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Would be interesting to see performance comparisons between this and the alternatives considered like eventfd.

Sure, the “hot path” is probably very fast for all, but what about the slow path?

eventfd always pays a syscall on both sides (~200-400ns) regardless of load. Tachyon slow path only kick in under genuine starvation: the consumer spins first, then FUTEX_WAIT, and the producer skips FUTEX_WAKE entirely if the consumer still spinning. At sustainable rates the slow path never activates.

> eventfd always pays a syscall on both sides (~200-400ns) regardless of load.

It’s fairly standard to make the waiting side spin a bit after processing some data, and only issue another wait syscall if no more data arrives during the spin period.

(For instance, io_uring, which does this kind of IPC with a kernel thread on the receiving side, literally lets you configure how long said kernel thread should spin[1].)

[1] https://unixism.net/loti/tutorial/sq_poll.html

Fair point. The real difference is the narrower: with a futex the producer can inspect consumer_sleeping directly in shared memory and skip the FUTEX_WAKE entirely if the consumer is still spinning. With eventfd you need a write() regardless, or you add shared state to gate it, which is essentially rebuilding futex. Same idea but slightly less clean.

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