Move partial unmap handler to the native signal handler (#3437)

* Initial commit with a lot of testing stuff.

* Partial Unmap Cleanup Part 1

* Fix some minor issues, hopefully windows tests.

* Disable partial unmap tests on macos for now

Weird issue.

* Goodbye magic number

* Add COMPlus_EnableAlternateStackCheck for tests

`COMPlus_EnableAlternateStackCheck` is needed for NullReferenceException handling to work on linux after registering the signal handler, due to how dotnet registers its own signal handler.

* Address some feedback

* Force retry when memory is mapped in memory tracking

This case existed before, but returning `false` no longer retries, so it would crash immediately after unprotecting the memory... Now, we return `true` to deliberately retry.

This case existed before (was just broken by this change) and I don't really want to look into fixing the issue right now. Technically, this means that on guest code partial unmaps will retry _due to this_ rather than hitting the handler. I don't expect this to cause any issues.

This should fix random crashes in Xenoblade Chronicles 2.

* Use IsRangeMapped

* Suppress MockMemoryManager.UnmapEvent warning

This event is not signalled by the mock memory manager.

* Remove 4kb mapping

3 files changed, 80 insertions, 232 deletions

diff --git a/Ryujinx.Memory/WindowsShared/PlaceholderManager.cs b/Ryujinx.Memory/WindowsShared/PlaceholderManager.cs
index 1b425d66..0937d462 100644
--- a/Ryujinx.Memory/WindowsShared/PlaceholderManager.cs
+++ b/Ryujinx.Memory/WindowsShared/PlaceholderManager.cs
@@ -1,5 +1,7 @@
+using Ryujinx.Common.Memory.PartialUnmaps;
 using System;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Runtime.Versioning;
 using System.Threading;
 
@@ -13,13 +15,10 @@ namespace Ryujinx.Memory.WindowsShared
     {
         private const ulong MinimumPageSize = 0x1000;
 
-        [ThreadStatic]
-        private static int _threadLocalPartialUnmapsCount;
-
         private readonly IntervalTree<ulong, ulong> _mappings;
         private readonly IntervalTree<ulong, MemoryPermission> _protections;
-        private readonly ReaderWriterLock _partialUnmapLock;
-        private int _partialUnmapsCount;
+        private readonly IntPtr _partialUnmapStatePtr;
+        private readonly Thread _partialUnmapTrimThread;
 
         /// <summary>
         /// Creates a new instance of the Windows memory placeholder manager.
@@ -28,7 +27,35 @@ namespace Ryujinx.Memory.WindowsShared
         {
             _mappings = new IntervalTree<ulong, ulong>();
             _protections = new IntervalTree<ulong, MemoryPermission>();
-            _partialUnmapLock = new ReaderWriterLock();
+
+            _partialUnmapStatePtr = PartialUnmapState.GlobalState;
+
+            _partialUnmapTrimThread = new Thread(TrimThreadLocalMapLoop);
+            _partialUnmapTrimThread.Name = "CPU.PartialUnmapTrimThread";
+            _partialUnmapTrimThread.IsBackground = true;
+            _partialUnmapTrimThread.Start();
+        }
+
+        /// <summary>
+        /// Gets a reference to the partial unmap state struct.
+        /// </summary>
+        /// <returns>A reference to the partial unmap state struct</returns>
+        private unsafe ref PartialUnmapState GetPartialUnmapState()
+        {
+            return ref Unsafe.AsRef<PartialUnmapState>((void*)_partialUnmapStatePtr);
+        }
+
+        /// <summary>
+        /// Trims inactive threads from the partial unmap state's thread mapping every few seconds.
+        /// Should be run in a Background thread so that it doesn't stop the program from closing.
+        /// </summary>
+        private void TrimThreadLocalMapLoop()
+        {
+            while (true)
+            {
+                Thread.Sleep(2000);
+                GetPartialUnmapState().TrimThreads();
+            }
         }
 
         /// <summary>
@@ -98,7 +125,8 @@ namespace Ryujinx.Memory.WindowsShared
         /// <param name="owner">Memory block that owns the mapping</param>
         public void MapView(IntPtr sharedMemory, ulong srcOffset, IntPtr location, IntPtr size, MemoryBlock owner)
         {
-            _partialUnmapLock.AcquireReaderLock(Timeout.Infinite);
+            ref var partialUnmapLock = ref GetPartialUnmapState().PartialUnmapLock;
+            partialUnmapLock.AcquireReaderLock();
 
             try
             {
@@ -107,7 +135,7 @@ namespace Ryujinx.Memory.WindowsShared
             }
             finally
             {
-                _partialUnmapLock.ReleaseReaderLock();
+                partialUnmapLock.ReleaseReaderLock();
             }
         }
 
