[PATCH] run-tests: "fix" race condition in race condition fix

[Bryan O'Sullivan]

# HG changeset patch
# User Bryan O'Sullivan <bryano at fb.com>
# Date 1453489213 28800
#      Fri Jan 22 11:00:13 2016 -0800
# Branch stable
# Node ID 6bb64e83ac188ee99528ad0237028f00047ab505
# Parent  0b752757a0c4f30ac755389014e2af9d2e0b4a3f
run-tests: "fix" race condition in race condition fix

Laurent's commit 3203dfe341f9 still suffers from a race: by the
time the "job" function tries to assign to channels[channel], that
list has been truncated to empty.  The result is that every job
thread raises an IndexError.

Earlier, I tried an approach of correctly locking channels, but
that caused run-tests to hang on KeyboardInterrupt sometimes.

This approach is strictly hackier, but seems to actually work
reliably.

diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -1526,13 +1526,16 @@ class TestSuite(unittest.TestSuite):
             channels[channel] = "=" + test.name[5:].split(".")[0]
             try:
                 test(result)
-                channels[channel] = ''
                 done.put(None)
             except KeyboardInterrupt:
-                channels[channel] = ''
+                pass
             except: # re-raises
                 done.put(('!', test, 'run-test raised an error, see traceback'))
                 raise
+            try:
+                channels[channel] = ''
+            except IndexError:
+                pass
 
         def stat():
             count = 0