# Poco

# template < class T >

# class BasicFIFOBuffer

Library: Foundation
Package: Core
Header: Poco/FIFOBuffer.h

## Description

A simple buffer class with support for re-entrant, FIFO-style read/write operations, as well as (optional) empty/non-empty/full (i.e. writable/readable) transition notifications. Buffer can be flagged with end-of-file and error flags, which renders it un-readable/writable.

Critical portions of code are protected by a recursive mutex. However, to achieve thread-safety in cases where multiple member function calls are involved and have to be atomic, the mutex must be locked externally.

Buffer size, as well as amount of unread data and available space introspections are supported as well.

This class is useful anywhere where a FIFO functionality is needed.

## Member Summary

Member Functions: advance, available, begin, buffer, copy, drain, getNotify, hasEOF, isEOF, isEmpty, isFull, isReadable, isValid, isWritable, mutex, next, operator [], peek, read, resize, setEOF, setError, setNotify, size, used, write

## Types

### Type

typedef T Type;

## Constructors

### BasicFIFOBuffer

BasicFIFOBuffer(
std::size_t size,
bool notify = false
);

Creates the FIFOBuffer.

### BasicFIFOBuffer

BasicFIFOBuffer(
T * pBuffer,
std::size_t size,
bool notify = false
);

Creates the FIFOBuffer.

### BasicFIFOBuffer

BasicFIFOBuffer(
const T * pBuffer,
std::size_t size,
bool notify = false
);

Creates the FIFOBuffer.

## Destructor

### ~BasicFIFOBuffer

~BasicFIFOBuffer();

Destroys the FIFOBuffer.

## Member Functions

### advance

void advance(
std::size_t length
);

Advances buffer by length elements. Should be called AFTER the data was copied into the buffer.

### available

std::size_t available() const;

Returns the size of the available portion of the buffer.

### begin

T * begin();

Returns the pointer to the beginning of the buffer.

### buffer

const Buffer < T > & buffer() const;

Returns const reference to the underlying buffer.

### copy

void copy(
const T * ptr,
std::size_t length
);

Copies the supplied data to the buffer and adjusts the used buffer size.

### drain

void drain(
std::size_t length = 0
);

Drains length number of elements from the buffer. If length is zero or greater than buffer current content length, buffer is emptied.

### getNotify

bool getNotify() const;

Returns true if notifications are enabled, false otherwise.

### hasEOF

bool hasEOF() const;

Returns true if EOF flag has been set.

### isEOF

bool isEOF() const;

Returns true if EOF flag has been set and buffer is empty.

### isEmpty

bool isEmpty() const;

Returns true is buffer is empty, false otherwise.

### isFull

bool isFull() const;

Returns true is buffer is full, false otherwise.

### isReadable

bool isReadable() const;

Returns true if buffer contains data and is not in error state.

### isValid

bool isValid() const;

Returns true if error flag is not set on the buffer, otherwise returns false.

### isWritable

bool isWritable() const;

Returns true if buffer is not full and is not in error state.

### mutex

Mutex & mutex();

Returns reference to mutex.

### next

T * next();

Returns the pointer to the next available position in the buffer.

### operator []

T & operator[] (
std::size_t index
);

Returns value at index position. Throws InvalidAccessException if index is larger than the last valid (used) buffer position.

### operator []

const T & operator[] (
std::size_t index
) const;

Returns value at index position. Throws InvalidAccessException if index is larger than the last valid (used) buffer position.

### peek

std::size_t peek(
T * pBuffer,
std::size_t length
) const;

Peeks into the data currently in the FIFO without actually extracting it. If length is zero, the return is immediate. If length is greater than used length, it is substituted with the the current FIFO used length.

Returns the number of elements copied in the supplied buffer.

### peek

std::size_t peek(
Poco::Buffer < T > & buffer,
std::size_t length = 0
) const;

Peeks into the data currently in the FIFO without actually extracting it. Resizes the supplied buffer to the size of data written to it. If length is not supplied by the caller or is greater than length of currently used data, the current FIFO used data length is substituted for it.

Returns the number of elements copied in the supplied buffer.

### read

std::size_t read(
T * pBuffer,
std::size_t length
);

Copies the data currently in the FIFO into the supplied buffer, which must be preallocated to at least the length size before calling this function.

Returns the size of the copied data.

### read

std::size_t read(
Poco::Buffer < T > & buffer,
std::size_t length = 0
);

Copies the data currently in the FIFO into the supplied buffer. Resizes the supplied buffer to the size of data written to it.

Returns the size of the copied data.

### resize

void resize(
std::size_t newSize,
bool preserveContent = true
);

Resizes the buffer. If preserveContent is true, the content of the old buffer is preserved. New size can be larger or smaller than the current size, but it must not be 0. Additionally, if the new length is smaller than currently used length and preserveContent is true, InvalidAccessException is thrown.

### setEOF

void setEOF(
bool eof = true
);

Sets end-of-file flag on the buffer.

Setting EOF flag to true prevents writing to the buffer; reading from the buffer will still be allowed until all data present in the buffer at the EOF set time is drained. After that, to re-enable FIFOBuffer for reading/writing, EOF must be set to false.

Setting EOF flag to false clears EOF state if it was previously set. If EOF was not set, it has no effect.

### setError

void setError(
bool error = true
);

Sets the error flag on the buffer and empties it. If notifications are enabled, they will be triggered if appropriate.

Setting error flag to true prevents reading and writing to the buffer; to re-enable FIFOBuffer for reading/writing, the error flag must be set to false.

### setNotify

void setNotify(
bool notify = true
);

Enables/disables notifications.

### size

std::size_t size() const;

Returns the size of the buffer.

### used

std::size_t used() const;

Returns the size of the used portion of the buffer.

### write

std::size_t write(
const T * pBuffer,
std::size_t length
);

Writes data from supplied buffer to the FIFO buffer. If there is no sufficient space for the whole buffer to be written, data up to available length is written. The length of data to be written is determined from the length argument. Function does nothing and returns zero if length argument is equal to zero.

Returns the length of data written.

### write

std::size_t write(
const Buffer < T > & buffer,
std::size_t length = 0
);

Writes data from supplied buffer to the FIFO buffer. If there is no sufficient space for the whole buffer to be written, data up to available length is written. The length of data to be written is determined from the length argument or buffer size (when length argument is default zero or greater than buffer size).

Returns the length of data written.

## Variables

### readable

mutable Poco::BasicEvent < bool > readable;

Event indicating "readability" of the buffer, triggered as follows:

* when buffer transitions from non-empty to empty,

    Readable event observers are notified, with false
    value as the argument

* when FIFOBuffer transitions from empty to non-empty,

    Readable event observers are notified, with true value
    as the argument

### writable

mutable Poco::BasicEvent < bool > writable;

Event indicating "writability" of the buffer, triggered as follows:

* when buffer transitions from non-full to full,

    Writable event observers are notified, with
    false value as the argument

* when buffer transitions from full to non-full,

    Writable event observers are notified, with
    true value as the argument