From b1ce1927022d374198441afafeb27199fc8a052a Mon Sep 17 00:00:00 2001
From: eunhhu <necpition205@gmail.com>
Date: Thu, 24 Sep 2026 17:14:54 +0100
Subject: Establish native micro runtime checkpoint

---
 research/experiments/002-buffer-retention/run.py | 300 +++++++++++++++++++++++
 1 file changed, 300 insertions(+)
 create mode 100644 research/experiments/002-buffer-retention/run.py

(limited to 'research/experiments/002-buffer-retention/run.py')

diff --git a/research/experiments/002-buffer-retention/run.py b/research/experiments/002-buffer-retention/run.py
new file mode 100644
index 0000000..49a693c
--- /dev/null
+++ b/research/experiments/002-buffer-retention/run.py
@@ -0,0 +1,300 @@
+#!/usr/bin/env python3
+"""Build, independently verify, and measure the retention experiment."""
+import argparse
+import csv
+import hashlib
+import json
+import os
+from pathlib import Path
+import platform
+import random
+import shlex
+import signal
+import statistics
+import struct
+import subprocess
+import tempfile
+import time
+
+ROOT = Path(__file__).resolve().parent
+FLAGS = ["-std=c17", "-Wall", "-Wextra", "-Wpedantic", "-Werror", "-O2", "-g"]
+
+
+def digest(path):
+    with open(path, "rb") as stream:
+        return hashlib.file_digest(stream, "sha256").hexdigest()
+
+
+def dump(path, value):
+    path.write_text(json.dumps(value, indent=2, ensure_ascii=False) + "\n")
+
+
+def build(cc, output, sanitizer=False):
+    command = [*cc, *FLAGS]
+    if sanitizer:
+        command += ["-fsanitize=address,undefined", "-fno-omit-frame-pointer"]
+    command += [str(ROOT / "benchmark.c"), "-o", str(output)]
+    result = subprocess.run(command, capture_output=True, text=True, check=True)
+    return {"command": command, "stderr": result.stderr, "sha256": digest(output),
+            "size_bytes": output.stat().st_size}
+
+
+def shape_for(shape, rng, i):
+    if shape == "sparse":
+        return 65536, 64
+    if shape == "dense":
+        return 65536, 49152
+    if shape == "mixed":
+        source = rng.choice([4096, 16384, 65536, 262144])
+        keep = max(16, source // rng.choice([1, 2, 4, 8, 64, 1024]))
+        return source, keep
+    if shape == "test":
+        return [(1, 1), (63, 17), (4097, 12), (65536, 49152), (127, 127)][i % 5]
+    raise ValueError(shape)
+
+
+def fixture(path, shape, count, seed):
+    rng = random.Random(seed)
+    expected = hashlib.sha256()
+    total = 0
+    with path.open("wb") as stream:
+        for i in range(count):
+            size, keep = shape_for(shape, rng, i)
+            offset = rng.randrange(size - keep + 1)
+            # All input bytes exist on disk; no sparse files or seeking past data.
+            tile = rng.randbytes(256)
+            payload = (tile * ((size + 255) // 256))[:size]
+            stream.write(struct.pack("<III", size, offset, keep))
+            stream.write(payload)
+            out = struct.pack("<I", keep) + payload[offset:offset + keep]
+            expected.update(out)
+            total += len(out)
+    return {"path": path.name, "shape": shape, "records": count, "seed": seed,
+            "input_bytes": path.stat().st_size, "input_sha256": digest(path),
+            "expected_output_bytes": total, "expected_output_sha256": expected.hexdigest()}
+
+
+def reference(data):
+    result = bytearray()
+    at = 0
+    while at < len(data):
+        if len(data) - at < 12:
+            raise ValueError("short header")
+        size, offset, keep = struct.unpack_from("<III", data, at)
+        at += 12
+        if not 0 < size <= 8 * 1024 * 1024 or not 0 < keep <= size or offset > size - keep:
+            raise ValueError("invalid frame")
+        if len(data) - at < size:
+            raise ValueError("short payload")
+        result.extend(struct.pack("<I", keep))
+        result.extend(data[at + offset:at + offset + keep])
+        at += size
+    return bytes(result)
+
+
+def command(binary, case, policy, *extra):
+    args = [str(binary), "--policy", policy["policy"], "--pool", str(policy.get("pool", 1)),
+            "--ratio", str(policy.get("ratio", 4)), "--budget", str(case.get("budget", 8388608)),
+            "--slots", str(case.get("slots", 512)), "--hold-us", str(case.get("hold_us", 0)),
+            "--service-us", str(case.get("service_us", 0))]
+    return args + list(extra)
+
+
+def metrics(stderr):
+    # Sanitizer diagnostics must not be silently ignored.
