Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in #124086

Copilot · 2026-02-06T13:11:44Z

Description

Fixes issue #123950 where Task.Delay freezes when system time jumps backwards on .NET 10 Linux - a regression from .NET 8 and 9.

The root cause was a missing #cmakedefine01 HAVE_CLOCK_MONOTONIC directive in src/coreclr/pal/src/config.h.in. While CMake was successfully detecting monotonic clock support, the configuration value was never propagated to the generated config.h header. This caused the runtime to fall back to wall-clock time (CLOCK_REALTIME) instead of monotonic clocks (CLOCK_MONOTONIC), making timing operations vulnerable to system time adjustments.

Changes

Fix applied:

src/coreclr/pal/src/config.h.in:
- Added #cmakedefine01 HAVE_CLOCK_MONOTONIC - Enables monotonic clock support, fixing the Task.Delay freeze when system time is adjusted backwards

This is a minimal one-line change that ensures the CMake-detected monotonic clock support is properly propagated to the C/C++ code.

Impact

The runtime will correctly use monotonic clocks on Linux for synchronization primitives and timing operations, making them immune to system time adjustments. This resolves the Task.Delay freeze behavior and restores .NET 8/9 behavior.

Original fix commit: jkotas@224e4bd

Original prompt

Create PR against main branch to investigate #123950. The PR should start with cherry picking jkotas@7518cab to validate the root cause of the issue

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

…inux Cherry-picked from jkotas@7518cab This change adds compile-time diagnostics to ensure that on Linux platforms, the HAVE_CLOCK_MONOTONIC and HAVE_PTHREAD_CONDATTR_SETCLOCK flags are properly set. This helps investigate the root cause of Task.Delay freezing when the system time is adjusted backwards, which should be using monotonic clocks instead of real-time clocks. Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

jkotas · 2026-02-06T13:41:51Z

@copilot Apply jkotas@224e4bd to see whether it fixes the issue

The CMake configuration was successfully detecting HAVE_CLOCK_MONOTONIC support, but the config.h.in template was missing the #cmakedefine01 directive, causing the macro to be undefined in the generated config.h. This resulted in the runtime falling back to wall-clock time (CLOCK_REALTIME) instead of monotonic clocks, causing Task.Delay to freeze when the system time was adjusted backwards. This change adds the missing #cmakedefine01 HAVE_CLOCK_MONOTONIC line to src/coreclr/pal/src/config.h.in, ensuring the CMake-detected value is properly propagated to the C/C++ code. Applies jkotas@224e4bd Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

Copilot · 2026-02-06T13:45:32Z

@copilot Apply jkotas@224e4bd to see whether it fixes the issue

Applied in f009787. The missing #cmakedefine01 HAVE_CLOCK_MONOTONIC in config.h.in prevented the CMake-detected value from being propagated to the code, causing the fallback to wall-clock time instead of monotonic clocks.

src/coreclr/pal/src/config.h.in

Found and fixed additional missing #cmakedefine directives across multiple config.h.in files: 1. src/coreclr/pal/src/config.h.in: Added HAVE_STRERRORNAME_NP - Checked in configure.cmake line 144 - Used in src/coreclr/pal/src/misc/utils.cpp for friendly error messages 2. src/mono/cmake/config.h.in: Added HAVE_SYSSIGNAME - Checked in configure.cmake line 117 - Used in src/mono/mono/utils/mono-signal-handler.c for signal name lookup These were the same type of issue as HAVE_CLOCK_MONOTONIC - CMake was successfully detecting these features, but the configuration values were not being propagated to the generated config.h headers due to missing #cmakedefine directives. Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

src/coreclr/pal/src/config.h.in

As requested, keeping only the one-line fix for HAVE_CLOCK_MONOTONIC in src/coreclr/pal/src/config.h.in and reverting all other changes: - Reverted diagnostic checks in synchmanager.cpp and pal_threading.c - Reverted HAVE_STRERRORNAME_NP addition - Reverted HAVE_SYSSIGNAME addition to mono config This PR now contains only the minimal fix for issue #123950. Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

src/coreclr/pal/src/config.h.in

Copilot

Pull request overview

This PR fixes a CoreCLR PAL build-configuration regression where CMake detected monotonic clock support, but the result was not propagated into the generated config.h, causing PAL timing code to fall back to CLOCK_REALTIME and making waits susceptible to backward system time jumps (issue #123950).

Changes:

Add #cmakedefine01 HAVE_CLOCK_MONOTONIC to src/coreclr/pal/src/config.h.in so the generated config.h reflects the CMake probe result.
Re-enables the CLOCK_MONOTONIC-based code paths guarded by HAVE_CLOCK_MONOTONIC (e.g., in SynchManager) when supported.

tannergooding · 2026-02-06T16:25:19Z

Are we considering this one for backport since it can impact all wait calls and their accuracy?

jkotas · 2026-02-06T16:27:42Z

Yes, I plan to submit backport request

jkotas · 2026-02-07T01:35:48Z

/ba-g known issues

jkotas · 2026-02-07T01:37:20Z

/backport to release/10.0

github-actions · 2026-02-07T01:37:28Z

Started backporting to release/10.0 (link to workflow run)

github-actions · 2026-02-07T01:39:17Z

@jkotas backporting to release/10.0 failed, the patch most likely resulted in conflicts. Please backport manually!

