Add single-threaded (lockless) mode to IOCP backend

[mvandeberg]

Summary by CodeRabbit

• New Features
  • Added single-threaded mode configuration to optimize performance by disabling synchronization overhead when cross-thread operations are not required.
  • Added runtime control over synchronization behavior in the scheduler for improved efficiency in single-threaded contexts.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 173882ef-c54c-4d7c-b6b1-9ef3496e47f2

📥 Commits

Reviewing files that changed from the base of the PR and between 9c7d1eb and 5b2feeb.

📒 Files selected for processing (3)

• include/boost/corosio/native/detail/iocp/win_mutex.hpp
• include/boost/corosio/native/detail/iocp/win_scheduler.hpp
• src/corosio/src/io_context.cpp

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📝 Walkthrough

Walkthrough

The pull request adds runtime enable/disable control to a Windows critical section wrapper class (win_mutex) and introduces single-threaded mode configuration for the Windows IOCP scheduler (win_scheduler). When disabled, mutex operations become no-ops; the scheduler can disable locking entirely in single-threaded mode. Configuration propagates from io_context to the scheduler, which controls mutex behavior.

Changes

Cohort / File(s)	Summary
Windows Mutex Control include/boost/corosio/native/detail/iocp/win_mutex.hpp	Added set_enabled(bool) and enabled() const methods with new enabled_ boolean member to allow runtime control of lock behavior; when disabled, lock() and unlock() skip EnterCriticalSection/LeaveCriticalSection calls, and try_lock() returns true immediately.
Windows Scheduler Configuration include/boost/corosio/native/detail/iocp/win_scheduler.hpp	Added configure_single_threaded(bool) method that sets internal flag and delegates mutex control to dispatch_mutex_.set_enabled(), disabling dispatch synchronization in single-threaded mode.
IO Context Scheduler Setup src/corosio/src/io_context.cpp	Updated apply_scheduler_options to invoke configure_single_threaded(true) on IOCP schedulers when single-threaded mode is requested, extending existing reactor-only behavior to Windows platform.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• Remove native_scheduler, cache service pointers at proper layers #222: Modifies win_scheduler single-threading behavior and scheduler refactoring with single_threaded_ flag management.
• Add runtime io_context_options for scheduler and service tuning #219: Updates IOCP scheduler and mutex codepaths with runtime single-threaded configuration and conditionally-enabled locking mechanisms.

Poem

🐰 A mutex learns to rest its weary brain,
No locks when single-threaded reigns,
The scheduler whispers, "peace, no strain,"
One thread, one path, no concurrent pain! 🔓

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding single-threaded (lockless) mode support to the IOCP backend through new configuration methods and runtime enable/disable control.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[cppalliance-bot]

An automated preview of the documentation is available at https://225.corosio.prtest3.cppalliance.org/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-04-06 18:57:06 UTC

[cppalliance-bot]

GCOVR code coverage report https://225.corosio.prtest3.cppalliance.org/gcovr/index.html
LCOV code coverage report https://225.corosio.prtest3.cppalliance.org/genhtml/index.html
Coverage Diff Report https://225.corosio.prtest3.cppalliance.org/diff-report/index.html

Build time: 2026-04-06 19:06:52 UTC