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Keep the exact nanoseconds of a modification time a program sets - #38
Files.setLastModifiedTime and BasicFileAttributeView.setTimes take nanoseconds, but java-web passed the time on as floating point milliseconds, and Node's utimesSync takes floating point seconds. At today's dates a double holds about a quarter of a microsecond, so a time set to the nanosecond read back changed:
Set
Read back before
After
1762300000123456789
1762300000123456787
1762300000123456789
1762300000999999999
1762300001000000000 (next second)
1762300000999999999
1000000000000000001
1000000000000000000
1000000000000000001
This made java/nio/file/attribute/BasicFileAttributeView/Basic.java fail now and then: it copies a directory's time onto a file and expects the same time back, which held only for some timestamps. It failed once in #37's CI.
The VFS now remembers the exact time a VM sets (setMtime(path, ms, ns)), with the mtime the backend reports right after. stat returns it as mtimeNs for as long as the backend still reports that mtime, so a change from anywhere else wins. It is kept only when the host stored about the time asked for, since a host can clamp it. fillStat and File.lastModified use it. This covers every backend: host files under Node, and memory and /files in the browser. File.setLastModified gets the same treatment, in milliseconds.
Also, docs/support.md now says that a --limit-modules list leaving jdk.localedata out turns locale data off (from #37's review).
Checks:
New program test test/java/FileTimes.java sets times to the nanosecond, copies a directory's time, and round-trips File.setLastModified, all compared with HotSpot. On master it prints the three wrong values above.
A time before 1970 cannot be set under Node: utimesSync treats a negative time as now. HotSpot's result there also depends on the file system (tmpfs stores 0, ext4 keeps it), so the test leaves it out.
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docs/support.md
src/fs.ts
src/natives/io.ts
src/natives/nio.ts
test/java/FileTimes.java
Summary
Summary by CodeRabbit
New Features
File modification times can now retain nanosecond precision when read and updated through Java I/O and NIO APIs.
Documentation
Clarified when the jdk.localedata module is enabled or excluded based on module-selection options.
VFS now tracks modification-time nanoseconds when the backend-reported time meets the matching condition. Java IO and NIO native paths pass and read those values. A Java test program prints timestamp-operation results. The Locales documentation clarifies jdk.localedata module selection.
Changes: Modification-Time Precision
Layer / File(s)
Summary
VFS nanosecond storage src/fs.ts
Stat adds optional mtimeNs. VFS.setMtime records the requested nanoseconds when the backend update succeeds and its reported time meets the matching condition. VFS.stat returns the stored value while the backend time matches, and removes it when it does not.
Java IO and NIO timestamp paths src/natives/io.ts, src/natives/nio.ts, test/java/FileTimes.java
Java IO and NIO paths pass nanoseconds to VFS and use available nanoseconds when reading timestamps. fillStat normalizes negative timestamps. FileTimes prints timestamp-operation results and removes its temporary file and directory.
sequenceDiagram
participant JavaFileNIO
participant NativeIO
participant NativeNIO
participant VFS
participant FilesystemBackend
JavaFileNIO->>NativeIO: setLastModifiedTime0 passes milliseconds and nanoseconds
JavaFileNIO->>NativeNIO: utimensat0 or futimens0 passes nanoseconds
NativeIO->>VFS: setMtime with milliseconds and optional nanoseconds
NativeNIO->>VFS: setMtime with milliseconds and nanoseconds
VFS->>FilesystemBackend: update modification time in milliseconds
FilesystemBackend-->>VFS: report modification time
VFS->>VFS: retain nanoseconds when reported time matches
VFS-->>NativeIO: stat with mtimeNs when available
VFS-->>NativeNIO: stat with mtimeNs when available
NativeIO-->>JavaFileNIO: return modification time in milliseconds
NativeNIO-->>JavaFileNIO: fill timestamp seconds and nanoseconds
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Possibly related PRs
Project516/java-web#37: Both PRs document or implement module-selection behavior for jdk.localedata.
Renaming a file or directory can lose its recorded timestamp precision, and a narrow negative-time case can return the wrong millisecond value. These bounded issues should be fixed or explicitly accepted before merging.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
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Resolution
Docstring Coverage
Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
Check name
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Explanation
Title check
The title clearly and concisely describes the primary change: preserving exact nanosecond modification times set by programs.
