AbstractFifo Class Reference
juce_core » containers

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.

struct MyFifo
{
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);
}
AbstractFifo abstractFifo { 1024 };
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

  numToWrite | indicates how many items you'd like to add to the buffer
  startIndex1 | on exit, this will contain the start index in your buffer at which your data should be written
  blockSize1 | on exit, this indicates how many items can be written to the block starting at startIndex1
  startIndex2 | on 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
  blockSize2 | on 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

  numWanted | indicates how many items you'd like to add to the buffer
  startIndex1 | on exit, this will contain the start index in your buffer at which your data should be written
  blockSize1 | on exit, this indicates how many items can be written to the block starting at startIndex1
  startIndex2 | on 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
  blockSize2 | on 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:

- juce_AbstractFifo.h

AbstractFifo::prepareToWrite
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.
AbstractFifo::finishedRead
void finishedRead(int numRead) noexcept
Called after reading from the FIFO, to indicate that this many items have now been consumed.
AbstractFifo::prepareToRead
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.
AbstractFifo
Encapsulates the logic required to implement a lock-free FIFO.
Definition: juce_AbstractFifo.h:79
AbstractFifo::finishedWrite
void finishedWrite(int numWritten) noexcept
Called after writing from the FIFO, to indicate that this many items have been added.