FAILURE MAP
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FA-47201 / Bounded deques / Open access

Deque rollback replays before-images in forward order · case 01

Deque rollback replays before-images in forward order.

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

ROOT CAUSE

Deque rollback replays before-images in forward order.

THE FAILURE

Deque rollback replays before-images in forward order.

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

Case contract

Undo a failed bounded ring mutation from a before-image journal. Replay writes newest-first, restore captured head/size/epoch, release reserved capacity, reclaim newly allocated blocks newest-first and consume the journal.

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):
    slots,journal,old_head,old_size,old_epoch,reserved,created=x
    restored=slots[:]
    for index,value in journal:restored[index]=value
    head=old_head
    size=old_size
    epoch=old_epoch
    permits=0
    reclaimed=created[::-1]
    remaining=[]
    return [restored,head,size,epoch,permits,reclaimed,remaining]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N+2,None],[[0,N],[0,N+1]],1,1,3,2,[4,5]]), {1: [[1, None], 1, 1, 3, 0, [5, 4], []], 2: [[2, None], 1, 1, 3, 0, [5, 4], []], 3: [[3, None], 1, 1, 3, 0, [5, 4], []], 4: [[4, None], 1, 1, 3, 0, [5, 4], []], 5: [[5, None], 1, 1, 3, 0, [5, 4], []]}[N])
check('1', solve([[N,N+1,N+2],[[1,None],[2,None]],0,1,2,1,[7]]), {1: [[1, None, None], 0, 1, 2, 0, [7], []], 2: [[2, None, None], 0, 1, 2, 0, [7], []], 3: [[3, None, None], 0, 1, 2, 0, [7], []], 4: [[4, None, None], 0, 1, 2, 0, [7], []], 5: [[5, None, None], 0, 1, 2, 0, [7], []]}[N])
check('2', solve([[N],[],0,1,4,0,[]]), {1: [[1], 0, 1, 4, 0, [], []], 2: [[2], 0, 1, 4, 0, [], []], 3: [[3], 0, 1, 4, 0, [], []], 4: [[4], 0, 1, 4, 0, [], []], 5: [[5], 0, 1, 4, 0, [], []]}[N])
check('3', solve([[None,N+1,None],[[1,N]],1,1,0,1,[8,9,10]]), {1: [[None, 1, None], 1, 1, 0, 0, [10, 9, 8], []], 2: [[None, 2, None], 1, 1, 0, 0, [10, 9, 8], []], 3: [[None, 3, None], 1, 1, 0, 0, [10, 9, 8], []], 4: [[None, 4, None], 1, 1, 0, 0, [10, 9, 8], []], 5: [[None, 5, None], 1, 1, 0, 0, [10, 9, 8], []]}[N])
check('4', solve([[N,N+1],[[0,None],[1,None]],1,0,2,2,[3,6]]), {1: [[None, None], 1, 0, 2, 0, [6, 3], []], 2: [[None, None], 1, 0, 2, 0, [6, 3], []], 3: [[None, None], 1, 0, 2, 0, [6, 3], []], 4: [[None, None], 1, 0, 2, 0, [6, 3], []], 5: [[None, None], 1, 0, 2, 0, [6, 3], []]}[N])
check('5', solve([[N+3,N+1],[[0,N],[0,N+2]],0,2,7,3,[4,7]]), {1: [[1, 2], 0, 2, 7, 0, [7, 4], []], 2: [[2, 3], 0, 2, 7, 0, [7, 4], []], 3: [[3, 4], 0, 2, 7, 0, [7, 4], []], 4: [[4, 5], 0, 2, 7, 0, [7, 4], []], 5: [[5, 6], 0, 2, 7, 0, [7, 4], []]}[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, None], 1, 1, 3, 0, [5, 4], []][[1, None], 1, 1, 3, 0, [5, 4], []]Failed
1[[1, None, None], 0, 1, 2, 0, [7], []][[1, None, None], 0, 1, 2, 0, [7], []]Passed
2[[1], 0, 1, 4, 0, [], []][[1], 0, 1, 4, 0, [], []]Passed
3[[None, 1, None], 1, 1, 0, 0, [10, 9, 8], []][[None, 1, None], 1, 1, 0, 0, [10, 9, 8], []]Passed
4[[None, None], 1, 0, 2, 0, [6, 3], []][[None, None], 1, 0, 2, 0, [6, 3], []]Passed
5[[3, 2], 0, 2, 7, 0, [7, 4], []][[1, 2], 0, 2, 7, 0, [7, 4], []]Failed

