FA-73596 / Rate limiter algorithms / Open access
Concurrency limiter with expiring leases: expiry runs only on acquire · case 01
Releasing an already expired lease is reported as a successful release.
ROOT CAUSE
Expired leases are reclaimed only when an acquire event arrives.
THE FAILURE
Expired leases are reclaimed only when an acquire event arrives.
Unsuccessful approach: Exempting the event's own id from expiry lets an expired holder release or re-acquire as if it still held the slot.
Case contract
Input {max_concurrent, lease_ms, events [[t, op, id]]}. Before every event, leases with start + lease_ms <= t expire. acquire returns "duplicate" (no change) for a held id, "granted" (recording t) when fewer than max_concurrent leases are held, else "rejected". release returns "released" for a held id and "unknown" otherwise, changing nothing. Return [results, sorted held ids].
Why this case matters
Concurrency limiters for workers and database pools use leases so that crashed holders eventually free their slot; expiry and release bookkeeping determine whether slots leak or double-count.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
cap = x['max_concurrent']
D = x['lease_ms']
held = {}
out = []
for t, op, ident in x['events']:
if op == 'acquire':
for k in [k for k, s in held.items() if s + D <= t]:
del held[k]
if ident in held:
out.append('duplicate')
elif len(held) < cap:
held[ident] = t
out.append('granted')
else:
out.append('rejected')
else:
if ident in held:
del held[ident]
out.append('released')
else:
out.append('unknown')
return [out, sorted(held)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1501, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[41, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1001, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [301, 'release', 'a'], [302, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[8, 'acquire', 'b'],
[172, 'acquire', 'c'],
[317, 'acquire', 'd'],
[462, 'acquire', 'a'],
[606, 'acquire', 'c'],
[769, 'acquire', 'd'],
[900, 'acquire', 'a'],
[1064, 'release', 'a'],
[1238, 'release', 'b'],
[1372, 'acquire', 'c'],
[1516, 'acquire', 'c'],
[1668, 'acquire', 'd']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'granted',
'rejected',
'rejected',
'duplicate',
'granted',
'granted',
'released',
'unknown',
'granted',
'duplicate',
'granted'],
['c', 'd']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[5, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1502, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[42, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1002, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [302, 'release', 'a'], [303, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[20, 'acquire', 'a'],
[161, 'acquire', 'a'],
[304, 'release', 'b'],
[482, 'acquire', 'c'],
[635, 'acquire', 'b'],
[780, 'acquire', 'd'],
[922, 'release', 'c'],
[1055, 'acquire', 'a'],
[1209, 'release', 'b'],
[1366, 'release', 'a'],
[1534, 'acquire', 'a'],
[1689, 'acquire', 'b']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'duplicate',
'unknown',
'granted',
'granted',
'rejected',
'released',
'granted',
'released',
'released',
'granted',
'granted'],
['a', 'b']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[6, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1503, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[43, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1003, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [303, 'release', 'a'], [304, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[7, 'acquire', 'a'],
[186, 'release', 'a'],
[319, 'acquire', 'a'],
[456, 'acquire', 'c'],
[610, 'acquire', 'a'],
[778, 'acquire', 'd'],
[935, 'acquire', 'c'],
[1055, 'acquire', 'a'],
[1219, 'release', 'a'],
[1368, 'acquire', 'b'],
[1500, 'acquire', 'a'],
[1677, 'acquire', 'b']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'released',
'granted',
'granted',
'duplicate',
'rejected',
'duplicate',
'granted',
'released',
'granted',
'granted',
'duplicate'],
['a', 'b']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[7, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1504, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[44, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1004, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [304, 'release', 'a'], [305, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[9, 'acquire', 'c'],
[172, 'acquire', 'd'],
[315, 'acquire', 'a'],
[473, 'acquire', 'a'],
[611, 'acquire', 'd'],
[785, 'acquire', 'c'],
[926, 'release', 'd'],
[1088, 'release', 'd'],
[1239, 'acquire', 'a'],
[1373, 'release', 'b'],
[1536, 'release', 'a'],
[1672, 'acquire', 'a']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'granted',
'rejected',
'rejected',
'duplicate',
