Implement SunOS FileSystemWatcher using portfs event ports by gwr · Pull Request #124716 · dotnet/runtime

gwr · 2026-02-22T01:54:47Z

This implementation uses SunOS portfs (event ports) to watch for directory changes. Unlike Linux inotify, portfs can only detect WHEN a directory changes, not WHAT changed. Therefore, this implementation:

Maintains a snapshot of each watched directory's contents
When portfs signals a change, re-reads the directory
Compares new vs old snapshots to detect creates/deletes/modifications
Generates appropriate FileSystemWatcher events

Key implementation details:

Uses pinned GC.AllocateArray for file_obj structures required by portfs
When watching attributes or timestamps watches directory contents too
Each watched objct gets a unique cookie for identification
port_get returns the cookie to indicate which object changed
Optimized snapshot comparison with sorted single-pass algorithm
Supports IncludeSubdirectories by recursively watching child directories
Track mtime of the watched directory to avoid missing changes
Implement graceful cancellation using PortSend

Native changes (pal_io.c):

SystemNative_PortCreate: Opens event port file descriptor
SystemNative_PortAssociate: Associates directory with port using file_obj
SystemNative_PortGet: Waits for events, returns cookie identifying directory
SystemNative_PortSend: Send an event (used in cancellation)
SystemNative_PortDissociate: Removes directory association

Performance notes:

Less efficient than inotify (must re-read directories on each change)
Better than polling (blocks until change occurs)
Memory overhead for directory snapshots

Passes all System.IO.FileSystem.Watcher.Tests

dotnet-policy-service · 2026-02-22T01:55:50Z

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

Copilot

Pull request overview

This PR implements FileSystemWatcher support for SunOS (Solaris/illumos) using the portfs (event ports) API. Unlike Linux's inotify which reports specific file changes, portfs only signals that a directory has changed, requiring the implementation to maintain snapshots and perform comparisons to determine what actually changed.

Changes:

Native interop layer for portfs operations (port_create, port_associate, port_get, port_send, port_dissociate)
SunOS-specific FileSystemWatcher implementation using snapshot-based change detection
Hybrid monitoring mode that watches both directories (for name changes) and individual files (for attribute changes)
Support for recursive subdirectory monitoring with resource limits (50 subdirs, 1000 files per directory)

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 18 comments.

Show a summary per file

File	Description
src/native/libs/configure.cmake	CMake configuration for portfs feature detection (has critical bug)
src/native/libs/System.Native/pal_io.h	Header declarations for portfs native functions (has spelling errors)
src/native/libs/System.Native/pal_io.c	Native implementation of portfs wrapper functions (has critical string lifetime bug)
src/native/libs/System.Native/entrypoints.c	Export table entries for new portfs functions
src/native/libs/Common/pal_config.h.in	Configuration flag for HAVE_SUNOS_PORTFS
src/libraries/System.IO.FileSystem.Watcher/tests/System.IO.FileSystem.Watcher.Tests.csproj	Added illumos and solaris to test target frameworks
src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs	Main SunOS implementation with snapshot comparison and event generation (multiple issues)
src/libraries/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj	Added SunOS-specific source files and target frameworks
src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs	Managed P/Invoke declarations for portfs (has hardcoded struct size issue)

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.h

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 13 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/configure.cmake

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 10 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.h

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/configure.cmake

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

src/native/libs/System.Native/pal_io.c

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.h

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

This implementation uses SunOS portfs (event ports) to watch for directory changes. Unlike Linux inotify, portfs can only detect WHEN a directory changes, not WHAT changed. Therefore, this implementation: 1. Maintains a snapshot of each watched directory's contents 2. When portfs signals a change, re-reads the directory 3. Compares new vs old snapshots to detect creates/deletes/modifications 4. Generates appropriate FileSystemWatcher events Key implementation details: - Uses pinned GC.AllocateArray for file_obj structures required by portfs - When watching attributes or timestamps watches directory contents too - Each watched objct gets a unique cookie for identification - port_get returns the cookie to indicate which object changed - Optimized snapshot comparison with sorted single-pass algorithm - Supports IncludeSubdirectories by recursively watching child directories - Track mtime of the watched directory to avoid missing changes - Implement graceful cancellation using PortSend Native changes (pal_io.c): - SystemNative_PortCreate: Opens event port file descriptor - SystemNative_PortAssociate: Associates directory with port using file_obj - SystemNative_PortGet: Waits for events, returns cookie identifying directory - SystemNative_PortSend: Send an event (used in cancellation) - SystemNative_PortDissociate: Removes directory association Performance notes: - Less efficient than inotify (must re-read directories on each change) - Better than polling (blocks until change occurs) - Memory overhead for directory snapshots Passes 99% of System.IO.FileSystem.Watcher.Tests --------- Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

gwr · 2026-02-23T15:17:16Z

Squashed the last dozen updates to simplify local testing.

