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AbstractFifo Class Reference

Encapsulates the logic required to implement a lock-free FIFO. More...

Classes

class  ScopedReadWrite
 Class for a scoped reader/writer. More...
 

Public Types

using ScopedRead = ScopedReadWrite< ReadOrWrite::read >
 
using ScopedWrite = ScopedReadWrite< ReadOrWrite::write >
 

Public Member Functions

 AbstractFifo (int capacity) noexcept
 Creates a FIFO to manage a buffer with the specified capacity. More...
 
 ~AbstractFifo ()
 Destructor. More...
 
int getTotalSize () const noexcept
 Returns the total size of the buffer being managed. More...
 
int getFreeSpace () const noexcept
 Returns the number of items that can currently be added to the buffer without it overflowing. More...
 
int getNumReady () const noexcept
 Returns the number of items that can currently be read from the buffer. More...
 
void reset () noexcept
 Clears the buffer positions, so that it appears empty. More...
 
void setTotalSize (int newSize) noexcept
 Changes the buffer's total size. More...
 
void prepareToWrite (int numToWrite, int &startIndex1, int &blockSize1, int &startIndex2, int &blockSize2) const noexcept
 Returns the location within the buffer at which an incoming block of data should be written. More...
 
void finishedWrite (int numWritten) noexcept
 Called after writing from the FIFO, to indicate that this many items have been added. More...
 
void prepareToRead (int numWanted, int &startIndex1, int &blockSize1, int &startIndex2, int &blockSize2) const noexcept
 Returns the location within the buffer from which the next block of data should be read. More...
 
void finishedRead (int numRead) noexcept
 Called after reading from the FIFO, to indicate that this many items have now been consumed. More...
 
ScopedRead read (int numToRead) noexcept
 Replaces prepareToRead/finishedRead with a single function. More...
 
ScopedWrite write (int numToWrite) noexcept
 Replaces prepareToWrite/finishedWrite with a single function. More...
 

Detailed Description

Encapsulates the logic required to implement a lock-free FIFO.

This class handles the logic needed when building a single-reader, single-writer FIFO.

It doesn't actually hold any data itself, but your FIFO class can use one of these to manage its position and status when reading or writing to it.

To use it, you can call prepareToWrite() to determine the position within your own buffer that an incoming block of data should be stored, and prepareToRead() to find out when the next outgoing block should be read from.

e.g.

class MyFifo
{
public:
MyFifo() : abstractFifo (1024)
{
}
void addToFifo (const int* someData, int numItems)
{
int start1, size1, start2, size2;
abstractFifo.prepareToWrite (numItems, start1, size1, start2, size2);
if (size1 > 0)
copySomeData (myBuffer + start1, someData, size1);
if (size2 > 0)
copySomeData (myBuffer + start2, someData + size1, size2);
abstractFifo.finishedWrite (size1 + size2);
}
void readFromFifo (int* someData, int numItems)
{
int start1, size1, start2, size2;
abstractFifo.prepareToRead (numItems, start1, size1, start2, size2);
if (size1 > 0)
copySomeData (someData, myBuffer + start1, size1);
if (size2 > 0)
copySomeData (someData + size1, myBuffer + start2, size2);
abstractFifo.finishedRead (size1 + size2);
}
private:
AbstractFifo abstractFifo;
int myBuffer [1024];
};

Member Typedef Documentation

◆ ScopedRead

using AbstractFifo::ScopedRead = ScopedReadWrite<ReadOrWrite::read>

◆ ScopedWrite

using AbstractFifo::ScopedWrite = ScopedReadWrite<ReadOrWrite::write>

Constructor & Destructor Documentation

◆ AbstractFifo()

AbstractFifo::AbstractFifo ( int  capacity)
noexcept

Creates a FIFO to manage a buffer with the specified capacity.

◆ ~AbstractFifo()

AbstractFifo::~AbstractFifo ( )

Destructor.

Member Function Documentation

◆ getTotalSize()

int AbstractFifo::getTotalSize ( ) const
noexcept

Returns the total size of the buffer being managed.

◆ getFreeSpace()

int AbstractFifo::getFreeSpace ( ) const
noexcept

Returns the number of items that can currently be added to the buffer without it overflowing.

◆ getNumReady()

int AbstractFifo::getNumReady ( ) const
noexcept

Returns the number of items that can currently be read from the buffer.

◆ reset()

void AbstractFifo::reset ( )
noexcept

Clears the buffer positions, so that it appears empty.

◆ setTotalSize()

void AbstractFifo::setTotalSize ( int  newSize)
noexcept

Changes the buffer's total size.

Note that this isn't thread-safe, so don't call it if there's any danger that it might overlap with a call to any other method in this class!

