├── .gitignore ├── LazyTask.Test ├── LazyTask.Test.csproj └── Tests.cs ├── LazyTask.sln ├── LazyTask ├── LazyTask.cs ├── LazyTask.csproj └── LazyTaskMethodBuilder.cs └── README.md /.gitignore: -------------------------------------------------------------------------------- 1 | ## Ignore Visual Studio temporary files, build results, and 2 | ## files generated by popular Visual Studio add-ons. 3 | ## 4 | ## Get latest from https://github.com/github/gitignore/blob/master/VisualStudio.gitignore 5 | 6 | # User-specific files 7 | *.rsuser 8 | *.suo 9 | *.user 10 | *.userosscache 11 | *.sln.docstates 12 | 13 | # User-specific files (MonoDevelop/Xamarin Studio) 14 | *.userprefs 15 | 16 | # Mono auto generated files 17 | mono_crash.* 18 | 19 | # Build results 20 | [Dd]ebug/ 21 | [Dd]ebugPublic/ 22 | [Rr]elease/ 23 | [Rr]eleases/ 24 | x64/ 25 | x86/ 26 | [Aa][Rr][Mm]/ 27 | [Aa][Rr][Mm]64/ 28 | bld/ 29 | [Bb]in/ 30 | [Oo]bj/ 31 | [Ll]og/ 32 | [Ll]ogs/ 33 | 34 | # Visual Studio 2015/2017 cache/options directory 35 | .vs/ 36 | # Uncomment if you have tasks that create the project's static files in wwwroot 37 | #wwwroot/ 38 | 39 | # Visual Studio 2017 auto generated files 40 | Generated\ Files/ 41 | 42 | # MSTest test Results 43 | [Tt]est[Rr]esult*/ 44 | [Bb]uild[Ll]og.* 45 | 46 | # NUnit 47 | *.VisualState.xml 48 | TestResult.xml 49 | nunit-*.xml 50 | 51 | # Build Results of an ATL Project 52 | [Dd]ebugPS/ 53 | [Rr]eleasePS/ 54 | dlldata.c 55 | 56 | # Benchmark Results 57 | BenchmarkDotNet.Artifacts/ 58 | 59 | # .NET Core 60 | project.lock.json 61 | project.fragment.lock.json 62 | artifacts/ 63 | 64 | # StyleCop 65 | StyleCopReport.xml 66 | 67 | # Files built by Visual Studio 68 | *_i.c 69 | *_p.c 70 | *_h.h 71 | *.ilk 72 | *.meta 73 | *.obj 74 | *.iobj 75 | *.pch 76 | *.pdb 77 | *.ipdb 78 | *.pgc 79 | *.pgd 80 | *.rsp 81 | *.sbr 82 | *.tlb 83 | *.tli 84 | *.tlh 85 | *.tmp 86 | *.tmp_proj 87 | *_wpftmp.csproj 88 | *.log 89 | *.vspscc 90 | *.vssscc 91 | .builds 92 | *.pidb 93 | *.svclog 94 | *.scc 95 | 96 | # Chutzpah Test files 97 | _Chutzpah* 98 | 99 | # Visual C++ cache files 100 | ipch/ 101 | *.aps 102 | *.ncb 103 | *.opendb 104 | *.opensdf 105 | *.sdf 106 | *.cachefile 107 | *.VC.db 108 | *.VC.VC.opendb 109 | 110 | # Visual Studio profiler 111 | *.psess 112 | *.vsp 113 | *.vspx 114 | *.sap 115 | 116 | # Visual Studio Trace Files 117 | *.e2e 118 | 119 | # TFS 2012 Local Workspace 120 | $tf/ 121 | 122 | # Guidance Automation Toolkit 123 | *.gpState 124 | 125 | # ReSharper is a .NET coding add-in 126 | _ReSharper*/ 127 | *.[Rr]e[Ss]harper 128 | *.DotSettings.user 129 | 130 | # TeamCity is a build add-in 131 | _TeamCity* 132 | 133 | # DotCover is a Code Coverage Tool 134 | *.dotCover 135 | 136 | # AxoCover is a Code Coverage Tool 137 | .axoCover/* 138 | !.axoCover/settings.json 139 | 140 | # Visual Studio code coverage results 141 | *.coverage 142 | *.coveragexml 143 | 144 | # NCrunch 145 | _NCrunch_* 146 | .*crunch*.local.xml 147 | nCrunchTemp_* 148 | 149 | # MightyMoose 150 | *.mm.* 151 | AutoTest.Net/ 152 | 153 | # Web workbench (sass) 154 | .sass-cache/ 155 | 156 | # Installshield output folder 157 | [Ee]xpress/ 158 | 159 | # DocProject is a documentation generator add-in 160 | DocProject/buildhelp/ 161 | DocProject/Help/*.HxT 162 | DocProject/Help/*.HxC 163 | DocProject/Help/*.hhc 164 | DocProject/Help/*.hhk 165 | DocProject/Help/*.hhp 166 | DocProject/Help/Html2 167 | DocProject/Help/html 168 | 169 | # Click-Once directory 170 | publish/ 171 | 172 | # Publish Web Output 173 | *.