+    text = stderr.decode().strip()
+    try:
+        result = json.loads(text)
+    except json.JSONDecodeError as exc:
+        raise AssertionError(f"Expected metrics only; tool/runtime diagnostics:\n{text}") from exc
+    assert result["unreleased_buffer_bytes"] == 0, result
+    assert result["peak_active_bytes"] <= result["peak_reserved_bytes"] <= result["budget_bytes"], result
+    return result
+
+
+def check(binary, tmp, policies):
+    checks = []
+    test = tmp / "test.frames"
+    fixture(test, "test", 45, 177)
+    data = test.read_bytes()
+    expected = reference(data)
+    for policy in policies:
+        for slow in [False, True]:
+            case = {"slots": 7, "hold_us": 100 if slow else 0, "budget": 300000}
+            result = subprocess.run(command(binary, case, policy), input=data, capture_output=True, timeout=15)
+            m = metrics(result.stderr)
+            assert result.returncode == 0 and m["status"] == "ok", (policy, result.stderr)
+            assert result.stdout == expected and m["emitted"] == 45
+            assert m["input_bytes"] == len(data) and m["output_bytes"] == len(expected)
+            assert m["live_at_stop_bytes"] == 0
+            checks.append(f'{policy["name"]}: byte equality, accounting, cleanup, slow={slow}')
+        # Truncation at both header and payload boundaries, including exact missing payload.
+        bad_inputs = [b"x", struct.pack("<III", 12, 0, 4),
+                      struct.pack("<III", 12, 0, 4) + b"123",
+                      struct.pack("<III", 12, 11, 4) + b"x" * 12,
+                      struct.pack("<III", 0, 0, 0),
+                      struct.pack("<III", 8 * 1024 * 1024 + 1, 0, 1)]
+        for bad in bad_inputs:
+            result = subprocess.run(command(binary, {"hold_us": 1000}, policy),
+                                    input=data[:13] + bad, capture_output=True, timeout=15)
+            m = metrics(result.stderr)
+            assert result.returncode == 2 and m["status"] in {"invalid_frame", "truncated_input"}
+        checks.append(f'{policy["name"]}: six malformed inputs with pending buffer cleanup')
+        result = subprocess.run(command(binary, {"hold_us": 1000}, policy, "--cancel-after", "3"),
+                                input=data, capture_output=True, timeout=15)
+        m = metrics(result.stderr)
+        prefix_end = 0
+        for _ in range(3):
+            prefix_end += 4 + struct.unpack_from("<I", expected, prefix_end)[0]
+        assert result.returncode == 3 and m["status"] == "cancelled" and m["emitted"] == 3
+        assert result.stdout == expected[:prefix_end]
+        checks.append(f'{policy["name"]}: cancellation preserves completed output prefix and releases pending buffers')
+        result = subprocess.run(command(binary, {}, policy), input=b"", capture_output=True, timeout=15)
+        assert result.returncode == 0 and metrics(result.stderr)["emitted"] == 0
+        checks.append(f'{policy["name"]}: empty stream')
+    # Tight budget must refuse a whole-frame requirement, while streaming projection can work.
