From a977f0d1b50da078d612c0302deda4ea154e8d4f Mon Sep 17 00:00:00 2001
From: Jamie Reece Wilson <me@reece.sx>
Date: Mon, 10 Jul 2023 13:12:17 +0100
Subject: [PATCH] [*] NT: backport unix optimization - no spin during spurious
 wake up

---
 .../Primitives/AuConditionMutex.NT.cpp        | 19 +++++++++++++++--
 .../Primitives/AuConditionMutex.NT.hpp        |  3 +++
 Source/Threading/Primitives/AuMutex.NT.cpp    | 21 ++++++++++++-------
 Source/Threading/Primitives/AuMutex.NT.hpp    |  2 ++
 4 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/Source/Threading/Primitives/AuConditionMutex.NT.cpp b/Source/Threading/Primitives/AuConditionMutex.NT.cpp
index 2311637e..dcaf89ab 100644
--- a/Source/Threading/Primitives/AuConditionMutex.NT.cpp
+++ b/Source/Threading/Primitives/AuConditionMutex.NT.cpp
@@ -48,17 +48,32 @@ namespace Aurora::Threading::Primitives
     #else
         return DoTryIf([=]()
         {
-            return !AuAtomicTestAndSet(&this->lock_.uWaitCount, 0);
+            return this->TryLockNoSpin();
         });
     #endif
     }
 
+    bool Win32ConditionMutex::TryLockNoSpin()
+    {
+    #if defined(AURORA_FORCE_SRW_LOCKS)
+        return ::TryAcquireSRWLockExclusive(&this->lock_);
+    #else
+        return AuAtomicTestAndSet(&this->lock_.uWaitCount, 0) == 0;
+    #endif
+    }
+
     void Win32ConditionMutex::Lock()
     {
     #if defined(AURORA_FORCE_SRW_LOCKS)
         ::AcquireSRWLockExclusive(&this->lock_);
     #else
-        while (!TryLock())
+
+        if (this->TryLock())
+        {
+            return;
+        }
+
+        while (!this->TryLockNoSpin())
         {
             auto &uValueRef = this->lock_.uWaitCount;
             auto uValue = uValueRef | 1;
diff --git a/Source/Threading/Primitives/AuConditionMutex.NT.hpp b/Source/Threading/Primitives/AuConditionMutex.NT.hpp
index da37790b..07771192 100644
--- a/Source/Threading/Primitives/AuConditionMutex.NT.hpp
+++ b/Source/Threading/Primitives/AuConditionMutex.NT.hpp
@@ -24,6 +24,7 @@ namespace Aurora::Threading::Primitives
 
     inline HANDLE gKeyedEventHandle { INVALID_HANDLE_VALUE };
 
+    // Actually NT5.x
     struct NT4Mutex
     {
         volatile AuUInt32 uWaitCount {}; // yields while bits are high, dec to release one from the semaphore yield
@@ -39,6 +40,8 @@ namespace Aurora::Threading::Primitives
         auline void Unlock() override;
         AuUInt GetOSHandle() override;
 
+        auline bool TryLockNoSpin();
+
     #if !defined(AURORA_FORCE_SRW_LOCKS)
         NT4Mutex lock_;
     #else
diff --git a/Source/Threading/Primitives/AuMutex.NT.cpp b/Source/Threading/Primitives/AuMutex.NT.cpp
index 4bc29d90..e240bbcc 100644
--- a/Source/Threading/Primitives/AuMutex.NT.cpp
+++ b/Source/Threading/Primitives/AuMutex.NT.cpp
@@ -48,10 +48,15 @@ namespace Aurora::Threading::Primitives
     {
         return DoTryIf([=]()
         {
-            return AuAtomicTestAndSet(&this->state_, 0) == 0;
+            return this->TryLockNoSpin();
         });
     }
 
+    bool MutexImpl::TryLockNoSpin()
+    {
+        return AuAtomicTestAndSet(&this->state_, 0) == 0;
+    }
+
     bool MutexImpl::HasLockImplementation()
     {
         return true;
@@ -77,7 +82,7 @@ namespace Aurora::Threading::Primitives
     {
         bool returnValue = false;
 
-        if (TryLock())
+        if (this->TryLock())
         {
             return true;
         }
@@ -87,7 +92,7 @@ namespace Aurora::Threading::Primitives
 
         if (gUseNativeWaitMutex)
         {
-            while (!TryLock())
+            while (!this->TryLockNoSpin())
             {
                 auto &uValueRef = this->state_;
                 auto uValue = uValueRef | 1;
@@ -110,13 +115,13 @@ namespace Aurora::Threading::Primitives
             ::AcquireSRWLockShared(&this->atomicHolder_);
 
             BOOL status = false;
-            while (!this->TryLock())
+            while (!this->TryLockNoSpin())
             {
                 AuUInt32 uTimeoutMS = INFINITE;
 
                 if (uTimeout != 0)
                 {
-                    uStartTime = Time::SteadyClockNS();
+                    auto uStartTime = Time::SteadyClockNS();
                     if (uStartTime >= uEndTime)
                     {
                         goto exitWin32;
@@ -146,7 +151,7 @@ namespace Aurora::Threading::Primitives
 
             if (!uTimeout)
             {
-                while (!TryLock())
+                while (!this->TryLockNoSpin())
                 {
                     auto &uValueRef = this->state_;
                     auto uValue = uValueRef | 1;
@@ -169,14 +174,14 @@ namespace Aurora::Threading::Primitives
                 auto uEndTimeWall   = AuTime::CurrentClockNS() + uTimeout;
                 bool bFailed {};
 
-                while (bFailed || (!TryLock()))
+                while (bFailed || (!this->TryLockNoSpin()))
                 {
                     auto uValue = uValueRef | 1;
 
                     if (!bFailed &&
                         AuTime::SteadyClockNS() >= uEndTimeSteady)
                     {
-                        returnValue = TryLock();
+                        returnValue = this->TryLock();
                         break;
                     }
 
diff --git a/Source/Threading/Primitives/AuMutex.NT.hpp b/Source/Threading/Primitives/AuMutex.NT.hpp
index 1a338ea8..dd8944e9 100644
--- a/Source/Threading/Primitives/AuMutex.NT.hpp
+++ b/Source/Threading/Primitives/AuMutex.NT.hpp
@@ -22,6 +22,8 @@ namespace Aurora::Threading::Primitives
         bool LockNS(AuUInt64 timeout) override;
         void Unlock() override;
 
+       auline bool TryLockNoSpin();
+
     private:
     #if defined(AURORA_FORCE_SRW_LOCKS)
         SRWLOCK atomicHolder_;