Add Windows thread affinity support by GagaLP · Pull Request #338 · celerity/celerity-runtime

GagaLP · 2026-07-14T16:17:44Z

Thread pinning was previously a no-op on Windows: thread_pinner only emitted a warning ("Thread pinning is currently not supported on Windows.") and did not apply any affinity settings, regardless of configuration.

This PR adds a real implementation by introducing a small pthread/cpu_set_t compatibility layer (platform_specific/affinity_win32.h/.cc). The layer maps the POSIX affinity APIs already used by Celerity (sched_getaffinity/sched_setaffinity, pthread_self, pthread_get/setaffinity_np, CPU_SET/CPU_ISSET/CPU_COUNT, etc.) to their Windows equivalents (GetActiveProcessorGroupCount, GROUP_AFFINITY, SetThreadGroupAffinity).

With this compatibility layer in place, affinity_win.cc no longer requires separate pinning logic and now closely mirrors the Linux implementation. It initializes and tears down the pinning plan in the same way and pins threads to sequential cores using the same approach.

One limitation to note: Windows organizes logical processors into groups of up to 64 processors, and a single GROUP_AFFINITY mask cannot span multiple groups. If a requested core set crosses a group boundary, the layer currently emits a warning and skips pinning instead of attempting cross-group affinity. This should not affect the common case of pinning a small number of sequential cores, but remains a limitation on systems with more than 64 logical processors.

Added corresponding tests in affinity_tests.cc.

github-actions · 2026-07-14T16:18:32Z

Check-perf-impact results: (ae6918621b46271c2f10d6eb978fe95d)

❓ No new benchmark data submitted. ❓
Please re-run the microbenchmarks and include the results if your commit could potentially affect performance.

PeterTh

Instead of duplicating the win.cc / unix.cc, I think the win version could just be reduced to a include of the helper header plus a include of the unix.cc, with an explanation (of the windows helper introducing compat with the unix impl).

PeterTh · 2026-08-03T14:23:16Z

 #ifdef _WIN32
-#define SKIP_UNSUPPORTED() SKIP("Affinity is not supported on Windows");
+#define SKIP_UNSUPPORTED() // SKIP("Affinity is not supported on Windows");
 #else
 #define SKIP_UNSUPPORTED()
 #endif


This whole code block (and the invocation sites) can just be removed.

PeterTh · 2026-08-03T14:30:21Z

@@ -0,0 +1,105 @@
+#pragma once
+


This file should have a comment at the start explaining its purpose (i.e. implementing unix-like affinity using windows APIs).

maybe the name should also be something like affinity_win32_adapter?

github-actions

⚠️ Clang-Tidy found issue(s) with the introduced code (1/5)

github-actions · 2026-08-05T13:56:42Z

+
+#include "log.h"
+
+using pthread_t = DWORD;


❌ clang-diagnostic-error ❌
unknown type name DWORD

github-actions · 2026-08-05T13:56:43Z

+
+using pthread_t = DWORD;
+
+struct cpu_set_t {


❌ clang-diagnostic-error ❌
definition of type cpu_set_t conflicts with typedef of the same name

github-actions · 2026-08-05T13:56:43Z

+	uint64_t bits[WORDS] = {};
+};
+
+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:56:43Z

+
+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:56:43Z

+
+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);


❌ clang-diagnostic-error ❌
while loop outside of a function

github-actions · 2026-08-05T13:56:43Z

+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:56:43Z

+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:56:43Z

+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:56:43Z

+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:56:43Z

+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected )

github-actions

⚠️ Clang-Tidy found issue(s) with the introduced code (2/5)

github-actions · 2026-08-05T13:56:55Z

+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:56:55Z

+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);


❌ clang-diagnostic-error ❌
redefinition of __sched_cpucount as different kind of symbol

github-actions · 2026-08-05T13:56:55Z

+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected expression

github-actions · 2026-08-05T13:56:56Z

+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);
+int CPU_EQUAL(const cpu_set_t* a, const cpu_set_t* b);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:56:56Z

