1 files changed, 80 insertions, 0 deletions
diff --git a/Ryujinx.Common/Memory/PartialUnmaps/NativeReaderWriterLock.cs b/Ryujinx.Common/Memory/PartialUnmaps/NativeReaderWriterLock.cs
new file mode 100644
index 00000000..5419b340
--- /dev/null
+++ b/Ryujinx.Common/Memory/PartialUnmaps/NativeReaderWriterLock.cs
@@ -0,0 +1,80 @@
+using System.Runtime.InteropServices;
+using System.Threading;
+
+using static Ryujinx.Common.Memory.PartialUnmaps.PartialUnmapHelpers;
+
+namespace Ryujinx.Common.Memory.PartialUnmaps
+{
+    /// <summary>
+    /// A simple implementation of a ReaderWriterLock which can be used from native code.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct NativeReaderWriterLock
+    {
+        public int WriteLock;
+        public int ReaderCount;
+
+        public static int WriteLockOffset;
+        public static int ReaderCountOffset;
+
+        /// <summary>
+        /// Populates the field offsets for use when emitting native code.
+        /// </summary>
+        static NativeReaderWriterLock()
+        {
+            NativeReaderWriterLock instance = new NativeReaderWriterLock();
+
+            WriteLockOffset = OffsetOf(ref instance, ref instance.WriteLock);
+            ReaderCountOffset = OffsetOf(ref instance, ref instance.ReaderCount);
+        }
+
+        /// <summary>
+        /// Acquires the reader lock.
+        /// </summary>
+        public void AcquireReaderLock()
+        {
+            // Must take write lock for a very short time to become a reader.
+
+            while (Interlocked.CompareExchange(ref WriteLock, 1, 0) != 0) { }
+
+            Interlocked.Increment(ref ReaderCount);
+
+            Interlocked.Exchange(ref WriteLock, 0);
+        }
+
+        /// <summary>
+        /// Releases the reader lock.
+        /// </summary>
+        public void ReleaseReaderLock()
+        {
+            Interlocked.Decrement(ref ReaderCount);
+        }
+
+        /// <summary>
+        /// Upgrades to a writer lock. The reader lock is temporarily released while obtaining the writer lock.
+        /// </summary>
+        public void UpgradeToWriterLock()
+        {
+            // Prevent any more threads from entering reader.
+            // If the write lock is already taken, wait for it to not be taken.
+
+            Interlocked.Decrement(ref ReaderCount);
+
+            while (Interlocked.CompareExchange(ref WriteLock, 1, 0) != 0) { }
+
+            // Wait for reader count to drop to 0, then take the lock again as the only reader.
+
+            while (Interlocked.CompareExchange(ref ReaderCount, 1, 0) != 0) { }
+        }
+
+        /// <summary>
+        /// Downgrades from a writer lock, back to a reader one.
+        /// </summary>
+        public void DowngradeFromWriterLock()
+        {
+            // Release the WriteLock.
+
+            Interlocked.Exchange(ref WriteLock, 0);
+        }
+    }
+}