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C++ promises and packaged tasks share a reference-counted state

devblogs.microsoft.com by Raymond Chen Editor score 7/10

The explanation models futures around a shared source object: promises fill it, while packaged tasks store a callable whose result or exception is later retrieved through a future. This mental model helps engineers reason about asynchronous value flow and object lifetimes in C++.

What

C++ std::packaged_task stores a callable and uses shared state, called the source, to pass its result to a future.

How

Invoking the task calls the stored callable and puts its value or exception in the source object, where the future can retrieve it.

Why it matters

The shared-state model clarifies how asynchronous work transfers results or exceptions between components in C++ programs.

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