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macOS: thread affinity handling (no-op guard + QoS performance-core hint) #3035

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macOS: thread affinity handling (no-op guard + QoS performance-core hint) #3035

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6 changes: 6 additions & 0 deletions rts/System/Platform/ThreadAffinityGuard.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@
#include "System/Log/ILog.h"
#ifdef _WIN32
#include <windows.h>
#elif defined(__APPLE__)
// macOS has no portable per-thread CPU affinity API; nothing to include.
#else
#include <sched.h>
#include <unistd.h>
Expand All @@ -18,6 +20,8 @@ ThreadAffinityGuard::ThreadAffinityGuard() : affinitySaved(false) {
if (!affinitySaved) {
LOG_L(L_WARNING, "GetThreadAffinityMask failed with error code: %lu", GetLastError());
}
#elif defined(__APPLE__)
// no portable affinity API on macOS; leave affinitySaved == false
#else
tid = syscall(SYS_gettid); // Get thread ID
CPU_ZERO(&savedAffinity);
Expand All @@ -36,6 +40,8 @@ ThreadAffinityGuard::~ThreadAffinityGuard() {
if (!SetThreadAffinityMask(threadHandle, savedAffinity)) {
LOG_L(L_WARNING, "SetThreadAffinityMask failed with error code: %lu", GetLastError());
}
#elif defined(__APPLE__)
// unreachable on macOS: affinitySaved is never set
#else
if (sched_setaffinity(tid, sizeof(cpu_set_t), &savedAffinity) != 0) {
LOG_L(L_WARNING, "Failed to restore thread affinity.");
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4 changes: 4 additions & 0 deletions rts/System/Platform/ThreadAffinityGuard.h
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Expand Up @@ -3,6 +3,8 @@

#ifdef _WIN32
#include <windows.h>
#elif defined(__APPLE__)
// macOS has no portable per-thread CPU affinity API; the guard is a no-op.
#else
#include <sched.h>
#endif
Expand All @@ -12,6 +14,8 @@ class ThreadAffinityGuard {
#ifdef _WIN32
DWORD_PTR savedAffinity;
HANDLE threadHandle;
#elif defined(__APPLE__)
// no affinity state to track on macOS
#else
cpu_set_t savedAffinity;
pid_t tid;
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15 changes: 13 additions & 2 deletions rts/System/Platform/Threading.cpp
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Expand Up @@ -17,7 +17,9 @@
#include <memory>
#include <numeric>
#include <cinttypes>
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__)
#if defined(__APPLE__)
#include <pthread/qos.h>
#elif defined(__FreeBSD__) || defined(__OpenBSD__)
#elif defined(_WIN32)
#include <windows.h>
#include "System/Platform/Win/DllLib.h"
Expand Down Expand Up @@ -277,7 +279,16 @@ namespace Threading {
if (coreMask == 0)
return (~0);

#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__)
#if defined(__APPLE__)
// macOS has no per-thread CPU affinity API. The closest equivalent is a
// QoS hint: QOS_CLASS_USER_INTERACTIVE biases the scheduler toward the
// performance cores (and away from the efficiency cores). We can't honor
// the specific coreMask, so apply the hint and report the affinity as
// "not set" (~0) -- final core placement is left to the scheduler.
pthread_set_qos_class_self_np(QOS_CLASS_USER_INTERACTIVE, 0);
return (~0);

#elif defined(__FreeBSD__) || defined(__OpenBSD__)
// These platforms don't support thread affinity; return ~0 ("not set")
return (~0);

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