Add `Timer` class polyfill for .NET Standard 1.0–1.1 via `Task.Delay` by Copilot · Pull Request #81 · Tyrrrz/PolyShim

Copilot · 2026-02-19T15:43:16Z

Original prompt

Create a polyfill for the Timer class on .NET Standard 1.0-1.2 by leveraging Task.Delay

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Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Tyrrrz · 2026-02-19T15:55:54Z

@copilot no need for tests since we can't run tests against such old targets

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot · 2026-02-19T15:57:23Z

@copilot no need for tests since we can't run tests against such old targets

Removed in 69ef4db.

PolyShim/NetCore10/Timer.cs

Copilot

Pull request overview

Adds a System.Threading.Timer polyfill intended to enable netstandard1.0–1.1 support (implemented via Task.Delay), and removes conditional exclusions so Timer/TimeProvider.CreateTimer APIs are available on those targets.

Changes:

Added PolyShim/NetCore10/Timer.cs implementing a Timer type for netstandard1.0–1.1.
Updated PolyShim/NetCore30/Timer.cs to include DisposeAsync polyfill without excluding netstandard1.0–1.1.
Updated PolyShim/Net80/TimeProvider.cs to expose CreateTimer / SystemTimeProviderTimer on netstandard1.0–1.1 and updated Signatures.md accordingly.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
PolyShim/NetCore10/Timer.cs	Introduces a Timer polyfill for `netstandard1.0–1.1` using `Task.Delay`.
PolyShim/NetCore30/Timer.cs	Removes the `netstandard1.0–1.1` exclusion so `DisposeAsync` extension applies there too.
PolyShim/Net80/TimeProvider.cs	Removes `netstandard1.0–1.1` exclusion for `CreateTimer` and timer wrapper implementation.
PolyShim/Signatures.md	Updates signature counts and lists `Timer` as a polyfilled type.

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PolyShim/NetCore10/Timer.cs

Copilot · 2026-02-19T16:11:51Z

PolyShim/NetCore10/Timer.cs

+                if (dueTime > TimeSpan.Zero)
+                    await Task.Delay(dueTime, cts.Token);
+
+                if (cts.IsCancellationRequested)
+                    return;
+
+                _callback(_state);
+
+                if (period == Timeout.InfiniteTimeSpan || period <= TimeSpan.Zero)
+                    return;


period <= TimeSpan.Zero is treated as “no periodic callbacks”. In the BCL, period == TimeSpan.Zero is valid and schedules callbacks back-to-back, while negative values (other than -1 / Infinite) should throw. Similarly, negative dueTime values (other than Infinite) should throw rather than being treated as immediate execution.

Copilot · 2026-02-19T16:11:51Z

PolyShim/NetCore10/Timer.cs

+    public void Dispose()
+    {
+        if (_disposed)
+            return;
+        _disposed = true;
+        var cts = Interlocked.Exchange(ref _cts, new CancellationTokenSource());
+        cts.Cancel();
+        cts.Dispose();


Dispose() swaps _cts with a newly-created CancellationTokenSource and never disposes that new instance. This leaves an undisposed CTS (and potentially its wait handle) rooted by the Timer instance. Consider setting _cts to null (making the field nullable) or reusing/discarding the existing CTS without allocating a replacement.

@copilot address this please

Fixed in fed084c — Dispose now cancels and disposes _cts directly without allocating a replacement.

PolyShim/NetCore10/Timer.cs

Tyrrrz · 2026-02-19T16:20:13Z

@copilot please address unresolved review comments

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot · 2026-02-19T16:29:43Z

@copilot please address unresolved review comments

Addressed in 2be4f52:

Change now throws directly (no try/catch swallowing)
ValidateTimes throws ArgumentOutOfRangeException for negative non-infinite values; period == 0 is treated as valid (uses await Task.Yield() to avoid a tight spin loop)
Dispose uses Interlocked.Exchange to atomically capture the CTS before cancelling/disposing

Tyrrrz

@copilot

Tyrrrz · 2026-02-19T16:33:59Z

PolyShim/NetCore10/Timer.cs

+    public Timer(TimerCallback callback)
+        : this(callback, null, Timeout.InfiniteTimeSpan, Timeout.InfiniteTimeSpan) { }
+
+    private static void ValidateTimes(TimeSpan dueTime, TimeSpan period)


If it's only used in one place, inline it

Done in fed084c — the validation is now inlined directly into CreateAndStart.

