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https://issues.apache.org/jira/browse/PLC4X-344?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17544273#comment-17544273
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Łukasz Dywicki commented on PLC4X-344:
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Thank you Robin for pointing out issue. By looking at transaction manager I can
see that there are more things than just that. We have explicit thread pool
size of 4 which makes maximum concurrency level. While its more than enough for
most of PLCs, it will get a conflict when request count specified for
connection is higher than 4. Its executor is also static which means same
thread pool will be used for all connections.
The tricky part for request transaction manager is a blocking an poll/write
attempt when concurrency limit is reached, without managing thread pool queue
itself. As far I remember there is a way to achieve similar effect with
blocking queue, yet then whole request tracking we have built is to be removed.
I think that we might simply swap request tracking with an atomic counter to
get whole thing on safe side. In principle whole tracking of running requests
could be avoided in favor of just counting active tasks.
> spi.transaction.RequestTransactionManager is not thread safe
> ------------------------------------------------------------
>
> Key: PLC4X-344
> URL: https://issues.apache.org/jira/browse/PLC4X-344
> Project: Apache PLC4X
> Issue Type: Bug
> Components: Driver-S7, PLC4J
> Environment: Siemens IOT 2050, debian. PLC4J via kotlin
> Reporter: Robin
> Priority: Major
> Attachments: errorConnect.png
>
>
> When running a s7 connection to an PLC sometimes the connection halts and
> this error is thrown in the log. It seems like the processWorklog function
> uses a thread safe queue but is itself not threadsafe throwing this error.
>
> We're using an single connection to the plc. Reading two datablocks. Each
> datablock is read by a different handler running in a separate thread but
> using the same instance of PLC4J.
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