Executors

Executors have quite a history in C++. The discussion began in early 2010. For the details, Detlef Vollmanns gives in his presentation Finally Executors for C++ an excellent overview.

My introduction to executors is mainly based on the proposals for the design of executors P0761, and for their formal description P0443. I also refer to the relatively new Modest Executor Proposal P1055.

What are executors?

Executors are the basic building blocks for execution in C++ and fulfill a similar role for execution, such as allocators for the containers in C++. Many proposals for executors are published, and many design decisions are still open. They should be part of C++23, but can probably be used much earlier to extend the C++ standard.

An executor consists of rules about where, when, and how to run a callable.

• Where: The callable may run on an internal or external processor, and that the result is read back from the internal or external processor.
• When: The callable may run immediately or just be scheduled.
• How: The

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