Measure the pin while the write is still parked

Message

The arm measured after the park ended, which passes whether or not the connection is serialised. It now takes a read AFTER the external commit and WHILE the write is parked: with the lock that read queues and returns current data; without it, it joins the pinned read transaction and returns the pre-commit count.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01NuSfnnNgQ81hjRygkkqWM6

Changed

 test/test-sqlite-connection-pin.sgl | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

Diff

test/test-sqlite-connection-pin.sglmodified

@@ -44,7 +44,14 @@

;; write completes, everything finalizes, the pin resolves before anyone

;; looks, and this test passes whether or not the connection is serialised.

;; That is exactly how the first version of this file was vacuous.

−47

(define PARK-BUDGET 0.30)

+47

;; The measuring read is taken AFTER the external commit and WHILE the shared

+48

;; write is still parked. That is the only moment the defect is visible:

+49

;; - without the lock it runs during the park, joins the read transaction

+50

;; pinned by the earlier read, and returns the PRE-COMMIT count;

+51

;; - with the lock it cannot run during the park at all -- it queues behind

+52

;; the write and returns current data, which is the fix working.

+53

;; Measuring after the park ends passes either way; that is how the first

+54

;; version of this file was vacuous.

(define failures '())

(define (fail! msg) (set! failures (cons msg failures)))

@@ -76,12 +83,12 @@

;;

;; `read-during?` is the ONLY difference between them.

(define (run-pin-arm name path read-during?)

−79

(sqlite-set-busy-budget! PARK-BUDGET)

(let ((C (make-db path))

(P #f)

(committed #f) (reheld #f) (released #f)

(started 0) (finished 0)

−84

(early 'not-taken)

+90

(early (quote not-taken))

+91

(during (quote not-taken))

(shared 'unset) (fresh 'unset))

(set! P (sqlite-open path))

(with-async

@@ -112,7 +119,12 @@

119

(go (when read-during?

120

(sleep 0.15)

121

(set! early (shared-count C))))

−115

;; The measurement, once the external commit is durable.

+122

;; THE MEASUREMENT: after the external commit, while the write is parked.

+123

(go (begin

+124

(let loop ((n 0))

+125

(when (and (not reheld) (< n 4000)) (sleep 0.005) (loop (+ n 1))))

+126

(set! during (shared-count C))))

+127

;; And a final reading once everything has drained.

128

(go (begin

129

(let loop ((n 0))

130

(when (and (not reheld) (< n 2000)) (sleep 0.005) (loop (+ n 1))))

@@ -128,7 +140,9 @@

140

(display (string-append " " name

141

": shared=" (number->string shared)

142

" fresh=" (number->string fresh)

−131

" early-read=" (if (eq? early 'not-taken) "not-taken"

+143

" during-park-read=" (if (eq? during (quote not-taken)) "not-taken"

+144

(number->string during))

+145

" early-read=" (if (eq? early (quote not-taken)) "not-taken"

146

(number->string early))

147

"\n"))

148

;; SETUP ASSERTIONS FIRST. Without these an "agree" could be two equal

@@ -142,7 +156,15 @@

156

(when (and read-during? (eq? early 'not-taken))

157

(fail! (string-append name ": SETUP -- the during-park read never happened, "

158

"so this arm did not test what it claims")))

−145

;; THE ASSERTION.

+159

;; THE ASSERTION: the read taken after the commit must see the commit.

+160

(when (eq? during (quote not-taken))

+161

(fail! (string-append name ": SETUP -- the during-park read never ran")))

+162

(when (and (not (eq? during (quote not-taken))) (not (= during (+ BASE SEED))))

+163

(fail! (string-append name ": THE CONNECTION IS PINNED. A read taken after the "

+164

"external commit returned " (number->string during)

+165

" rows, not " (number->string (+ BASE SEED))

+166

". It ran while a write on the same connection was parked "

+167

"and joined a read transaction that could not be released.")))

168

(when (not (equal? shared fresh))

169

(fail! (string-append name ": THE CONNECTION IS PINNED. It reports "

170

(number->string shared)