Hi Salva,
As far as I know,
1. Out : Collector[T] could not support multi-thread accessing,
namely there could be only one thread writing records at one time. If there are
multiple threads using `out`, the access should need to be coordinated in some
way (for example, use lock, or use a queue to cache record and let a single
thread output them with `out`.
2. With the current implementation, `Out` would not be
recreated. However, I think it is implementation related, if the processing
logic still happens in the `processElement` method, is it possible to always
use the `out` object passed into the method?
Best,
Yun
------------------------------------------------------------------
From:Salva Alcántara <salcantara...@gmail.com>
Send Time:2020 Feb. 12 (Wed.) 13:33
To:user <user@flink.apache.org>
Subject:Using multithreaded library within ProcessFunction with callbacks
relying on the out parameter
I am working on a `CoProcessFunction` that uses a third party library for
detecting certain patterns of events based on some rules. So, in the end,
the `ProcessElement1` method is basically forwarding the events to this
library and registering a callback so that, when a match is detected, the
CoProcessFunction can emit an output event. For achieving this, the callback
relies on a reference to the `out: Collector[T]` parameter in
`ProcessElement1`.
Having said that, I am not sure whether this use case is well-supported by
Flink, since:
1. There might be multiple threads spanned by the third party library (let's
I have not any control over the amount of threads spanned, this is decided
by the library)
2. I am not sure whether `out` might be recreated or something by Flink at
some point, invalidating the references in the callbacks, making them crash
So far I have not observed any issues, but I have just run my program in the
small. It would be great to hear from the experts whether my approach is
valid or not.
PS: Also posted in
https://stackoverflow.com/questions/60181678/using-multithreaded-library-within-processfunction-with-callbacks-relying-on-the
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