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C++ futures share a state that carries a value, exception, or consumed result

devblogs.microsoft.com by Raymond Chen 3 min read Editor score 7/10

The mental model treats promises, futures, and related types as a shared state protected by a mutex and condition variable, tracking whether a value or exception is set or consumed. This clarifies the synchronization and lifecycle behind asynchronous C++ code.

What

C++ futures, promises, packaged tasks, and async operations share a state that carries a value or exception for retrieval.

How

The source permits setting a result once, uses a mutex and condition variable for synchronization, and lets consumers wait, retrieve, or consume the result.

Why it matters

This mental model clarifies how asynchronous results, exception propagation, and thread-safe waiting fit together in concurrent systems.

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