This class supports the writing of recordings to disk. More...

#include <ThreadedFileWriter.h>

Classes
class	TFWBuffer
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.
bool	ReOpen (QString newFilename="")
	Reopens the file we are writing to or opens a new file.
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	SetWriteBufferMinWriteSize (uint newMinSize=kMinWriteSize)
	Sets the minumum number of bytes to write to disk in a single write.
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 writes to disk.
void	SyncLoop (void)
	The thread run method that calls Sync(void).
void	TrimEmptyBuffers (void)
Private Attributes
QString	filename
int	flags
mode_t	mode
int	fd
bool	flush
bool	in_dtor
bool	ignore_writes
uint	tfw_min_write_size
uint	totalBufferUse
QMutex	buflock
QList< TFWBuffer * >	writeBuffers
QList< TFWBuffer * >	emptyBuffers
TFWWriteThread *	writeThread
TFWSyncThread *	syncThread
QWaitCondition	bufferEmpty
QWaitCondition	bufferHasData
QWaitCondition	bufferSyncWait
Static Private Attributes
static const uint	kMaxBufferSize = 128 * 1024 * 1024
static const uint	kMinWriteSize = 64 * 1024
	Minimum to write to disk in a single write, when not flushing buffer.
Friends
class	TFWWriteThread
class	TFWSyncThread

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 40 of file ThreadedFileWriter.h.

Constructor & Destructor Documentation

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

Creates a threaded file writer.

Definition at line 59 of file ThreadedFileWriter.cpp.

ThreadedFileWriter::~ThreadedFileWriter ( )

Commits all writes and closes the file.

Definition at line 148 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 104 of file ThreadedFileWriter.cpp.

Referenced by FileRingBuffer::FileRingBuffer(), named_output_file_common(), and ReOpen().

bool ThreadedFileWriter::ReOpen ( QString newFilename = "" )

Reopens the file we are writing to or opens a new file.

Returns:: true if we successfully open the file.

Parameters:

newFilename optional name of new file to open

Definition at line 80 of file ThreadedFileWriter.cpp.

Referenced by FileRingBuffer::ReOpen().

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 269 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.

Parameters:

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

Definition at line 198 of file ThreadedFileWriter.cpp.

Referenced by ASIStreamHandler::run(), and RingBuffer::Write().

void ThreadedFileWriter::SetWriteBufferMinWriteSize ( uint newMinSize = kMinWriteSize )

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

This is ignored during a Flush(void)

Definition at line 346 of file ThreadedFileWriter.cpp.

Referenced by RingBuffer::SetWriteBufferMinWriteSize().

void ThreadedFileWriter::Sync ( void )

Flush data written to the file descriptor to disk.

This prevents freezing up Linux disk access on a running CFQ, AS, or Deadline as the disk write schedulers. It does this via two mechanism. One is a data sync using the best mechanism available (fdatasync then fsync). The second is by telling the kernel we do not intend to use the data just written anytime soon so other processes time-slices will not be used to deal with our excess dirty pages.

Note:: We used to also use sync_file_range on Linux, however this is incompatible with newer filesystems such as BRTFS and does not actually sync any blocks that have not been allocated yet so it was never really appropriate for ThreadedFileWriter.; We use standard posix calls for this, so any operating system supporting the calls will benefit, but this has been designed with Linux in mind. Other OS's may benefit from revisiting this function.

Definition at line 327 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 290 of file ThreadedFileWriter.cpp.

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

void ThreadedFileWriter::DiskLoop ( void ) [protected]

The thread run method that actually calls writes to disk.

Definition at line 374 of file ThreadedFileWriter.cpp.

Referenced by TFWWriteThread::run().

void ThreadedFileWriter::SyncLoop ( void ) [protected]

The thread run method that calls Sync(void).