'granted',
'unknown',
'unknown',
'granted',
'unknown',
'released',
'granted'],
['a']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[8, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1505, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[45, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1005, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [305, 'release', 'a'], [306, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[14, 'acquire', 'b'],
[177, 'release', 'a'],
[334, 'release', 'd'],
[476, 'acquire', 'a'],
[631, 'release', 'a'],
[764, 'acquire', 'b'],
[901, 'acquire', 'a'],
[1084, 'release', 'b'],
[1200, 'acquire', 'b'],
[1376, 'release', 'd'],
[1506, 'release', 'a'],
[1680, 'acquire', 'a']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'unknown',
'unknown',
'granted',
'released',
'granted',
'granted',
'released',
'granted',
'unknown',
'unknown',
'granted'],
['a', 'b']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[9, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]]]
for label, args, expected in cases[N - 1]:
check(label, solve(args), expected)
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| lease expires exactly | [['granted', 'rejected', 'granted', 'released'], []] | [['granted', 'rejected', 'granted', 'released'], []] | Passed |
| unknown release | [['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']] | [['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']] | Passed |
| duplicate acquire | [['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']] | [['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']] | Passed |
| release after expiry | [['granted', 'released', 'granted'], ['b']] | [['granted', 'unknown', 'granted'], ['b']] | Failed |
| random leases | [['granted', 'granted', 'rejected', 'rejected', 'duplicate', 'granted', 'granted', 'released', 'unknown', 'granted', 'duplicate', 'granted'], ['c', 'd']] | [['granted', 'granted', 'rejected', 'rejected', 'duplicate', 'granted', 'granted', 'released', 'unknown', 'granted', 'duplicate', 'granted'], ['c', 'd']] | Passed |
| full pool | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | Passed |
SHA-256 / e27e16739b5ab120c9d6e0da5e3799d819c1693e2a116d2c4965089b284c1bcd
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
cap = x['max_concurrent']
D = x['lease_ms']
held = {}
out = []
for t, op, ident in x['events']:
for k in [k for k, s in held.items() if s + D <= t and k != ident]:
del held[k]
if op == 'acquire':
if ident in held:
out.append('duplicate')
elif len(held) < cap:
held[ident] = t
out.append('granted')
else:
out.append('rejected')
else:
if ident in held:
del held[ident]
out.append('released')
else:
out.append('unknown')
return [out, sorted(held)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1501, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[41, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1001, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [301, 'release', 'a'], [302, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[8, 'acquire', 'b'],
[172, 'acquire', 'c'],
[317, 'acquire', 'd'],
[462, 'acquire', 'a'],
[606, 'acquire', 'c'],
[769, 'acquire', 'd'],
[900, 'acquire', 'a'],
[1064, 'release', 'a'],
[1238, 'release', 'b'],
[1372, 'acquire', 'c'],
[1516, 'acquire', 'c'],
[1668, 'acquire', 'd']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'granted',
'rejected',
'rejected',
'duplicate',
'granted',
'granted',
'released',
'unknown',
'granted',
'duplicate',
'granted'],
['c', 'd']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[5, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1502, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[42, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1002, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [302, 'release', 'a'], [303, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[20, 'acquire', 'a'],
[161, 'acquire', 'a'],
[304, 'release', 'b'],
[482, 'acquire', 'c'],
[635, 'acquire', 'b'],
[780, 'acquire', 'd'],
[922, 'release', 'c'],
[1055, 'acquire', 'a'],
[1209, 'release', 'b'],
[1366, 'release', 'a'],
[1534, 'acquire', 'a'],
[1689, 'acquire', 'b']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'duplicate',
'unknown',
'granted',
'granted',
'rejected',
'released',
'granted',
'released',
'released',
'granted',
'granted'],
['a', 'b']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[6, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1503, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[43, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1003, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [303, 'release', 'a'], [304, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[7, 'acquire', 'a'],
[186, 'release', 'a'],
[319, 'acquire', 'a'],
[456, 'acquire', 'c'],
