KisCacheStateValue Class Reference

#include <kis_lock_free_cache.h>

Public Types
typedef int	SeqValue

Public Member Functions
bool	endRead (int seq) const
void	endWrite (int seq)
void	invalidate ()
bool	startRead (int *seq) const
bool	startWrite (int *seq)

Private Member Functions
int	incrementSeqNo (int value)

Private Attributes
QAtomicInt	m_value

Static Private Attributes
static const int	IsValidMask = 0x0100
static const int	SeqNoIncrement = 0x0200
static const int	SeqNoMask = ~(WritersCountMask | IsValidMask)
static const int	WritersCountIncrement = 0x0001
static const int	WritersCountMask = 0x00FF

Detailed Description

This class implements a state variable for a lockfree cache object. The implementation is actually a variation of a 'seqlock', but with a simple modification: the values of "cache validity", "number of writers" and "sequence number" are multiplexed in a single int value.

Definition at line 19 of file kis_lock_free_cache.h.

Member Typedef Documentation

SeqValue

typedef int KisCacheStateValue::SeqValue

Definition at line 27 of file kis_lock_free_cache.h.

Member Function Documentation

endRead()

bool KisCacheStateValue::endRead ( int seq ) const

inline

Definition at line 45 of file kis_lock_free_cache.h.

                                       {
        bool result = seq == m_value;
        return result;
    }

References m_value.

endWrite()

void KisCacheStateValue::endWrite ( int seq )

inline

Definition at line 68 of file kis_lock_free_cache.h.

                                  {
        int oldValue;
        int newValue;
        do {
            oldValue = m_value;
 
            if (oldValue == seq) {
                newValue = (incrementSeqNo(oldValue) - WritersCountIncrement) | IsValidMask;
            } else {
                newValue = (incrementSeqNo(oldValue) - WritersCountIncrement) & ~IsValidMask;
            }
        } while(!m_value.testAndSetOrdered(oldValue, newValue));
    }

References incrementSeqNo(), IsValidMask, m_value, and WritersCountIncrement.

incrementSeqNo()

int KisCacheStateValue::incrementSeqNo ( int value )

inlineprivate

Definition at line 83 of file kis_lock_free_cache.h.

                                  {
        // handle overflow properly
        if ((value & SeqNoMask) == SeqNoMask) {
            value = value & ~SeqNoMask;
        } else {
            value += SeqNoIncrement;
        }
        return value;
    }

References SeqNoIncrement, SeqNoMask, and value().

invalidate()

void KisCacheStateValue::invalidate ( )

inline

Definition at line 29 of file kis_lock_free_cache.h.

                             {
        int oldValue;
        int newValue = -1;
        do {
            oldValue = m_value;
            newValue = incrementSeqNo(oldValue) & ~IsValidMask;
        } while(!m_value.testAndSetOrdered(oldValue, newValue));
    }

References incrementSeqNo(), and m_value.

startRead()

bool KisCacheStateValue::startRead ( int * seq ) const

inline

Definition at line 38 of file kis_lock_free_cache.h.

                                          {
        *seq = m_value;
 
        return (*seq & IsValidMask) &&
            !(*seq & WritersCountMask);
    }

References IsValidMask, m_value, and WritersCountMask.

startWrite()

bool KisCacheStateValue::startWrite ( int * seq )

inline

Definition at line 51 of file kis_lock_free_cache.h.

                                     {
        int oldValue;
        int newValue;
        do {
            oldValue = m_value;
            if ((oldValue & IsValidMask) ||
                (oldValue & WritersCountMask)) {
 
                return false;
            }
            newValue = incrementSeqNo(oldValue) + WritersCountIncrement;
        } while(!m_value.testAndSetOrdered(oldValue, newValue));
 
        *seq = newValue;
        return true;
    }

References incrementSeqNo(), IsValidMask, m_value, WritersCountIncrement, and WritersCountMask.

Member Data Documentation

IsValidMask

const int KisCacheStateValue::IsValidMask = 0x0100

staticprivate

Definition at line 23 of file kis_lock_free_cache.h.

m_value

QAtomicInt KisCacheStateValue::m_value

private

Definition at line 94 of file kis_lock_free_cache.h.

SeqNoIncrement

const int KisCacheStateValue::SeqNoIncrement = 0x0200

staticprivate

Definition at line 25 of file kis_lock_free_cache.h.

SeqNoMask

const int KisCacheStateValue::SeqNoMask = ~(WritersCountMask | IsValidMask)

staticprivate

Definition at line 24 of file kis_lock_free_cache.h.

WritersCountIncrement

const int KisCacheStateValue::WritersCountIncrement = 0x0001

staticprivate

Definition at line 22 of file kis_lock_free_cache.h.

WritersCountMask

const int KisCacheStateValue::WritersCountMask = 0x00FF

staticprivate

Definition at line 21 of file kis_lock_free_cache.h.

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

• libs/image/kis_lock_free_cache.h