Description check
The description directly explains the nanosecond preservation changes, affected APIs, tests, backend behavior, and known limitation.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
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Write docstrings for the functions missing them to satisfy the coverage threshold.
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A rabbit checks the clock at night And keeps the nanos tucked in tight Through IO paths the times now flow NIO reads what VFS knows The locale notes explain the way The bunny hops and bounds away
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The PR preserves exact nanosecond precision for file modification times by storing the requested timestamp in the VFS when the backend confirms it kept the time (within 1ms). stat returns this stored nanosecond value as mtimeNs while the backend's mtime remains unchanged, so a later external modification wins. The change spans the VFS layer, native IO and NIO bindings, and adds a test that matches HotSpot behavior on nanosecond-capable file systems.
review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict approve
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Actionable comments posted: 2
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @src/fs.ts:
- Line 61: Update the setTimes handling around VFS.rename and VFS.remove: after
a successful rename, rekey the source timestamp and all descendant records to
the destination prefix, clearing existing destination-prefix records first;
after a successful remove, clear the removed path’s record. Match normalized
paths by complete path segments so similarly prefixed sibling paths are not
treated as descendants, and leave records unchanged when either operation fails.
Review comments at @src/natives/io.ts:
- Line 457: Update the mtimeNs-to-milliseconds conversion so negative nanosecond
timestamps round down rather than truncate toward zero, matching HotSpot’s
behavior for File.lastModified(). Preserve the existing conversion for
nonnegative values and the mtime fallback when mtimeNs is unavailable.
---
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Write docstrings for the functions missing them to satisfy the coverage
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Reviewing files that changed from the base of the PR and between aaa3c8f and 78385d6.
Files selected for processing: 5
docs/support.md
src/fs.ts
src/natives/io.ts
src/natives/nio.ts
test/java/FileTimes.java
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The PR preserves exact nanosecond modification times set by Java programs. The VFS now records the requested nanoseconds alongside the backend's reported millisecond time, and returns the exact value on stat as long as the backend's time hasn't changed. This fixes round-trip failures in BasicFileAttributeView tests. Changes span the VFS (fs.ts), IO and NIO natives, and add a comprehensive test (FileTimes.java). Docs updated for --limit-modules behavior. All checks pass.
review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict approve
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The PR preserves exact nanosecond modification times set by Java programs. It adds an mtimeNs field to Stat, a setTimes map in VFS to remember the exact time a VM set (keyed by the backend's reported mtime), and threads the nanoseconds through setMtime calls from both java.io.File and java.nio.file. stat returns the stored nanoseconds while the backend's mtime matches; rename moves the entries; remove deletes them. A new test FileTimes.java verifies round-trips for the three timestamps that previously failed. All checks pass.
review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict approve
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Files.setLastModifiedTimeandBasicFileAttributeView.setTimestake nanoseconds, but java-web passed the time on as floating point milliseconds, and Node'sutimesSynctakes floating point seconds. At today's dates a double holds about a quarter of a microsecond, so a time set to the nanosecond read back changed:17623000001234567891762300000123456787176230000012345678917623000009999999991762300001000000000(next second)1762300000999999999100000000000000000110000000000000000001000000000000000001This made
java/nio/file/attribute/BasicFileAttributeView/Basic.javafail now and then: it copies a directory's time onto a file and expects the same time back, which held only for some timestamps. It failed once in #37's CI.The VFS now remembers the exact time a VM sets (
setMtime(path, ms, ns)), with the mtime the backend reports right after.statreturns it asmtimeNsfor as long as the backend still reports that mtime, so a change from anywhere else wins. It is kept only when the host stored about the time asked for, since a host can clamp it.fillStatandFile.lastModifieduse it. This covers every backend: host files under Node, and memory and/filesin the browser.File.setLastModifiedgets the same treatment, in milliseconds.Also, docs/support.md now says that a
--limit-moduleslist leavingjdk.localedataout turns locale data off (from #37's review).Checks:
test/java/FileTimes.javasets times to the nanosecond, copies a directory's time, and round-tripsFile.setLastModified, all compared with HotSpot. On master it prints the three wrong values above.java/nio/file/attribute/BasicFileAttributeView/Basic.javapasses.pnpm typecheckandpnpm testpass (145 tests).Noticed, not fixed:
utimesSynctreats a negative time as now. HotSpot's result there also depends on the file system (tmpfs stores 0, ext4 keeps it), so the test leaves it out.