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FA-46581 / Bounded deques / Open access

Retired deque slot is prepended to FIFO reuse order · case 01

Retired deque slot is prepended to FIFO reuse order.

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

ROOT CAUSE

Retired deque slot is prepended to FIFO reuse order.

THE FAILURE

Retired deque slot is prepended to FIFO reuse order.

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

Case contract

Retire one occupied deque slot. Clear its payload, advance that slot generation, append its index to the free list, decrement live count and invalidate the retired [index,generation] handle.

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,index,generations,free,live=x
    storage=slots[:]
    storage[index]=None
    versions=generations[:]
    versions[index]+=1
    available=[index]+free
    count=live-1
    old_handle=[index,generations[index]]
    valid=False
    return [storage,versions,available,count,old_handle,valid,len(available)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,None],1,[2,4,0],[2],2]), {1: [[1, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 2: [[2, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 3: [[3, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 4: [[4, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 5: [[5, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2]}[N])
check('1', solve([[N],0,[N],[],1]), {1: [[None], [2], [0], 0, [0, 1], False, 1], 2: [[None], [3], [0], 0, [0, 2], False, 1], 3: [[None], [4], [0], 0, [0, 3], False, 1], 4: [[None], [5], [0], 0, [0, 4], False, 1], 5: [[None], [6], [0], 0, [0, 5], False, 1]}[N])
check('2', solve([[None,N,None,N+1],3,[1,2,3,4],[0,2],2]), {1: [[None, 1, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 2: [[None, 2, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 3: [[None, 3, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 4: [[None, 4, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 5: [[None, 5, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3]}[N])
check('3', solve([[N,N+1,N+2],0,[N,N+1,N+2],[],3]), {1: [[None, 2, 3], [2, 2, 3], [0], 2, [0, 1], False, 1], 2: [[None, 3, 4], [3, 3, 4], [0], 2, [0, 2], False, 1], 3: [[None, 4, 5], [4, 4, 5], [0], 2, [0, 3], False, 1], 4: [[None, 5, 6], [5, 5, 6], [0], 2, [0, 4], False, 1], 5: [[None, 6, 7], [6, 6, 7], [0], 2, [0, 5], False, 1]}[N])
check('4', solve([[N,None,N+1],2,[3,0,7],[1],2]), {1: [[1, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 2: [[2, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 3: [[3, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 4: [[4, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 5: [[5, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2]}[N])
check('5', solve([[None,N],1,[4,N],[0],1]), {1: [[None, None], [4, 2], [0, 1], 0, [1, 1], False, 2], 2: [[None, None], [4, 3], [0, 1], 0, [1, 2], False, 2], 3: [[None, None], [4, 4], [0, 1], 0, [1, 3], False, 2], 4: [[None, None], [4, 5], [0, 1], 0, [1, 4], False, 2], 5: [[None, None], [4, 6], [0, 1], 0, [1, 5], False, 2]}[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[[1, None, None], [2, 5, 0], [1, 2], 1, [1, 4], False, 2][[1, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2]Failed
1[[None], [2], [0], 0, [0, 1], False, 1][[None], [2], [0], 0, [0, 1], False, 1]Passed
2[[None, 1, None, None], [1, 2, 3, 5], [3, 0, 2], 1, [3, 4], False, 3][[None, 1, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3]Failed
3[[None, 2, 3], [2, 2, 3], [0], 2, [0, 1], False, 1][[None, 2, 3], [2, 2, 3], [0], 2, [0, 1], False, 1]Passed
4[[1, None, None], [3, 0, 8], [2, 1], 1, [2, 7], False, 2][[1, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2]Failed
5[[None, None], [4, 2], [1, 0], 0, [1, 1], False, 2][[None, None], [4, 2], [0, 1], 0, [1, 1], False, 2]Failed

