Experimental Physics and
Industrial Control System

Érico Nogueira Rolim via Tech-talk <tech-talk at aps.anl.gov> · Fri, 8 Jul 2022 13:28:17 +0000

Hi!

I have a custom class that inherits from asynPortDriver, but it also overrides the readUInt32Digital, readInt32 and readFloat64 methods, such that they read values from hardware to provide up to date information. Most of our records for this IOC use SCAN set to I/O Intr, and we update values read from hardware when processing writes into hardware. However, we have some records for which we needed to use periodical SCAN ('0.1 second', in this case), due to their monitoring purpose, and they use the aforementioned read* methods to obtain values from hardware.

Unfortunately, when the IOC is exited (with 'exit' in the IOC shell, for example), it seems our asynPortDriver is destroyed before the thread responsible for the record updates is. This leads to multiple use-after-free issues during IOC exit; they can be seen with pthread_mutex_* functions returning EINVAL, and sometimes triggering assertions in our backend.

What is the recommended way forward here? Having things misbehave during exit is not the worst that could happen, but it's still an issue. The alternative I can see is adding a thread that polls through these HW values and using I/O Intr for the records. I think this would always work, but it feels ugly, given that Epics already has periodical SCAN functionality.

Thank you,
Érico

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System