From bcd9827c3b845f357ff5a3dab19b02ba88617c44 Mon Sep 17 00:00:00 2001
From: David Wilson <dw@botanicus.net>
Date: Sat, 19 Jan 2019 22:23:31 +0000
Subject: [PATCH] core: Latch.empty() improvements

- throw LatchError if the latch is closed.
- wrap with the lock to avoid unexpected weirdness.
---
 mitogen/core.py     | 14 ++++++++++++--
 tests/latch_test.py |  7 +++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/mitogen/core.py b/mitogen/core.py
index fb182e3c..8c03145f 100644
--- a/mitogen/core.py
+++ b/mitogen/core.py
@@ -742,7 +742,8 @@ class Sender(object):
         self.context.send(
             Message.dead(
                 reason=self.explicit_close_msg,
-                handle=self.dst_handle)
+                handle=self.dst_handle
+            )
         )
 
     def __repr__(self):
@@ -1884,8 +1885,17 @@ class Latch(object):
         though a subsequent call to :meth:`get` will block, since another
         waiting thread may be woken at any moment between :meth:`empty` and
         :meth:`get`.
+
+        :raises LatchError:
+            The latch has already been marked closed.
         """
-        return len(self._queue) == 0
+        self._lock.acquire()
+        try:
+            if self.closed:
+                raise LatchError()
+            return len(self._queue) == 0
+        finally:
+            self._lock.release()
 
     def _get_socketpair(self):
         """
diff --git a/tests/latch_test.py b/tests/latch_test.py
index 5be12d73..6ae43221 100644
--- a/tests/latch_test.py
+++ b/tests/latch_test.py
@@ -21,6 +21,13 @@ class EmptyTest(testlib.TestCase):
         latch.put(None)
         self.assertTrue(not latch.empty())
 
+    def test_closed_is_empty(self):
+        latch = self.klass()
+        latch.put(None)
+        latch.close()
+        self.assertRaises(mitogen.core.LatchError,
+            lambda: latch.empty())
+
 
 class GetTest(testlib.TestCase):
     klass = mitogen.core.Latch