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FA-46801 / Bounded deques / Open access

Final drain fails to wake terminal deque consumers · case 01

Final drain fails to wake terminal deque consumers.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Final drain fails to wake terminal deque consumers.

VERIFIED REPAIR

Restore the documented last drain wake invariant in graceful-close.

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

Case contract

Graceful close forbids future insertion but permits draining buffered values. Empty closed deque reports closed rather than empty. Terminal consumer waiters wake exactly on first empty close or final drain.

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):
    a,closed,op,value,cap,waiters=x
    if op=='close':
        wakes=waiters if not a and not closed else []
        return [a,True,None,wakes,not closed]
    if op=='push':
        if closed or len(a)==cap:return [a,closed,None,[],False]
        return [a+[value],closed,None,[],True]
    if not a:return [a,closed,'closed' if closed else 'empty',[],False]
    result=a[1:]
    wakes=[]
    return [result,closed,a[0],wakes,True]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N],False,"close",0,3,[1,2]]), {1: [[1], True, None, [], True], 2: [[2], True, None, [], True], 3: [[3], True, None, [], True], 4: [[4], True, None, [], True], 5: [[5], True, None, [], True]}[N])
check('1', solve([[],False,"close",0,3,[1,2]]), {1: [[], True, None, [1, 2], True], 2: [[], True, None, [1, 2], True], 3: [[], True, None, [1, 2], True], 4: [[], True, None, [1, 2], True], 5: [[], True, None, [1, 2], True]}[N])
check('2', solve([[],True,"close",0,3,[1,2]]), {1: [[], True, None, [], False], 2: [[], True, None, [], False], 3: [[], True, None, [], False], 4: [[], True, None, [], False], 5: [[], True, None, [], False]}[N])
check('3', solve([[N],True,"push",N+1,3,[1]]), {1: [[1], True, None, [], False], 2: [[2], True, None, [], False], 3: [[3], True, None, [], False], 4: [[4], True, None, [], False], 5: [[5], True, None, [], False]}[N])
check('4', solve([[N,N+1],True,"pop",0,3,[1]]), {1: [[2], True, 1, [], True], 2: [[3], True, 2, [], True], 3: [[4], True, 3, [], True], 4: [[5], True, 4, [], True], 5: [[6], True, 5, [], True]}[N])
check('5', solve([[N],True,"pop",0,3,[1,2]]), {1: [[], True, 1, [1, 2], True], 2: [[], True, 2, [1, 2], True], 3: [[], True, 3, [1, 2], True], 4: [[], True, 4, [1, 2], True], 5: [[], True, 5, [1, 2], True]}[N])
check('6', solve([[],True,"pop",0,3,[1]]), {1: [[], True, 'closed', [], False], 2: [[], True, 'closed', [], False], 3: [[], True, 'closed', [], False], 4: [[], True, 'closed', [], False], 5: [[], True, 'closed', [], False]}[N])
check('7', solve([[],False,"pop",0,3,[1]]), {1: [[], False, 'empty', [], False], 2: [[], False, 'empty', [], False], 3: [[], False, 'empty', [], False], 4: [[], False, 'empty', [], False], 5: [[], False, 'empty', [], False]}[N])
check('8', solve([[N],False,"push",N+1,3,[]]), {1: [[1, 2], False, None, [], True], 2: [[2, 3], False, None, [], True], 3: [[3, 4], False, None, [], True], 4: [[4, 5], False, None, [], True], 5: [[5, 6], False, None, [], 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[[1], True, None, [], True][[1], True, None, [], True]Passed
1[[], True, None, [1, 2], True][[], True, None, [1, 2], True]Passed
2[[], True, None, [], False][[], True, None, [], False]Passed
3[[1], True, None, [], False][[1], True, None, [], False]Passed
4[[2], True, 1, [], True][[2], True, 1, [], True]Passed
5[[], True, 1, [], True][[], True, 1, [1, 2], True]Failed
6[[], True, 'closed', [], False][[], True, 'closed', [], False]Passed
7[[], False, 'empty', [], False][[], False, 'empty', [], False]Passed
8[[1, 2], False, None, [], True][[1, 2], False, None, [], True]Passed

