Re: Need an InputStream with Timeout (or equivalent)
I (think I) need an InputStream implementation that provides a timeout
I'm currently working with a proprietary serial device that, when a command
is written to the serial output stream, will eventually return one or more
data blocks. Each block will be "guaranteed" to be returned within a time
period (t). (i.e the device will not necessarily return an immediate
response). Once each block is returned the timer should re-set and the next
block will return in time(t).
So far, I have implemented the serial interface using the RxTx package.
(as an aside, kudos to the developers - research suggested that implementing
serial comms in Java was going to be a nightmare.) The RxTx package has made
things very easy and presents comms with the serial port through their own
InputStream and OutputStream implementations.
Preliminary testing has shown that the traditional
"while (data = input,read() > -1)" doesn't work here as the RxTx
implementation will always return -1 if there is no data available rather
than block until data is present and input.available() will return 0 if
there is no data (as expected). I got my first pass at this to work by
inserting Thread.sleep() commands but obviously this is not ideal.
That's because RxTx has a serious bug (that they have refused to fix for
years) and will not reliably do blocking I/O. Use Sun's implementation
if you want it to work.
I then found that the SerialEventListner facility makes it easy to
cater for responses that don't happen immediately by notifying when there
is something on the serial input stream to read.
But, unless I'm missing something, neither of these methods will cater for
the situation where the device completely fails to respond within time(t)
- which according to the device specs is a hard-failure from which the
device will not recover.
Googling has suggested two possible routes. Older messages prior to the
introduction of the NIO package suggest a convoluted method of creating a
timer thread to monitor the buffer that should be filled by the serial input
stream. Later posts suggest that using NIO is the way to go.
I've never used the NIO package and info I've found on Google suggest that
this is may not be an easy thing to do.
So my questions are these;
1) Is a timeout enabled InputStream what I need?
2) Assuming Yes - is there an implementation available somewhere? (I've
tried Apache-Commons, the usual first stop but found nothing)
3) Is there a tutorial available that will guide me through my first
dealings with NIO.
Look at Sun's Comm API. It has receive timeouts built in.
Sun no longer supports their Windows version of Comm API but it still
works just fine on XP at least and probably on Vista as well although I
haven't tested it. Sun does have a Linux and Solaris APIs that are current.
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