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Project516 merged 3 commits into from
Nov 4, 2026
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Keep the exact nanoseconds of a modification time a program sets #38

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78385d6
Keep the exact nanoseconds of a modification time a program sets, for…
Project516 Nov 4, 2026
f559372
Move a set time with its file on rename, drop it on remove, and round…
Project516 Nov 4, 2026
e1bd1ca
Merge branch 'master' into p516/exact-mtime
Project516 Nov 4, 2026
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3 changes: 2 additions & 1 deletion docs/support.md
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Expand Up @@ -19,7 +19,8 @@ java-web targets headless Java: console apps, libraries and javac.

Locales other than English need `cheerpjInit({ localeData: true })`, or
`--locale-data` under Node (`localeData: true` for `runNode`). Adding
`jdk.localedata` or `ALL-SYSTEM` with `--add-modules` turns it on too. Turn it on
`jdk.localedata` or `ALL-SYSTEM` with `--add-modules` turns it on too, and a
`--limit-modules` list that leaves `jdk.localedata` out turns it off. Turn it on
when a program formats numbers, dates or currencies, or prints month and day
names, for a locale other than English: for example
`String.format(Locale.GERMANY, ...)`, or a German default locale. Without it,
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39 changes: 33 additions & 6 deletions src/fs.ts
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Expand Up @@ -4,6 +4,9 @@ export interface Stat {
dir: boolean;
size: number;
mtime: number;
// the modification time in nanoseconds, when it was set with more precision
// than mtime keeps
mtimeNs?: bigint;
// permission and special bits, when the backend can report them
mode?: number;
// a character device; it streams and is never read whole
Expand Down Expand Up @@ -54,6 +57,8 @@ export function normalize(path: string): string {
}

export class VFS {
// path -> the time a VM set, and the mtime the backend reported right after
private setTimes = new Map<string, { ms: number; ns: bigint }>();
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private mounts: { prefix: string; backend: Backend }[] = [];
private hidden: string[] = [];

Expand Down Expand Up @@ -113,7 +118,12 @@ export class VFS {
if (this.hidden.length && this.isHidden(n)) return null;
const r = this.resolve(path);
const s = r ? r[0].stat(r[1]) : null;
if (s) return s;
if (s) {
const set = this.setTimes.get(n);
if (set?.ms === s.mtime) return { ...s, mtimeNs: set.ns };
if (set) this.setTimes.delete(n);
return s;
}
if (normalize(path) === "/" || this.mountsUnder(path).length > 0 || this.isMountPoint(path)) {
return { dir: true, size: 0, mtime: 0 };
}
Expand Down Expand Up @@ -170,23 +180,40 @@ export class VFS {

remove(path: string): boolean {
const r = this.resolve(path);
return !!r && r[0].writable && !!r[0].remove?.(r[1]);
if (!r || !r[0].writable || !r[0].remove?.(r[1])) return false;
this.setTimes.delete(normalize(path));
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return true;
}

rename(from: string, to: string): boolean {
const a = this.resolve(from), b = this.resolve(to);
if (!a || !b || a[0] !== b[0] || !a[0].writable) return false;
return !!a[0].rename?.(a[1], b[1]);
if (!a || !b || a[0] !== b[0] || !a[0].writable || !a[0].rename?.(a[1], b[1])) return false;
// set times move with the files, which keep their times
const src = normalize(from), dst = normalize(to);
const under = (p: string, root: string) => p === root || p.startsWith(root + "/");
const moved = [...this.setTimes].filter(([p]) => under(p, src));
for (const p of [...this.setTimes.keys()]) if (under(p, src) || under(p, dst)) this.setTimes.delete(p);
for (const [p, set] of moved) this.setTimes.set(dst + p.slice(src.length), set);
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return true;
}

writable(path: string): boolean {
const r = this.resolve(path);
return !!r && r[0].writable;
}

