For the past decade, every C++ programmer who wanted to do real concurrent work has had the same conversation with themselves. std::async is a toy. std::thread is too low-level. std::future doesn’t compose. So you reach for TBB, or another third-party library, or a thread pool you wrote in 2017, or std::coroutine that you have to wire up to an executor you also wrote yourself.
C++26 finally puts an answer in the standard library: std::execution, which is C++’s execution control library, also known as senders/receivers, also known as P2300. It is the largest single addition to the language since modules, and it is going to take the community a few years to digest. This post is a tour. We’ll start with the parallel algorithm policies you may already know, build up to senders/receivers, schedulers, cancellation, and end with a worked example that ties everything together.
What is std::execution
std::execution defines a model for describing asynchronous work and provides a small set of generic algorithms for composing those descriptions into larger ones. The actual execution is delegated to a scheduler, which is a handle to whatever resource happens to run the work: a thread pool, a GPU queue, an I/O reactor, or the calling thread itself.
The three core abstractions are:
- A scheduler is a lightweight handle that says where work runs.
- A sender is a lazy description of what work runs. It produces one of three completion signals: a value, an error, or “stopped” (cancelled).
- A receiver is the callback object that consumes those signals. You almost never write one by hand; the algorithms wire them up for you.
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