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WIP: Usubscribe from events on the next subscription (PyTango#292) #1095
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Deposit unsubscription on a queue and execute it on the next subscription. Meanwhile mark the attribute as zombie - do not process any events and do not return it by the factory.
This is necessary for Sardana test suite which restart the device server in between the tests. If the GC does not destroy the TangoDevice on time for the next test then we receive API_EventTimeout errors which then enable polling and this situation is hard to control in the tests. With the zombie flag we mark a TangoDevice as disposable and ask the factory for a new one.
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One could also try to play manually with GC. Something like:
(I have not tried neither of them) |
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The root issue was solved in tango-controls/cppTango#699. |
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Similarly to #1091 and #1093, this PR tries to workaround tango-controls/pytango#292.
I tried this PR with sardana-org/sardana#1312 ( which reverts the Sardana workaround and use zombie concept in tests) and it works corrrectly for the sardanatestsuite and for the stress macro posted in #1093 (comment). So, IMO it is a satisfactory workaround.
Note that it has one side effect - it keeps garbage collected attributes subscribed until some new attribute is subscribed. To mitigate this effect attributes are marked as zombies - their push event return immediately. Also this should happen only for the configuration events - the change events should be unsubscribed with the last
TaurusModel.removeListenercall. Also if one wants to increase the frequency of unsubscribes thetangoattribute._empty_unsub_queue()could be called more frequently.