SHA-256 / dbd22a39fb07dca1311c6c1f09e55ef720d267ae997707fe456f1aae07a3121f

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    a,closed,op,value,cap,waiters=x
    if op=='close':
        wakes=waiters if not a and not closed else []
        return [a,True,None,wakes,not closed]
    if op=='push':
        if closed or len(a)==cap:return [a,closed,None,[],False]
        return [a+[value],closed,None,[],True]
    if not a:return [a,closed,'closed' if closed else 'empty',[],False]
    result=a[1:]
    wakes=waiters if closed and not result and len(waiters)==1 else []
    return [result,closed,a[0],wakes,True]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N],False,"close",0,3,[1,2]]), {1: [[1], True, None, [], True], 2: [[2], True, None, [], True], 3: [[3], True, None, [], True], 4: [[4], True, None, [], True], 5: [[5], True, None, [], True]}[N])
check('1', solve([[],False,"close",0,3,[1,2]]), {1: [[], True, None, [1, 2], True], 2: [[], True, None, [1, 2], True], 3: [[], True, None, [1, 2], True], 4: [[], True, None, [1, 2], True], 5: [[], True, None, [1, 2], True]}[N])
check('2', solve([[],True,"close",0,3,[1,2]]), {1: [[], True, None, [], False], 2: [[], True, None, [], False], 3: [[], True, None, [], False], 4: [[], True, None, [], False], 5: [[], True, None, [], False]}[N])
check('3', solve([[N],True,"push",N+1,3,[1]]), {1: [[1], True, None, [], False], 2: [[2], True, None, [], False], 3: [[3], True, None, [], False], 4: [[4], True, None, [], False], 5: [[5], True, None, [], False]}[N])
check('4', solve([[N,N+1],True,"pop",0,3,[1]]), {1: [[2], True, 1, [], True], 2: [[3], True, 2, [], True], 3: [[4], True, 3, [], True], 4: [[5], True, 4, [], True], 5: [[6], True, 5, [], True]}[N])
check('5', solve([[N],True,"pop",0,3,[1,2]]), {1: [[], True, 1, [1, 2], True], 2: [[], True, 2, [1, 2], True], 3: [[], True, 3, [1, 2], True], 4: [[], True, 4, [1, 2], True], 5: [[], True, 5, [1, 2], True]}[N])
check('6', solve([[],True,"pop",0,3,[1]]), {1: [[], True, 'closed', [], False], 2: [[], True, 'closed', [], False], 3: [[], True, 'closed', [], False], 4: [[], True, 'closed', [], False], 5: [[], True, 'closed', [], False]}[N])
check('7', solve([[],False,"pop",0,3,[1]]), {1: [[], False, 'empty', [], False], 2: [[], False, 'empty', [], False], 3: [[], False, 'empty', [], False], 4: [[], False, 'empty', [], False], 5: [[], False, 'empty', [], False]}[N])
check('8', solve([[N],False,"push",N+1,3,[]]), {1: [[1, 2], False, None, [], True], 2: [[2, 3], False, None, [], True], 3: [[3, 4], False, None, [], True], 4: [[4, 5], False, None, [], True], 5: [[5, 6], False, None, [], 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[[1], True, None, [], True][[1], True, None, [], True]Passed
1[[], True, None, [1, 2], True][[], True, None, [1, 2], True]Passed
2[[], True, None, [], False][[], True, None, [], False]Passed
3[[1], True, None, [], False][[1], True, None, [], False]Passed
4[[2], True, 1, [], True][[2], True, 1, [], True]Passed
5[[], True, 1, [], True][[], True, 1, [1, 2], True]Failed
6[[], True, 'closed', [], False][[], True, 'closed', [], False]Passed
7[[], False, 'empty', [], False][[], False, 'empty', [], False]Passed
8[[1, 2], False, None, [], True][[1, 2], False, None, [], True]Passed

