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Coroutine

Principle

A coroutine mechanism implemented based on the C++20 coroutine standard. According to the standard, a coroutine function, in addition to containing the co_xxx keyword expressions, also has special requirements for its return type. These requirements can generally be divided into two main categories: one supports a single return value coroutine, commonly referred to as a task, while the other supports multiple return values, typically called a generator.

The coroutine standard does not directly define the coroutine mechanism but rather abstracts and standardizes the API part of the coroutine mechanism while separating the fine-grained SPI (Service Provider Interface) part, which remains invisible to the user. The coroutine mechanism operates through the following flow: User -> API -> Compiler -> SPI -> Coroutine mechanism. The overall operation mode is:

• The end user expresses coroutine semantics using unified keyword operators, such as co_await and co_return.
• The end user defines the coroutine mechanism being utilized through the coroutine function’s return type.
• The compiler handles the coroutine suspension and resumption in stages, according to the operator semantics defined in the standard.
• The compiler invokes the corresponding functions of the coroutine framework at specific standard points before suspension and after resumption.

Submodule Documentation

• task
• future_awaitable
• cancellable
• futex

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