C# 8 understanding await using syntax

Question

I have next method:

public async Task<IEnumerable<Quote>> GetQuotesAsync()
{
    using var connection = new SqlConnection(_connectionString);

    var allQuotes = await connection.QueryAsync<Quote>(@"SELECT [Symbol], [Bid], [Ask], [Digits] FROM [QuoteEngine].[RealtimeData]");

    return allQuotes;
}

Everything fine and clear, connection will be disposed at the end of scope.

But resharper suggests to change it to:

public async Task<IEnumerable<Quote>> GetQuotesAsync()
{
    await using var connection = new SqlConnection(_connectionString);

    var allQuotes = await connection.QueryAsync<Quote>(@"SELECT [Symbol], [Bid], [Ask], [Digits] FROM [QuoteEngine].[RealtimeData]");

    return allQuotes;
}

It adds await before using and code is compiled successfully. What does it mean and when do we need to do that?

Klaus Gütter · Accepted Answer · 2021-12-05T17:15:52.163

205

Similar as using (...) uses IDisposable to clean up resources, await using (...) uses IAsyncDisposable. This allows to perform also time-consuming tasks (e.g involving I/O) on cleanup without blocking.

edited Dec 05 '21 at 17:15

answered Nov 10 '19 at 19:06

Klaus Gütter

11,151
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1

what is the consequence of using `using` when I could use `await using`? – Overlord Zurg Apr 21 '23 at 14:55
2

`using` will call `Dispose()` rather than `await DisposeAsync()` and therefore unneccesarily block the current thread for some time. It depends on the type of object how undesirable the difference is. – Klaus Gütter Apr 22 '23 at 05:38

Pavel Anikhouski · Answer 2 · 2020-01-07T10:14:47.473

33

If SqlConnection implements IAsyncDisposable interface, Resharper suggests you to switch to await using to dispose it asynchronously using DisposeAsync method

public interface IAsyncDisposable
{
    ValueTask DisposeAsync();
}

edited Jan 07 '20 at 10:14

answered Nov 10 '19 at 19:07

Pavel Anikhouski

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C# 8 understanding await using syntax

2 Answers2

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