+    large = struct.pack("<III", 1048576, 17, 64) + b"a" * 1048576
+    for policy in policies:
+        result = subprocess.run(command(binary, {"budget": 131072, "slots": 1}, policy),
+                                input=large, capture_output=True, timeout=15)
+        m = metrics(result.stderr)
+        assert m["status"] == ("ok" if policy["policy"] == "project" else "budget_too_small")
+    checks.append("frame larger than buffer budget: bounded refusal versus projection")
+    if Path("/dev/full").exists():
+        with open("/dev/full", "wb") as sink:
+            result = subprocess.run(command(binary, {"hold_us": 1000}, policies[0]), input=data,
+                                    stdout=sink, stderr=subprocess.PIPE, timeout=15)
+        assert result.returncode == 2 and metrics(result.stderr)["status"] == "output_failed"
+        checks.append("real output failure through /dev/full, pending buffers released")
+    # Real signal cancellation after allocation, while waiting for the delayed sink.
+    with test.open("rb") as source, open(os.devnull, "wb") as sink:
+        proc = subprocess.Popen(command(binary, {"hold_us": 500000}, policies[0]),
+                                stdin=source, stdout=sink, stderr=subprocess.PIPE)
+        time.sleep(0.08)
+        proc.send_signal(signal.SIGTERM)
+        _, error = proc.communicate(timeout=5)
+    assert proc.returncode == 3 and metrics(error)["status"] == "cancelled", error
+    checks.append("SIGTERM interrupts delayed sink and releases buffers")
+    if platform.system() == "Linux":
+        # Regression: inherited rusage peak cannot stand in for current-image HWM.
+        resident = tmp / "rss.frames"
+        fixture(resident, "sparse", 512, 817)
+        values = {}
+        for policy in [{"policy": "borrow"}, {"policy": "project"}]:
+            with resident.open("rb") as source, open(os.devnull, "wb") as sink:
+                result = subprocess.run(command(binary, {"hold_us": 10000}, policy),
+                                        stdin=source, stdout=sink, stderr=subprocess.PIPE, timeout=15)
+            m = metrics(result.stderr)
+            assert result.returncode == 0 and m["rss_peak_source"] == "linux_proc_vmhwm_approximate"
+            assert m["rss_peak_bytes"] > 0
+            values[policy["policy"]] = m["rss_peak_bytes"]
+        # Only a sanity check for this deliberately wide memory gap, not exact RSS arithmetic.
+        assert values["borrow"] > values["project"], values
+        checks.append("current-image VmHWM distinguishes large retained sources from small projections")
+    return checks
+
+
+def sample(binary, source, output, case, policy):
+    with source.open("rb") as inp, output.open("wb") as out:
+        result = subprocess.run(command(binary, case, policy), stdin=inp, stdout=out,
+                                stderr=subprocess.PIPE, timeout=30)
+    m = metrics(result.stderr)
+    assert result.returncode == 0 and m["status"] == "ok", result.stderr
+    return m
+
+
+def summarize(rows):
+    result = []
+    names = ["elapsed_ns", "cpu_ns", "peak_reserved_bytes", "peak_active_bytes", "rss_peak_bytes",
+             "copy_bytes", "active_byte_seconds", "latency_mean_ns", "latency_p99_upper_ns",
+             "budget_waits", "allocations", "reuses"]
+    groups = sorted({(r["case"], r["variant"]) for r in rows})
+    for case, variant in groups:
+        group = [r for r in rows if (r["case"], r["variant"]) == (case, variant)]
+        value = {"case": case, "variant": variant, "samples": len(group)}
+        for name in names:
+            values = [r[name] for r in group]
+            value[name] = {"median": statistics.median(values), "min": min(values), "max": max(values)}
+        result.append(value)
+    return result
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--check-only", action="store_true")
+    parser.add_argument("--output", type=Path)
+    args = parser.parse_args()
+    if not args.check_only and args.output is None:
+        parser.error("provide --check-only or --output (new directory)")
+    if args.output:
+        args.output.mkdir(parents=True, exist_ok=False)
+    cc = shlex.split(os.environ.get("CC", "cc"))
+    plan = json.loads((ROOT / "plan.json").read_text())
+    affinity = None
