Abstract: Writing correct and efficient concurrent programs still remains a challenge. Explicit concurrency is difficult, error prone, and creates code which is hard to maintain and debug. This type of concurrency also treats modular program design and concurrency as separate goals, where modularity often suffers.

To solve these problems, we are designing a new language that we call Panini. In this paper, we focus on Panini's asynchronous, typed events, which reconcile the modularity goal promoted by the implicit invocation design style with the concurrency goal of exposing potential concurrency between the execution of subjects and observers.

Since modularity is improved and concurrency is implicit in Panini, programs are easier to reason about and maintain. Furthermore, races and deadlocks are avoided entirely, yielding programs with a guaranteed sequential semantics.

To evaluate our language design and implementation we show several examples of its usage as well as an empirical study of program performance.

We found that not only is developing and understanding Panini programs significantly easier compared to standard concurrent object-oriented programs, but performance of Panini programs is also comparable to their equivalent hand-tuned versions written using Java's fork-join framework.