Use Task.WaitAsync in SemaphoreSlim.WaitAsync

[stephentoub]

Method	Toolchain	Mean	Ratio	Allocated
WithCT	\main\CoreRun.exe	1.103 us	1.00	496 B
WithCT	\pr\CoreRun.exe	1.032 us	0.94	440 B
WithTimeout	\main\CoreRun.exe	1.492 us	1.00	888 B
WithTimeout	\pr\CoreRun.exe	1.103 us	0.74	536 B
WithCTandTimeout	\main\CoreRun.exe	1.589 us	1.00	904 B
WithCTandTimeout	\pr\CoreRun.exe	1.200 us	0.75	536 B

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Diagnosers;
using BenchmarkDotNet.Running;
using System;
using System.Threading.Tasks;
using System.Threading;

[MemoryDiagnoser]
public class Program
{
    public static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private SemaphoreSlim _sem = new SemaphoreSlim(0, 1);
    private CancellationTokenSource _cts = new CancellationTokenSource();

    [Benchmark]
    public Task WithCT()
    {
        Task t = _sem.WaitAsync(_cts.Token);
        _sem.Release();
        return t;
    }

    [Benchmark]
    public Task WithTimeout()
    {
        Task t = _sem.WaitAsync(TimeSpan.FromMinutes(1));
        _sem.Release();
        return t;
    }

    [Benchmark]
    public Task WithCTandTimeout()
    {
        Task t = _sem.WaitAsync(TimeSpan.FromMinutes(1), _cts.Token);
        _sem.Release();
        return t;
    }
}

[ghost]

Tagging subscribers to this area: @mangod9
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Method	Toolchain	Mean	Ratio	Allocated
WithCT	\main\CoreRun.exe	1.103 us	1.00	496 B
WithCT	\pr\CoreRun.exe	1.032 us	0.94	440 B
WithTimeout	\main\CoreRun.exe	1.492 us	1.00	888 B
WithTimeout	\pr\CoreRun.exe	1.103 us	0.74	536 B
WithCTandTimeout	\main\CoreRun.exe	1.589 us	1.00	904 B
WithCTandTimeout	\pr\CoreRun.exe	1.200 us	0.75	536 B

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Diagnosers;
using BenchmarkDotNet.Running;
using System;
using System.Threading.Tasks;
using System.Threading;

[MemoryDiagnoser]
public class Program
{
    public static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private SemaphoreSlim _sem = new SemaphoreSlim(0, 1);
    private CancellationTokenSource _cts = new CancellationTokenSource();

    [Benchmark]
    public Task WithCT()
    {
        Task t = _sem.WaitAsync(_cts.Token);
        _sem.Release();
        return t;
    }

    [Benchmark]
    public Task WithTimeout()
    {
        Task t = _sem.WaitAsync(TimeSpan.FromMinutes(1));
        _sem.Release();
        return t;
    }

    [Benchmark]
    public Task WithCTandTimeout()
    {
        Task t = _sem.WaitAsync(TimeSpan.FromMinutes(1), _cts.Token);
        _sem.Release();
        return t;
    }
}

Author:	stephentoub
Assignees:	-
Labels:	area-System.Threading, tenet-performance
Milestone:	6.0.0

[mangod9]

Appears that there are some test failures though.

[stephentoub]

Yes, there's one test deterministically failing. I know why. What I need to figure out is why it ever passed prior to this :-)

[davidfowl]

Why not Task.Yield()? Do you care about avoiding the sync context?

[stephentoub]

Do you care about avoiding the sync context?

Always :)

[davidfowl]

What about the extra delegate allocation tho 🙃

[stephentoub]

What about the extra delegate allocation tho

That occurs only if cancellation is requested? I'm not worried about it :)