+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);
+int CPU_EQUAL(const cpu_set_t* a, const cpu_set_t* b);


❌ clang-diagnostic-error ❌
expected parameter declarator

github-actions · 2026-08-05T13:56:56Z

+static constexpr unsigned PROCS_PER_GROUP = 64;
+
+struct cpu_topology_entry {
+	WORD group;


❌ clang-diagnostic-error ❌
unknown type name WORD

github-actions · 2026-08-05T13:56:56Z

+
+struct cpu_topology_entry {
+	WORD group;
+	WORD count;


❌ clang-diagnostic-error ❌
unknown type name WORD

github-actions · 2026-08-05T13:56:56Z

+using cpu_topology = std::vector<cpu_topology_entry>;
+
+struct windows_topology_policy {
+	static WORD get_group_count() { return GetActiveProcessorGroupCount(); }


❌ clang-diagnostic-error ❌
unknown type name WORD

github-actions · 2026-08-05T13:56:56Z

+
+#include "log.h"
+
+using pthread_t = DWORD;


❌ clang-diagnostic-error ❌
unknown type name DWORD

github-actions · 2026-08-05T13:56:56Z

+
+using pthread_t = DWORD;
+
+struct cpu_set_t {


❌ clang-diagnostic-error ❌
definition of type cpu_set_t conflicts with typedef of the same name

github-actions

⚠️ Clang-Tidy found issue(s) with the introduced code (3/5)

github-actions · 2026-08-05T13:57:09Z

+	uint64_t bits[WORDS] = {};
+};
+
+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:57:09Z

+
+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:57:09Z

+
+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);


❌ clang-diagnostic-error ❌
while loop outside of a function

github-actions · 2026-08-05T13:57:09Z

+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:57:09Z

+inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;
+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:57:09Z

+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:57:09Z

+
+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:57:09Z

+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:57:09Z

+void CPU_ZERO(cpu_set_t* set);
+void CPU_SET(unsigned cpu, cpu_set_t* set);
+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected unqualified-id

github-actions · 2026-08-05T13:57:09Z

+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);


❌ clang-diagnostic-error ❌
redefinition of __sched_cpucount as different kind of symbol

github-actions

⚠️ Clang-Tidy found issue(s) with the introduced code (4/5)

github-actions · 2026-08-05T13:57:22Z

+void CPU_CLR(unsigned cpu, cpu_set_t* set);
+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);


❌ clang-diagnostic-error ❌
expected expression

github-actions · 2026-08-05T13:57:22Z

+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);
+int CPU_EQUAL(const cpu_set_t* a, const cpu_set_t* b);


❌ clang-diagnostic-error ❌
expected )

github-actions · 2026-08-05T13:57:22Z

+int CPU_ISSET(unsigned cpu, const cpu_set_t* set);
+
+int CPU_COUNT(const cpu_set_t* set);
+int CPU_EQUAL(const cpu_set_t* a, const cpu_set_t* b);


❌ clang-diagnostic-error ❌
expected parameter declarator

github-actions · 2026-08-05T13:57:22Z

+static constexpr unsigned PROCS_PER_GROUP = 64;
+
+struct cpu_topology_entry {
+	WORD group;


❌ clang-diagnostic-error ❌
unknown type name WORD

github-actions · 2026-08-05T13:57:22Z

+
+struct cpu_topology_entry {
+	WORD group;
+	WORD count;


❌ clang-diagnostic-error ❌
unknown type name WORD

github-actions · 2026-08-05T13:57:22Z

+using cpu_topology = std::vector<cpu_topology_entry>;
+
+struct windows_topology_policy {
+	static WORD get_group_count() { return GetActiveProcessorGroupCount(); }