SHA-256 / e3e8d66af0cf5097e4088e21fe2efbb87f8381e2cc05f6fd14b3031c79648a0e

3 / The verified repair

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

N = 1
observations = []
def solve(x):
    a,closed,op,value,cap,waiters=x
    if op=='close':
        wakes=waiters if not a and not closed else []
        return [a,True,None,wakes,not closed]
    if op=='push':
        if closed or len(a)==cap:return [a,closed,None,[],False]
        return [a+[value],closed,None,[],True]
    if not a:return [a,closed,'closed' if closed else 'empty',[],False]
    result=a[1:]
    wakes=waiters if closed and not result else []
    return [result,closed,a[0],wakes,True]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N],False,"close",0,3,[1,2]]), {1: [[1], True, None, [], True], 2: [[2], True, None, [], True], 3: [[3], True, None, [], True], 4: [[4], True, None, [], True], 5: [[5], True, None, [], True]}[N])
check('1', solve([[],False,"close",0,3,[1,2]]), {1: [[], True, None, [1, 2], True], 2: [[], True, None, [1, 2], True], 3: [[], True, None, [1, 2], True], 4: [[], True, None, [1, 2], True], 5: [[], True, None, [1, 2], True]}[N])
check('2', solve([[],True,"close",0,3,[1,2]]), {1: [[], True, None, [], False], 2: [[], True, None, [], False], 3: [[], True, None, [], False], 4: [[], True, None, [], False], 5: [[], True, None, [], False]}[N])
check('3', solve([[N],True,"push",N+1,3,[1]]), {1: [[1], True, None, [], False], 2: [[2], True, None, [], False], 3: [[3], True, None, [], False], 4: [[4], True, None, [], False], 5: [[5], True, None, [], False]}[N])
check('4', solve([[N,N+1],True,"pop",0,3,[1]]), {1: [[2], True, 1, [], True], 2: [[3], True, 2, [], True], 3: [[4], True, 3, [], True], 4: [[5], True, 4, [], True], 5: [[6], True, 5, [], True]}[N])
check('5', solve([[N],True,"pop",0,3,[1,2]]), {1: [[], True, 1, [1, 2], True], 2: [[], True, 2, [1, 2], True], 3: [[], True, 3, [1, 2], True], 4: [[], True, 4, [1, 2], True], 5: [[], True, 5, [1, 2], True]}[N])
check('6', solve([[],True,"pop",0,3,[1]]), {1: [[], True, 'closed', [], False], 2: [[], True, 'closed', [], False], 3: [[], True, 'closed', [], False], 4: [[], True, 'closed', [], False], 5: [[], True, 'closed', [], False]}[N])
check('7', solve([[],False,"pop",0,3,[1]]), {1: [[], False, 'empty', [], False], 2: [[], False, 'empty', [], False], 3: [[], False, 'empty', [], False], 4: [[], False, 'empty', [], False], 5: [[], False, 'empty', [], False]}[N])
check('8', solve([[N],False,"push",N+1,3,[]]), {1: [[1, 2], False, None, [], True], 2: [[2, 3], False, None, [], True], 3: [[3, 4], False, None, [], True], 4: [[4, 5], False, None, [], True], 5: [[5, 6], False, None, [], 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[[1], True, None, [], True][[1], True, None, [], True]Passed
1[[], True, None, [1, 2], True][[], True, None, [1, 2], True]Passed
2[[], True, None, [], False][[], True, None, [], False]Passed
3[[1], True, None, [], False][[1], True, None, [], False]Passed
4[[2], True, 1, [], True][[2], True, 1, [], True]Passed
5[[], True, 1, [1, 2], True][[], True, 1, [1, 2], True]Passed
6[[], True, 'closed', [], False][[], True, 'closed', [], False]Passed
7[[], False, 'empty', [], False][[], False, 'empty', [], False]Passed
8[[1, 2], False, None, [], True][[1, 2], False, None, [], True]Passed

SHA-256 / 5c27617c44c18a7cce4d334b8ac196a75b6ceb4e05051c33b168c9e88261d661

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 2026-09-29T14:44:35.573171+00:00.

Case digest / 3e81d105f092f11dc46e3544ef83928e5ba7ffd77cee53436cc12ec32dfb8891