[610, 'acquire', 'a'],
[778, 'acquire', 'd'],
[935, 'acquire', 'c'],
[1055, 'acquire', 'a'],
[1219, 'release', 'a'],
[1368, 'acquire', 'b'],
[1500, 'acquire', 'a'],
[1677, 'acquire', 'b']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'released',
'granted',
'granted',
'duplicate',
'rejected',
'duplicate',
'granted',
'released',
'granted',
'granted',
'duplicate'],
['a', 'b']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[7, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1504, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[44, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1004, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [304, 'release', 'a'], [305, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[9, 'acquire', 'c'],
[172, 'acquire', 'd'],
[315, 'acquire', 'a'],
[473, 'acquire', 'a'],
[611, 'acquire', 'd'],
[785, 'acquire', 'c'],
[926, 'release', 'd'],
[1088, 'release', 'd'],
[1239, 'acquire', 'a'],
[1373, 'release', 'b'],
[1536, 'release', 'a'],
[1672, 'acquire', 'a']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'granted',
'rejected',
'rejected',
'duplicate',
'granted',
'unknown',
'unknown',
'granted',
'unknown',
'released',
'granted'],
['a']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[8, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]],
[['lease expires exactly',
{'events': [[0, 'acquire', 'a'],
[999, 'acquire', 'b'],
[1000, 'acquire', 'b'],
[1505, 'release', 'b']],
'lease_ms': 1000,
'max_concurrent': 1},
[['granted', 'rejected', 'granted', 'released'], []]],
['unknown release',
{'events': [[0, 'acquire', 'a'],
[10, 'acquire', 'b'],
[20, 'release', 'zz'],
[30, 'acquire', 'c'],
[45, 'release', 'a']],
'lease_ms': 5000,
'max_concurrent': 2},
[['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']]],
['duplicate acquire',
{'events': [[0, 'acquire', 'a'],
[800, 'acquire', 'a'],
[1005, 'acquire', 'b'],
[1100, 'acquire', 'c']],
'lease_ms': 1000,
'max_concurrent': 2},
[['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']]],
['release after expiry',
{'events': [[0, 'acquire', 'a'], [305, 'release', 'a'], [306, 'acquire', 'b']],
'lease_ms': 300,
'max_concurrent': 1},
[['granted', 'unknown', 'granted'], ['b']]],
['random leases',
{'events': [[14, 'acquire', 'b'],
[177, 'release', 'a'],
[334, 'release', 'd'],
[476, 'acquire', 'a'],
[631, 'release', 'a'],
[764, 'acquire', 'b'],
[901, 'acquire', 'a'],
[1084, 'release', 'b'],
[1200, 'acquire', 'b'],
[1376, 'release', 'd'],
[1506, 'release', 'a'],
[1680, 'acquire', 'a']],
'lease_ms': 600,
'max_concurrent': 2},
[['granted',
'unknown',
'unknown',
'granted',
'released',
'granted',
'granted',
'released',
'granted',
'unknown',
'unknown',
'granted'],
['a', 'b']]],
['full pool',
{'events': [[0, 'acquire', 'a'],
[1, 'acquire', 'b'],
[2, 'acquire', 'c'],
[3, 'release', 'a'],
[9, 'acquire', 'c']],
'lease_ms': 10000,
'max_concurrent': 2},
[['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']]]]]
for label, args, expected in cases[N - 1]:
check(label, solve(args), expected)
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 fixture | Actual | Expected | Outcome |
|---|---|---|---|
| lease expires exactly | [['granted', 'rejected', 'granted', 'released'], []] | [['granted', 'rejected', 'granted', 'released'], []] | Passed |
| unknown release | [['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']] | [['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']] | Passed |
| duplicate acquire | [['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']] | [['granted', 'duplicate', 'granted', 'granted'], ['b', 'c']] | Passed |
| release after expiry | [['granted', 'released', 'granted'], ['b']] | [['granted', 'unknown', 'granted'], ['b']] | Failed |
| random leases | [['granted', 'granted', 'rejected', 'rejected', 'duplicate', 'granted', 'granted', 'released', 'unknown', 'granted', 'duplicate', 'granted'], ['c', 'd']] | [['granted', 'granted', 'rejected', 'rejected', 'duplicate', 'granted', 'granted', 'released', 'unknown', 'granted', 'duplicate', 'granted'], ['c', 'd']] | Passed |
| full pool | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | Passed |
SHA-256 / cf76c6aeda4b6d60b86afdcb723209107f5c3ce7bd33b15c9b1866ec6ad5b3c1
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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Sign in to the archive ↗Verification & scope
A deterministic, bounded teaching model with stipulated constants and pre-hashed or explicitly hashed inputs; it is not a production implementation and makes no claim of conformance to any library or paper beyond the stated contract. 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 2026-09-29T14:48:48.966336+00:00.
Case digest / 74e800c5a70583597b09b1bfd1cba690d217ca0ff0474a0b6fec340f965979b2