git am output

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Creating an empty commit: Initial plan
Applying: Investigating #123950: Add diagnostic checks for monotonic clock on Linux
.git/rebase-apply/patch:19: trailing whitespace.
#if !HAVE_CLOCK_MONOTONIC 
warning: 1 line adds whitespace errors.
Using index info to reconstruct a base tree...
M	src/coreclr/pal/src/synchmgr/synchmanager.cpp
M	src/native/libs/System.Native/pal_threading.c
Falling back to patching base and 3-way merge...
Auto-merging src/coreclr/pal/src/synchmgr/synchmanager.cpp
Auto-merging src/native/libs/System.Native/pal_threading.c
Applying: Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in
Applying: Add missing CMake feature definitions to config.h.in files
Applying: Revert extra changes, keep only HAVE_CLOCK_MONOTONIC fix
error: sha1 information is lacking or useless (src/coreclr/pal/src/config.h.in).
error: could not build fake ancestor
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0005 Revert extra changes, keep only HAVE_CLOCK_MONOTONIC fix
Error: The process '/usr/bin/git' failed with exit code 128

Link to workflow output

Fixes issue #123950 where Task.Delay freezes when system time jumps backwards on .NET 10 Linux - a regression from .NET 8 and 9. The root cause was a missing `#cmakedefine01 HAVE_CLOCK_MONOTONIC` directive in `src/coreclr/pal/src/config.h.in`. While CMake was successfully detecting monotonic clock support, the configuration value was never propagated to the generated config.h header. This caused the runtime to fall back to wall-clock time (CLOCK_REALTIME) instead of monotonic clocks (CLOCK_MONOTONIC), making timing operations vulnerable to system time adjustments. --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

…otnet#124086) Fixes issue dotnet#123950 where Task.Delay freezes when system time jumps backwards on .NET 10 Linux - a regression from .NET 8 and 9. The root cause was a missing `#cmakedefine01 HAVE_CLOCK_MONOTONIC` directive in `src/coreclr/pal/src/config.h.in`. While CMake was successfully detecting monotonic clock support, the configuration value was never propagated to the generated config.h header. This caused the runtime to fall back to wall-clock time (CLOCK_REALTIME) instead of monotonic clocks (CLOCK_MONOTONIC), making timing operations vulnerable to system time adjustments. --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

Backport of #124086 to release/10.0 ## Customer Impact - [X] Customer reported - [ ] Found internally Task.Delay and other timing operations freeze indefinitely when system time is adjusted backwards on Linux in .NET 10. Reported by two different customers. ## Regression - [X] Yes - [ ] No Add missing `#cmakedefine01 HAVE_CLOCK_MONOTONIC` to `src/coreclr/pal/src/config.h.in`. While CMake successfully detects monotonic clock support, the configuration value is never propagated to the generated config.h header. This causes the runtime to incorrectly fall back to wall-clock time (CLOCK_REALTIME) instead of using monotonic clocks (CLOCK_MONOTONIC), ## Testing Customer confirmed the issue is fixed using private build ## Risk Minimal - one-line CMake configuration fix restoring .NET 8/9 behavior. Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com> Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

Initial plan

d3bf5db

Copilot AI assigned Copilot and jkotas Feb 6, 2026

Copilot started work on behalf of jkotas February 6, 2026 13:12 View session

github-actions bot added the needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners label Feb 6, 2026

Copilot AI changed the title ~~[WIP] Cherry pick commit for investigating dotnet issue #123950~~ Investigate #123950: Add compile-time diagnostics for monotonic clock configuration Feb 6, 2026

Copilot finished work on behalf of jkotas February 6, 2026 13:20

Copilot AI requested a review from jkotas February 6, 2026 13:20

Copilot started work on behalf of jkotas February 6, 2026 13:42 View session

Copilot AI changed the title ~~Investigate #123950: Add compile-time diagnostics for monotonic clock configuration~~ Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in Feb 6, 2026

Copilot finished work on behalf of jkotas February 6, 2026 13:46

jkotas reviewed Feb 6, 2026

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Copilot started work on behalf of jkotas February 6, 2026 14:05 View session

github-actions bot added area-PAL-coreclr and removed needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners labels Feb 6, 2026

Copilot AI changed the title ~~Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in~~ Fix #123950: Add missing CMake feature definitions to config.h.in files Feb 6, 2026

Copilot AI requested a review from jkotas February 6, 2026 14:13

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jkotas reviewed Feb 6, 2026

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Copilot started work on behalf of jkotas February 6, 2026 15:04 View session

Copilot AI changed the title ~~Fix #123950: Add missing CMake feature definitions to config.h.in files~~ Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in Feb 6, 2026

Copilot finished work on behalf of jkotas February 6, 2026 15:11

Copilot AI requested a review from jkotas February 6, 2026 15:11

tannergooding reviewed Feb 6, 2026

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tannergooding approved these changes Feb 6, 2026

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stephentoub approved these changes Feb 6, 2026

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stephentoub marked this pull request as ready for review February 6, 2026 16:15

Copilot AI review requested due to automatic review settings February 6, 2026 16:15

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This was referenced Feb 6, 2026

Test failure: baseservices/exceptions/stackoverflow/stackoverflowtester/stackoverflowtester.cmd #110173

Open

Tests failing on tvos with "The app 'net.dot.System.Runtime.Tests' terminated with signal 11" #124072

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jkotas merged commit 109ebb3 into main Feb 7, 2026
104 of 108 checks passed

jkotas deleted the copilot/investigate-dotnet-issue-123950 branch February 7, 2026 01:36

Copilot AI mentioned this pull request Feb 7, 2026

[release/10.0] Add missing HAVE_CLOCK_MONOTONIC to config.h.in #124121

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dotnet-maestro bot mentioned this pull request Feb 7, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#4719

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Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in #124086

Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in #124086

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Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in #124086

Fix #123950: Add missing HAVE_CLOCK_MONOTONIC to config.h.in #124086

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