Cooperation between multiple userspace runtimes? [LWN.net]

Cooperation between multiple userspace runtimes?

Posted Feb 4, 2026 19:53 UTC (Wed) by josh (subscriber, #17465)
Parent article: API changes for the futex robust list

Are there any efforts trying to figure out how to coordinate between multiple prospective users of the robust list? As far as I can tell, you can only have one per thread, and libc doesn't provide any way to integrate with theirs when using futex natively rather than via libc's locks.

By contrast, as I understand it, a great deal of effort went into a userspace ABI that supports multiple users of rseq.

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Cooperation between multiple userspace runtimes?

Posted Feb 4, 2026 20:11 UTC (Wed) by pm215 (subscriber, #98099) [Link] (1 responses)

The new API seems to give multiple lists per thread, and the CREATE_LIST operation causes the kernel to return the index of some not currently used list, so I think that means different users don't need to cooperate -- the only restriction is that you can't have more than some fixed number (6? 8? 10?) of such independent users of a robust-list.

Cooperation between multiple userspace runtimes?

Posted Feb 4, 2026 20:21 UTC (Wed) by josh (subscriber, #17465) [Link]

...apparently I should read more closely, thank you. That's exactly what I was looking for, and that sounds perfect.