1//=== FileOutputBuffer.h - File Output Buffer -------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Utility for creating a in-memory buffer that will be written to a file.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_SUPPORT_FILEOUTPUTBUFFER_H
14#define LLVM_SUPPORT_FILEOUTPUTBUFFER_H
15
16#include "llvm/ADT/StringRef.h"
17#include "llvm/Support/DataTypes.h"
18#include "llvm/Support/Error.h"
19
20namespace llvm {
21/// FileOutputBuffer - This interface provides simple way to create an in-memory
22/// buffer which will be written to a file. During the lifetime of these
23/// objects, the content or existence of the specified file is undefined. That
24/// is, creating an OutputBuffer for a file may immediately remove the file.
25/// If the FileOutputBuffer is committed, the target file's content will become
26/// the buffer content at the time of the commit. If the FileOutputBuffer is
27/// not committed, the file will be deleted in the FileOutputBuffer destructor.
28class FileOutputBuffer {
29public:
30 enum {
31 /// Set the 'x' bit on the resulting file.
32 F_executable = 1,
33
34 /// Don't use mmap and instead write an in-memory buffer to a file when this
35 /// buffer is closed.
36 F_no_mmap = 2,
37 };
38
39 /// Factory method to create an OutputBuffer object which manages a read/write
40 /// buffer of the specified size. When committed, the buffer will be written
41 /// to the file at the specified path.
42 ///
43 /// When F_modify is specified and \p FilePath refers to an existing on-disk
44 /// file \p Size may be set to -1, in which case the entire file is used.
45 /// Otherwise, the file shrinks or grows as necessary based on the value of
46 /// \p Size. It is an error to specify F_modify and Size=-1 if \p FilePath
47 /// does not exist.
48 static Expected<std::unique_ptr<FileOutputBuffer>>
49 create(StringRef FilePath, size_t Size, unsigned Flags = 0);
50
51 /// Returns a pointer to the start of the buffer.
52 virtual uint8_t *getBufferStart() const = 0;
53
54 /// Returns a pointer to the end of the buffer.
55 virtual uint8_t *getBufferEnd() const = 0;
56
57 /// Returns size of the buffer.
58 virtual size_t getBufferSize() const = 0;
59
60 /// Returns path where file will show up if buffer is committed.
61 StringRef getPath() const { return FinalPath; }
62
63 /// Flushes the content of the buffer to its file and deallocates the
64 /// buffer. If commit() is not called before this object's destructor
65 /// is called, the file is deleted in the destructor. The optional parameter
66 /// is used if it turns out you want the file size to be smaller than
67 /// initially requested.
68 virtual Error commit() = 0;
69
70 /// If this object was previously committed, the destructor just deletes
71 /// this object. If this object was not committed, the destructor
72 /// deallocates the buffer and the target file is never written.
73 virtual ~FileOutputBuffer() {}
74
75 /// This removes the temporary file (unless it already was committed)
76 /// but keeps the memory mapping alive.
77 virtual void discard() {}
78
79protected:
80 FileOutputBuffer(StringRef Path) : FinalPath(Path) {}
81
82 std::string FinalPath;
83};
84} // end namespace llvm
85
86#endif
87