From 0b2abc49fb9e1fffadb8e0c0e72ccd00fc479d62 Mon Sep 17 00:00:00 2001
From: Jamie Reece Wilson <me@reece.sx>
Date: Sat, 19 Aug 2023 19:54:56 +0100
Subject: [PATCH] [+] A small header only futex

---
 .../Threading/Waitables/FutexWaitable.hpp     | 150 ++++++++++++++++++
 .../Aurora/Threading/Waitables/Waitables.hpp  |   3 +-
 2 files changed, 152 insertions(+), 1 deletion(-)
 create mode 100644 Include/Aurora/Threading/Waitables/FutexWaitable.hpp

diff --git a/Include/Aurora/Threading/Waitables/FutexWaitable.hpp b/Include/Aurora/Threading/Waitables/FutexWaitable.hpp
new file mode 100644
index 00000000..e7412bd8
--- /dev/null
+++ b/Include/Aurora/Threading/Waitables/FutexWaitable.hpp
@@ -0,0 +1,150 @@
+/***
+    Copyright (C) 2023 J Reece Wilson (a/k/a "Reece"). All rights reserved.
+
+    File: FutexWaitable.hpp
+    Date: 2023-08-19
+    Author: Reece
+***/
+#pragma once
+
+#include "../WakeOnAddress.hpp"
+#include "../SpinTime.hpp"
+
+namespace Aurora::Threading::Waitables
+{
+    struct FutexWaitable final : IWaitable
+    {
+        inline constexpr FutexWaitable()
+        {}
+
+        AU_NO_COPY_NO_MOVE(FutexWaitable);
+
+        inline bool TryLock() override
+        {
+            if (AuAtomicTestAndSet(&this->uAtomicState, 0u))
+            {
+                return true;
+            }
+
+        #if defined(AURORA_ARCH_X86) || defined(AURORA_ARCH_X64)
+            for (AU_ITERATE_N(i, AuUInt(1u) << AuUInt(Threading::GetSpinCountTimeout())))
+            {
+                _mm_pause();
+
+                if (AuAtomicTestAndSet(&this->uAtomicState, 0u))
+                {
+                    return true;
+                }
+            }
+        #else
+            static const AuUInt32 kRef { 1 };
+            if (TryWaitOnAddress(&this->uAtomicState, &kRef, sizeof(kRef)))
+            {
+                if (AuAtomicTestAndSet(&this->uAtomicState, 0u))
+                {
+                    return true;
+                }
+            }
+        #endif
+
+            return false;
+        }
+
+        inline bool HasOSHandle(AuMach &mach) override
+        {
+            return false;
+        }
+
+        inline bool HasLockImplementation() override
+        {
+            return true;
+        }
+
+        inline void Unlock() override
+        {
+            this->uAtomicState = 0;
+
+            if (auto uSleeping = this->uAtomicSleeping)
+            {
+                WakeOnAddress(&this->uAtomicState);
+            }
+        }
+
+        inline void Lock() override
+        {
+            static const AuUInt32 kRef { 1 };
+
+            while (!TryLock())
+            {
+                AuAtomicAdd(&this->uAtomicSleeping, 1u);
+                WaitOnAddress(&this->uAtomicState, &kRef, sizeof(kRef), 0);
+                AuAtomicSub(&this->uAtomicSleeping, 1u);
+            }
+        }
+
+        inline bool LockMS(AuUInt64 qwTimeout) override
+        {
+            return LockNS(AuMSToNS<AuUInt64>(qwTimeout));
+        }
+
+        inline bool LockAbsMS(AuUInt64 qwTimeout) override
+        {
+            return LockAbsNS(AuMSToNS<AuUInt64>(qwTimeout));
+        }
+
+        inline bool LockNS(AuUInt64 qwTimeout) override
+        {
+            static const AuUInt32 kRef { 1 };
+            if (AuAtomicTestAndSet(&this->uAtomicState, 0u))
+            {
+                return true;
+            }
+
+            auto qwEndTime = Time::SteadyClockNS() + qwTimeout;
+
+            while (!TryLock())
+            {
+                bool bStatus {};
+
+                AuAtomicAdd(&this->uAtomicSleeping, 1u);
+                bStatus = WaitOnAddressSteady(&this->uAtomicState, &kRef, sizeof(kRef), qwEndTime);
+                AuAtomicSub(&this->uAtomicSleeping, 1u);
+
+                if (!bStatus)
+                {
+                    return TryLock();
+                }
+            }
+
+            return true;
+        }
+
+        inline bool LockAbsNS(AuUInt64 qwTimeoutAbs) override
+        {
+            static const AuUInt32 kRef { 1 };
+            if (AuAtomicTestAndSet(&this->uAtomicState, 0u))
+            {
+                return true;
+            }
+
+            while (!TryLock())
+            {
+                bool bStatus {};
+
+                AuAtomicAdd(&this->uAtomicSleeping, 1u);
+                bStatus = WaitOnAddressSteady(&this->uAtomicState, &kRef, sizeof(kRef), qwTimeoutAbs);
+                AuAtomicSub(&this->uAtomicSleeping, 1u);
+
+                if (!bStatus)
+                {
+                    return TryLock();
+                }
+            }
+
+            return true;
+        }
+
+        AuUInt32 uAtomicState {};
+        AuUInt32 uAtomicSleeping {};
+    };
+}
\ No newline at end of file
diff --git a/Include/Aurora/Threading/Waitables/Waitables.hpp b/Include/Aurora/Threading/Waitables/Waitables.hpp
index e9f7674a..848f6b90 100644
--- a/Include/Aurora/Threading/Waitables/Waitables.hpp
+++ b/Include/Aurora/Threading/Waitables/Waitables.hpp
@@ -8,4 +8,5 @@
 #pragma once
 
 #include "CBWaitable.hpp"
-#include "BooleanWaitable.hpp"
\ No newline at end of file
+#include "BooleanWaitable.hpp"
+#include "FutexWaitable.hpp"
\ No newline at end of file