[Pp]ublish.xml 174 | *.azurePubxml 175 | # Note: Comment the next line if you want to checkin your web deploy settings, 176 | # but database connection strings (with potential passwords) will be unencrypted 177 | *.pubxml 178 | *.publishproj 179 | 180 | # Microsoft Azure Web App publish settings. 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2 | using System.Collections.Generic; 3 | using System.Threading; 4 | using System.Threading.Tasks; 5 | using NUnit.Framework; 6 | 7 | namespace LazyTask.Test 8 | { 9 | public class Tests 10 | { 11 | [Test] 12 | [TestCase(false, false)] 13 | [TestCase(false, true)] 14 | [TestCase(true, false)] 15 | [TestCase(true, true)] 16 | public async Task TestBasic(bool asyncWait, bool asyncAction) 17 | { 18 | int counter = 0; 19 | 20 | var lt = LazyAction(); 21 | if (asyncWait) 22 | { 23 | await Task.Delay(1); 24 | } 25 | Assert.AreEqual(0, counter); 26 | 27 | int res = await lt; 28 | 29 | Assert.AreEqual(1, counter); 30 | Assert.AreEqual(42, res); 31 | 32 | async LazyTask LazyAction() 33 | { 34 | counter++; 35 | if (asyncAction) 36 | { 37 | await Task.Delay(1); 38 | } 39 | return 42; 40 | } 41 | } 42 | 43 | 44 | [Test] 45 | [TestCase(false, false)] 46 | [TestCase(false, true)] 47 | [TestCase(true, false)] 48 | [TestCase(true, true)] 49 | public async Task TestException(bool asyncWait, bool asyncAction) 50 | { 51 | int counter = 0; 52 | 53 | var lt = LazyAction(); 54 | if (asyncWait) 55 | { 56 | await Task.Delay(1); 57 | } 58 | Assert.AreEqual(0, counter); 59 | 60 | Exception ex = null; 61 | try 62 | { 63 | await lt; 64 | } 65 | catch (Exception e) 66 | { 67 | ex = e; 68 | } 69 | 70 | Assert.AreEqual(1, counter); 71 | Assert.NotNull(ex); 72 | Assert.AreEqual("Err", ex.Message); 73 | 74 | async LazyTask LazyAction() 75 | { 76 | counter++; 77 | if (asyncAction) 78 | { 79 | await Task.Delay(1); 80 | } 81 | throw new Exception("Err"); 82 | } 83 | } 84 | 85 | [Test] 86 | public void TestMultiThreading() 87 | { 88 | //The test shows that locks are really required in LazyTasks 89 | 90 | int counter = 0; 91 | 92 | ManualResetEvent syncStart = new ManualResetEvent(false); 93 | 94 | const int num = 100; 95 | const int threadsNum = 10; 96 | 97 | for (int i = 0; i < num; i++) 98 | { 99 | 100 | var lt = LazyAction(); 101 | 102 | List threads = new List(); 103 | 104 | for (int j = 0; j < threadsNum; j++) 105 | { 106 | threads.Add(new Thread(() => ThreadBody(lt))); 107 | } 108 | 109 | foreach (var thread in threads) 110 | { 111 | thread.Start(); 112 | } 113 | 114 | syncStart.Set(); 115 | 116 | foreach (var thread in threads) 117 | { 118 | thread.Join(); 119 | } 120 | } 121 | 122 | Assert.AreEqual(num, counter); 123 | 124 | void ThreadBody(LazyTask lt) 125 | { 126 | AutoResetEvent ev = new AutoResetEvent(false); 127 | 128 | syncStart.WaitOne(); 129 | 130 | lt.OnCompleted(() => 131 | { 132 | Assert.AreEqual(42, lt.GetResult()); 133 | ev.Set(); 134 | }); 135 | ev.WaitOne(); 136 | } 137 | 138 | async LazyTask LazyAction() 139 | { 140 | counter++; 141 | await Task.Delay(1); 142 | return 42; 143 | } 144 | } 145 | 146 | } 147 | } -------------------------------------------------------------------------------- /LazyTask.sln: -------------------------------------------------------------------------------- 1 |  2 | Microsoft Visual Studio Solution File, Format Version 12.00 3 | # Visual Studio Version 16 4 | VisualStudioVersion = 16.0.30114.105 5 | MinimumVisualStudioVersion = 10.0.40219.1 6 | Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "LazyTask", "LazyTask\LazyTask.csproj", "{4F06344F-E9E1-4AB3-A979-32DBC544CF5A}" 7 | EndProject 8 | Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "LazyTask.Test", "LazyTask.Test\LazyTask.Test.csproj", "{FE42FE8F-0AB1-4A05-B827-C243F0226CB2}" 9 | EndProject 10 | Global 11 | GlobalSection(SolutionConfigurationPlatforms) = preSolution 12 | Debug|Any CPU = Debug|Any CPU 13 | Release|Any CPU = Release|Any CPU 14 | EndGlobalSection 15 | GlobalSection(ProjectConfigurationPlatforms) = postSolution 16 | {4F06344F-E9E1-4AB3-A979-32DBC544CF5A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU 17 | {4F06344F-E9E1-4AB3-A979-32DBC544CF5A}.Debug|Any CPU.Build.0 = Debug|Any CPU 18 | {4F06344F-E9E1-4AB3-A979-32DBC544CF5A}.Release|Any CPU.ActiveCfg = Release|Any CPU 19 | {4F06344F-E9E1-4AB3-A979-32DBC544CF5A}.Release|Any CPU.Build.0 = Release|Any CPU 20 | {FE42FE8F-0AB1-4A05-B827-C243F0226CB2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU 21 | {FE42FE8F-0AB1-4A05-B827-C243F0226CB2}.Debug|Any CPU.Build.0 = Debug|Any CPU 22 | {FE42FE8F-0AB1-4A05-B827-C243F0226CB2}.Release|Any CPU.ActiveCfg = Release|Any CPU 23 | {FE42FE8F-0AB1-4A05-B827-C243F0226CB2}.Release|Any CPU.Build.0 = Release|Any CPU 24 | EndGlobalSection 25 | GlobalSection(SolutionProperties) = preSolution 26 | HideSolutionNode = FALSE 27 | EndGlobalSection 28 | GlobalSection(ExtensibilityGlobals) = postSolution 29 | SolutionGuid = {05EE4180-BFE0-48CA-ACBC-54F3127D8081} 30 | EndGlobalSection 31 | EndGlobal 32 | -------------------------------------------------------------------------------- /LazyTask/LazyTask.cs: -------------------------------------------------------------------------------- 1 | using System; 2 | using System.Runtime.CompilerServices; 3 | using System.Runtime.ExceptionServices; 4 | 5 | namespace LazyTask 6 | { 7 | [AsyncMethodBuilder(typeof(LazyTaskMethodBuilder<>))] 8 | public class LazyTask : INotifyCompletion 9 | { 10 | private readonly object _syncObj = new object(); 11 | 12 | private T _result; 13 | 14 | private Exception _exception; 15 | 16 | private IAsyncStateMachine _asyncStateMachine; 17 | 18 | private Action _continuation; 19 | 20 | internal LazyTask() 21 | { 22 | } 23 | 24 | public T GetResult() 25 | { 26 | lock (this._syncObj) 27 | { 28 | if (this._exception != null) 29 | { 30 | ExceptionDispatchInfo.Throw(this._exception); 31 | } 32 | 33 | if (!this.IsCompleted) 34 | { 35 | throw new Exception("Not Completed"); 36 | } 37 | 38 | return this._result; 39 | } 40 | } 41 | 42 | public bool IsCompleted { get; private set; } 43 | 44 | public void OnCompleted(Action continuation) 45 | { 46 | lock (this._syncObj) 47 | { 48 | if (this._asyncStateMachine != null) 49 | { 50 | try 51 | { 52 | this._asyncStateMachine.MoveNext(); 53 | } 54 | finally 55 | { 56 | this._asyncStateMachine = null; 57 | } 58 | } 59 | if (this._continuation == null) 60 | { 61 | this._continuation = continuation; 62 | } 63 | else 64 | { 65 | this._continuation += continuation; 66 | } 67 | this.TryCallContinuation(); 68 | } 69 | } 70 | 71 | public LazyTask GetAwaiter() => this; 72 | 73 | internal void SetResult(T result) 74 | { 75 | lock (this._syncObj) 76 | { 77 | this._result = result; 78 | this.IsCompleted = true; 79 | this.TryCallContinuation(); 80 | } 81 | } 82 | 83 | internal void SetException(Exception exception) 84 | { 85 | lock (this._syncObj) 86 | { 87 | this._exception = exception; 88 | this.IsCompleted = true; 89 | this.TryCallContinuation(); 90 | } 91 | } 92 | 93 | internal void SetStateMachine(IAsyncStateMachine stateMachine) 94 | { 95 | this._asyncStateMachine = stateMachine; 96 | } 97 | 98 | private void TryCallContinuation() 99 | { 100 | if (this.IsCompleted && this._continuation != null) 101 | { 102 | try 103 | { 104 | this._continuation(); 105 | } 106 | finally 107 | { 108 | this._continuation = null; 109 | } 110 | } 111 | } 112 | } 113 | } 114 | -------------------------------------------------------------------------------- /LazyTask/LazyTask.csproj: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | netstandard2.1 5 | 6 | 7 | 8 | -------------------------------------------------------------------------------- /LazyTask/LazyTaskMethodBuilder.cs: -------------------------------------------------------------------------------- 1 | using System; 2 | using System.Runtime.CompilerServices; 3 | 4 | namespace LazyTask 5 | { 6 | public class LazyTaskMethodBuilder 7 | { 8 | public LazyTaskMethodBuilder() => this.Task = new LazyTask(); 9 | 10 | public static LazyTaskMethodBuilder Create() => new LazyTaskMethodBuilder(); 11 | 12 | public void Start(ref TStateMachine stateMachine) where TStateMachine : IAsyncStateMachine 13 | { 14 | //instead of stateMachine.MoveNext(); 15 | this.Task.SetStateMachine(stateMachine); 16 | } 17 | 18 | public void SetStateMachine(IAsyncStateMachine stateMachine) { } 19 | 20 | public void SetException(Exception exception) => this.Task.SetException(exception); 21 | 22 | public void SetResult(T result) => this.Task.SetResult(result); 23 | 24 | public void AwaitOnCompleted(ref TAwaiter awaiter, ref TStateMachine stateMachine) 25 | where TAwaiter : INotifyCompletion 26 | where TStateMachine : IAsyncStateMachine 27 | => 28 | this.GenericAwaitOnCompleted(ref awaiter, ref stateMachine); 29 | 30 | public void AwaitUnsafeOnCompleted(ref TAwaiter awaiter, 31 | ref TStateMachine stateMachine) 32 | where TAwaiter : ICriticalNotifyCompletion 33 | where TStateMachine : IAsyncStateMachine 34 | => 35 | this.GenericAwaitOnCompleted(ref awaiter, ref stateMachine); 36 | 37 | public void GenericAwaitOnCompleted(ref TAwaiter awaiter, ref TStateMachine stateMachine) 38 | where TAwaiter : INotifyCompletion 39 | where TStateMachine : IAsyncStateMachine 40 | { 41 | awaiter.OnCompleted(stateMachine.MoveNext); 42 | } 43 | 44 | public LazyTask Task { get; } 45 | } 46 | } -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # LazyTask 2 | [Writing “Lazy Task” Using New Features of C# 7 (on medium.com)](https://medium.com/@0x1000000/writing-lazy-task-using-new-features-of-c-7-7e9b3f2fda07?source=friends_link&sk=0b5456443aad6b12d0b3f8e117b669bf) 3 | 4 | [Video version with more details](https://youtu.be/zq15I0QB6eM) 5 | --------------------------------------------------------------------------------