netloc):
     """Time a single roundtrip to the netloc.
 
+    :param netloc: string of "host:port"
+    :returns: the fastest ping time for a given netloc and number of tries.
+    or Pinger.UNREACHABLE if ping times out.
+    :rtype: float
+
     Note that we don't use actual ICMP pings, because cmd-line ping is
     inflexible and platform-dependent, so shelling out to it is annoying,
     and the ICMP python lib can only be called by the superuser.
     """
-    if netloc in _global_pinger_memo:
-      return _global_pinger_memo[netloc]
+    netloc_info = (netloc, self._timeout, self._tries)
+    if netloc_info in _global_pinger_memo:
+      return _global_pinger_memo[netloc_info]
 
     host, colon, portstr = netloc.partition(':')
     port = int(portstr) if portstr else None
@@ -48,7 +54,7 @@ def ping(self, netloc):
       except Exception:
         new_rt_secs = Pinger.UNREACHABLE
       rt_secs = min(rt_secs, new_rt_secs)
-    _global_pinger_memo[netloc] = rt_secs
+    _global_pinger_memo[netloc_info] = rt_secs
     return rt_secs
 
   def pings(self, netlocs):

tests/python/pants_test/cache/test_pinger.py

@@ -59,6 +59,12 @@ def test_pinger_timeout_config(self):
     self.assertLess(ping_results[self.fast_netloc], 1)
     self.assertEqual(ping_results[self.slow_netloc], Pinger.UNREACHABLE)
 
+  def test_global_pinger_memo(self):
+    fast_pinger = Pinger(timeout=self.slow_seconds, tries=2)
+    slow_pinger = Pinger(timeout=self.timeout_seconds, tries=2)
+    self.assertEqual(fast_pinger.pings([self.slow_netloc])[0][1], Pinger.UNREACHABLE)
+    self.assertNotEqual(slow_pinger.pings([self.slow_netloc])[0][1], Pinger.UNREACHABLE)
+
   def tearDown(self):
     for server in self.servers:
       server.shutdown()