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feat: use spinlocks for selector maps
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| #ifndef SpinLock_h | ||
| #define SpinLock_h | ||
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| /** | ||
| WARNING: | ||
| Do NOT use this. | ||
| More ofthen than not a normal mutex is better and this spinlock is really unfair in multi threading | ||
| This is only supposed to be used in places where the function is very fast and the expected concurrency is very low | ||
| If any of those things are false, this WILL be slower and worse than a mutex or a read write mutex | ||
| The only place this is currently used is for caching selectors, which take ns to run and are not locked to a specific isolate. | ||
| */ | ||
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| struct SpinMutex { | ||
| std::atomic<bool> lock_ = {0}; | ||
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| inline void lock() noexcept { | ||
| for (;;) { | ||
| // Optimistically assume the lock is free on the first try | ||
| if (!lock_.exchange(true, std::memory_order_acquire)) { | ||
| return; | ||
| } | ||
| // Wait for lock to be released without generating cache misses | ||
| while (lock_.load(std::memory_order_relaxed)) { | ||
| // Issue X86 PAUSE or ARM YIELD instruction to reduce contention between | ||
| // hyper-threads | ||
| //__builtin_ia32_pause(); | ||
| } | ||
| } | ||
| } | ||
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| bool try_lock() noexcept { | ||
| // First do a relaxed load to check if lock is free in order to prevent | ||
| // unnecessary cache misses if someone does while(!try_lock()) | ||
| return !lock_.load(std::memory_order_relaxed) && | ||
| !lock_.exchange(true, std::memory_order_acquire); | ||
| } | ||
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| inline void unlock() noexcept { | ||
| lock_.store(false, std::memory_order_release); | ||
| } | ||
| }; | ||
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| struct SpinLock { | ||
| SpinMutex& _mutex; | ||
| SpinLock(SpinMutex& m) : _mutex(m) { | ||
| _mutex.lock(); | ||
| } | ||
| ~SpinLock() { | ||
| _mutex.unlock(); | ||
| } | ||
| }; | ||
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| #endif /* SpinLock_h */ |
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