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48c34e7635
Recently, in merge commit2718c90448, we added the ability to cancel pending view-update requests when we detect that the target node went down. This is important for view updates because these have a very long timeout (5 minutes), and we wanted to make this timeout even longer. However, the implementation caused a race: Between *creating* the update's request handler (create_write_response_handler()) and actually starting the request with this handler (mutate_begin()), there is a preemption point and we may end up deleting the request handler before starting the request. So mutate_begin() must gracefully handle the case of a missing request handler, and not crash with a segmentation fault as it did before this patch. Eventually the lifetime management of request handlers could be refactored to avoid this delicate fix (which requires more comments to explain than code), or even better, it would be more correct to cancel individual writes when a node goes down, not drop the entire handler (see issue #4523). However, for now, let's not do such invasive changes and just fix bug that we set out to fix. Fixes #4386. Signed-off-by: Nadav Har'El <nyh@scylladb.com> Message-Id: <20190620123949.22123-1-nyh@scylladb.com> (cherry picked from commit6e87bca65d)