From 2b0ed79729d0fa7e9272a7d85e27f39605086dda Mon Sep 17 00:00:00 2001
From: Jamie Reece Wilson <me@reece.sx>
Date: Thu, 8 Feb 2024 03:54:48 +0000
Subject: [PATCH] [*] NT Condvar hardening: Windows XP-7 hardening of the spin
 condition when racing against multiple threads

---
 .../Primitives/AuConditionVariable.NT.cpp     | 45 +++++++++++++++++++
 .../Primitives/AuConditionVariable.NT.hpp     |  1 +
 2 files changed, 46 insertions(+)

diff --git a/Source/Threading/Primitives/AuConditionVariable.NT.cpp b/Source/Threading/Primitives/AuConditionVariable.NT.cpp
index 2479dd21..a890823f 100644
--- a/Source/Threading/Primitives/AuConditionVariable.NT.cpp
+++ b/Source/Threading/Primitives/AuConditionVariable.NT.cpp
@@ -158,6 +158,11 @@ namespace Aurora::Threading::Primitives
                         return true;
                     }
 
+                    if (!gUseNativeWaitCondvar)
+                    {
+                        this->SignalSpuriously();
+                    }
+                    
                     this->AddWaiter();
                 }
             }
@@ -213,6 +218,11 @@ namespace Aurora::Threading::Primitives
                     return bRet;
                 }
 
+                if (!gUseNativeWaitCondvar)
+                {
+                    this->SignalSpuriously();
+                }
+
                 this->AddWaiter();
             }
         }
@@ -324,6 +334,41 @@ namespace Aurora::Threading::Primitives
         });
     #endif
     }
+    
+    void ConditionVariableNT::SignalSpuriously()
+    {
+    #if !defined(AURORA_FORCE_SRW_LOCKS)
+        auto original = this->wlist;
+        auto expected = original;
+        expected = expected >> kShiftCountByBits;
+
+        if (expected)
+        {
+            // NOTE: missing this->signalCount atomic increment to force another AddWaiter under successful keyedevent return
+            while (expected)
+            {
+                if (AuAtomicCompareExchange(&this->wlist, ((expected - 1) << kShiftCountByBits)  /*intentional clear*/, original) == original)
+                {
+                    if (gUseNativeWaitCondvar)
+                    {
+                        InternalLTSWakeOne((void *)&this->wlist);
+                    }
+                    else
+                    {
+                        pNtReleaseKeyedEvent(gKeyedEventHandle, (void *)&this->wlist, FALSE, nullptr);
+                    }
+
+                    return;
+                }
+
+                original = this->wlist;
+                expected = original >> kShiftCountByBits;
+            }
+        }
+    #else
+        ::WakeConditionVariable(&this->winCond_);
+    #endif
+    }
 
     void ConditionVariableNT::Signal()
     {
diff --git a/Source/Threading/Primitives/AuConditionVariable.NT.hpp b/Source/Threading/Primitives/AuConditionVariable.NT.hpp
index ae9c38ff..ecaa123b 100644
--- a/Source/Threading/Primitives/AuConditionVariable.NT.hpp
+++ b/Source/Threading/Primitives/AuConditionVariable.NT.hpp
@@ -19,6 +19,7 @@ namespace Aurora::Threading::Primitives
         
         bool WaitForSignalNsEx(Win32ConditionMutex *pMutex, AuUInt64 timeout, bool bSpin = true);
         void Signal();
+        auline void SignalSpuriously();
         void Broadcast();
         void BroadcastN(AuUInt32 nBroadcast);