Async Streams introduced in .NET 6.0

Async Streams: .NET 6.0 introduces the concept of asynchronous streams, making it easier and more efficient to generate and consume data asynchronously. It can be operatedwith and syntax, and is suitable for scenarios that process large amounts of data or need to interact with slow data sources. yield returnawait foreach

Here's a simple example using asynchronous streams:

public async IAsyncEnumerable<int> GenerateDataAsync()
{
    for (int i = 0; i < 10; i++)
    {
        // 模拟异步操作
        await Task.Delay(100);
        
        yield return i;
    }
}

public async Task ConsumeDataAsync()
{
    await foreach (int item in GenerateDataAsync())
    {
        Console.WriteLine(item);
    }
}

In the above example, GenerateDataAsyncthe method is an async method that returns a IAsyncEnumerable<int>. In this method, use yield returnthe keyword to generate data one by one. Between each data generation, await Task.Delay(100)the delay of an asynchronous operation is simulated by .

ConsumeDataAsyncmethod is another asynchronous method that await foreachreads data from an asynchronous stream one by one using the syntax and prints each data item on the console.

Using asynchronous streams, you can easily write asynchronous code to process streams of data without fetching all the data at once. This is especially useful when working with large datasets or when you need to interact with slow data sources, improving performance and resource utilization.

It should be noted that the asynchronous stream is only applicable to .NET 6.0 and later versions , and the keyword needs to be used in the asynchronous method yield returnto generate data one by one.

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When using asynchronous streams, you can asynchronously produce and consume data in a number of ways. Here are some common examples of using asynchronous streams in .NET 6.0:

1. Generate data from an asynchronous data source:

In this example, data is read from the database through an asynchronous operation, and yield returnthe data is produced one by one using . In this way, data can be fetched from the database and consumed in an asynchronous manner.  

public async IAsyncEnumerable<int> GenerateDataAsync()
{
    // 从数据库中异步读取数据
    using (var connection = new SqlConnection(connectionString))
    {
        await connection.OpenAsync();
        using (var command = new SqlCommand("SELECT * FROM MyTable", connection))
        using (var reader = await command.ExecuteReaderAsync())
        {
            while (await reader.ReadAsync())
            {
                int value = reader.GetInt32(0);
                yield return value;
            }
        }
    }
}

• Process large datasets using asynchronous streams

In this example, the GenerateLargeDataAsync method asynchronously generates large amounts of data one by one. In the ProcessLargeDataAsync method, use await foreach to consume data one by one. This avoids loading large amounts of data at once and processes it on demand. 

public async IAsyncEnumerable<int> GenerateLargeDataAsync()
{
    // 逐个产生大量数据
    for (int i = 0; i < 1000000; i++)
    {
        await Task.Delay(10);
        yield return i;
    }
}

public async Task ProcessLargeDataAsync()
{
    await foreach (int item in GenerateLargeDataAsync())
    {
        // 处理每个数据项
    }
}

• Interact with slow data sources:

 In this example, FetchDataFromSlowSourceAsyncthe method fetches data one by one from the slow data source through asynchronous operations and yield returnproduces the data one by one using the . In this way, data can be processed as soon as it is available without having to wait for the entire data source to be loaded.

public async IAsyncEnumerable<string> FetchDataFromSlowSourceAsync()
{
    while (true)
    {
        // 从慢速数据源异步获取数据
        string data = await SlowSource.GetDataAsync();
        if (data == null)
        {
            yield break; // 数据源已耗尽，停止产生数据
        }
        
        yield return data;
    }
}