[llvm] [CAS] Add MappedFileRegionBumpPtr (PR #114099)

[Steven Wu via llvm-commits]

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@@ -0,0 +1,127 @@
+//===- MappedFileRegionBumpPtr.h --------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// This file declares interface for MappedFileRegionBumpPtr, a bump pointer
+/// allocator, backed by a memory-mapped file.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CAS_MAPPEDFILEREGIONBUMPPTR_H
+#define LLVM_CAS_MAPPEDFILEREGIONBUMPPTR_H
+
+#include "llvm/Support/Alignment.h"
+#include "llvm/Support/FileSystem.h"
+#include <atomic>
+
+namespace llvm::cas {
+
+/// Allocator for an owned mapped file region that supports thread-safe and
+/// process-safe bump pointer allocation.
+///
+/// This allocator is designed to create a sparse file when supported by the
+/// filesystem's \c ftruncate so that it can be used with a large maximum size.
+/// It will also attempt to shrink the underlying file down to its current
+/// allocation size when the last concurrent mapping is closed.
+///
+/// Process-safe. Uses file locks when resizing the file during initialization
+/// and destruction.
+///
+/// Thread-safe, assuming all threads use the same instance to talk to a given
+/// file/mapping. Unsafe to have multiple instances talking to the same file
+/// in the same process since file locks will misbehave. Clients should
+/// coordinate (somehow).
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cachemeifyoucan wrote:

Removing. This is from old file lock implementation. 

https://github.com/llvm/llvm-project/pull/114099