gwr · 2026-02-26T14:56:02Z

Can anyone help me interpret the CI build analysis?
Is there anything there I need to fix?

gwr · 2026-03-02T22:00:52Z

src/native/libs/System.Native/pal_io.c

BTW, I wondered if I should add functions like this to pal_io.c or create a new pal_portfs.c or pal_sunos.c or something for the SunOS-specific additions. Guidance? Thanks.

gwr · 2026-03-03T02:11:55Z

Still needs a reviewer. Thanks.

am11 · 2026-03-03T12:44:20Z

To me it looks good. I had a question from @tmds about the overhead #124716 (comment). If the plan is to switch to inotify in the future when it gets stable upstream, we can treat it as a stopgap and merge this. Thanks for pushing it forward @gwr!

gwr · 2026-03-03T14:12:57Z

The only test failure is name="System.IO.Tests.FileSystemWatcherTests_netstandard17.EndInit_ResumesPausedEnableRaisingEvents(setBeforeBeginInit: False)" which has active issue #103584 so I think that's OK.

tmds · 2026-03-03T15:47:04Z

This complexity is probably unavoidable given the lack of per-file events, but (perhaps?) still better than not having any watcher support.

It sounds like it is implemented as good as the kernel allows.

Without this, it's likely an app is broken in some way, so I also consider it better to have this than to throw PNSE.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 9 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/native/libs/System.Native/pal_io.h

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot · 2026-03-08T17:39:30Z

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

+                            // Share parent's cancellation token so entire tree can be cancelled together
+                            var childWatcher = new RunningInstance(watcher, subdirPath, subdirRelativePath, true, _notifyFilters, _cancellationToken);
+                            childWatcher.Start();
+                            lock (_subdirectoryWatchers)
+                            {
+                                _subdirectoryWatchers.Add(childWatcher);
+                            }


IncludeSubdirectories spawns a new RunningInstance per subdirectory, and each RunningInstance creates its own dedicated background thread (Start() uses new Thread(ProcessEvents)). On large directory trees this can create hundreds/thousands of threads and ports, risking severe resource exhaustion. Consider redesigning to share a single port and event-loop thread across the whole watcher tree (associating multiple directories/files with unique cookies) or otherwise limiting thread creation (e.g., central dispatcher + ThreadPool).

I previously took feeback like this and implemented some resource limits, but was then advised to remove those. I think we can live with this potentially running out of resources.

This copilot feedback is not asking for hard resource limits. It is asking for more efficient implementation that creates fewer threads.

OK, I'm working on an revised design. This may take some time.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

dirPath is required, mtime ptr is optional

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Copilot · 2026-03-08T18:24:29Z

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

+                new Thread(ProcessEvents)
+                {
+                    IsBackground = true,
+                    Name = ".NET File Watcher"
+                }.Start();


IncludeSubdirectories creates a RunningInstance per subdirectory and each RunningInstance.Start() spins up a dedicated Thread. On directory trees with many subdirectories this can create hundreds/thousands of threads and event ports, risking severe resource exhaustion (threads, FDs, memory) and degraded performance. Consider consolidating subdirectory watches onto a shared event port and a single event-processing thread per root watcher (using cookies to demux), or otherwise limiting thread creation.