@@ -221,7 +249,8 @@ namespace Ryujinx.Memory.WindowsShared
         /// <param name="owner">Memory block that owns the mapping</param>
         public void UnmapView(IntPtr sharedMemory, IntPtr location, IntPtr size, MemoryBlock owner)
         {
-            _partialUnmapLock.AcquireReaderLock(Timeout.Infinite);
+            ref var partialUnmapLock = ref GetPartialUnmapState().PartialUnmapLock;
+            partialUnmapLock.AcquireReaderLock();
 
             try
             {
@@ -229,7 +258,7 @@ namespace Ryujinx.Memory.WindowsShared
             }
             finally
             {
-                _partialUnmapLock.ReleaseReaderLock();
+                partialUnmapLock.ReleaseReaderLock();
             }
         }
 
@@ -265,11 +294,6 @@ namespace Ryujinx.Memory.WindowsShared
 
                 if (IsMapped(overlap.Value))
                 {
-                    if (!WindowsApi.UnmapViewOfFile2(WindowsApi.CurrentProcessHandle, (IntPtr)overlap.Start, 2))
-                    {
-                        throw new WindowsApiException("UnmapViewOfFile2");
-                    }
-
                     // Tree operations might modify the node start/end values, so save a copy before we modify the tree.
                     ulong overlapStart = overlap.Start;
                     ulong overlapEnd = overlap.End;
@@ -291,30 +315,46 @@ namespace Ryujinx.Memory.WindowsShared
                         // This is necessary because Windows does not support partial view unmaps.
                         // That is, you can only fully unmap a view that was previously mapped, you can't just unmap a chunck of it.
 
-                        LockCookie lockCookie = _partialUnmapLock.UpgradeToWriterLock(Timeout.Infinite);
-
-                        _partialUnmapsCount++;
+                        ref var partialUnmapState = ref GetPartialUnmapState();
+                        ref var partialUnmapLock = ref partialUnmapState.PartialUnmapLock;
+                        partialUnmapLock.UpgradeToWriterLock();
 
-                        if (overlapStartsBefore)
+                        try
                         {
-                            ulong remapSize = startAddress - overlapStart;
-
-                            MapViewInternal(sharedMemory, overlapValue, (IntPtr)overlapStart, (IntPtr)remapSize);
-                            RestoreRangeProtection(overlapStart, remapSize);
+                            partialUnmapState.PartialUnmapsCount++;
+
+                            if (!WindowsApi.UnmapViewOfFile2(WindowsApi.CurrentProcessHandle, (IntPtr)overlapStart, 2))
+                            {
+                                throw new WindowsApiException("UnmapViewOfFile2");
+                            }
+
+                            if (overlapStartsBefore)
+                            {
+                                ulong remapSize = startAddress - overlapStart;
+
+                                MapViewInternal(sharedMemory, overlapValue, (IntPtr)overlapStart, (IntPtr)remapSize);
+                                RestoreRangeProtection(overlapStart, remapSize);
+                            }
+
+                            if (overlapEndsAfter)
+                            {
+                                ulong overlappedSize = endAddress - overlapStart;
+                                ulong remapBackingOffset = overlapValue + overlappedSize;
+                                ulong remapAddress = overlapStart + overlappedSize;
+                                ulong remapSize = overlapEnd - endAddress;
+
+                                MapViewInternal(sharedMemory, remapBackingOffset, (IntPtr)remapAddress, (IntPtr)remapSize);
+                                RestoreRangeProtection(remapAddress, remapSize);
+                            }
                         }
-
-                        if (overlapEndsAfter)
+                        finally
                         {
-                            ulong overlappedSize = endAddress - overlapStart;
-                            ulong remapBackingOffset = overlapValue + overlappedSize;
-                            ulong remapAddress = overlapStart + overlappedSize;
-                            ulong remapSize = overlapEnd - endAddress;
-
-                            MapViewInternal(sharedMemory, remapBackingOffset, (IntPtr)remapAddress, (IntPtr)remapSize);
-                            RestoreRangeProtection(remapAddress, remapSize);
+                            partialUnmapLock.DowngradeFromWriterLock();
                         }
-
-                        _partialUnmapLock.DowngradeFromWriterLock(ref lockCookie);
+                    }
+                    else if (!WindowsApi.UnmapViewOfFile2(WindowsApi.CurrentProcessHandle, (IntPtr)overlapStart, 2))
+                    {
+                        throw new WindowsApiException("UnmapViewOfFile2");
                     }
                 }
             }
@@ -394,7 +434,8 @@ namespace Ryujinx.Memory.WindowsShared
         /// <returns>True if the reprotection was successful, false otherwise</returns>
         public bool ReprotectView(IntPtr address, IntPtr size, MemoryPermission permission)
         {
-            _partialUnmapLock.AcquireReaderLock(Timeout.Infinite);
+            ref var partialUnmapLock = ref GetPartialUnmapState().PartialUnmapLock;
+            partialUnmapLock.AcquireReaderLock();
 
