\begin{abstract}
  Multi-threaded programs have traditionally fallen into one of two domains:
  {\em cooperative} and {\em competitive}.
  %threading, which maximizes the throughput of a large number
  %of equally important threads, and competitive threading, which focuses on
  %responsiveness of threads which may have different requirements and
  %priorities.
%
These two domains have traditionally remained mostly disjoint, with
cooperative threading used for increasing {\em throughput} in
compute-intensive applications such as scientific workloads and
cooperative threading used for increasing {\em responsiveness} in
interactive applications such as GUIs and games.
% usually using a single
%processors.
%
As multicore hardware becomes increasingly mainstream, there is a need
for bridging these two disjoint worlds, because many applications mix
interaction and computation and would benefit from both cooperative
and competitive threading.
%


In this paper, we present techniques for programming and reasoning
about {\em parallel interactive} applications that can use both
cooperative and competitive threading.
%
Our techniques enable the programmer to write rich parallel
interactive programs by creating and synchronizing with threads as
needed, and by assigning threads user-defined and partially ordered
priorities.
%
To ensure important responsiveness properties, we present a modal type
system analogous to S4 modal logic that precludes low-priority threads from
delaying high-priority threads, thereby statically preventing a
crucial set of {\em priority-inversion} bugs.
%, which can have serious
%and even disastrous consequences.
%
We then present a cost model that allows reasoning about
responsiveness and completion time of well-typed programs.
%
The cost model extends the traditional work-span model for
cooperative threading to account for competitive scheduling decisions
needed to ensure responsiveness.
%
Finally, we show that our proposed techniques are realistic by
implementing them as an extension to the Standard ML language.
\end{abstract}