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: 8 // 9 // 6. Trademarks. This License does not grant permission to use the trade 10 // names, trademarks, service marks, or product names of the Licensor 11 // and its affiliates, except as required to comply with Section 4(c) of 12 // the License and to reproduce the content of the NOTICE file. 13 // 14 // You may obtain a copy of the Apache License at 15 // 16 // http://www.apache.org/licenses/LICENSE-2.0 17 // 18 // Unless required by applicable law or agreed to in writing, software 19 // distributed under the Apache License with the above modification is 20 // distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 21 // KIND, either express or implied. See the Apache License for the specific 22 // language governing permissions and limitations under the Apache License. 23 // 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 37 PXR_NAMESPACE_OPEN_SCOPE 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. 49 class TfSafeOutputFile 50 { 51 TfSafeOutputFile(TfSafeOutputFile const &) = delete; 52 TfSafeOutputFile &operator=(TfSafeOutputFile const &) = delete; 53 public: 54 TfSafeOutputFile() = default; 55 TfSafeOutputFile(TfSafeOutputFile && other)56 TfSafeOutputFile(TfSafeOutputFile &&other) 57 : _file(other._file) 58 , _targetFileName(std::move(other._targetFileName)) 59 , _tempFileName(std::move(other._tempFileName)) 60 { other._file = nullptr; } 61 62 TfSafeOutputFile &operator=(TfSafeOutputFile &&other) { 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(). 71 TF_API ~TfSafeOutputFile(); 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 *. Get()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 }; 107 108 PXR_NAMESPACE_CLOSE_SCOPE 109 110 #endif // PXR_BASE_TF_SAFE_OUTPUT_FILE_H 111