             try
             {
@@ -402,7 +443,7 @@ namespace Ryujinx.Memory.WindowsShared
             }
             finally
             {
-                _partialUnmapLock.ReleaseReaderLock();
+                partialUnmapLock.ReleaseReaderLock();
             }
         }
 
@@ -659,31 +700,5 @@ namespace Ryujinx.Memory.WindowsShared
                 ReprotectViewInternal((IntPtr)protAddress, (IntPtr)(protEndAddress - protAddress), protection.Value, true);
             }
         }
-
-        /// <summary>
-        /// Checks if an access violation handler should retry execution due to a fault caused by partial unmap.
-        /// </summary>
-        /// <remarks>
-        /// Due to Windows limitations, <see cref="UnmapView"/> might need to unmap more memory than requested.
-        /// The additional memory that was unmapped is later remapped, however this leaves a time gap where the
-        /// memory might be accessed but is unmapped. Users of the API must compensate for that by catching the
-        /// access violation and retrying if it happened between the unmap and remap operation.
-        /// This method can be used to decide if retrying in such cases is necessary or not.
-        /// </remarks>
-        /// <returns>True if execution should be retried, false otherwise</returns>
-        public bool RetryFromAccessViolation()
-        {
-            _partialUnmapLock.AcquireReaderLock(Timeout.Infinite);
-
-            bool retry = _threadLocalPartialUnmapsCount != _partialUnmapsCount;
-            if (retry)
-            {
-                _threadLocalPartialUnmapsCount = _partialUnmapsCount;
-            }
-
-            _partialUnmapLock.ReleaseReaderLock();
-
-            return retry;
-        }
     }
 }
\ No newline at end of file
diff --git a/Ryujinx.Memory/WindowsShared/PlaceholderManager4KB.cs b/Ryujinx.Memory/WindowsShared/PlaceholderManager4KB.cs
deleted file mode 100644
index fc056a2f..00000000
--- a/Ryujinx.Memory/WindowsShared/PlaceholderManager4KB.cs
+++ /dev/null
@@ -1,170 +0,0 @@
-using System;
-using System.Runtime.Versioning;
-
-namespace Ryujinx.Memory.WindowsShared
-{
-    /// <summary>
-    /// Windows 4KB memory placeholder manager.
-    /// </summary>
-    [SupportedOSPlatform("windows")]
-    class PlaceholderManager4KB
-    {
-        private const int PageSize = MemoryManagementWindows.PageSize;
-
-        private readonly IntervalTree<ulong, byte> _mappings;
-
-        /// <summary>
-        /// Creates a new instance of the Windows 4KB memory placeholder manager.
-        /// </summary>
-        public PlaceholderManager4KB()
-        {
-            _mappings = new IntervalTree<ulong, byte>();
-        }
-
-        /// <summary>
-        /// Unmaps the specified range of memory and marks it as mapped internally.
-        /// </summary>
-        /// <remarks>
-        /// Since this marks the range as mapped, the expectation is that the range will be mapped after calling this method.
-        /// </remarks>
-        /// <param name="location">Memory address to unmap and mark as mapped</param>
-        /// <param name="size">Size of the range in bytes</param>
-        public void UnmapAndMarkRangeAsMapped(IntPtr location, IntPtr size)
-        {
-            ulong startAddress = (ulong)location;
-            ulong unmapSize = (ulong)size;
-            ulong endAddress = startAddress + unmapSize;
-
-            var overlaps = Array.Empty<IntervalTreeNode<ulong, byte>>();
-            int count = 0;
-
-            lock (_mappings)
-            {
-                count = _mappings.Get(startAddress, endAddress, ref overlaps);
-            }
-
-            for (int index = 0; index < count; index++)
-            {
-                var overlap = overlaps[index];
-
-                // Tree operations might modify the node start/end values, so save a copy before we modify the tree.
-                ulong overlapStart = overlap.Start;
-                ulong overlapEnd = overlap.End;
-                ulong overlapValue = overlap.Value;
-
-                _mappings.Remove(overlap);
-
-                ulong unmapStart = Math.Max(overlapStart, startAddress);
-                ulong unmapEnd = Math.Min(overlapEnd, endAddress);
-
-                if (overlapStart < startAddress)
-                {
-                    startAddress = overlapStart;
-                }
-
-                if (overlapEnd > endAddress)
-                {
