From 3be79a33b059ba22f25c7db93743b758717d8b68 Mon Sep 17 00:00:00 2001
From: Augustin Cavalier <waddlesplash@gmail.com>
Date: Thu, 5 Sep 2024 17:45:31 -0400
Subject: [PATCH] kernel/util: Introduce BumpAllocator.

A basic bump allocator that can handle arbitrary amounts of allocations,
so long as all are allocated and freed in a "stack"-like manner.

(Actually it could be extended to support non-stack-like operation,
but that would require more logic that isn't needed at the moment.)

Change-Id: I47077146ea282600130778d312f7d86bd8c032e0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8238
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Reviewed-by: Michael Lotz <mmlr@mlotz.ch>
---
 .../build/private/kernel/util/BumpAllocator.h |   1 +
 headers/private/kernel/util/BumpAllocator.h   | 112 ++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 headers/build/private/kernel/util/BumpAllocator.h
 create mode 100644 headers/private/kernel/util/BumpAllocator.h

diff --git a/headers/build/private/kernel/util/BumpAllocator.h b/headers/build/private/kernel/util/BumpAllocator.h
new file mode 100644
index 0000000000..614d216e8d
--- /dev/null
+++ b/headers/build/private/kernel/util/BumpAllocator.h
@@ -0,0 +1 @@
+#include <../private/kernel/util/BumpAllocator.h>
diff --git a/headers/private/kernel/util/BumpAllocator.h b/headers/private/kernel/util/BumpAllocator.h
new file mode 100644
index 0000000000..ad6660e552
--- /dev/null
+++ b/headers/private/kernel/util/BumpAllocator.h
@@ -0,0 +1,112 @@
+/*
+ * Copyright 2024, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _BUMP_ALLOCATOR_H
+#define _BUMP_ALLOCATOR_H
+
+
+#include <stdlib.h>
+
+#include <OS.h>
+#include <SupportDefs.h>
+
+
+template<size_t InlineDataSize = (16 * sizeof(void*)), size_t SlabSize = 4096>
+class BumpAllocator {
+public:
+	BumpAllocator()
+		:
+		fCurrentSlab((Slab*)fInlineData)
+	{
+		fCurrentSlab->previous = NULL;
+		fCurrentSlab->total = sizeof(fInlineData) - sizeof(Slab);
+		fCurrentSlab->remaining = fCurrentSlab->total;
+	}
+
+	~BumpAllocator()
+	{
+		if (fCurrentSlab != (Slab*)fInlineData)
+			Free(NULL);
+
+		if (!IsEmpty())
+			debugger("BumpAllocator: deleted with allocations still active!");
+	}
+
+	bool IsEmpty() const
+	{
+		return fCurrentSlab == (Slab*)fInlineData
+			&& fCurrentSlab->remaining == fCurrentSlab->total;
+	}
+
+	void* Allocate(size_t _size)
+	{
+		const size_t size = _size + sizeof(Allocation);
+		if (size > SlabSize)
+			debugger("BumpAllocator: can't allocate larger than the slab size");
+		if (fCurrentSlab->remaining < size) {
+			// We need a new slab.
+			Slab* newSlab = (Slab*)malloc(SlabSize);
+			if (newSlab == NULL)
+				return NULL;
+
+			newSlab->previous = fCurrentSlab;
+			newSlab->total = SlabSize - sizeof(Slab);
+			newSlab->remaining = newSlab->total;
+			fCurrentSlab = newSlab;
+		}
+
+		fCurrentSlab->remaining -= size;
+		uint8* pointer = fCurrentSlab->data + fCurrentSlab->remaining;
+
+		Allocation* allocation = (Allocation*)pointer;
+		allocation->size = size;
+		return allocation->data;
+	}
+
+	void Free(void* _pointer)
+	{
+		if (fCurrentSlab->remaining == fCurrentSlab->total) {
+			// Free the current slab.
+			Slab* previous = fCurrentSlab->previous;
+			free(fCurrentSlab);
+			fCurrentSlab = previous;
+		}
+		if (_pointer == NULL)
+			return;
+
+		Allocation* allocation = (((Allocation*)_pointer) - 1);
+
+		// This needs to be the last thing allocated.
+		uint8* last = fCurrentSlab->data + fCurrentSlab->remaining;
+		if ((uint8*)allocation != last) {
+			debugger("BumpAllocator: out-of-order free");
+			return;
+		}
+
+		fCurrentSlab->remaining += allocation->size;
+	}
+
+private:
+#if __cplusplus >= 201103L
+#	define FLA_SIZE
+#else
+#	define FLA_SIZE 0
+#endif
+	struct Slab {
+		Slab*		previous;
+		uint32		total;
+		uint32		remaining;
+		uint8		data[FLA_SIZE];
+	};
+	struct Allocation {
+		uint32		size;	/*!< includes sizeof(Allocation) */
+		uint32		_pad;
+		uint8		data[FLA_SIZE];
+#undef FLA_SIZE
+	};
+	Slab*			fCurrentSlab;
+	uint8			fInlineData[InlineDataSize - sizeof(Slab*)];
+};
+
+#endif	/* _BUMP_ALLOCATOR_H */