setMtime(path: string, ms: number): boolean {
// ns, when given, is the exact time asked for. Hosts keep times as floating
// point seconds or milliseconds, which lose nanoseconds, so stat reports ns
// for as long as the file keeps the time this set.
setMtime(path: string, ms: number, ns?: bigint): boolean {
const r = this.resolve(path);
return !!r && r[0].writable && !!r[0].setMtime?.(r[1], ms);
if (!r || !r[0].writable || !r[0].setMtime?.(r[1], ms)) return false;
const n = normalize(path);
const st = ns === undefined ? null : r[0].stat(r[1]);
// only a time the host kept, give or take its rounding; a host can clamp it
if (st && Math.abs(st.mtime - ms) < 1) this.setTimes.set(n, { ms: st.mtime, ns: ns! });
else this.setTimes.delete(n);
return true;
}

denied(path: string): boolean {
Expand Down
14 changes: 10 additions & 4 deletions src/natives/io.ts
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Expand Up @@ -195,9 +195,9 @@ export function syncPath(t: JThread, abs: string) {
}

// Pending writes go out first, so closing the file later does not change the time again.
export function setMtime(t: JThread, abs: string, ms: number): boolean {
export function setMtime(t: JThread, abs: string, ms: number, ns?: bigint): boolean {
syncPath(t, abs);
return t.vm.fs.setMtime(abs, ms);
return t.vm.fs.setMtime(abs, ms, ns);
}

export function fileOf(t: JThread, fd: number): OpenFile {
Expand Down Expand Up @@ -452,7 +452,13 @@ export const natives: Natives = {
const abs = resolvePath(t, pathOf(t, f));
return !!t.vm.fs.stat(abs) && t.vm.fs.access(abs, access);
},
[`${UFS}.getLastModifiedTime0(Ljava/io/File;)J`]: (t, [, f]) => BigInt(Math.floor(t.vm.fs.stat(resolvePath(t, pathOf(t, f)))?.mtime ?? 0)),
[`${UFS}.getLastModifiedTime0(Ljava/io/File;)J`]: (t, [, f]) => {
const st = t.vm.fs.stat(resolvePath(t, pathOf(t, f)));
if (st?.mtimeNs === undefined) return BigInt(Math.floor(st?.mtime ?? 0));
// down, as HotSpot divides a negative time
const ms = st.mtimeNs / 1_000_000n;
return st.mtimeNs < 0n && ms * 1_000_000n !== st.mtimeNs ? ms - 1n : ms;
},
[`${UFS}.getLength0(Ljava/io/File;)J`]: (t, [, f]) => {
const abs = resolvePath(t, pathOf(t, f));
syncPath(t, abs);
Expand All @@ -477,7 +483,7 @@ export const natives: Natives = {
[`${UFS}.createDirectory0(Ljava/io/File;)Z`]: (t, [, f]) => t.vm.fs.mkdir(resolvePath(t, pathOf(t, f))),
[`${UFS}.rename0(Ljava/io/File;Ljava/io/File;)Z`]: (t, [, a, b]) =>
renamePath(t, resolvePath(t, pathOf(t, a)), resolvePath(t, pathOf(t, b))),
[`${UFS}.setLastModifiedTime0(Ljava/io/File;J)Z`]: (t, [, f, ms]) => setMtime(t, resolvePath(t, pathOf(t, f)), Number(ms)),
[`${UFS}.setLastModifiedTime0(Ljava/io/File;J)Z`]: (t, [, f, ms]) => setMtime(t, resolvePath(t, pathOf(t, f)), Number(ms), BigInt(ms) * 1_000_000n),
[`${UFS}.setReadOnly0(Ljava/io/File;)Z`]: (t, [, f]) => chmod(t, f, (m) => m & ~0o222),
[`${UFS}.getSpace0(Ljava/io/File;I)J`]: () => 0n,
[`${UFS}.getNameMax0(Ljava/lang/String;)J`]: () => 255n,
Expand Down
12 changes: 9 additions & 3 deletions src/natives/nio.ts
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Expand Up @@ -82,7 +82,13 @@ function fillAttrs(t: JThread, attrs: JObject, p: string): number {
function fillStat(t: JThread, attrs: JObject, st: Stat, writable: boolean, ino: number, size = st.size, nlink = 1) {
const vm = t.vm, A = "sun/nio/fs/UnixFileAttributes";
const mode = st.device ? S_IFCHR | 0o666 : (st.dir ? S_IFDIR : S_IFREG) | (st.mode ?? (st.dir ? (writable ? 0o755 : 0o555) : (writable ? 0o644 : 0o444)));
const sec = BigInt(Math.floor(st.mtime / 1000)), nsec = BigInt(Math.floor((st.mtime % 1000) * 1e6));
let sec = BigInt(Math.floor(st.mtime / 1000)), nsec = BigInt(Math.floor((st.mtime % 1000) * 1e6));
if (st.mtimeNs !== undefined) {
sec = st.mtimeNs / 1_000_000_000n;
nsec = st.mtimeNs % 1_000_000_000n;
// before 1970: whole seconds round down, nanoseconds stay positive
if (nsec < 0n) [sec, nsec] = [sec - 1n, nsec + 1_000_000_000n];
}
vm.setField(attrs, A, "st_mode", mode);
vm.setField(attrs, A, "st_ino", BigInt(ino));
vm.setField(attrs, A, "st_dev", 1n);
Expand Down Expand Up @@ -215,11 +221,11 @@ export const natives: Natives = {
[`${N}utimensat0(IJJJI)V`]: (t, [, p, , mtime]) => {
const abs = path(t, p);
if (!t.vm.fs.stat(abs)) unixError(ENOENT);
if (!setMtime(t, abs, Number(mtime) / 1e6)) unixError(EROFS);
if (!setMtime(t, abs, Number(mtime) / 1e6, BigInt(mtime))) unixError(EROFS);
},
[`${N}futimens0(IJJ)V`]: (t, [fd, , mtime]) => {
const f = fileOf(t, fd);
if (!setMtime(t, f.path, Number(mtime) / 1e6)) unixError(EROFS);
if (!setMtime(t, f.path, Number(mtime) / 1e6, BigInt(mtime))) unixError(EROFS);
},
[`${N}opendir0(J)J`]: (t, [p]) => {
const abs = path(t, p);
Expand Down
38 changes: 38 additions & 0 deletions test/java/FileTimes.java
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@@ -0,0 +1,38 @@
import java.io.File;
import java.nio.file.*;
import java.nio.file.attribute.*;
import java.util.concurrent.TimeUnit;

