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FA-46486 / Bounded deques / Open access

Free-block cache disposes newest retained IDs instead of evicted oldest IDs · case 01

Free-block cache disposes newest retained IDs instead of evicted oldest IDs.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Free-block cache disposes newest retained IDs instead of evicted oldest IDs.

VERIFIED REPAIR

Restore the documented disposal side invariant in block-release.

Unsuccessful approach: The partial repair still applies the incorrect transition to an admitted boundary or multi-element case.

Case contract

A deque block with outstanding borrowers cannot be freed. Otherwise clear its live references, append to a bounded free-block cache and dispose the oldest surplus block identities.

Why this case matters

Controlled bounded deque implementation model with explicit storage and lifecycle observations.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    pool,identity,borrowed,limit,live=x
    if borrowed:return [pool,False,live,[]]
    references=[]
    combined=pool+[identity]
    saved=combined[-limit:] if limit else []
    disposed=combined[len(saved):]
    return [saved,True,references,disposed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[1,2],3,False,2,[N,N+1]]), {1: [[2, 3], True, [], [1]], 2: [[2, 3], True, [], [1]], 3: [[2, 3], True, [], [1]], 4: [[2, 3], True, [], [1]], 5: [[2, 3], True, [], [1]]}[N])
check('1', solve([[1],2,True,3,[N]]), {1: [[1], False, [1], []], 2: [[1], False, [2], []], 3: [[1], False, [3], []], 4: [[1], False, [4], []], 5: [[1], False, [5], []]}[N])
check('2', solve([[],4,False,0,[N,N+1]]), {1: [[], True, [], [4]], 2: [[], True, [], [4]], 3: [[], True, [], [4]], 4: [[], True, [], [4]], 5: [[], True, [], [4]]}[N])
check('3', solve([[2],5,False,3,[N]]), {1: [[2, 5], True, [], []], 2: [[2, 5], True, [], []], 3: [[2, 5], True, [], []], 4: [[2, 5], True, [], []], 5: [[2, 5], True, [], []]}[N])
check('4', solve([[1,2,3],4,False,1,[N]]), {1: [[4], True, [], [1, 2, 3]], 2: [[4], True, [], [1, 2, 3]], 3: [[4], True, [], [1, 2, 3]], 4: [[4], True, [], [1, 2, 3]], 5: [[4], True, [], [1, 2, 3]]}[N])
check('5', solve([[],7,False,2,[]]), {1: [[7], True, [], []], 2: [[7], True, [], []], 3: [[7], True, [], []], 4: [[7], True, [], []], 5: [[7], True, [], []]}[N])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
0[[2, 3], True, [], [3]][[2, 3], True, [], [1]]Failed
1[[1], False, [1], []][[1], False, [1], []]Passed
2[[], True, [], [4]][[], True, [], [4]]Passed
3[[2, 5], True, [], []][[2, 5], True, [], []]Passed
4[[4], True, [], [2, 3, 4]][[4], True, [], [1, 2, 3]]Failed
5[[7], True, [], []][[7], True, [], []]Passed

