The foundation for these classes is a class of simple doubly-linked lists,
LkList, which can contain heterogeneous sets of arbitrary objects
that instantiate subclasses of the LkListElt class.
The LkList class is the basis for the FlexPipe class. A FlexPipe
is a linked list of items in FIFO order that behaves like a pipe with one
reader and one or more writers. Reading from a FlexPipe may be blocking or
non-blocking; writing is always non-blocking, because the capacity of the
pipe is limited only by available memory -- it's a linked list rather than
an array. This means that a FlexPipe can easily handle arbitrarily spiky
traffic, so long as the reader always eventually catches up. (For
flow-controlled inter-thread communication, use PipedOutput and
PipedInput.)
One basic use of FlexPipes is the movement of arbitrary arrays of bytes
among data-handling threads. Non-flow-controlled instances of the
ByteArrayPipe classs enable a multi-threaded application to
operate at high speed consistently, unaffected by surges and lulls in
data arrival rate.
This tolerance of transient peaks in traffic makes FlexPipes especially
handy for implementing highly distributed systems based on network
communications. Because output to a FlexPipe never blocks, slow processing
of input in one node of a distributed application need never slow down the
application as a whole: if network input traffic is received by one thread
but processed by another, and the input data are passed from one to the
other via a FlexPipe, the performance of the aggregate application is
limited only by the performance of the network itself. The
InetReqPipe subclass of FlexPipe is designed to simplify
development of applications along these lines.
Finally, the LkList class is also the basis for the
Timeline class. A Timeline is a linked list of events that are
scheduled for occurrence at some time in the future. Timeline events are
encapsulated in TimelineEvent objects, which are LkListElts that
have scheduled occurrence times and that additionally implement the abstract
method handleEvent. TimelineEvents in a Timeline are
ordered by scheduled occurrence time. The Timeline object includes a
background thread that watches the clock and simply calls each TimelineEvent's
handleEvent method when its scheduled occurrence time is reached.
The combination of Timelines and InetReqPipes can serve as a simple but fairly powerful platform for building event-driven distributed software in Java.