What actually happens inside a C# async method when it reaches an await?

What happens when an async method awaits?

Explain the async state machine, continuation scheduling, and exception flow when a C# method awaits a Task.

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When an async method reaches an await, it first checks whether the awaited operation is already complete. If not, the method stores the state it needs later and returns an incomplete Task to its caller instead of blocking the thread. When the operation completes, the continuation resumes from that point. If the awaited operation failed, its exception is observed at the await expression.

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Compiler-generated state machines, Task continuations, exception propagation, and why async code can look synchronous while executing asynchronously.

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An async method preserves normal-looking control flow by storing enough state to pause at an incomplete await and continue after the operation finishes. That mechanism explains exception timing, object lifetime across awaits, and the cost of large numbers of pending operations.
When an async method reaches an await, it first checks whether the awaited operation is already complete. If not, the method stores the state it needs later and returns an incomplete Task to its caller instead of blocking the thread. When the operation completes, the continuation resumes from that point. If the awaited operation failed, its exception is observed at the await expression.
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The compiler transforms an async method into a state machine. Local variables that are needed after the await are kept as part of that state, and the continuation is scheduled when the awaited Task completes. This is why async code can be written in a normal top-to-bottom style even though execution may pause and resume later. The trade-off is that async methods have some allocation and state-machine overhead, so I avoid making hot CPU-only paths async without a real reason.

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Thinking the call stack simply stays blocked at the await line.
Forgetting that exceptions are captured into the returned Task.
Capturing large objects across awaits without noticing object lifetime.
Ignoring the cost of async state machines in tight CPU-only loops.
Starting async work and forgetting to await it.

What actually happens inside a C# async method when it reaches an await?

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