SHA-256 / b68e9b70ccc158aad7e314e9abffdeaffcfa5633f5d349716e0196caf49050a5

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    slots,journal,old_head,old_size,old_epoch,reserved,created=x
    restored=slots[:]
    for index,value in (reversed(journal) if len(created)<=1 else journal):restored[index]=value
    head=old_head
    size=old_size
    epoch=old_epoch
    permits=0
    reclaimed=created[::-1]
    remaining=[]
    return [restored,head,size,epoch,permits,reclaimed,remaining]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N+2,None],[[0,N],[0,N+1]],1,1,3,2,[4,5]]), {1: [[1, None], 1, 1, 3, 0, [5, 4], []], 2: [[2, None], 1, 1, 3, 0, [5, 4], []], 3: [[3, None], 1, 1, 3, 0, [5, 4], []], 4: [[4, None], 1, 1, 3, 0, [5, 4], []], 5: [[5, None], 1, 1, 3, 0, [5, 4], []]}[N])
check('1', solve([[N,N+1,N+2],[[1,None],[2,None]],0,1,2,1,[7]]), {1: [[1, None, None], 0, 1, 2, 0, [7], []], 2: [[2, None, None], 0, 1, 2, 0, [7], []], 3: [[3, None, None], 0, 1, 2, 0, [7], []], 4: [[4, None, None], 0, 1, 2, 0, [7], []], 5: [[5, None, None], 0, 1, 2, 0, [7], []]}[N])
check('2', solve([[N],[],0,1,4,0,[]]), {1: [[1], 0, 1, 4, 0, [], []], 2: [[2], 0, 1, 4, 0, [], []], 3: [[3], 0, 1, 4, 0, [], []], 4: [[4], 0, 1, 4, 0, [], []], 5: [[5], 0, 1, 4, 0, [], []]}[N])
check('3', solve([[None,N+1,None],[[1,N]],1,1,0,1,[8,9,10]]), {1: [[None, 1, None], 1, 1, 0, 0, [10, 9, 8], []], 2: [[None, 2, None], 1, 1, 0, 0, [10, 9, 8], []], 3: [[None, 3, None], 1, 1, 0, 0, [10, 9, 8], []], 4: [[None, 4, None], 1, 1, 0, 0, [10, 9, 8], []], 5: [[None, 5, None], 1, 1, 0, 0, [10, 9, 8], []]}[N])
check('4', solve([[N,N+1],[[0,None],[1,None]],1,0,2,2,[3,6]]), {1: [[None, None], 1, 0, 2, 0, [6, 3], []], 2: [[None, None], 1, 0, 2, 0, [6, 3], []], 3: [[None, None], 1, 0, 2, 0, [6, 3], []], 4: [[None, None], 1, 0, 2, 0, [6, 3], []], 5: [[None, None], 1, 0, 2, 0, [6, 3], []]}[N])
check('5', solve([[N+3,N+1],[[0,N],[0,N+2]],0,2,7,3,[4,7]]), {1: [[1, 2], 0, 2, 7, 0, [7, 4], []], 2: [[2, 3], 0, 2, 7, 0, [7, 4], []], 3: [[3, 4], 0, 2, 7, 0, [7, 4], []], 4: [[4, 5], 0, 2, 7, 0, [7, 4], []], 5: [[5, 6], 0, 2, 7, 0, [7, 4], []]}[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, None], 1, 1, 3, 0, [5, 4], []][[1, None], 1, 1, 3, 0, [5, 4], []]Failed
1[[1, None, None], 0, 1, 2, 0, [7], []][[1, None, None], 0, 1, 2, 0, [7], []]Passed
2[[1], 0, 1, 4, 0, [], []][[1], 0, 1, 4, 0, [], []]Passed
3[[None, 1, None], 1, 1, 0, 0, [10, 9, 8], []][[None, 1, None], 1, 1, 0, 0, [10, 9, 8], []]Passed
4[[None, None], 1, 0, 2, 0, [6, 3], []][[None, None], 1, 0, 2, 0, [6, 3], []]Passed
5[[3, 2], 0, 2, 7, 0, [7, 4], []][[1, 2], 0, 2, 7, 0, [7, 4], []]Failed

SHA-256 / 6d15af6a042b2b2b8f3f93ec978672a5e7c693a3a4a4f2e3124f3e88a1ffc86d

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 6 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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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 2026-09-29T14:44:39.549989+00:00.

Case digest / 7f6050ef5879424203b9a48332ad9ff684b6e7486e3bcaa0b50320ab416a180a