❌ clang-diagnostic-error ❌
unknown type name WORD

github-actions · 2026-08-05T13:57:22Z

+// compiles unchanged.
+#include "platform_specific/affinity_win32_adapter.h"
+
+#include "affinity.unix.cc"


⚠️ bugprone-suspicious-include ⚠️
suspicious #include of file with .cc extension

github-actions · 2026-08-05T13:57:22Z

+int CPU_COUNT(const cpu_set_t* set);
+int CPU_EQUAL(const cpu_set_t* a, const cpu_set_t* b);
+
+int sched_getaffinity(int pid, size_t cpusetsize, cpu_set_t* mask);


⚠️ readability-redundant-declaration ⚠️
redundant sched_getaffinity declaration

Suggested change

int sched_getaffinity(int pid, size_t cpusetsize, cpu_set_t* mask);

github-actions · 2026-08-05T13:57:22Z

+int CPU_EQUAL(const cpu_set_t* a, const cpu_set_t* b);
+
+int sched_getaffinity(int pid, size_t cpusetsize, cpu_set_t* mask);
+int sched_setaffinity(int pid, size_t cpusetsize, const cpu_set_t* mask);


⚠️ readability-redundant-declaration ⚠️
redundant sched_setaffinity declaration

Suggested change

int sched_setaffinity(int pid, size_t cpusetsize, const cpu_set_t* mask);

github-actions · 2026-08-05T13:57:22Z

+int sched_getaffinity(int pid, size_t cpusetsize, cpu_set_t* mask);
+int sched_setaffinity(int pid, size_t cpusetsize, const cpu_set_t* mask);
+
+pthread_t pthread_self();


⚠️ readability-redundant-declaration ⚠️
redundant pthread_self declaration

Suggested change

pthread_t pthread_self();

github-actions

⚠️ Clang-Tidy found issue(s) with the introduced code (5/5)

github-actions · 2026-08-05T13:57:35Z

+
+pthread_t pthread_self();
+
+int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize, const cpu_set_t* mask);


⚠️ readability-redundant-declaration ⚠️
redundant pthread_setaffinity_np declaration

Suggested change

int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize, const cpu_set_t* mask);

github-actions · 2026-08-05T13:57:35Z

+pthread_t pthread_self();
+
+int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize, const cpu_set_t* mask);
+int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize, cpu_set_t* mask);


⚠️ readability-redundant-declaration ⚠️
redundant pthread_getaffinity_np declaration

Suggested change

int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize, cpu_set_t* mask);

github-actions · 2026-08-05T13:57:35Z

+	WORD group;
+	WORD count;


⚠️ cppcoreguidelines-pro-type-member-init ⚠️
constructor does not initialize these fields: group, count

Suggested change

WORD group;

WORD count;

WORD group{};

WORD count{};

coveralls · 2026-08-05T14:09:35Z

Coverage Report for CI Build 31012551030

Coverage remained the same at 95.067%

Details

Coverage remained the same as the base build.
Patch coverage: No coverable lines changed in this PR.
No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

Coverage Stats


Relevant Lines:	7261
Covered Lines:	7156
Line Coverage:	98.55%
Relevant Branches:	3686
Covered Branches:	3251
Branch Coverage:	88.2%
Branches in Coverage %:	Yes
Coverage Strength:	2235776.15 hits per line

💛 - Coveralls

GagaLP requested a review from PeterTh July 14, 2026 16:17

PeterTh requested changes Aug 3, 2026

View reviewed changes

Enable preliminary thread affinity/pinning support on Windows

90901f4

GagaLP force-pushed the thread-affinity-windows branch from 1aacd2d to 90901f4 Compare August 5, 2026 13:55

github-actions Bot reviewed Aug 5, 2026

View reviewed changes


		inline constexpr unsigned CPU_SETSIZE = cpu_set_t::CPU_SETSIZE;

		void CPU_ZERO(cpu_set_t* set);


		pthread_t pthread_self();

		int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize, const cpu_set_t* mask);

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