+    if hasattr(os, "sched_getaffinity"):
+        affinity = min(os.sched_getaffinity(0))
+        os.sched_setaffinity(0, {affinity})
+    with tempfile.TemporaryDirectory(prefix="pure-retention-") as folder:
+        tmp = Path(folder)
+        native, sanitized = tmp / "bench", tmp / "bench-sanitized"
+        builds = [build(cc, native), build(cc, sanitized, True)]
+        verification = {"native": check(native, tmp, plan["policies"]),
+                        "asan_ubsan": check(sanitized, tmp, plan["policies"])}
+        print(f'Verified {sum(map(len, verification.values()))} scenario groups (native + ASan/UBSan).', flush=True)
+        if args.check_only:
+            return
+        sources = {name: digest(ROOT / name) for name in ["benchmark.c", "run.py", "plan.json"]}
+        environment = {"platform": platform.platform(), "machine": platform.machine(),
+                       "python": platform.python_version(), "cpu_affinity": affinity,
+                       "compiler": subprocess.check_output([*cc, "--version"], text=True),
+                       "builds": builds, "source_sha256": sources,
+                       "clock": "CLOCK_MONOTONIC; CPU = CLOCK_PROCESS_CPUTIME_ID",
+                       "timing": "includes file IO, scheduling, deliberate sleep, metrics, buffer cleanup; excludes startup/build/fixture/verification",
+                       "limitations": "shared host; unregulated thermals; cached files; output page cache, no fsync; synthetic closed-loop arrivals",
+                       "started_utc": time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())}
+        if Path("/proc/cpuinfo").exists():
+            environment["cpuinfo"] = Path("/proc/cpuinfo").read_text()
+        dump(args.output / "environment.json", environment)
+        dump(args.output / "verification.json", verification)
+        dump(args.output / "plan.json", plan)
+        (args.output / "sources").mkdir()
+        for name in sources:
+            (args.output / "sources" / name).write_bytes((ROOT / name).read_bytes())
+        fixtures, rows = [], []
+        rng = random.Random(plan["seed"])
+        for case in plan["cases"]:
+            source, output = tmp / "input.frames", tmp / "output.frames"
+            info = fixture(source, case["shape"], case["records"], plan["seed"])
+            info["case"] = case["name"]
+            fixtures.append(info)
+            # Warm each strategy once. The following measurements use fresh processes.
+            for policy in plan["policies"]:
+                sample(native, source, output, case, policy)
+                assert digest(output) == info["expected_output_sha256"]
+            for repeat in range(plan["repeats"]):
+                order = list(plan["policies"])
+                rng.shuffle(order)
+                for policy in order:
+                    m = sample(native, source, output, case, policy)
+                    assert m["accepted"] == m["emitted"] == case["records"]
+                    assert m["input_bytes"] == info["input_bytes"]
+                    assert m["output_bytes"] == info["expected_output_bytes"]
+                    assert digest(output) == info["expected_output_sha256"]
+                    rows.append({"case": case["name"], "variant": policy["name"], "repeat": repeat, **m})
+            dump(args.output / "raw.json", rows)
+            dump(args.output / "fixtures.json", fixtures)
+            print(f'Completed {case["name"]}: {len(plan["policies"])} variants x {plan["repeats"]} trials.', flush=True)
+        dump(args.output / "summary.json", summarize(rows))
+        with (args.output / "raw.csv").open("w") as out:
+            writer = csv.DictWriter(out, fieldnames=list(rows[0]))
+            writer.writeheader()
+            writer.writerows(rows)
+        # Detect accidental source edits during a measurement run.
+        assert sources == {name: digest(ROOT / name) for name in sources}
+        dump(args.output / "complete.json", {"samples": len(rows), "all_output_hashes_match": True,
+                                             "finished_utc": time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime())})
+        print(args.output.resolve())
+
+
+if __name__ == "__main__":
+    main()
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