ThreadedFileWriter Class Reference

#include <ThreadedFileWriter.h>

Detailed Description

This class supports the writing of recordings to disk.

This class allows us manage the buffering when writing to disk. We write to the kernel image of the disk using one thread, and sync the kernel's image of the disk to hardware using another thread. The goal here so to block as little as possible when the classes using this class want to add data to the stream.

Definition at line 10 of file ThreadedFileWriter.h.


Public Member Functions
	ThreadedFileWriter (const QString &fname, int flags, mode_t mode)
	Creates a threaded file writer.
	~ThreadedFileWriter ()
	Commits all writes and closes the file.
bool	Open (void)
	Opens the file we will be writing to.
long long	Seek (long long pos, int whence)
	Seek to a position within stream; May be unsafe.
uint	Write (const void *data, uint count)
	Writes data to the end of the write buffer.
void	SetWriteBufferSize (uint newSize=TFW_DEF_BUF_SIZE)
	Sets the total size of the write buffer.
void	SetWriteBufferMinWriteSize (uint newMinSize=TFW_MIN_WRITE_SIZE)
	Sets the minumum number of bytes to write to disk in a single write.
uint	BufUsed (void)
	Number of bytes queued for write by the write thread.
uint	BufFree (void)
	Number of bytes that can be written without blocking.
void	Sync (void)
	flush data written to the file descriptor to disk.
void	Flush (void)
	Allow DiskLoop() to flush buffer completely ignoring low watermark.
Protected Member Functions
void	DiskLoop (void)
	The thread run method that actually calls safe_write().
void	SyncLoop (void)
	The thread run method that calls Sync(void).
Static Protected Member Functions
static void *	boot_writer (void *)
	Thunk that runs ThreadedFileWriter::DiskLoop(void).
static void *	boot_syncer (void *)
	Thunk that runs ThreadedFileWriter::SyncLoop(void).
Private Attributes
QString	filename
int	flags
mode_t	mode
int	fd
bool	no_writes
bool	flush
bool	write_is_blocked
bool	in_dtor
bool	ignore_writes
long long	tfw_min_write_size
uint	rpos
	points to end of data written to disk
uint	wpos
	points to end of data added to buffer
QMutex	buflock
	lock needed to update rpos and wpos
long long	written
char *	buf
unsigned long	tfw_buf_size
pthread_t	writer
pthread_t	syncer
QWaitCondition	bufferEmpty
QWaitCondition	bufferHasData
QWaitCondition	bufferSyncWait
QWaitCondition	bufferWroteData
Static Private Attributes
static const uint	TFW_DEF_BUF_SIZE = 210241024
	Default buffer size.
static const uint	TFW_MAX_WRITE_SIZE = TFW_DEF_BUF_SIZE / 4
	Maximum to write to disk in a single write.
static const uint	TFW_MIN_WRITE_SIZE = TFW_DEF_BUF_SIZE / 32
	Minimum to write to disk in a single write, when not flushing buffer.

Constructor & Destructor Documentation

ThreadedFileWriter::ThreadedFileWriter	(	const QString &	fname,
		int	flags,
		mode_t	mode
	)

Creates a threaded file writer.

Definition at line 120 of file ThreadedFileWriter.cpp.

ThreadedFileWriter::~ThreadedFileWriter ( )

Commits all writes and closes the file.

Definition at line 168 of file ThreadedFileWriter.cpp.

Member Function Documentation

bool ThreadedFileWriter::Open ( void )

Opens the file we will be writing to.

Returns:: true if we successfully open the file.

Definition at line 141 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::RingBuffer().

long long ThreadedFileWriter::Seek	(	long long	pos,
		int	whence
	)

Seek to a position within stream; May be unsafe.

This method is unsafe if Start() has been called and the call us not preceeded by StopReads(). You probably want to follow Seek() with a StartReads() in this case.

This method assumes that we don't seek very often. It does not use a high performance approach... we just block until the write thread empties the buffer.

Definition at line 257 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::WriterSeek().

uint ThreadedFileWriter::Write	(	const void *	data,
		uint	count
	)

Writes data to the end of the write buffer.

NOTE: This blocks while buffer is in use by the write to disk thread.

Parameters:

	data	pointer to data to write to disk
	count	size of data in bytes

Definition at line 201 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::Write().

void ThreadedFileWriter::SetWriteBufferSize ( uint newSize = TFW_DEF_BUF_SIZE )

Sets the total size of the write buffer.

WARNING: This is not safe when another thread is writing to the buffer.

Definition at line 307 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::SetWriteBufferSize().

void ThreadedFileWriter::SetWriteBufferMinWriteSize ( uint newMinSize = TFW_MIN_WRITE_SIZE )

Sets the minumum number of bytes to write to disk in a single write.

This is ignored during a Flush(void)

Definition at line 327 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::SetWriteBufferMinWriteSize().

uint ThreadedFileWriter::BufUsed ( void )

Number of bytes queued for write by the write thread.

Definition at line 426 of file ThreadedFileWriter.cpp.

Referenced by DiskLoop(), Flush(), and RingBuffer::IsIOBound().

uint ThreadedFileWriter::BufFree ( void )

Number of bytes that can be written without blocking.

Definition at line 435 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::IsIOBound(), and Write().

void ThreadedFileWriter::Sync ( void )

flush data written to the file descriptor to disk.

NOTE: This doesn't even try flush our queue of data. This only ensures that data which has already been sent to the kernel for this file is written to disk. This means that if this backend is writing the data over a network filesystem like NFS, then the data will be visible to the NFS server after this is called. It is also useful in preventing the kernel from buffering up so many writes that they steal the CPU for a long time when the write to disk actually occurs.

Definition at line 291 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::Sync(), SyncLoop(), and RingBuffer::WriterFlush().

void ThreadedFileWriter::Flush ( void )

Allow DiskLoop() to flush buffer completely ignoring low watermark.

Definition at line 267 of file ThreadedFileWriter.cpp.

Referenced by Seek(), SetWriteBufferSize(), RingBuffer::WriterFlush(), and ~ThreadedFileWriter().

void * ThreadedFileWriter::boot_writer ( void * wotsit ) [static, protected]

Thunk that runs ThreadedFileWriter::DiskLoop(void).

Definition at line 97 of file ThreadedFileWriter.cpp.

Referenced by Open().

void ThreadedFileWriter::DiskLoop ( void ) [protected]

The thread run method that actually calls safe_write().