From 20d28e80a5c861a9d5f449ea911ab75b4f37ad0d Mon Sep 17 00:00:00 2001
From: Jef <jef@targetspot.com>
Date: Tue, 24 Sep 2024 14:54:57 +0200
Subject: Initial community commit

---
 Src/nu/LockFreeItem.h | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 Src/nu/LockFreeItem.h

(limited to 'Src/nu/LockFreeItem.h')

diff --git a/Src/nu/LockFreeItem.h b/Src/nu/LockFreeItem.h
new file mode 100644
index 00000000..b3cc0649
--- /dev/null
+++ b/Src/nu/LockFreeItem.h
@@ -0,0 +1,47 @@
+#pragma once
+#include <windows.h>
+
+/* This data structure holds one item, and returns you the old item when you replace it 
+   it's sort of a "stack of 1" */
+
+template <class value_t>
+class LockFreeItem
+{
+public:
+	typedef value_t *ptr_t;
+	LockFreeItem() { item = 0; }
+	
+	value_t *GetItem()
+	{
+		for(;;) // keep trying until we get this right
+		{
+			volatile ptr_t ret;
+			InterlockedExchangePointer(&ret, item);
+			if (InterlockedCompareExchangePointer((volatile PVOID *)&item, 0, ret) == ret)
+				return ret;
+		}
+	}
+
+	// returns the previous value
+	value_t *SetItem(value_t *new_item)
+	{
+		for(;;) // keep trying until we get this right
+		{
+			volatile ptr_t ret;
+			InterlockedExchangePointer(&ret, item);
+			if (InterlockedCompareExchangePointer((volatile PVOID *)&item, new_item, ret) == ret)
+				return ret;
+		}
+	}
+
+	// if there's already a value, returns what you passed in
+	value_t *SetItemIfZero(value_t *new_item)
+	{
+		if (InterlockedCompareExchangePointer((volatile PVOID *)&item, new_item, 0) == 0)
+				return 0;
+		else
+			return new_item;
+	}
+
+	volatile ptr_t item;
+};
\ No newline at end of file
-- 
cgit