Timing granularity - how precise can I be?

Question

I have heard noises about Java not being able to handle extremely precise timing tasks. Specifically, I have heard that Timers and Thread.sleep() do not generally perform as might be expected.
I am working on an application involving serial port traffic, and the spec includes an 80 millisecond timeout between the beginning and end of a packet (If the packet is not complete within 80 milliseconds, drop it and reset the listener).
Can I expect this level of precision to work accurately? Are the numbers I get from System.currentTimeInMillis() likely to correspond, to the millisecond, to the actual time the byte arrives at the UART?
If not, I welcome suggestions about how to make this happen.

Answer 1

You certainly don't need RTJ and you don't need to
worry about the precision of Java timers either. See
http://java.sun.com/products/javacomm/javadocs/javax/c
omm/CommPort.html#enableReceiveTimeout(int). This
says that the timeout is implemented by the serial
port driver, not by Java.Interesting, but not useful in this case :
"when this many milliseconds have elapsed, return immediately from read, regardless of bytes in input buffer."
The timeout I am monitoring is between the first and last bytes of a message, not for any data recieved.