abort_on_expiry chaining

[bhalevy]

Abort will be requested on the abort_on_expiry::abort_source() either when the timeout expires or abort is requested on the chained abort_source, the earliest of which.

The motivation for this feature is to be able to abort rpc messages either on timeout or via an external abort source (that may be triggered e.g. on shutdown).

[avikivity]

Please make the title clearer.

[avikivity]

Abort will be requested on the abort_on_expiry::abort_source() either when the timeout expires or abort is requested on the chained abort_source, the earliest of which.

This is unclear. What's the context here?

The motivation for this feature is to be able to abort rpc messages either on timeout or via an external abort source (that may be triggered e.g. on shutdown).

[bhalevy]

@avikivity please see alternative here: https://github.com/scylladb/seastar/pull/1435 these are generic combiners that could be used to combine abort_on_expiry with another abort_source in a generic way and without increasing the footprint of abort_on_expiry