badgerdb::File Class Reference

Class which represents a file in the filesystem containing database pages. More...

#include <file.h>

Inheritance diagram for badgerdb::File:

Public Member Functions
	File (const std::string &name, const bool create_new)
virtual	~File ()
virtual Page	allocatePage (PageId &new_page_number)=0
virtual Page	readPage (const PageId page_number) const =0
virtual void	writePage (const PageId page_number, const Page &new_page)=0
virtual void	deletePage (const PageId page_number)=0
const std::string &	filename () const
PageId	getFirstPageNo ()

Static Public Member Functions
static void	remove (const std::string &filename)
static bool	isOpen (const std::string &filename)
static bool	exists (const std::string &filename)

Protected Types
typedef std::map< std::string, std::shared_ptr< std::fstream > >	StreamMap
typedef std::map< std::string, int >	CountMap

Protected Member Functions
void	openIfNeeded (const bool create_new)
void	close ()
FileHeader	readHeader () const
void	writeHeader (const FileHeader &header)

Static Protected Member Functions
static std::streampos	pagePosition (const PageId page_number)

Protected Attributes
std::string	filename_
std::shared_ptr< std::fstream >	stream_

Static Protected Attributes
static StreamMap	open_streams_
static CountMap	open_counts_

Friends
class	FileIterator

Detailed Description

Class which represents a file in the filesystem containing database pages.

The File class wraps a stream to an underlying file on disk. Files contain fixed-sized pages, and they never deallocate space (though they do reuse deleted pages if possible). If multiple File objects refer to the same underlying file, they will share the stream in memory. If a file that has already been opened (possibly by another query), then the File class detects this (by looking in the open_streams_ map) and just returns a file object with the already created stream for the file without actually opening the UNIX file again.

Warning

This class is not threadsafe.

Definition at line 75 of file file.h.

Constructor & Destructor Documentation

badgerdb::File::File	(	const std::string &	name,
		const bool	create_new
	)

Constructs a file object representing a file on the filesystem.

Parameters

name	Name of file.
create_new	Whether to create a new file.

Exceptions

FileExistsException	If the underlying file exists and create_new is true.
FileNotFoundException	If the underlying file doesn't exist and create_new is false.

Definition at line 67 of file file.cpp.

                                                       : filename_(name) {
  openIfNeeded(create_new);

  if (create_new) {
    // File starts with 1 page (the header).
    FileHeader header = {1 /* num_pages */, 0 /* first_used_page */,
                         0 /* num_free_pages */, 0 /* first_free_page */};
    writeHeader(header);
  }
}

badgerdb::File::~File ( )

virtual

Destructor that automatically closes the underlying file if no other File objects are using it.

Definition at line 57 of file file.cpp.

            {
  close();
}

Member Function Documentation

virtual Page badgerdb::File::allocatePage ( PageId &  new_page_number )

pure virtual

Allocates a new page in the file.

Returns

The new page.

Implemented in badgerdb::BlobFile, and badgerdb::PageFile.

void badgerdb::File::close ( )

protected

Closes the underlying file stream in <stream_>. This method only closes the file if no other File objects exist that access the same file.

Definition at line 105 of file file.cpp.

                 {
  if(open_counts_[filename_] > 0)
    --open_counts_[filename_];

  stream_.reset();
  assert(open_counts_[filename_] >= 0);

  if (open_counts_[filename_] == 0) {
    open_streams_.erase(filename_);
    open_counts_.erase(filename_);
  }
}

virtual void badgerdb::File::deletePage ( const PageId  page_number )

pure virtual

Deletes a page from the file.

Parameters

page_number

Number of page to delete.

Implemented in badgerdb::BlobFile, and badgerdb::PageFile.

bool badgerdb::File::exists ( const std::string &  filename )

static

Returns true if the file exists and is open.

Parameters

filename

Name of the file.

Definition at line 46 of file file.cpp.

                                           {
  std::fstream file(filename);
  if(file)
  {
    file.close();
    return true;
  }

  return false;
}

const std::string& badgerdb::File::filename ( ) const

inline

Returns the name of the file this object represents.

Returns

Name of file.

Definition at line 158 of file file.h.

{ return filename_; }

PageId badgerdb::File::getFirstPageNo

(

)

Returns pageid of first page in the file.

Returns

Iterator at first page of file.

Definition at line 62 of file file.cpp.

                            {
  const FileHeader& header = readHeader();
  return header.first_used_page;
}

bool badgerdb::File::isOpen ( const std::string &  filename )

static

Returns true if the file exists and is open.

Parameters

filename

Name of the file.

Definition at line 39 of file file.cpp.

