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Echo cancellation for prospect.

This commit is contained in:
Tony Garnock-Jones 2016-02-11 22:26:53 -05:00
parent fd7dc03dc6
commit 01b6bf92ee
3 changed files with 43 additions and 12 deletions
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14
prospect/examples/example-meta-echo.rkt
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@ -1,16 +1,16 @@
#lang prospect
;; Demonstrates a (hopefully soon historical!) bug in Syndicate.
;; Test case for a historical bug in Syndicate.
;;
;; When the bug exists, this program receives four patch events in
;; When the bug existed, this program receiveed four SCN events in
;; total, whereas it should receive only two.
;;
;; While metamessages are "echo cancelled", and receivers only ever
;; get one copy of a sent metamessage no matter how many metas there
;; are, state changes are not (yet). Issuing a quick enough "pulse" of
;; metaassertion while maintaining interest in it leads to an "echo":
;; While metamessages were "echo cancelled", and receivers only ever
;; got one copy of a sent metamessage no matter how many metas there
;; were, state changes were not. Issuing a quick enough "pulse" of
;; metaassertion while maintaining interest in it led to an "echo":
;; multiple receipts of the pulse.
;;
;; The fix is to adjust the implementation of state change
;; The fix was to adjust the implementation of state change
;; notifications to cancel the echo for metaassertions.
(require prospect/pretty)

28
prospect/mux.rkt
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@ -67,7 +67,23 @@
delta
delta-aggregate))
(define at-meta-everything (pattern->trie #t (at-meta ?)))
(define only-meta (datum-tset 'meta))
(define (echo-cancelled-trie t)
(trie-subtract t
at-meta-everything
#:combiner (lambda (v1 v2)
(if (tset-member? v1 'meta)
only-meta
#f))))
(define (compute-patches old-m new-m label delta delta-aggregate)
(define delta-aggregate/no-echo
(if (meta-label? label)
delta-aggregate
(patch (trie-prune-branch (patch-added delta-aggregate) struct:at-meta)
(trie-prune-branch (patch-removed delta-aggregate) struct:at-meta))))
(define old-routing-table (mux-routing-table old-m))
(define new-routing-table (mux-routing-table new-m))
(define affected-pids
@ -77,15 +93,17 @@
(cond [(equal? pid label)
(define feedback
(patch-union
(patch (biased-intersection new-routing-table (patch-added delta))
(biased-intersection old-routing-table (patch-removed delta)))
(patch (biased-intersection (patch-added delta-aggregate)
(patch (echo-cancelled-trie
(biased-intersection new-routing-table (patch-added delta)))
(echo-cancelled-trie
(biased-intersection old-routing-table (patch-removed delta))))
(patch (biased-intersection (patch-added delta-aggregate/no-echo)
(mux-interests-of new-m label))
(biased-intersection (patch-removed delta-aggregate)
(biased-intersection (patch-removed delta-aggregate/no-echo)
(mux-interests-of old-m label)))))
(cons label feedback)]
[else
(cons pid (view-patch delta-aggregate (mux-interests-of old-m pid)))]))
(cons pid (view-patch delta-aggregate/no-echo (mux-interests-of old-m pid)))]))
(and (not (meta-label? label))
(drop-patch
(compute-aggregate-patch delta label old-routing-table #:remove-meta? #t)))))

13
prospect/route.rkt
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@ -32,6 +32,7 @@
trie-match-trie
trie-append
trie-relabel
trie-prune-branch
SOL
SOV
@ -605,6 +606,18 @@
[(kv (treap-to-alist m)) #:when (not (eq? (car kv) ?))]
(rupdate acc (car kv) (walk (cdr kv))))])))
;; Trie Sigma -> Trie
;; Outright removes tries reachable from m via edges labelled with s.
;; Useful for removing (at-meta *) when the success value along that
;; branch doesn't matter.
(define (trie-prune-branch m s)
(match m
[#f #f]
[(wildcard-sequence k)
(collapse-wildcard-sequences (rupdate (expand-wildseq k) s (trie-empty)))]
[(success _) m]
[(? treap? h) (rupdate h s (trie-empty))]))
;; Trie Sigma -> Trie
(define (trie-step m s)
(match m