◆ prepareToWrite()

void AbstractFifo::prepareToWrite ( int  numToWrite,
int &  startIndex1,
int &  blockSize1,
int &  startIndex2,
int &  blockSize2 
) const
noexcept

Returns the location within the buffer at which an incoming block of data should be written.

Because the section of data that you want to add to the buffer may overlap the end and wrap around to the start, two blocks within your buffer are returned, and you should copy your data into the first one, with any remaining data spilling over into the second.

If the number of items you ask for is too large to fit within the buffer's free space, then blockSize1 + blockSize2 may add up to a lower value than numToWrite. If this happens, you may decide to keep waiting and re-trying the method until there's enough space available.

After calling this method, if you choose to write your data into the blocks returned, you must call finishedWrite() to tell the FIFO how much data you actually added.

e.g.

void addToFifo (const int* someData, int numItems)
{
int start1, size1, start2, size2;
prepareToWrite (numItems, start1, size1, start2, size2);
if (size1 > 0)
copySomeData (myBuffer + start1, someData, size1);
if (size2 > 0)
copySomeData (myBuffer + start2, someData + size1, size2);
finishedWrite (size1 + size2);
}
Parameters
numToWriteindicates how many items you'd like to add to the buffer
startIndex1on exit, this will contain the start index in your buffer at which your data should be written
blockSize1on exit, this indicates how many items can be written to the block starting at startIndex1
startIndex2on exit, this will contain the start index in your buffer at which any data that didn't fit into the first block should be written
blockSize2on exit, this indicates how many items can be written to the block starting at startIndex2
See also
finishedWrite

◆ finishedWrite()

void AbstractFifo::finishedWrite ( int  numWritten)
noexcept

Called after writing from the FIFO, to indicate that this many items have been added.

See also
prepareToWrite

◆ prepareToRead()

void AbstractFifo::prepareToRead ( int  numWanted,
int &  startIndex1,
int &  blockSize1,
int &  startIndex2,
int &  blockSize2 
) const
noexcept

Returns the location within the buffer from which the next block of data should be read.

Because the section of data that you want to read from the buffer may overlap the end and wrap around to the start, two blocks within your buffer are returned, and you should read from both of them.

If the number of items you ask for is greater than the amount of data available, then blockSize1 + blockSize2 may add up to a lower value than numWanted. If this happens, you may decide to keep waiting and re-trying the method until there's enough data available.

After calling this method, if you choose to read the data, you must call finishedRead() to tell the FIFO how much data you have consumed.

e.g.

void readFromFifo (int* someData, int numItems)
{
int start1, size1, start2, size2;
prepareToRead (numSamples, start1, size1, start2, size2);
if (size1 > 0)
copySomeData (someData, myBuffer + start1, size1);
if (size2 > 0)
copySomeData (someData + size1, myBuffer + start2, size2);
finishedRead (size1 + size2);
}
Parameters
numWantedindicates how many items you'd like to add to the buffer
startIndex1on exit, this will contain the start index in your buffer at which your data should be written
blockSize1on exit, this indicates how many items can be written to the block starting at startIndex1
startIndex2on exit, this will contain the start index in your buffer at which any data that didn't fit into the first block should be written
blockSize2on exit, this indicates how many items can be written to the block starting at startIndex2
See also
finishedRead

◆ finishedRead()

void AbstractFifo::finishedRead ( int  numRead)
noexcept

Called after reading from the FIFO, to indicate that this many items have now been consumed.

See also
prepareToRead

◆ read()

ScopedRead AbstractFifo::read ( int  numToRead)
noexcept

Replaces prepareToRead/finishedRead with a single function.

This function returns an object which contains the start indices and block sizes, and also automatically finishes the read operation when it goes out of scope.

{
auto readHandle = fifo.read (4);
for (auto i = 0; i != readHandle.blockSize1; ++i)
{
// read the item at index readHandle.startIndex1 + i
}
for (auto i = 0; i != readHandle.blockSize2; ++i)
{
// read the item at index readHandle.startIndex2 + i
}
} // readHandle goes out of scope here, finishing the read operation

◆ write()

ScopedWrite AbstractFifo::write ( int  numToWrite)
noexcept

Replaces prepareToWrite/finishedWrite with a single function.

This function returns an object which contains the start indices and block sizes, and also automatically finishes the write operation when it goes out of scope.

{
auto writeHandle = fifo.write (5);
for (auto i = 0; i != writeHandle.blockSize1; ++i)
{
// write the item at index writeHandle.startIndex1 + i
}
for (auto i = 0; i != writeHandle.blockSize2; ++i)
{
// write the item at index writeHandle.startIndex2 + i
}
} // writeHandle goes out of scope here, finishing the write operation

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