This DataObject is a Lock-Free implementation, such that reads and writes can happen concurrently without priority inversions. More...

#include <DataObjectLockFree.hpp>

Inheritance diagram for RTT::base::DataObjectLockFree< T >:

[legend]

List of all members.

Classes
struct	DataBuf
Public Types
typedef T	DataType
Public Member Functions
virtual void	data_sample (const DataType &sample)
	DataObjectLockFree (const T &initial_value=T(), unsigned int max_threads=2)
virtual DataType	Get () const
virtual void	Get (DataType &pull) const
virtual void	Set (const DataType &push)
	~DataObjectLockFree ()
Public Attributes
const unsigned int	MAX_THREADS
	The maximum number of threads.
Private Types
typedef DataBuf *	PtrType
typedef DataBuf	ValueType
typedef DataBuf *volatile	VolPtrType
Private Attributes
const unsigned int	BUF_LEN
DataBuf *	data
VolPtrType	read_ptr
VolPtrType	write_ptr

Detailed Description

template<class T>
class RTT::base::DataObjectLockFree< T >

This DataObject is a Lock-Free implementation, such that reads and writes can happen concurrently without priority inversions.

When there are more writes than reads, the last write will be returned. The internal buffer can get full if too many concurrent reads are taking to long. In that case, each new read will read the element the previous read returned.

     * The following Truth table applies when a Low Priority thread is
     * preempted by a High Priority thread :
     *
     *   L\H | Set | Get |
     *   Set | Ok  | Ok  |
     *   Get | Ok  | Ok  |
     *
     * legend : L : Low Priority thread
     *          H : High Priority thread
     *          Blk: Blocks High Priority thread (bad!)
     *          internal::NA : Not allowed !
     *

Further, multiple reads may occur before, during and after a write operation simultaneously. The buffer needs readers+2*writers elements to be guaranteed non blocking.

Definition at line 77 of file DataObjectLockFree.hpp.

Member Typedef Documentation

template<class T>

typedef T RTT::base::DataObjectLockFree< T >::DataType

The type of the data.

Reimplemented from RTT::base::DataObjectInterface< T >.

Reimplemented in RTT::base::DataObject< T >.

Definition at line 84 of file DataObjectLockFree.hpp.

template<class T>

typedef DataBuf* RTT::base::DataObjectLockFree< T >::PtrType [private]

Definition at line 116 of file DataObjectLockFree.hpp.

template<class T>

typedef DataBuf RTT::base::DataObjectLockFree< T >::ValueType [private]

Definition at line 115 of file DataObjectLockFree.hpp.

template<class T>

typedef DataBuf* volatile RTT::base::DataObjectLockFree< T >::VolPtrType [private]

Definition at line 114 of file DataObjectLockFree.hpp.

Constructor & Destructor Documentation

template<class T>

RTT::base::DataObjectLockFree< T >::DataObjectLockFree	(	const T &	initial_value = `T()`,
		unsigned int	max_threads = `2`
	)		`[inline]`

Construct a DataObjectLockFree by name.

Parameters:

_name	The name of this DataObject.
initial_value	The initial value of this DataObject.

Definition at line 133 of file DataObjectLockFree.hpp.

template<class T>

RTT::base::DataObjectLockFree< T >::~DataObjectLockFree ( ) [inline]

Definition at line 144 of file DataObjectLockFree.hpp.

Member Function Documentation

template<class T>

virtual void RTT::base::DataObjectLockFree< T >::data_sample ( const DataType & sample ) [inline, virtual]

Provides a data sample to initialize this data object. As such enough storage space can be allocated before the actual writing begins.

Parameters:

sample

Implements RTT::base::DataObjectInterface< T >.

Definition at line 218 of file DataObjectLockFree.hpp.

template<class T>

virtual DataType RTT::base::DataObjectLockFree< T >::Get ( ) const [inline, virtual]

Get a copy of the data. This method will allocate memory twice if data is not a value type. Use Get(DataType&) for the non-allocating version.

Returns:: A copy of the data.

Implements RTT::base::DataObjectInterface< T >.

Definition at line 155 of file DataObjectLockFree.hpp.

template<class T>

virtual void RTT::base::DataObjectLockFree< T >::Get ( DataType & pull ) const [inline, virtual]

Get a copy of the Data (non allocating). If pull has reserved enough memory to store the copy, no memory will be allocated.

Parameters:

pull	A copy of the data.

Implements RTT::base::DataObjectInterface< T >.

Definition at line 164 of file DataObjectLockFree.hpp.

template<class T>

virtual void RTT::base::DataObjectLockFree< T >::Set ( const DataType & push ) [inline, virtual]

Set the data to a certain value (non blocking).

Parameters:

push	The data which must be set.

This method can not be called concurrently (only one producer). With a minimum of 3 buffers, if the write_ptr+1 field is not occupied, it will remain so because the read_ptr is at write_ptr-1 (and can not increment the counter on write_ptr+1). Hence, no locking is needed.

Implements RTT::base::DataObjectInterface< T >.

Definition at line 191 of file DataObjectLockFree.hpp.