source: trunk/src/kernel/qasyncio.cpp@ 92

/****************************************************************************
** $Id: qasyncio.cpp 2 2005-11-16 15:49:26Z dmik $
**
** Implementation of asynchronous I/O classes
**
** Created : 970617
**
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** LICENSE.QPL included in the packaging of this file.
**
** This file may be distributed and/or modified under the terms of the
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** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.
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**********************************************************************/

#include "qasyncio.h"
#include "qiodevice.h"
#include <stdlib.h>

#ifndef QT_NO_ASYNC_IO

/*!
  \class QAsyncIO qasyncio.h
  \obsolete
  \brief The QAsyncIO class encapsulates I/O asynchronicity.

  The Qt classes for asynchronous input/output provide a simple
  mechanism to allow large files or slow data sources to be processed
  without using large amounts of memory or blocking the user interface.

  This facility is used in Qt to drive animated images.  See QImageConsumer.
*/


/*!
  Destroys the async IO object.
*/
QAsyncIO::~QAsyncIO()
{
}

/*!
  Ensures that only one object, \a obj and function, \a member, can
  respond to changes in readiness.
*/
void QAsyncIO::connect(QObject* obj, const char *member)
{
    signal.disconnect(0, 0);
    signal.connect(obj, member);
}

/*!
  Derived classes should call this when they change from being
  unready to ready.
*/
void QAsyncIO::ready()
{
    signal.activate();
}



/*!
  \class QDataSink qasyncio.h
  \obsolete
  \brief The QDataSink class is an asynchronous consumer of data.

  A data sink is an object which receives data from some source in an
  asynchronous manner.  This means that at some time not determined by
  the data sink, blocks of data are given to it from processing.  The
  data sink is able to limit the maximum size of such blocks which it
  is currently able to process.

  \sa QAsyncIO, QDataSource, QDataPump
*/

/*!
  \fn int QDataSink::readyToReceive()

  The data sink should return a value indicating how much data it is ready
  to consume.  This may be 0.
*/

/*!
  This should be called whenever readyToReceive() might have become non-zero.
  It is merely calls QAsyncIO::ready() if readyToReceive() is non-zero.
*/
void QDataSink::maybeReady()
{
    if (readyToReceive()) ready();
}

/*!
  \fn void QDataSink::receive(const uchar*, int count)

  This function is called to provide data for the data sink.  The \a count
  will be no more than the amount indicated by the most recent call to
  readyToReceive().  The sink must use all the provided data.
*/

/*!
  \fn void QDataSink::eof()

  This function will be called when no more data is available for
  processing.
*/


/*!
  \class QDataSource qasyncio.h
  \obsolete
  \brief The QDataSource class is an asynchronous producer of data.

  A data source is an object which provides data from some source in an
  asynchronous manner.  This means that at some time not determined by
  the data source, blocks of data will be taken from it for processing.
  The data source is able to limit the maximum size of such blocks which
  it is currently able to provide.

  \sa QAsyncIO, QDataSink, QDataPump
*/

/*!
  \fn int QDataSource::readyToSend()

  The data source should return a value indicating how much data it is ready
  to provide.  This may be 0.  If the data source knows it will never be
  able to provide any more data (until after a rewind()), it may return -1.
*/

/*!
  This should be called whenever readyToSend() might have become non-zero.
  It is merely calls QAsyncIO::ready() if readyToSend() is non-zero.
*/
void QDataSource::maybeReady()
{
    if (readyToSend()) ready();
}

/*!
  \fn void QDataSource::sendTo(QDataSink*, int count)

  This function is called to extract data from the source, by sending
  it to the given data sink.  The \a count will be no more than the amount
  indicated by the most recent call to readyToSend().  The source must
  use all the provided data, and the sink will be prepared to accept at
  least this much data.
*/

/*!
  This function should return TRUE if the data source can be rewound.

  The default returns FALSE.
*/
bool QDataSource::rewindable() const
{
    return FALSE;
}

/*!
  If this function is called with \a on set to TRUE, and rewindable()
  is TRUE, then the data source must take measures to allow the rewind()
  function to subsequently operate as described.  If rewindable() is FALSE,
  the function should call QDataSource::enableRewind(), which aborts with
  a qFatal() error.

