One of the biggest problems that developers have had with this
library is that it has been difficult to define and handle new kinds
of event - beyond the file/socket I/O and delayed task events that we
support by default.
In particular, it has been difficult to implement input devices (such
as encoders) when we want to signal a new event (such as the
availability of new frame data) from an external thread. The 'watch
variable' mechanism - although it can be used - is not particular
well-suited for this purpose. Furthermore, the model code in
"DeviceSource.cpp" has not been particular helpful, because it
doesn't really describe what to do to handle events that are signaled
from an external thread.
To overcome this, I have now installed a new version (2010.12.11) of
the "LIVE555 Streaming Media" library that now includes a new 'event
trigger' mechanism for "TaskScheduler" (and its subclass,
"BasicTaskScheduler").
Specifically, you can now - using the new function
TaskScheduler::createEventTrigger()
- register an event handler function, to be associated with a
particular 'event trigger id'. At some later time, you can call
TaskScheduler:: triggerEvent()
with this 'event trigger id' as parameter, and this will cause the
event handler function to get called (from within the event loop).
For more details, see "UsageEnvironment/include/UsageEnvironment.hh"
One nice feature of this mechanism is that - unlike other library
routines - the "triggerEvent()" function can be called from a
separate thread. This makes it easier to implement input device
classes.
I have also updated (and, I hope, significantly improved) the model
code in "liveMedia/DeviceSource.cpp". This code describes how to
implement an input device class that uses the new 'event trigger'
mechanism (with the event possibly being signaled from an external
thread).
If you're implementing (or have already implemented) an input device
class, then I encourage you to take a look at the new "DeviceSource"
code - and perhaps use this as a model for your code.
--
Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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