SHA-256 / 1749383f12d5fb288fc36db04ff787784c3a4e3eb7a0ebd078114a54bd029488

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    slots,index,generations,free,live=x
    storage=slots[:]
    storage[index]=None
    versions=generations[:]
    versions[index]+=1
    available=free+[index] if not free else [index]+free
    count=live-1
    old_handle=[index,generations[index]]
    valid=False
    return [storage,versions,available,count,old_handle,valid,len(available)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,None],1,[2,4,0],[2],2]), {1: [[1, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 2: [[2, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 3: [[3, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 4: [[4, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2], 5: [[5, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2]}[N])
check('1', solve([[N],0,[N],[],1]), {1: [[None], [2], [0], 0, [0, 1], False, 1], 2: [[None], [3], [0], 0, [0, 2], False, 1], 3: [[None], [4], [0], 0, [0, 3], False, 1], 4: [[None], [5], [0], 0, [0, 4], False, 1], 5: [[None], [6], [0], 0, [0, 5], False, 1]}[N])
check('2', solve([[None,N,None,N+1],3,[1,2,3,4],[0,2],2]), {1: [[None, 1, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 2: [[None, 2, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 3: [[None, 3, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 4: [[None, 4, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3], 5: [[None, 5, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3]}[N])
check('3', solve([[N,N+1,N+2],0,[N,N+1,N+2],[],3]), {1: [[None, 2, 3], [2, 2, 3], [0], 2, [0, 1], False, 1], 2: [[None, 3, 4], [3, 3, 4], [0], 2, [0, 2], False, 1], 3: [[None, 4, 5], [4, 4, 5], [0], 2, [0, 3], False, 1], 4: [[None, 5, 6], [5, 5, 6], [0], 2, [0, 4], False, 1], 5: [[None, 6, 7], [6, 6, 7], [0], 2, [0, 5], False, 1]}[N])
check('4', solve([[N,None,N+1],2,[3,0,7],[1],2]), {1: [[1, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 2: [[2, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 3: [[3, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 4: [[4, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2], 5: [[5, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2]}[N])
check('5', solve([[None,N],1,[4,N],[0],1]), {1: [[None, None], [4, 2], [0, 1], 0, [1, 1], False, 2], 2: [[None, None], [4, 3], [0, 1], 0, [1, 2], False, 2], 3: [[None, None], [4, 4], [0, 1], 0, [1, 3], False, 2], 4: [[None, None], [4, 5], [0, 1], 0, [1, 4], False, 2], 5: [[None, None], [4, 6], [0, 1], 0, [1, 5], False, 2]}[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[[1, None, None], [2, 5, 0], [1, 2], 1, [1, 4], False, 2][[1, None, None], [2, 5, 0], [2, 1], 1, [1, 4], False, 2]Failed
1[[None], [2], [0], 0, [0, 1], False, 1][[None], [2], [0], 0, [0, 1], False, 1]Passed
2[[None, 1, None, None], [1, 2, 3, 5], [3, 0, 2], 1, [3, 4], False, 3][[None, 1, None, None], [1, 2, 3, 5], [0, 2, 3], 1, [3, 4], False, 3]Failed
3[[None, 2, 3], [2, 2, 3], [0], 2, [0, 1], False, 1][[None, 2, 3], [2, 2, 3], [0], 2, [0, 1], False, 1]Passed
4[[1, None, None], [3, 0, 8], [2, 1], 1, [2, 7], False, 2][[1, None, None], [3, 0, 8], [1, 2], 1, [2, 7], False, 2]Failed
5[[None, None], [4, 2], [1, 0], 0, [1, 1], False, 2][[None, None], [4, 2], [0, 1], 0, [1, 1], False, 2]Failed

SHA-256 / 4a799812a7c0a02ed623f71e8facfe5fded1efe2111474f590de718655540ebb

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 2026-09-29T14:44:33.641560+00:00.

Case digest / 42f6dd38aefed0f6fb58a725fb56f74bc839b9a2f717b7b95ee888f5a8739350