Async Programming - Windows Documentation

Asynchronous Programming in Windows

Asynchronous programming enables responsive UI and efficient resource usage by allowing tasks to run without blocking the main thread. Windows provides several models and APIs to implement async operations.

Common Patterns

Callback-based (IUnknown::SetEventCallback)
Future/Promise (WRL::AsyncOperation)
Task-based (C++/WinRT co_await)
Thread pool (ThreadPoolQueueWorkItem)

Key API Calls

API	Description
`IAsyncOperation<T>`	Represents an async operation that returns a result.
`ThreadPool::RunAsync`	Runs a work item on the thread pool.
`AsyncStatus`	Enum describing the state of an async operation.
`co_await`	Language support for awaiting async operations.

Code Samples

// Example: Asynchronous file read using C++/WinRT
#include <winrt/Windows.Storage.Streams.h>
using namespace winrt;
using namespace Windows::Storage;
using namespace Windows::Storage::Streams;

IAsyncOperation<hstring> ReadTextAsync(StorageFile file)
{
    auto buffer = co_await FileIO::ReadBufferAsync(file);
    co_return winrt::to_hstring(buffer);
}

// Usage
auto file = co_await StorageFile::GetFileFromPathAsync(L"C:\\example.txt");
auto content = co_await ReadTextAsync(file);

Best Practices

Always capture weak_ptr when using lambdas to avoid leaks.
Prefer co_await over raw callbacks for readability.
Handle cancellation with IAsyncActionWithProgress::Cancel.
Keep UI updates on the UI thread via DispatcherQueue::TryEnqueue.