fix: wire SetCPUTrackingEnabled to start/stop TimerCreateCpuProfiler

[korniltsev-grafanista-yolo-vibecoder239]

Summary

Fixes #259 — dynamic CPU profiling toggle was not working on Linux.

• SetStackSamplerEnabled only controlled StackSamplerLoopManager (wall-time + manual CPU loop), but on Linux the actual CPU profiler is TimerCreateCpuProfiler — a completely independent service that was never started/stopped by the toggle API.
• ProfilerSignalManager::IgnoreSignal() set SIGPROF to SIG_IGN but did not reset its internal _handler and _isHandlerInPlace state, so RegisterHandler() would short-circuit on re-start and the signal handler was never re-registered.

Changes

• CorProfilerCallback::SetStackSamplerEnabled — start/stop _pCpuProfiler alongside _pStackSamplerLoopManager on Linux
• ProfilerSignalManager::IgnoreSignal — reset _handler and _isHandlerInPlace after successfully ignoring the signal, so a subsequent RegisterHandler() call re-installs the handler

Test plan

• make -C itest itest/dynamic-cpu/glibc/8.0 — integration test from test: add integration test reproducing dynamic CPU profiling bug (#259) #278

🤖 Generated with Claude Code

---

Note

Medium Risk
Touches Linux CPU-profiler start/stop and signal-handler installation logic; mistakes here can disable profiling or destabilize signal handling, but changes are localized and guarded by existing checks.

Overview
Fixes Linux dynamic CPU profiling toggling by starting/stopping the timer-based _pCpuProfiler alongside _pStackSamplerLoopManager in CorProfilerCallback::SetStackSamplerEnabled.

Hardens ProfilerSignalManager so SIGPROF handler registration can be reliably re-installed after being ignored/replaced: _handler and _isHandlerInPlace are now atomic, internal state is reset on IgnoreSignal(), and previous sigaction state capture is tracked via _previousActionCaptured to avoid clobbering the saved handler (with UnRegisterHandler() now test-only).

^{Reviewed by Cursor Bugbot for commit 78d85df. Bugbot is set up for automated code reviews on this repo. Configure here.}

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: a812673a4a

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{Bugbot Autofix is ON, but it could not run because the branch was deleted or merged before autofix could start.}

^{Reviewed by Cursor Bugbot for commit a812673. Configure here.}

[korniltsev-grafanista]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 0cdf638895

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[korniltsev-grafanista]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: bf15233886

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[korniltsev-grafanista]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: dcb093b553

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Preserve prior SIG_IGN action when installing handler

The new if (oldAction.sa_handler != SIG_IGN) guard drops the previous action whenever the process had already set this signal to ignore before the profiler starts. In that case _previousAction is left at its default-initialized value, so later unregistration/destruction restores the signal to default instead of restoring SIG_IGN, changing process signal semantics after profiler shutdown (applies to any ProfilerSignalManager, including SIGUSR1 and SIGPROF). This regression is introduced by the conditional assignment here.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: dcb093b553

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Skip duplicate timer profiler start on manual enable

Calling SetStackSamplerEnabled(true) now invokes _pCpuProfiler->Start() immediately, but CorProfilerCallback::StartServices() still unconditionally starts _pCpuProfiler later and treats a false return as startup failure. In managed-activation/SSI flows where this toggle can run before delayed service startup, the second Start() call hits ServiceBase's "already started" path, causing StartServices() to fail and trigger StopServices(), so profiling may never fully start. Guard this call (or make it idempotent) so pre-start toggles do not poison the later startup sequence.

Useful? React with 👍 / 👎.

[marcsanmi]

Might want to take a look at this @korniltsev-grafanista

[korniltsev-grafanista]

Do you think this is valid concern? What should we do?

[marcsanmi]

Only for SSI/delayed-start flows for what I can understand (?) Something like this might help:

if (_pCpuProfiler != nullptr)
{
    if (!_pCpuProfiler->IsStarted())
    {
        success = _pCpuProfiler->Start();
        LogServiceStart(success, _pCpuProfiler->GetName());
        result &= success;
    }
}