1 //=== FileOutputBuffer.h - File Output Buffer -------------------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
9 // Utility for creating a in-memory buffer that will be written to a file.
11 //===----------------------------------------------------------------------===//
13 #ifndef LLVM_SUPPORT_FILEOUTPUTBUFFER_H
14 #define LLVM_SUPPORT_FILEOUTPUTBUFFER_H
16 #include "llvm/ADT/SmallString.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/Support/DataTypes.h"
19 #include "llvm/Support/Error.h"
20 #include "llvm/Support/FileSystem.h"
23 /// FileOutputBuffer - This interface provides simple way to create an in-memory
24 /// buffer which will be written to a file. During the lifetime of these
25 /// objects, the content or existence of the specified file is undefined. That
26 /// is, creating an OutputBuffer for a file may immediately remove the file.
27 /// If the FileOutputBuffer is committed, the target file's content will become
28 /// the buffer content at the time of the commit. If the FileOutputBuffer is
29 /// not committed, the file will be deleted in the FileOutputBuffer destructor.
30 class FileOutputBuffer {
33 /// set the 'x' bit on the resulting file
36 /// Don't use mmap and instead write an in-memory buffer to a file when this
41 /// Factory method to create an OutputBuffer object which manages a read/write
42 /// buffer of the specified size. When committed, the buffer will be written
43 /// to the file at the specified path.
45 /// When F_modify is specified and \p FilePath refers to an existing on-disk
46 /// file \p Size may be set to -1, in which case the entire file is used.
47 /// Otherwise, the file shrinks or grows as necessary based on the value of
48 /// \p Size. It is an error to specify F_modify and Size=-1 if \p FilePath
50 static Expected<std::unique_ptr<FileOutputBuffer>>
51 create(StringRef FilePath, size_t Size, unsigned Flags = 0);
53 /// Returns a pointer to the start of the buffer.
54 virtual uint8_t *getBufferStart() const = 0;
56 /// Returns a pointer to the end of the buffer.
57 virtual uint8_t *getBufferEnd() const = 0;
59 /// Returns size of the buffer.
60 virtual size_t getBufferSize() const = 0;
62 /// Returns path where file will show up if buffer is committed.
63 StringRef getPath() const { return FinalPath; }
65 /// Flushes the content of the buffer to its file and deallocates the
66 /// buffer. If commit() is not called before this object's destructor
67 /// is called, the file is deleted in the destructor. The optional parameter
68 /// is used if it turns out you want the file size to be smaller than
69 /// initially requested.
70 virtual Error commit() = 0;
72 /// If this object was previously committed, the destructor just deletes
73 /// this object. If this object was not committed, the destructor
74 /// deallocates the buffer and the target file is never written.
75 virtual ~FileOutputBuffer() {}
77 /// This removes the temporary file (unless it already was committed)
78 /// but keeps the memory mapping alive.
79 virtual void discard() {}
82 FileOutputBuffer(StringRef Path) : FinalPath(Path) {}
84 std::string FinalPath;
86 } // end namespace llvm