  For example, a network connection may choose to use a disk cache
  of input only if rewinding is enabled before the first buffer-full of
  data is discarded, returning FALSE in rewindable() if that first buffer
  is discarded.
*/
void QDataSource::enableRewind( bool /* on */ )
{
    qFatal( "Attempted to make unrewindable QDataSource rewindable" );
}

/*!
  This function rewinds the data source.  This may only be called if
  enableRewind(TRUE) has been previously called.
*/
void QDataSource::rewind()
{
    qFatal("Attempted to rewind unrewindable QDataSource");
}

/*!
  \class QIODeviceSource qasyncio.h
  \obsolete
  \brief The QIODeviceSource class is a QDataSource that draws data from a QIODevice.

  This class encapsulates retrieving data from a QIODevice (such as a QFile).
*/

/*!
  Constructs a QIODeviceSource from the QIODevice \a device.  The QIODevice
  \e must be dynamically allocated, becomes owned by the QIODeviceSource,
  and will be deleted when the QIODeviceSource is destroyed. \a buffer_size
  determines the size of buffering to use between asynchronous operations.
  The higher the \a buffer_size, the more efficient, but the less interleaved
  the operation will be with other processing.
*/
QIODeviceSource::QIODeviceSource(QIODevice* device, int buffer_size) :
    buf_size(buffer_size),
    buffer(new uchar[buf_size]),
    iod(device),
    rew(FALSE)
{
}

/*!
  Destroys the QIODeviceSource, deleting the QIODevice from which it was
  constructed.
*/
QIODeviceSource::~QIODeviceSource()
{
    delete iod;
    delete [] buffer;
}

/*!
  Ready until end-of-file.
*/
int QIODeviceSource::readyToSend()
{
    if ( iod->status() != IO_Ok || !(iod->state() & IO_Open) )
        return -1;

    int n = QMIN((uint)buf_size, iod->size()-iod->at()); // ### not 64-bit safe
                                                         // ### not large file safe
    return n ? n : -1;
}

/*!
  Reads a block of data and sends up to \a n bytes to the \a sink.
*/
void QIODeviceSource::sendTo(QDataSink* sink, int n)
{
    iod->readBlock((char*)buffer, n);
    sink->receive(buffer, n);
}

/*!
  All QIODeviceSource's are rewindable.
*/
bool QIODeviceSource::rewindable() const
{
    return TRUE;
}

/*!
  If \a on is set to TRUE then rewinding is enabled.  
  No special action is taken.  If \a on is set to 
  FALSE then rewinding is disabled.
*/
void QIODeviceSource::enableRewind(bool on)
{
    rew = on;
}

/*!
  Calls reset() on the QIODevice.
*/
void QIODeviceSource::rewind()
{
    if (!rew) {
        QDataSource::rewind();
    } else {
        iod->reset();
        ready();
    }
}


/*!
  \class QDataPump qasyncio.h
  \obsolete
  \brief The QDataPump class moves data from a QDataSource to a QDataSink during event processing.

  For a QDataSource to provide data to a QDataSink, a controller must exist
  to examine the QDataSource::readyToSend() and QDataSink::readyToReceive()
  methods and respond to the QASyncIO::activate() signal of the source and
  sink.  One very useful way to do this is interleaved with other event
  processing.  QDataPump provides this - create a pipe between a source
  and a sink, and data will be moved during subsequent event processing.

  Note that each source can only provide data to one sink and each sink
  can only receive data from one source (although it is quite possible
  to write a multiplexing sink that is multiple sources).
*/

/*!
  Constructs a QDataPump to move data from a given \a data_source
  to a given \a data_sink.
*/
QDataPump::QDataPump(QDataSource* data_source, QDataSink* data_sink) :
    source(data_source), sink(data_sink)
{
    source->connect(this, SLOT(kickStart()));
    sink->connect(this, SLOT(kickStart()));
    connect(&timer, SIGNAL(timeout()), this, SLOT(tryToPump()));
    timer.start(0, TRUE);
}

void QDataPump::kickStart()
{
    if (!timer.isActive()) {
        interval = 0;
        timer.start(0, TRUE);
    }
}

void QDataPump::tryToPump()
{
    int supply, demand;

    supply = source->readyToSend();
    demand = sink->readyToReceive();
    if (demand <= 0) {
        return;
    }
    interval = 0;
    if (supply < 0) {
        // All done (until source signals change in readiness)
        sink->eof();
        return;
    }
    if (!supply)
        return;
    source->sendTo(sink, QMIN(supply, demand));

    timer.start(0, TRUE);
}

#endif // QT_NO_ASYNC_IO