// A modification time set to the nanosecond reads back the same, as HotSpot
// gives it on a file system that keeps nanoseconds.
public class FileTimes {
public static void main(String[] args) throws Exception {
Path dir = Files.createTempDirectory("times");
Path file = Files.createFile(dir.resolve("f"));
try {
long[] times = { 1762300000123456789L, 1762300000999999999L, 1000000000000000001L };
for (long ns : times) {
FileTime t = FileTime.from(ns, TimeUnit.NANOSECONDS);
Files.setLastModifiedTime(file, t);
FileTime back = Files.readAttributes(file, BasicFileAttributes.class).lastModifiedTime();
System.out.println(ns + " " + back.equals(t) + " " + back.to(TimeUnit.NANOSECONDS));
}
// the directory's time, as java/nio/file/attribute/BasicFileAttributeView/Basic.java copies it
FileTime dirTime = Files.readAttributes(dir, BasicFileAttributes.class).lastModifiedTime();
Files.getFileAttributeView(file, BasicFileAttributeView.class).setTimes(dirTime, null, null);
System.out.println("dir time " + Files.getLastModifiedTime(file).equals(dirTime));
// the exact time moves with the file
FileTime exact = FileTime.from(1762300000123456789L, TimeUnit.NANOSECONDS);
Files.setLastModifiedTime(file, exact);
Path moved = Files.move(file, dir.resolve("g"));
System.out.println("moved " + Files.getLastModifiedTime(moved).equals(exact));
Files.move(moved, file);
File f = file.toFile();
f.setLastModified(1762300000123L);
System.out.println("File " + f.lastModified() + " " + Files.getLastModifiedTime(file).toMillis());
} finally {
Files.delete(file);
Files.delete(dir);
}
}
}
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