Tyrrrz · 2026-02-19T16:34:47Z

PolyShim/NetCore10/Timer.cs

+    public void Dispose()
+    {
+        if (_disposed)
+            return;
+        _disposed = true;
+        var cts = Interlocked.Exchange(ref _cts, new CancellationTokenSource());
+        cts.Cancel();
+        cts.Dispose();


@copilot address this please

Tyrrrz · 2026-02-19T16:34:57Z

PolyShim/NetCore10/Timer.cs

+    public void Dispose()
+    {
+        if (_disposed)
+            return;
+        _disposed = true;
+        var cts = Interlocked.Exchange(ref _cts, new CancellationTokenSource());
+        cts.Cancel();
+        cts.Dispose();


@copilot address this please

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

…uctor Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

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PolyShim/NetCore10/Timer.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

…e race recheck Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

codecov · 2026-02-20T13:40:24Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (8a9074f) to head (03a32ae).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@     Coverage Diff      @@
##   master   #81   +/-   ##
============================
============================

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Initial plan

5874690

Copilot AI assigned Copilot and Tyrrrz Feb 19, 2026

Copilot started work on behalf of Tyrrrz February 19, 2026 15:43 View session

Tyrrrz added the enhancement New feature or request label Feb 19, 2026

Add Timer class polyfill for .NET Standard 1.0-1.1 using Task.Delay

2e6b4b3

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add polyfill for Timer class on .NET Standard 1.0-1.2~~ Add Timer class polyfill for .NET Standard 1.0–1.1 via Task.Delay Feb 19, 2026

Copilot AI requested a review from Tyrrrz February 19, 2026 15:56

Copilot finished work on behalf of Tyrrrz February 19, 2026 15:56

Copilot started work on behalf of Tyrrrz February 19, 2026 15:56 View session

Remove Timer tests (can't run against netstandard 1.0-1.1 targets)

69ef4db

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot finished work on behalf of Tyrrrz February 19, 2026 15:57

Tyrrrz reviewed Feb 19, 2026

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PolyShim/NetCore10/Timer.cs Show resolved Hide resolved

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Tyrrrz marked this pull request as ready for review February 19, 2026 16:04

Copilot AI review requested due to automatic review settings February 19, 2026 16:04

Copilot started reviewing on behalf of Tyrrrz February 19, 2026 16:05 View session

Tyrrrz changed the title ~~Add Timer class polyfill for .NET Standard 1.0–1.1 via Task.Delay~~ Add Timer class polyfill for .NET Standard 1.0–1.1 via Task.Delay Feb 19, 2026

Tyrrrz changed the title ~~Add Timer class polyfill for .NET Standard 1.0–1.1 via Task.Delay~~ Add Timer class polyfill for .NET Standard 1.0–1.1 via Task.Delay Feb 19, 2026

Copilot AI reviewed Feb 19, 2026

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Copilot started work on behalf of Tyrrrz February 19, 2026 16:20 View session

Address review feedback on Timer polyfill

2be4f52

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI requested a review from Tyrrrz February 19, 2026 16:30

Copilot finished work on behalf of Tyrrrz February 19, 2026 16:30

Copilot started work on behalf of Tyrrrz February 19, 2026 16:33 View session

Tyrrrz reviewed Feb 19, 2026

View reviewed changes

Fix callback exception surfacing in Timer polyfill

585ca1f

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot started work on behalf of Tyrrrz February 19, 2026 21:12 View session

Move Start after CTS exchange; null-check callback in full-arg constr…

458a10a

…uctor Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI requested a review from Tyrrrz February 19, 2026 21:15

Copilot finished work on behalf of Tyrrrz February 19, 2026 21:15

Tyrrrz requested a review from Copilot February 19, 2026 21:18

Copilot started reviewing on behalf of Tyrrrz February 19, 2026 21:18 View session

Tyrrrz approved these changes Feb 19, 2026

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Copilot AI reviewed Feb 19, 2026

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Update PolyShim/NetCore10/Timer.cs

5b71532

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot started work on behalf of Tyrrrz February 19, 2026 21:34 View session

Guard cts.Cancel() against ObjectDisposedException in Dispose/Schedul…

9a54c8b

…e race recheck Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI requested a review from Tyrrrz February 19, 2026 21:36

Copilot finished work on behalf of Tyrrrz February 19, 2026 21:36

Copilot started work on behalf of Tyrrrz February 19, 2026 21:37 View session

Guard oldCts.Cancel() against ObjectDisposedException in Schedule

03a32ae

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot finished work on behalf of Tyrrrz February 19, 2026 21:39

Tyrrrz approved these changes Feb 20, 2026

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Tyrrrz merged commit 8d7308a into master Feb 20, 2026
5 checks passed

Tyrrrz deleted the copilot/add-timer-class-polyfill branch February 20, 2026 13:40

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