FA-73586 / Rate limiter algorithms / Open access
Concurrency limiter with expiring leases: unknown release frees someone else's slot · case 01
A stray release from a client that never acquired evicts the oldest legitimate holder.
ROOT CAUSE
Releasing an unheld id removes the oldest lease, as a counter-based semaphore would.
THE FAILURE
Releasing an unheld id removes the oldest lease, as a counter-based semaphore would.
Unsuccessful approach: Reporting success for an unknown id hides the protocol error from the caller.
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']:
for k in [k for k, s in held.items() if s + D <= t]:
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:
if held:
del held[min(held, key=held.get)]
out.append('released')
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', 'released', 'granted', 'released'], ['c']] | [['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']] | Failed |
| 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', 'released', 'granted', 'duplicate', 'granted'], ['c', 'd']] | [['granted', 'granted', 'rejected', 'rejected', 'duplicate', 'granted', 'granted', 'released', 'unknown', 'granted', 'duplicate', 'granted'], ['c', 'd']] | Failed |
| full pool | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | Passed |
SHA-256 / 4eb361dad5fa37ee1eed9b4397eb4fbe43f0fbdc56d9c1e38145af3d2409f9c3
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]:
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('released')
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', 'released', 'rejected', 'released'], ['b']] | [['granted', 'granted', 'unknown', 'rejected', 'released'], ['b']] | Failed |
| 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', 'released', 'granted', 'duplicate', 'granted'], ['c', 'd']] | [['granted', 'granted', 'rejected', 'rejected', 'duplicate', 'granted', 'granted', 'released', 'unknown', 'granted', 'duplicate', 'granted'], ['c', 'd']] | Failed |
| full pool | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | [['granted', 'granted', 'rejected', 'released', 'granted'], ['b', 'c']] | Passed |
SHA-256 / 65706bcc30e2df3ecd1ae082c7412fa6209448b0256395609ab07995c149926d
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 / 5b162824a3b300f85bba34bb8fea9847f52bb055dff9271a1ec7852a6d3809ac