[tahoe-lafs-trac-stream] [Tahoe-LAFS] #1449: drop-upload: updates to files may be lost if few servers are connected (e.g. soon after starting the gateway)

[Tahoe-LAFS]

#1449: drop-upload: updates to files may be lost if few servers are connected
(e.g. soon after starting the gateway)
-------------------------------------+-------------------------------------
     Reporter:  davidsarah           |      Owner:  daira
         Type:  defect               |     Status:  assigned
     Priority:  major                |  Milestone:  1.11.0
    Component:  code-frontend-drop-  |    Version:  1.8.2
  upload                             |   Keywords:  drop-upload
   Resolution:                       |  preservation docs error otf-magic-
Launchpad Bug:                       |  folder-objective2
-------------------------------------+-------------------------------------

Comment (by daira):

 On #tahoe-lafs:
 > daira: dawuud: the current code in `DropUploader._notify` will (in the
 `path not in self._pending` branch) call `_append_to_deque` which adds the
 path to `self._pending`, then process the deque (synchronously), then add
 the path to `self._pending` again
 > daira: the second `self._pending.add(path)` is wrong and should be
 deleted
 > daira: processing the deque synchronously also may cause problems
 > daira: it may be the change to synchronous processing that made the
 tests work, but I think we probably have to change it back to asynchronous
 > daira: in particular, note that the deferred that is returned by
 `_process` is dropped by the call to `func(*fields[1:])` in
 `_process_deque`
 > daira: so this code will try to upload things in parallel...
 > daira: which may work for immutable files, but is a bad idea for
 mutables, especially directories
 > daira: I'll rebase the code as it is, anyway, so that we can review it
 more easily

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1449#comment:13>
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