wait.h

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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

 
#pragma once
#include <stddef.h>
#if defined(__i386__) || defined(_M_IX86)
    #include <immintrin.h>
#elif defined (_M_ARM64) || defined(_M_ARM)
    #include <intrin.h>
#elif defined(__aarch64__) || defined(__arm__)
    #if defined(__ARM_ACLE)
        #include <arm_acle.h>
    #elif defined (__GNUC__)
        // HACK: GCC for ARM doesn't fully implement the ARM C Language
        // extensions and thus chooses to not define __ARM_ACLE.
        // Since ACLE are not available, use inline assembly, which
        // GCC permits.
 
        __attribute__((__always_inline__))
        static inline void __yield(void) { __asm__ volatile ("yield"); }
 
        __attribute__((__always_inline__))
        static inline void __isb(unsigned int) {
            __asm__ volatile ("isb 15" ::: "memory");
        }
    #else
        #error Compiling for ARM, but ACLE are not available?
    #endif
#endif
 
#ifdef __cplusplus
    #include <atomic>
    using atomic_size_t = std::atomic<size_t>;
    extern "C" {
#else
    #include <stdatomic.h>
#endif

extern atomic_size_t chic_catastrophe_threshold;

void chic_yield(void);

static inline void busy_wait_hint(void) {
#if defined(__i386__) || defined(_M_IX86)
    _mm_pause();
#elif defined(__aarch64__) || defined(_M_ARM64)
    __isb(15);
#elif defined(__arm__) || defined(_M_ARM)
    __yield();
#elif defined(__riscv) && defined(__riscv_zihintpause)
    __asm__ volatile ("pause");
#endif
}

static inline void busy_wait_on(const void *addr) {
#if defined(__riscv) && defined(__riscv_zawrs)
    __asm__ volatile (
        "lr.w %0, (%0)\n\t"
        "wrs.sto"
        : "+r" (addr)
    );
#else
    busy_wait_hint();
    busy_wait_hint();
    busy_wait_hint();
    busy_wait_hint();
    (void)(addr);
#endif
}
 
#ifdef __cplusplus
    }
#endif