PDelayChannel Class Reference

#include <delaychan.h>

Inheritance diagram for PDelayChannel:


Construction
enum	Mode { DelayReadsOnly, DelayWritesOnly, DelayReadsAndWrites }
	PDelayChannel (Mode mode, unsigned frameDelay, PINDEX frameSize=0, unsigned maximumSlip=250, unsigned minimumDelay=10)
	PDelayChannel (PChannel &channel, Mode mode, unsigned frameDelay, PINDEX frameSize=0, unsigned maximumSlip=250, unsigned minimumDelay=10)
Public Member Functions
Overrides from class PChannel
virtual PBoolean	Read (void *buf, PINDEX len)
virtual PBoolean	Write (const void *buf, PINDEX len)
Protected Member Functions
virtual void	Wait (PINDEX count, PTimeInterval &nextTick)
Protected Attributes
Mode	mode
unsigned	frameDelay
PINDEX	frameSize
PTimeInterval	maximumSlip
PTimeInterval	minimumDelay
PTimeInterval	nextReadTick
PTimeInterval	nextWriteTick

Detailed Description

Class for implementing a "delay line" channel. This indirect channel can be placed in a channel I/O chain to limit the speed of I/O. This can be useful if blocking is not available and buffers could be overwritten if the I/O occurs at full speed.

There are two modes of operation. In stream more, data can be read/written no faster than a fixed time for a fixed number of bytes. So, for example, you can say than 320 bytes must take 20 milliseconds, and thus if the application writes 640 byets it will delay 40 milliseconds before the next write.

In frame mode, the rate limiting applies to individual read or write operations. So you can say that each read takes 30 milliseconds even if on 4 bytes is read, and the same time if 24 bytes are read.

Member Enumeration Documentation

enum PDelayChannel::Mode

Enumerator:

DelayReadsOnly
DelayWritesOnly
DelayReadsAndWrites

Constructor & Destructor Documentation

PDelayChannel::PDelayChannel	(	Mode	mode,
		unsigned	frameDelay,
		PINDEX	frameSize = `0`,
		unsigned	maximumSlip = `250`,
		unsigned	minimumDelay = `10`
	)

Create a new delay channel with the specified delays. A value of zero for the numBytes parameter indicates that the delay is in frame mode.

The maximum skip time is the number of milliseconds that the delay may "catch up" by using zero delays. This is caused by the Read() or Write() not being called for a time by external factors.

Parameters:

mode	Mode for delay channel
frameDelay	Delay time in milliseconds
frameSize	Bytes to apply to the delay time.
maximumSlip	Maximum slip time in milliseconds
minimumDelay	Minimim delay (usually OS time slice)

PDelayChannel::PDelayChannel	(	PChannel &	channel,
		Mode	mode,
		unsigned	frameDelay,
		PINDEX	frameSize = `0`,
		unsigned	maximumSlip = `250`,
		unsigned	minimumDelay = `10`
	)

Create a new delay channel with the specified delays and channel. A value of zero for the numBytes parameter indicates that the delay is in frame mode.

The maximum skip time is the number of milliseconds that the delay may "catch up" by using zero delays. This is caused by the Read() or Write() not being called for a time by external factors.

Parameters:

channel	channel to use
mode	Mode for delay channel
frameDelay	Delay time in milliseconds
frameSize	Bytes to apply to the delay time.
maximumSlip	Maximum slip time in milliseconds
minimumDelay	Minimim delay (usually OS time slice)

Member Function Documentation

virtual PBoolean PDelayChannel::Read	(	void *	buf,
		PINDEX	len
	)			`[virtual]`

Low level read from the file channel. The read timeout is ignored for file I/O. The GetLastReadCount() function returns the actual number of bytes read.

The GetErrorCode() function should be consulted after Read() returns PFalse to determine what caused the failure.

Returns:: PTrue indicates that at least one character was read from the channel. PFalse means no bytes were read due to timeout or some other I/O error.

Parameters:

buf	Pointer to a block of memory to receive the read bytes.
len	Maximum number of bytes to read into the buffer.

Reimplemented from PIndirectChannel.

virtual void PDelayChannel::Wait	(	PINDEX	count,
		PTimeInterval &	nextTick
	)			`[protected, virtual]`

virtual PBoolean PDelayChannel::Write	(	const void *	buf,
		PINDEX	len
	)			`[virtual]`

Low level write to the file channel. The write timeout is ignored for file I/O. The GetLastWriteCount() function returns the actual number of bytes written.

The GetErrorCode() function should be consulted after Write() returns PFalse to determine what caused the failure.