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2d957cd46f
Summary: resolves T12767 Reviewers: ivica Reviewed By: ivica Subscribers: miljen Tags: #spacetime Maniphest Tasks: T12767 Differential Revision: https://repo.mireo.local/D25970
59 lines
1.7 KiB
C++
59 lines
1.7 KiB
C++
#ifndef ASYNC_MQTT5_SPINLOCK_HPP
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#define ASYNC_MQTT5_SPINLOCK_HPP
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#include <atomic>
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namespace async_mqtt5::detail {
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#if defined(_MSC_VER)
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/* prefer using intrinsics directly instead of winnt.h macro */
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/* http://software.intel.com/en-us/forums/topic/296168 */
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//#include <intrin.h>
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#if defined(_M_AMD64) || defined(_M_IX86)
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#pragma intrinsic(_mm_pause)
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#define __pause() _mm_pause()
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/* (if pause not supported by older x86 assembler, "rep nop" is equivalent)*/
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/*#define __pause() __asm rep nop */
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#elif defined(_M_IA64)
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#pragma intrinsic(__yield)
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#define __pause() __yield()
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#else
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#define __pause() YieldProcessor()
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#endif
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#elif defined(__x86_64__) || defined(__i386__)
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#define __pause() __asm__ __volatile__ ("pause")
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#elif defined(__arm__) || defined(__arm64__) || defined(__aarch64__)
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#define __pause() __asm__ __volatile__ ("yield")
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#endif
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// https://rigtorp.se/spinlock/
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class spinlock {
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std::atomic<bool> lock_ { false };
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public:
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void lock() noexcept {
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for (;;) {
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// Optimistically assume the lock is free on the first try
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if (!lock_.exchange(true, std::memory_order_acquire))
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return;
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// Wait for lock to be released without generating cache misses
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while (lock_.load(std::memory_order_relaxed)) __pause();
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}
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}
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bool try_lock() noexcept {
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// First do a relaxed load to check if lock is free in order to prevent
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// unnecessary cache misses if someone does while(!try_lock())
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return !lock_.load(std::memory_order_relaxed) &&
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!lock_.exchange(true, std::memory_order_acquire);
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}
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void unlock() noexcept {
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lock_.store(false, std::memory_order_release);
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}
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};
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} // end namespace async_mqtt5::detail
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#endif // !ASYNC_MQTT5_SPINLOCK_HPP
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