youbot::DataObjectLockFree< T > Class Template Reference

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

#include <DataObjectLockFree.hpp>

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

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Detailed Description

template<class T>
class youbot::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 75 of file DataObjectLockFree.hpp.

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Member Typedef Documentation

template<class T>

typedef T youbot::DataObjectLockFree< T >::DataType

The type of the data.

Definition at line 81 of file DataObjectLockFree.hpp.

template<class T>

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

Definition at line 116 of file DataObjectLockFree.hpp.

template<class T>

typedef DataBuf youbot::DataObjectLockFree< T >::ValueType [private]

Definition at line 115 of file DataObjectLockFree.hpp.

template<class T>

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

Definition at line 114 of file DataObjectLockFree.hpp.

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Constructor & Destructor Documentation

template<class T>

youbot::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>

youbot::DataObjectLockFree< T >::~DataObjectLockFree

(

)

[inline]

Definition at line 142 of file DataObjectLockFree.hpp.

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Member Function Documentation

template<class T>

virtual void youbot::DataObjectLockFree< T >::data_sample

(

const DataType &

sample

)

[inline, virtual]

Definition at line 223 of file DataObjectLockFree.hpp.

template<class T>

virtual DataType youbot::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.

Definition at line 154 of file DataObjectLockFree.hpp.

template<class T>

virtual void youbot::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.

Definition at line 168 of file DataObjectLockFree.hpp.

template<class T>

virtual void youbot::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.

Definition at line 196 of file DataObjectLockFree.hpp.

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Member Data Documentation

template<class T>

const unsigned int youbot::DataObjectLockFree< T >::BUF_LEN [private]

Conversion of number of threads to size of buffer.

Definition at line 93 of file DataObjectLockFree.hpp.

template<class T>

DataBuf* youbot::DataObjectLockFree< T >::data [private]

A 3 element Data buffer

Definition at line 124 of file DataObjectLockFree.hpp.

template<class T>

const unsigned int youbot::DataObjectLockFree< T >::MAX_THREADS

The maximum number of threads.

When used in data flow, this is always 2.

Definition at line 88 of file DataObjectLockFree.hpp.

template<class T>

VolPtrType youbot::DataObjectLockFree< T >::read_ptr [private]

Definition at line 118 of file DataObjectLockFree.hpp.

template<class T>

VolPtrType youbot::DataObjectLockFree< T >::write_ptr [private]

Definition at line 119 of file DataObjectLockFree.hpp.

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

• DataObjectLockFree.hpp