Assists in writing snapshot files to the local filesystem. More...

#include <SnapshotFile.h>

Inheritance diagram for LogCabin::Storage::SnapshotFile::Writer:

Classes
struct	SharedMMap
	Allocates an object that is shared across processes. More...
Public Member Functions
	Writer (const Storage::Layout &storageLayout)
	Constructor.
	~Writer ()
	Destructor.
void	discard ()
	Throw away the file.
void	flushToOS ()
	Flush changes just down to the operating system's buffer cache.
void	seekToEnd ()
	Seek to the end of the file, in case another process has written to it.
uint64_t	save ()
	Flush changes all the way down to the disk and close the file.
uint64_t	getBytesWritten () const
	Return the number of bytes written so far.
void	writeMessage (const google::protobuf::Message &message)
	Write the given ProtoBuf message to the stream.
void	writeRaw (const void *data, uint64_t length)
	Write some raw bytes to the stream.
Public Attributes
SharedMMap< std::atomic < uint64_t > >	sharedBytesWritten
	This value is incremented every time bytes are written to the Writer from any process holding this Writer.
Private Attributes
Storage::FilesystemUtil::File	parentDir
	A handle to the directory containing the snapshot.
std::string	stagingName
	The temporary name of 'file' before it is closed.
Storage::FilesystemUtil::File	file
	Wraps the raw file descriptor; in charge of closing it when done.
uint64_t	bytesWritten
	The number of bytes accumulated in the file so far.

Detailed Description

Assists in writing snapshot files to the local filesystem.

Definition at line 78 of file SnapshotFile.h.

Constructor & Destructor Documentation

LogCabin::Storage::SnapshotFile::Writer::Writer ( const Storage::Layout & storageLayout ) [explicit]

Constructor.

Parameters:

storageLayout The directories in which to create the snapshot (in a file called "snapshot" in the snapshotDir). TODO(ongaro): what if it can't be written?

Definition at line 163 of file SnapshotFile.cc.

LogCabin::Storage::SnapshotFile::Writer::~Writer ( )

Destructor.

If the file hasn't been explicitly saved or discarded, prints a warning and discards the file.

Definition at line 178 of file SnapshotFile.cc.

Member Function Documentation

void LogCabin::Storage::SnapshotFile::Writer::discard ( )

Throw away the file.

If you call this after the file has been closed, it will PANIC.

Definition at line 187 of file SnapshotFile.cc.

void LogCabin::Storage::SnapshotFile::Writer::flushToOS ( )

Flush changes just down to the operating system's buffer cache.

Leave the file open for additional writes.

This is useful when forking child processes to write to the file. The correct procedure for that is: 0. write stuff 1. call flushToOS() 2. fork 3. child process: write stuff 4. child process: call flushToOS() 5. child process: call _exit() 6. parent process: call seekToEnd() 7. parent process: write stuff 8. parent process: call save()

Definition at line 196 of file SnapshotFile.cc.

void LogCabin::Storage::SnapshotFile::Writer::seekToEnd ( )

Seek to the end of the file, in case another process has written to it.

Subsequent calls to getBytesWritten() will include data written by other processes.

Definition at line 202 of file SnapshotFile.cc.

uint64_t LogCabin::Storage::SnapshotFile::Writer::save ( )

Flush changes all the way down to the disk and close the file.

If you call this after the file has been closed, it will PANIC.