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authorRichard van der Hoff <richard@matrix.org>2018-04-27 11:07:40 +0100
committerRichard van der Hoff <richard@matrix.org>2018-04-27 11:07:40 +0100
commit9255a6cb17716c022ebae1dbe9c142b78ca86ea7 (patch)
tree185b1b00af216695daca391eb62a871e78d32e49 /synapse/util/logcontext.py
parentMerge pull request #3134 from matrix-org/erikj/fix_admin_media_api (diff)
downloadsynapse-9255a6cb17716c022ebae1dbe9c142b78ca86ea7.tar.xz
Improve exception handling for background processes
There were a bunch of places where we fire off a process to happen in the
background, but don't have any exception handling on it - instead relying on
the unhandled error being logged when the relevent deferred gets
garbage-collected.

This is unsatisfactory for a number of reasons:
 - logging on garbage collection is best-effort and may happen some time after
   the error, if at all
 - it can be hard to figure out where the error actually happened.
 - it is logged as a scary CRITICAL error which (a) I always forget to grep for
   and (b) it's not really CRITICAL if a background process we don't care about
   fails.

So this is an attempt to add exception handling to everything we fire off into
the background.
Diffstat (limited to 'synapse/util/logcontext.py')
-rw-r--r--synapse/util/logcontext.py7
1 files changed, 6 insertions, 1 deletions
diff --git a/synapse/util/logcontext.py b/synapse/util/logcontext.py
index d59adc236e..d6587e4409 100644
--- a/synapse/util/logcontext.py
+++ b/synapse/util/logcontext.py
@@ -305,7 +305,12 @@ def run_in_background(f, *args, **kwargs):
     deferred returned by the funtion completes.
 
     Useful for wrapping functions that return a deferred which you don't yield
-    on.
+    on (for instance because you want to pass it to deferred.gatherResults()).
+
+    Note that if you completely discard the result, you should make sure that
+    `f` doesn't raise any deferred exceptions, otherwise a scary-looking
+    CRITICAL error about an unhandled error will be logged without much
+    indication about where it came from.
     """
     current = LoggingContext.current_context()
     res = f(*args, **kwargs)