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

[Copilot]

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

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[jkotas]

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

[Copilot]

@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.

[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]

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

[jkotas]

Yes, I plan to submit backport request

[jkotas]

/ba-g known issues

[jkotas]

/backport to release/10.0

[github-actions]

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

[github-actions]

@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