Threaded Dispatcher

[shikokuchuo]

Closes #74. Addresses key remaining issue of #97.

To use:

daemons(dispatcher = NA)

Requires the dispatcher branch of dev nanonext.

Implementation currently benefits from:

• stack-allocated objects ensuring memory safety
• higher efficiency with re-use of Aios etc.

This is a straight port of existing dispatcher using inproc sockets, only somewhat optimised. To keep things as light as possible, there is currently limited information retrieval from the dispatcher thread.

Resultant performance is good, and is closer to the non-dispatcher rather than dispatcher case.

Does not yet support the interfaces required for crew autoscaling.

A re-design is yet possible prior to merge.

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[shikokuchuo]

Initial overhead benchmarking shows threaded dispatcher at ~1.2x non-dispatcher case. Not a bad result at all given this is prior to any optimization.

library(mirai)
library(future)

daemons(8, dispatcher = FALSE, .compute = "non-dispatcher")
#> [1] 8
daemons(8, dispatcher = NA, .compute = "threaded-dispatcher")
#> [1] 8
daemons(8, dispatcher = TRUE, .compute = "dispatcher")
#> [1] 8
plan("multisession", workers = 8)

bench::mark(
  mirai(1, .compute = "non-dispatcher")[],
  mirai(1, .compute = "threaded-dispatcher")[],
  mirai(1, .compute = "dispatcher")[],
  value(future(1)),
  relative = TRUE
)
#> # A tibble: 4 × 6
#>   expression                             min median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr>                           <dbl>  <dbl>     <dbl>     <dbl>    <dbl>
#> 1 "mirai(1, .compute = \"non-dispatc… 1   e0   1         782.      5.37      Inf
#> 2 "mirai(1, .compute = \"threaded-di… 1.26e0   1.16      699.      1         Inf
#> 3 "mirai(1, .compute = \"dispatcher\… 1.57e0   1.57      470.      1         Inf
#> 4 "value(future(1))"                  1.08e3 893.          1     278.        NaN

^{Created on 2024-09-03 with reprex v2.1.1}

[shikokuchuo]

FYI @wlandau this is now ready to merge from my side as experimental. I still have to add documentation and tests.

It doesn't have the same interfaces to support autoscaling, but otherwise works similarly to existing dispatcher. I'll open another thread so we can track {crew}-related discussions - it may be we find more efficient ways of doing things.

[wlandau]

Very exciting work! Looking forward to digging into specifics.

[shikokuchuo]

Dispatcher branch is merged at nanonext.

[shikokuchuo]

For the record, at point of merge, threaded dispatcher overhead at ~15%. This is really quite good as it has kept up with improvements in base performance over this period.

library(mirai)
library(future)

daemons(8, dispatcher = FALSE, .compute = "non-dispatcher")
#> [1] 8
daemons(8, dispatcher = NA, .compute = "threaded-dispatcher")
#> [1] 8
daemons(8, dispatcher = TRUE, .compute = "dispatcher")
#> [1] 8
plan("multisession", workers = 8)

bench::mark(
  mirai(1, .compute = "non-dispatcher")[],
  mirai(1, .compute = "threaded-dispatcher")[],
  mirai(1, .compute = "dispatcher")[],
  value(future(1)),
  relative = TRUE
)
#> # A tibble: 4 × 6
#>   expression                             min median `itr/sec` mem_alloc `gc/sec`
#>   <bch:expr>                           <dbl>  <dbl>     <dbl>     <dbl>    <dbl>
#> 1 "mirai(1, .compute = \"non-dispatc… 1   e0   1         791.      8.66      Inf
#> 2 "mirai(1, .compute = \"threaded-di… 1.21e0   1.15      700.      1         Inf
#> 3 "mirai(1, .compute = \"dispatcher\… 1.53e0   1.59      506.      1         NaN
#> 4 "value(future(1))"                  1.02e3 945.          1     278.        NaN

^{Created on 2024-09-11 with reprex v2.1.1}