When using the async method in a synchronous context, when does the thread return to the thread pool?

When using async in a synchronous context (for example, calling an async method without await), the thread that called this method will continue execution without waiting for the asynchronous operation to complete. The async method itself starts a task that runs in a thread pool or another context, and when this task finishes, the thread from the thread pool is released and returned to the pool.

That is, the thread returns to the thread pool immediately after the asynchronous operation completes, not at the moment of calling async. If the async method is called with await, then the calling thread can be freed for other tasks, and execution will continue after the asynchronous operation completes.

Example:

async Task<int> GetDataAsync() {
    await Task.Delay(1000); // simulate asynchronous work
    return 42;
}

void SyncMethod() {
    var task = GetDataAsync(); // async is called, but without await
    // here, the thread is not blocked and continues working
}

Thus, the thread returns to the pool after the asynchronous task completes, allowing efficient resource utilization.