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FileOutputBuffer creates a temp file and on commit atomically renames the temp file to the destination file. Sometimes we want to modify an existing file in place, but still have the atomicity guarantee. To do this we can initialize the contents of the temp file from the destination file (if it exists), that way the resulting FileOutputBuffer can have only selective bytes modified. Committing will then atomically replace the destination file as desired. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335902 91177308-0d34-0410-b5e6-96231b3b80d8
87 lines
3.3 KiB
C++
87 lines
3.3 KiB
C++
//=== FileOutputBuffer.h - File Output Buffer -------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Utility for creating a in-memory buffer that will be written to a file.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_FILEOUTPUTBUFFER_H
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#define LLVM_SUPPORT_FILEOUTPUTBUFFER_H
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#include "llvm/ADT/SmallString.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/Support/DataTypes.h"
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#include "llvm/Support/Error.h"
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#include "llvm/Support/FileSystem.h"
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namespace llvm {
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/// FileOutputBuffer - This interface provides simple way to create an in-memory
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/// buffer which will be written to a file. During the lifetime of these
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/// objects, the content or existence of the specified file is undefined. That
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/// is, creating an OutputBuffer for a file may immediately remove the file.
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/// If the FileOutputBuffer is committed, the target file's content will become
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/// the buffer content at the time of the commit. If the FileOutputBuffer is
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/// not committed, the file will be deleted in the FileOutputBuffer destructor.
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class FileOutputBuffer {
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public:
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enum {
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/// set the 'x' bit on the resulting file
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F_executable = 1,
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/// the contents of the new file are initialized from the file that exists
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/// at the location (if present). This allows in-place modification of an
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/// existing file.
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F_modify = 2
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};
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/// Factory method to create an OutputBuffer object which manages a read/write
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/// buffer of the specified size. When committed, the buffer will be written
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/// to the file at the specified path.
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///
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/// When F_modify is specified and \p FilePath refers to an existing on-disk
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/// file \p Size may be set to -1, in which case the entire file is used.
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/// Otherwise, the file shrinks or grows as necessary based on the value of
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/// \p Size. It is an error to specify F_modify and Size=-1 if \p FilePath
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/// does not exist.
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static Expected<std::unique_ptr<FileOutputBuffer>>
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create(StringRef FilePath, size_t Size, unsigned Flags = 0);
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/// Returns a pointer to the start of the buffer.
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virtual uint8_t *getBufferStart() const = 0;
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/// Returns a pointer to the end of the buffer.
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virtual uint8_t *getBufferEnd() const = 0;
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/// Returns size of the buffer.
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virtual size_t getBufferSize() const = 0;
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/// Returns path where file will show up if buffer is committed.
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StringRef getPath() const { return FinalPath; }
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/// Flushes the content of the buffer to its file and deallocates the
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/// buffer. If commit() is not called before this object's destructor
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/// is called, the file is deleted in the destructor. The optional parameter
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/// is used if it turns out you want the file size to be smaller than
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/// initially requested.
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virtual Error commit() = 0;
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/// If this object was previously committed, the destructor just deletes
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/// this object. If this object was not committed, the destructor
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/// deallocates the buffer and the target file is never written.
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virtual ~FileOutputBuffer() {}
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protected:
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FileOutputBuffer(StringRef Path) : FinalPath(Path) {}
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std::string FinalPath;
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};
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} // end namespace llvm
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#endif
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