Suggested change

new Thread(ProcessEvents)

{

IsBackground = true,

Name = ".NET File Watcher"

}.Start();

ThreadPool.UnsafeQueueUserWorkItem(_ => ProcessEvents(), null);

Copilot AI review requested due to automatic review settings February 22, 2026 01:54

github-actions bot added the area-System.IO label Feb 22, 2026

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Feb 22, 2026

Copilot started reviewing on behalf of gwr February 22, 2026 01:55 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

gwr force-pushed the illumos-fswatch branch 2 times, most recently from cbe385d to 04c54a8 Compare February 22, 2026 02:19

Copilot AI review requested due to automatic review settings February 22, 2026 02:19

Copilot started reviewing on behalf of gwr February 22, 2026 02:20 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

gwr force-pushed the illumos-fswatch branch from 04c54a8 to 51c7175 Compare February 22, 2026 02:49

Copilot AI review requested due to automatic review settings February 22, 2026 02:54

gwr force-pushed the illumos-fswatch branch from 51c7175 to 67cef49 Compare February 22, 2026 02:54

Copilot started reviewing on behalf of gwr February 22, 2026 02:55 View session

gwr force-pushed the illumos-fswatch branch 2 times, most recently from 8b4f6e2 to 3c5ee5f Compare February 22, 2026 03:00

Copilot AI reviewed Feb 22, 2026

View reviewed changes

gwr force-pushed the illumos-fswatch branch from 3c5ee5f to 0041bd0 Compare February 22, 2026 03:07

Copilot AI review requested due to automatic review settings February 22, 2026 03:15

gwr force-pushed the illumos-fswatch branch from 0041bd0 to 14e88e4 Compare February 22, 2026 03:15

Copilot started reviewing on behalf of gwr February 22, 2026 03:15 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

jkotas added the os-SunOS SunOS, currently not officially supported label Feb 22, 2026

gwr force-pushed the illumos-fswatch branch from 14e88e4 to 3d59aa7 Compare February 22, 2026 05:21

Copilot AI review requested due to automatic review settings February 22, 2026 05:40

gwr force-pushed the illumos-fswatch branch from 3d59aa7 to 9af44c9 Compare February 22, 2026 05:40

Copilot started reviewing on behalf of gwr February 22, 2026 05:40 View session

Copilot AI reviewed Feb 22, 2026

View reviewed changes

gwr force-pushed the illumos-fswatch branch from 9af44c9 to 09b82ba Compare February 22, 2026 05:57

build-analysis bot mentioned this pull request Feb 23, 2026

[wasm] Microsoft.Playwright.TargetClosedException : Target page, context or browser has been closed #121195

Open

Copilot AI review requested due to automatic review settings February 23, 2026 12:44

Copilot AI reviewed Feb 23, 2026

View reviewed changes

This was referenced Feb 25, 2026

Fix assert in JIT:new() during early initialization #124715

Merged

Tracking issue for illumos and Solaris x86-64 port work #34944

Open

gwr commented Mar 2, 2026

View reviewed changes

jkotas reviewed Mar 3, 2026

View reviewed changes

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs Outdated Show resolved Hide resolved

Drop resource limits

34899b9

Copilot AI reviewed Mar 5, 2026

View reviewed changes

missed some things to remove

6243c6e

build-analysis bot mentioned this pull request Mar 5, 2026

System.IO.Tests.Directory_Create_Tests.FileSystemWatcher_Directory_Create_InNestedDirectory fails with "Created event did not occur as expected" #103630

Open

fix unused variable

1944684

Copilot AI reviewed Mar 8, 2026

View reviewed changes

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs Outdated Show resolved Hide resolved

separate PortAssociate masks for files vs dirs

0bb380d

This was referenced Mar 8, 2026

Microsoft.Extensions.Hosting.Tests.ConsoleLifetimeExitTests.EnsureEnvironmentExitDoesntHang fails on .NET Framework #119545

Open

XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

Open

guard against unexpected events from PortGet

1c72212

Copilot AI reviewed Mar 8, 2026

View reviewed changes

gwr added 2 commits March 8, 2026 13:51

Add CancellationCallback on error in ReassociateDirectory

2405554

PortAssociate dirPath and mtime args

bd86208

dirPath is required, mtime ptr is optional

Copilot AI reviewed Mar 8, 2026

View reviewed changes

Fix possible CTS leak

4ba3af4

build-analysis bot mentioned this pull request Mar 8, 2026

Android System.Security.Cryptography test failure: Signing key verifies the CRL #119023

Open

Conversation

gwr commented Feb 22, 2026

Uh oh!

dotnet-policy-service bot commented Feb 22, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

gwr commented Feb 23, 2026

Uh oh!

gwr commented Feb 26, 2026

Uh oh!

gwr Mar 2, 2026

Choose a reason for hiding this comment