bugfix: make most_recent_exception thread-local

As long as event processors aren't called in the transport, but in the
the thread where the exception was captured, this should still cover the
most important cases.

The old version was really not working at all if you consider exceptions
happening on different threads

Author: untitaker

sentry_sdk/utils.py

@@ -354,14 +354,14 @@ def __len__(self):
 
 class DefaultEventProcessor(object):
     def __init__(self):
-        self._most_recent_exception = None
+        self._most_recent_exception = ContextVar("most-recent-exception")
 
     def __call__(self, event):
         if event._exc_value is None:
             return
-        if self._most_recent_exception is event._exc_value:
+        if self._most_recent_exception.get(None) is event._exc_value:
             raise SkipEvent()
-        self._most_recent_exception = event._exc_value
+        self._most_recent_exception.set(event._exc_value)
 
 
 class SkipEvent(Exception):