FA-11546 / Filesystem semantics / Open access

Duplicated descriptors advance independent read positions · case 01

Duplicated descriptors advance independent read positions.

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

ROOT CAUSE

A duplicated descriptor is modeled as a fresh open-file description.

VERIFIED REPAIR

Use one shared position for reads through either duplicated descriptor.

Unsuccessful approach: Synchronizing positions only after the first read still loses later interleavings.

Case contract

Deterministic in-memory filesystem model. Two descriptors are duplicates of one open-file description at offset zero. Return text read by alternating descriptors for nonnegative requested lengths; EOF reads return empty text.

Why this case matters

An offline semantic experiment for file API clients; it models only the stated operations, not a complete operating system.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(text, lengths):
    positions=[0,0]
    out=[]
    for i,k in enumerate(lengths):
     d=i%2; p=positions[d]; out.append(text[p:p+k]); positions[d]+=len(out[-1])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
s='abcdef'+str(N)
check('interleaved duplicate reads',solve(s,[1,1,1,1]),['a','b','c','d'])
check('one read',solve(s,[2]),['ab'])
check('zero length does not advance',solve(s,[0,2,1]),['','ab','c'])
check('EOF clips count',solve(s,[100,1]),[s,''])
check('empty file',solve('',[N,1]),['',''])
check('no reads',solve(s,[]),[])
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
interleaved duplicate reads	`['a', 'a', 'b', 'b']`	`['a', 'b', 'c', 'd']`	Failed
one read	`['ab']`	`['ab']`	Passed
zero length does not advance	`['', 'ab', 'a']`	`['', 'ab', 'c']`	Failed
EOF clips count	`['abcdef1', 'a']`	`['abcdef1', '']`	Failed
empty file	`['', '']`	`['', '']`	Passed
no reads	`[]`	`[]`	Passed

SHA-256 / 94f5674aed72a2865dd4865ca0dae86aa970a1e4cdb7407a7a319e2b882953b5

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(text, lengths):
    positions=[0,0]
    out=[]
    for i,k in enumerate(lengths):
     d=i%2; p=positions[d]; out.append(text[p:p+k]); positions[d]+=len(out[-1])
     if i==0: positions[1]=positions[0]
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
s='abcdef'+str(N)
check('interleaved duplicate reads',solve(s,[1,1,1,1]),['a','b','c','d'])
check('one read',solve(s,[2]),['ab'])
check('zero length does not advance',solve(s,[0,2,1]),['','ab','c'])
check('EOF clips count',solve(s,[100,1]),[s,''])
check('empty file',solve('',[N,1]),['',''])
check('no reads',solve(s,[]),[])
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
interleaved duplicate reads	`['a', 'b', 'b', 'c']`	`['a', 'b', 'c', 'd']`	Failed
one read	`['ab']`	`['ab']`	Passed
zero length does not advance	`['', 'ab', 'a']`	`['', 'ab', 'c']`	Failed
EOF clips count	`['abcdef1', '']`	`['abcdef1', '']`	Passed
empty file	`['', '']`	`['', '']`	Passed
no reads	`[]`	`[]`	Passed

SHA-256 / 65c5b223bb800bd6e8acbbaecb88ae506f24cdcb5ea3f959134f3e46f814c65c

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(text, lengths):
    position=0
    out=[]
    for k in lengths:
     part=text[position:position+k]; out.append(part); position+=len(part)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
s='abcdef'+str(N)
check('interleaved duplicate reads',solve(s,[1,1,1,1]),['a','b','c','d'])
check('one read',solve(s,[2]),['ab'])
check('zero length does not advance',solve(s,[0,2,1]),['','ab','c'])
check('EOF clips count',solve(s,[100,1]),[s,''])
check('empty file',solve('',[N,1]),['',''])
check('no reads',solve(s,[]),[])
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
interleaved duplicate reads	`['a', 'b', 'c', 'd']`	`['a', 'b', 'c', 'd']`	Passed
one read	`['ab']`	`['ab']`	Passed
zero length does not advance	`['', 'ab', 'c']`	`['', 'ab', 'c']`	Passed
EOF clips count	`['abcdef1', '']`	`['abcdef1', '']`	Passed
empty file	`['', '']`	`['', '']`	Passed
no reads	`[]`	`[]`	Passed

SHA-256 / 887c1824232cdfc64308ffe6a627059bb33c26b321e6f8d34a6b677a080f2047

Verification & scope

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 2026-09-29T14:38:48.884763+00:00.

Case digest / ed9370828dff00c7b5ac0081fdabe76f2f183aa8e7009bfc74c1e14036e9ec65