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Merge pull request #85167 from RandomShaper/good_spinlock

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Enhance SpinLock
This commit is contained in:
Thaddeus Crews 2024-11-10 12:12:36 -06:00
commit 01ad56da38
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GPG Key ID: 62181B86FE9E5D84
3 changed files with 61 additions and 5 deletions
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1
SConstruct
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@ -851,6 +851,7 @@ if env.msvc and not methods.using_clang(env): # MSVC
"/wd4245",
"/wd4267",
"/wd4305", # C4305 (truncation): double to float or real_t, too hard to avoid.
"/wd4324", # C4820 (structure was padded due to alignment specifier)
"/wd4514", # C4514 (unreferenced inline function has been removed)
"/wd4714", # C4714 (function marked as __forceinline not inlined)
"/wd4820", # C4820 (padding added after construct)

47
core/os/spin_lock.h
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@ -33,6 +33,10 @@
#include "core/typedefs.h"
#ifdef _MSC_VER
#include <intrin.h>
#endif
#if defined(__APPLE__)
#include <os/lock.h>
@ -52,19 +56,52 @@ public:
#else
#include "core/os/thread.h"
#include <atomic>
class SpinLock {
mutable std::atomic_flag locked = ATOMIC_FLAG_INIT;
_ALWAYS_INLINE_ static void _cpu_pause() {
#if defined(_MSC_VER)
// ----- MSVC.
#if defined(_M_ARM) || defined(_M_ARM64) // ARM.
__yield();
#elif defined(_M_IX86) || defined(_M_X64) // x86.
_mm_pause();
#endif
#elif defined(__GNUC__) || defined(__clang__)
// ----- GCC/Clang.
#if defined(__i386__) || defined(__x86_64__) // x86.
__builtin_ia32_pause();
#elif defined(__arm__) || defined(__aarch64__) // ARM.
asm volatile("yield");
#elif defined(__powerpc__) || defined(__ppc__) || defined(__PPC__) // PowerPC.
asm volatile("or 27,27,27");
#elif defined(__riscv) // RISC-V.
asm volatile(".insn i 0x0F, 0, x0, x0, 0x010");
#endif
#endif
}
static_assert(std::atomic_bool::is_always_lock_free);
class alignas(Thread::CACHE_LINE_BYTES) SpinLock {
mutable std::atomic<bool> locked = ATOMIC_VAR_INIT(false);
public:
_ALWAYS_INLINE_ void lock() const {
while (locked.test_and_set(std::memory_order_acquire)) {
// Continue.
while (true) {
bool expected = false;
if (locked.compare_exchange_weak(expected, true, std::memory_order_acquire, std::memory_order_relaxed)) {
break;
}
do {
_cpu_pause();
} while (locked.load(std::memory_order_relaxed));
}
}
_ALWAYS_INLINE_ void unlock() const {
locked.clear(std::memory_order_release);
locked.store(false, std::memory_order_release);
}
};

18
core/os/thread.h
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@ -42,6 +42,8 @@
#include "core/templates/safe_refcount.h"
#include "core/typedefs.h"
#include <new>
#ifdef MINGW_ENABLED
#define MINGW_STDTHREAD_REDUNDANCY_WARNING
#include "thirdparty/mingw-std-threads/mingw.thread.h"
@ -85,6 +87,20 @@ public:
void (*term)() = nullptr;
};
#if defined(__cpp_lib_hardware_interference_size) && !defined(ANDROID_ENABLED) // This would be OK with NDK >= 26.
#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Winterference-size"
#endif
static constexpr size_t CACHE_LINE_BYTES = std::hardware_destructive_interference_size;
#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif
#else
// At a negligible memory cost, we use a conservatively high value.
static constexpr size_t CACHE_LINE_BYTES = 128;
#endif
private:
friend class Main;
@ -135,6 +151,8 @@ public:
typedef uint64_t ID;
static constexpr size_t CACHE_LINE_BYTES = sizeof(void *);
enum : ID {
UNASSIGNED_ID = 0,
MAIN_ID = 1