SHA-256 / 47b7b25f78ede865e307d1c1a8634b75697c83fe736288b0e60285d593f0fc64

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    pool,identity,borrowed,limit,live=x
    if borrowed:return [pool,False,live,[]]
    references=[]
    combined=pool+[identity]
    saved=combined[-limit:] if limit else []
    disposed=combined[:len(combined)-len(saved)] if not saved else combined[len(saved):]
    return [saved,True,references,disposed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[1,2],3,False,2,[N,N+1]]), {1: [[2, 3], True, [], [1]], 2: [[2, 3], True, [], [1]], 3: [[2, 3], True, [], [1]], 4: [[2, 3], True, [], [1]], 5: [[2, 3], True, [], [1]]}[N])
check('1', solve([[1],2,True,3,[N]]), {1: [[1], False, [1], []], 2: [[1], False, [2], []], 3: [[1], False, [3], []], 4: [[1], False, [4], []], 5: [[1], False, [5], []]}[N])
check('2', solve([[],4,False,0,[N,N+1]]), {1: [[], True, [], [4]], 2: [[], True, [], [4]], 3: [[], True, [], [4]], 4: [[], True, [], [4]], 5: [[], True, [], [4]]}[N])
check('3', solve([[2],5,False,3,[N]]), {1: [[2, 5], True, [], []], 2: [[2, 5], True, [], []], 3: [[2, 5], True, [], []], 4: [[2, 5], True, [], []], 5: [[2, 5], True, [], []]}[N])
check('4', solve([[1,2,3],4,False,1,[N]]), {1: [[4], True, [], [1, 2, 3]], 2: [[4], True, [], [1, 2, 3]], 3: [[4], True, [], [1, 2, 3]], 4: [[4], True, [], [1, 2, 3]], 5: [[4], True, [], [1, 2, 3]]}[N])
check('5', solve([[],7,False,2,[]]), {1: [[7], True, [], []], 2: [[7], True, [], []], 3: [[7], True, [], []], 4: [[7], True, [], []], 5: [[7], True, [], []]}[N])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
0[[2, 3], True, [], [3]][[2, 3], True, [], [1]]Failed
1[[1], False, [1], []][[1], False, [1], []]Passed
2[[], True, [], [4]][[], True, [], [4]]Passed
3[[2, 5], True, [], []][[2, 5], True, [], []]Passed
4[[4], True, [], [2, 3, 4]][[4], True, [], [1, 2, 3]]Failed
5[[7], True, [], []][[7], True, [], []]Passed

SHA-256 / 185ed6f51d684d768538413d18c3be0868bd4dfb9b1891e8ab213b33db8f68f9

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    pool,identity,borrowed,limit,live=x
    if borrowed:return [pool,False,live,[]]
    references=[]
    combined=pool+[identity]
    saved=combined[-limit:] if limit else []
    disposed=combined[:len(combined)-len(saved)]
    return [saved,True,references,disposed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[1,2],3,False,2,[N,N+1]]), {1: [[2, 3], True, [], [1]], 2: [[2, 3], True, [], [1]], 3: [[2, 3], True, [], [1]], 4: [[2, 3], True, [], [1]], 5: [[2, 3], True, [], [1]]}[N])
check('1', solve([[1],2,True,3,[N]]), {1: [[1], False, [1], []], 2: [[1], False, [2], []], 3: [[1], False, [3], []], 4: [[1], False, [4], []], 5: [[1], False, [5], []]}[N])
check('2', solve([[],4,False,0,[N,N+1]]), {1: [[], True, [], [4]], 2: [[], True, [], [4]], 3: [[], True, [], [4]], 4: [[], True, [], [4]], 5: [[], True, [], [4]]}[N])
check('3', solve([[2],5,False,3,[N]]), {1: [[2, 5], True, [], []], 2: [[2, 5], True, [], []], 3: [[2, 5], True, [], []], 4: [[2, 5], True, [], []], 5: [[2, 5], True, [], []]}[N])
check('4', solve([[1,2,3],4,False,1,[N]]), {1: [[4], True, [], [1, 2, 3]], 2: [[4], True, [], [1, 2, 3]], 3: [[4], True, [], [1, 2, 3]], 4: [[4], True, [], [1, 2, 3]], 5: [[4], True, [], [1, 2, 3]]}[N])
check('5', solve([[],7,False,2,[]]), {1: [[7], True, [], []], 2: [[7], True, [], []], 3: [[7], True, [], []], 4: [[7], True, [], []], 5: [[7], True, [], []]}[N])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
0[[2, 3], True, [], [1]][[2, 3], True, [], [1]]Passed
1[[1], False, [1], []][[1], False, [1], []]Passed
2[[], True, [], [4]][[], True, [], [4]]Passed
3[[2, 5], True, [], []][[2, 5], True, [], []]Passed
4[[4], True, [], [1, 2, 3]][[4], True, [], [1, 2, 3]]Passed
5[[7], True, [], []][[7], True, [], []]Passed

SHA-256 / e0dfa3c1510b34330ba19826d7a1d23d2fa44d854fcb297a228cd8d550ed424f

Verification & scope

Offline finite deterministic model; no claim of production implementation or concurrent memory-model conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:44:32.505836+00:00.

Case digest / fdfe8eae93535d0a21158019f85eaf6ab02c3b216440109c1420e56c1c8f685c