Abstract Actors are a popular mechanism for indirectly expressing concurrency. This article examines an implementation in the concurrent dialect of C++, C++, which runs actors on shared‐memory multi‐processor computers. The C++ actor system targets 32–256+ multi‐core shared‐memory computers that form the backbone of high‐performance computing, rather than distributed actor communication or robust execution via parentage fallback used by other actor systems. Five new mechanisms are presented to achieve expressibility, robustness, high performance, and scalability of actor applications across multiple cores: explicit life time (storage management) of actors and messages, combining actors and coroutines, a forward message‐trace and backward message‐return for debugging and failures, a new promise call‐back for ask sends, and an actor implementation that inverts the actor execution‐model by decoupling actor mailboxes with high levels of sharding. Microbenchmarks compare the new actor features with CAF, Protoactor, and classic and typed Akka.

Summary C∀ is a polymorphic, nonobject‐oriented, concurrent, backwards compatible extension of the C programming language. This paper discusses the design philosophy and implementation of its advanced control‐flow and concurrent/parallel features, along with the supporting runtime written in C∀. These features are created from scratch as ISO C has only low‐level and/or unimplemented concurrency, so C programmers continue to rely on library approaches like pthreads. C∀ introduces modern language‐level control‐flow mechanisms, like generators, coroutines, user‐level threading, and monitors for mutual exclusion and synchronization. The runtime provides significant programmer simplification and safety by eliminating spurious wakeup and monitor barging. The runtime also ensures multiple monitors can be safely acquired in a deadlock‐free way, and this feature is fully integrated with all monitor synchronization mechanisms. All control‐flow features integrate with the C∀ polymorphic type‐system and exception handling, while respecting the expectations and style of C programmers. Experimental results show comparable performance of the new features with similar mechanisms in other concurrent programming languages.