                                           {
  if (!exists(filename)) {
    return false;
  }
  return open_counts_.find(filename) != open_counts_.end();
}

void badgerdb::File::openIfNeeded ( const bool  create_new )

protected

Opens the underlying file named in filename_. This method only opens the file if no other File objects exist that access the same filesystem file; otherwise, it reuses the existing stream.

Parameters

create_new

Whether to create a new file.

Exceptions

FileExistsException	If the underlying file exists and create_new is true.
FileNotFoundException	If the underlying file doesn't exist and create_new is false.

Definition at line 78 of file file.cpp.

                                             {
  if (open_counts_.find(filename_) != open_counts_.end()) { //exists an entry already
    ++open_counts_[filename_];
    stream_ = open_streams_[filename_];
  } else {
    std::ios_base::openmode mode =
        std::fstream::in | std::fstream::out | std::fstream::binary;
    const bool already_exists = exists(filename_);
    if (create_new) {
      // Error if we try to overwrite an existing file.
      if (already_exists) {
        throw FileExistsException(filename_);
      }
      // New files have to be truncated on open.
      mode = mode | std::fstream::trunc;
    } else {
      // Error if we try to open a file that doesn't exist.
      if (!already_exists) {
        throw FileNotFoundException(filename_);
      }
    }
    stream_.reset(new std::fstream(filename_, mode));
    open_streams_[filename_] = stream_;
    open_counts_[filename_] = 1;
  }
}

static std::streampos badgerdb::File::pagePosition ( const PageId  page_number )

inlinestaticprotected

Returns the position of the page with the given number in the file (as an offset from the beginning of the file).

Parameters

page_number

Number of page.

Returns

Position of page in file.

Definition at line 175 of file file.h.

                                                             {
    return sizeof(FileHeader) + ((page_number - 1) * Page::SIZE);
  }

FileHeader badgerdb::File::readHeader ( ) const

protected

Reads the header for this file from disk.

Returns

The file header.

Definition at line 118 of file file.cpp.

                                  {
  FileHeader header;
  stream_->seekg(0 /* pos */, std::ios::beg);
  stream_->read(reinterpret_cast<char*>(&header), sizeof(FileHeader));
  return header;
}

virtual Page badgerdb::File::readPage ( const PageId  page_number ) const

pure virtual

Reads an existing page from the file.

Parameters

page_number

Number of page to read.

Returns

The page.

Exceptions

InvalidPageException

If the page doesn't exist in the file or is not currently used.

Implemented in badgerdb::BlobFile, and badgerdb::PageFile.

void badgerdb::File::remove ( const std::string &  filename )

static

Deletes an existing file.

Parameters

filename

Name of the file.

Exceptions

FileNotFoundException	If the file doesn't exist.
FileOpenException	If the file is currently open.

Definition at line 29 of file file.cpp.

                                           {
  if (!exists(filename)) {
    throw FileNotFoundException(filename);
  }
  if (isOpen(filename)) {
    throw FileOpenException(filename);
  }
  std::remove(filename.c_str());
}

void badgerdb::File::writeHeader ( const FileHeader &  header )

protected

Writes the given header to the disk as the header for this file.

Parameters

header

File header to write.

Definition at line 125 of file file.cpp.

                                               {
  stream_->seekp(0 /* pos */, std::ios::beg);
  stream_->write(reinterpret_cast<const char*>(&header), sizeof(FileHeader));
  stream_->flush();
}

virtual void badgerdb::File::writePage ( const PageId  page_number, const Page &  new_page  )

pure virtual

Writes a page into the file at the given page number. No bounds checking is performed.

Parameters

page_number	Number of page whose contents to replace.
new_page	Page to write.

Implemented in badgerdb::BlobFile, and badgerdb::PageFile.

Member Data Documentation

std::string badgerdb::File::filename_

protected

Name of the file this object represents.

Definition at line 229 of file file.h.

File::CountMap badgerdb::File::open_counts_

staticprotected

Counts for opened files.

Definition at line 224 of file file.h.

File::StreamMap badgerdb::File::open_streams_

staticprotected

Streams for opened files.

Definition at line 219 of file file.h.

std::shared_ptr<std::fstream> badgerdb::File::stream_

protected

Stream for underlying filesystem object.

Definition at line 234 of file file.h.

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The documentation for this class was generated from the following files:

• /afs/cs.wisc.edu/u/h/a/haiyun/private/cs564-spr17/projects/p3/Btree/src/file.h
• /afs/cs.wisc.edu/u/h/a/haiyun/private/cs564-spr17/projects/p3/Btree/src/file.cpp