[Live-devel] Behavior of DeviceSource::doGetNextFrame() when no data available

[Clem Taylor]

On 8/10/06, David Arnold <darnold at futurec.net> wrote:
> What should a DeviceSource, such as a frame grabber, do in doGetNextFrame()
> when it determines there is no frame available?  I find no answer in the
> FAQ.  The comment in DeviceSource.cpp reads:

You need to reschedule a retry.

In my device source (which I copied from one of the examples), after
reading and validating the frame from the device it uses
scheduleDelayedTask with a 0 delay to schedule a call to
'afterGetting'. If a frame is not available it uses
scheduleDelayedTask to retry reading a frame from the device at some
point in the future. If you have a read selectable file descriptor for
your device then there is a more efficient method to do this.

For example:
        /* poll again in 5ms */
        nextTask() = envir().taskScheduler().scheduleDelayedTask (
            5 * 1000, (TaskFunc*) dspRetryGet, this );

                                          --Clem