-                    endAddress = overlapEnd;
-                }
-
-                ulong currentAddress = unmapStart;
-                while (currentAddress < unmapEnd)
-                {
-                    WindowsApi.UnmapViewOfFile2(WindowsApi.CurrentProcessHandle, (IntPtr)currentAddress, 2);
-                    currentAddress += PageSize;
-                }
-            }
-
-            _mappings.Add(startAddress, endAddress, 0);
-        }
-
-        /// <summary>
-        /// Unmaps views at the specified memory range.
-        /// </summary>
-        /// <param name="location">Address of the range</param>
-        /// <param name="size">Size of the range in bytes</param>
-        public void UnmapView(IntPtr location, IntPtr size)
-        {
-            ulong startAddress = (ulong)location;
-            ulong unmapSize = (ulong)size;
-            ulong endAddress = startAddress + unmapSize;
-
-            var overlaps = Array.Empty<IntervalTreeNode<ulong, byte>>();
-            int count = 0;
-
-            lock (_mappings)
-            {
-                count = _mappings.Get(startAddress, endAddress, ref overlaps);
-            }
-
-            for (int index = 0; index < count; index++)
-            {
-                var overlap = overlaps[index];
-
-                // Tree operations might modify the node start/end values, so save a copy before we modify the tree.
-                ulong overlapStart = overlap.Start;
-                ulong overlapEnd = overlap.End;
-
-                _mappings.Remove(overlap);
-
-                if (overlapStart < startAddress)
-                {
-                    _mappings.Add(overlapStart, startAddress, 0);
-                }
-
-                if (overlapEnd > endAddress)
-                {
-                    _mappings.Add(endAddress, overlapEnd, 0);
-                }
-
-                ulong unmapStart = Math.Max(overlapStart, startAddress);
-                ulong unmapEnd = Math.Min(overlapEnd, endAddress);
-
-                ulong currentAddress = unmapStart;
-                while (currentAddress < unmapEnd)
-                {
-                    WindowsApi.UnmapViewOfFile2(WindowsApi.CurrentProcessHandle, (IntPtr)currentAddress, 2);
-                    currentAddress += PageSize;
-                }
-            }
-        }
-
-        /// <summary>
-        /// Unmaps mapped memory at a given range.
-        /// </summary>
-        /// <param name="location">Address of the range</param>
-        /// <param name="size">Size of the range in bytes</param>
-        public void UnmapRange(IntPtr location, IntPtr size)
-        {
-            ulong startAddress = (ulong)location;
-            ulong unmapSize = (ulong)size;
-            ulong endAddress = startAddress + unmapSize;
-
-            var overlaps = Array.Empty<IntervalTreeNode<ulong, byte>>();
-            int count = 0;
-
-            lock (_mappings)
-            {
-                count = _mappings.Get(startAddress, endAddress, ref overlaps);
-            }
-
-            for (int index = 0; index < count; index++)
-            {
-                var overlap = overlaps[index];
-
-                // Tree operations might modify the node start/end values, so save a copy before we modify the tree.
-                ulong unmapStart = Math.Max(overlap.Start, startAddress);
-                ulong unmapEnd = Math.Min(overlap.End, endAddress);
-
-                _mappings.Remove(overlap);
-
-                ulong currentAddress = unmapStart;
-                while (currentAddress < unmapEnd)
-                {
-                    WindowsApi.UnmapViewOfFile2(WindowsApi.CurrentProcessHandle, (IntPtr)currentAddress, 2);
-                    currentAddress += PageSize;
-                }
-            }
-        }
-    }
-}
\ No newline at end of file
diff --git a/Ryujinx.Memory/WindowsShared/WindowsApi.cs b/Ryujinx.Memory/WindowsShared/WindowsApi.cs
index 297bd1ee..cbb7d99e 100644
--- a/Ryujinx.Memory/WindowsShared/WindowsApi.cs
+++ b/Ryujinx.Memory/WindowsShared/WindowsApi.cs
@@ -76,6 +76,9 @@ namespace Ryujinx.Memory.WindowsShared
         [DllImport("kernel32.dll")]
         public static extern uint GetLastError();
 
+        [DllImport("kernel32.dll")]
+        public static extern int GetCurrentThreadId();
+
         public static MemoryProtection GetProtection(MemoryPermission permission)
         {
             return permission switch