catch and log exceptions in the interval timer function (#1145)

Instead of letting the thread die, we log the exception with
a stack trace to ease debugging.

Author: beniwohli

elasticapm/utils/threading.py

@@ -30,10 +30,13 @@
 
 from __future__ import absolute_import
 
+import logging
 import os
 import threading
 from timeit import default_timer
 
+logger = logging.getLogger("elasticapm.utils.threading")
+
 
 class IntervalTimer(threading.Thread):
     """
@@ -77,11 +80,15 @@ def run(self):
                 # we've been cancelled, time to go home
                 return
             start = default_timer()
-            rval = self._function(*self._args, **self._kwargs)
-            if self._evaluate_function_interval and isinstance(rval, (int, float)):
-                interval_override = rval
-            else:
-                interval_override = None
+            try:
+                rval = self._function(*self._args, **self._kwargs)
+                if self._evaluate_function_interval and isinstance(rval, (int, float)):
+                    interval_override = rval
+                else:
+                    interval_override = None
+            except Exception:
+                logger.error("Exception in interval timer function", exc_info=True)
+
             execution_time = default_timer() - start
 
     def cancel(self):

tests/utils/threading_tests.py

@@ -32,6 +32,7 @@
 import mock
 
 from elasticapm.utils.threading import IntervalTimer
+from tests.utils import assert_any_record_contains
 
 
 def test_interval_timer():
@@ -75,3 +76,16 @@ def test_interval_timer_interval_override_non_number():
         timer.cancel()
     time.sleep(0.05)
     assert not timer.is_alive()
+
+
+def test_interval_timer_exception(caplog):
+    def my_func():
+        return 1 / 0
+
+    with caplog.at_level("ERROR", "elasticapm.utils.threading"):
+        timer = IntervalTimer(function=my_func, interval=0.1)
+        timer.start()
+        time.sleep(0.25)
+        assert timer.is_alive()
+    timer.cancel()
+    assert_any_record_contains(caplog.records, "Exception in interval timer function")