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safeOutputFile.h
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1 //
2 // Copyright 2017 Pixar
3 //
4 // Licensed under the Apache License, Version 2.0 (the "Apache License")
5 // with the following modification; you may not use this file except in
6 // compliance with the Apache License and the following modification to it:
7 // Section 6. Trademarks. is deleted and replaced with:
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14 // You may obtain a copy of the Apache License at
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24 #ifndef PXR_BASE_TF_SAFE_OUTPUT_FILE_H
25 #define PXR_BASE_TF_SAFE_OUTPUT_FILE_H
26 
27 /// \file tf/safeOutputFile.h
28 /// Safe file writer with FILE * interface.
29 
30 #include "pxr/pxr.h"
31 #include "pxr/base/tf/api.h"
32 
33 #include <cstdio>
34 #include <memory>
35 #include <string>
36 
38 
39 /// \class TfSafeOutputFile
40 ///
41 /// Opens a file for output, either for update "r+" or to completely replace
42 /// "w+". In the case of complete replacement, create a sibling temporary file
43 /// to write to instead. When writing is complete, rename the temporary file
44 /// over the target file. This provides some safety to other processes reading
45 /// the existing file (at least on unix-like OSs). They will continue to see
46 /// the existing contents of the old file. If we overwrote the file itself,
47 /// then those other processes would see undefined, possibly partially updated
48 /// content.
50 {
51  TfSafeOutputFile(TfSafeOutputFile const &) = delete;
52  TfSafeOutputFile &operator=(TfSafeOutputFile const &) = delete;
53 public:
54  TfSafeOutputFile() = default;
55 
57  : _file(other._file)
58  , _targetFileName(std::move(other._targetFileName))
59  , _tempFileName(std::move(other._tempFileName))
60  { other._file = nullptr; }
61 
63  _file = other._file;
64  _targetFileName = std::move(other._targetFileName);
65  _tempFileName = std::move(other._tempFileName);
66  other._file = nullptr;
67  return *this;
68  }
69 
70  /// Destructor invokes Close().
72 
73  /// Open \p fileName for update ("r+").
74  TF_API static TfSafeOutputFile Update(std::string const &fileName);
75 
76  /// Arrange for \p fileName to be replaced. Create a sibling temporary file
77  /// and open that for writing. When Close() is called (or the destructor is
78  /// run) close the temporary file and rename it over \p fileName.
79  TF_API static TfSafeOutputFile Replace(std::string const &fileName);
80 
81  /// Close the file. If the file was opened with Replace(), rename the
82  /// temporary file over the target file to replace it.
83  TF_API void Close();
84 
85  /// Close the file. If the file was opened with Replace(), the temporary
86  /// file is removed and not renamed over the target file. It is an error
87  /// to call this for files opened for Update.
88  TF_API void Discard();
89 
90  /// Return the opened FILE *.
91  FILE *Get() const { return _file; }
92 
93  /// If the underlying file was opened by Update(), return it. The caller
94  /// takes responsibility for closing the file later. It is an error to call
95  /// this for files opened for Replace.
96  TF_API FILE *ReleaseUpdatedFile();
97 
98  /// Return true if this TfSafeOutputFile was created by a call to Update(),
99  /// false otherwise.
100  TF_API bool IsOpenForUpdate() const;
101 
102 private:
103  FILE *_file = nullptr;
104  std::string _targetFileName;
105  std::string _tempFileName;
106 };
107 
109 
110 #endif // PXR_BASE_TF_SAFE_OUTPUT_FILE_H
static TF_API TfSafeOutputFile Replace(std::string const &fileName)
#define TF_API
Definition: api.h:40
TF_API bool IsOpenForUpdate() const
FILE * Get() const
Return the opened FILE *.
TF_API FILE * ReleaseUpdatedFile()
TfSafeOutputFile & operator=(TfSafeOutputFile &&other)
static TF_API TfSafeOutputFile Update(std::string const &fileName)
Open fileName for update ("r+").
TF_API ~TfSafeOutputFile()
Destructor invokes Close().
GLsizei const GLchar *const * string
Definition: glew.h:1844
PXR_NAMESPACE_CLOSE_SCOPE PXR_NAMESPACE_OPEN_SCOPE
Definition: path.h:1346
TF_API void Close()
#define PXR_NAMESPACE_CLOSE_SCOPE
Definition: pxr.h:91
TF_API void Discard()
TfSafeOutputFile()=default
TfSafeOutputFile(TfSafeOutputFile &&other)