System.Timers F# snippets (dotnet#8861)

Author: albert-du

snippets/fsharp/System.Timers/ElapsedEventArgs/Overview/AsyncHandlerEx1.fs

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+module AsyncHanderEx
+// <Snippet3>
+open System
+open System.Threading.Tasks
+open System.Timers
+
+let handleTimer () =
+    printfn "\nHandler not implemented..."
+    raise (NotImplementedException()): Task
+
+let timer = new Timer 1000
+timer.Elapsed.AddHandler(fun sender e -> task { do! handleTimer () } |> ignore)
+timer.Start()
+printf "Press any key to exit... "
+Console.ReadKey() |> ignore
+
+// The example displays output like the following:
+//   Press any key to exit...
+//   Handler not implemented...
+//
+//   Unhandled Exception: System.NotImplementedException: The method or operation is not implemented.
+//      at Example.HandleTimer()
+//      at Example.<<Main>b__0>d__2.MoveNext()
+//   --- End of stack trace from previous location where exception was thrown ---
+//      at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c__DisplayClass2.<ThrowAsync>b__5(Object state)
+//      at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
+//      at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
+//      at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
+//      at System.Threading.ThreadPoolWorkQueue.Dispatch()
+// </Snippet3>

snippets/fsharp/System.Timers/ElapsedEventArgs/Overview/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="AsyncHandlerEx1.fs" />
+    <Compile Include="timer1.fs" />
+    <Compile Include="timer2a.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.Timers/ElapsedEventArgs/Overview/timer1.fs

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+module timer1
+
+// <Snippet1>
+open System.Timers
+
+let onTimedEvent source (e: ElapsedEventArgs) =
+    printfn $"The Elapsed event was raised at {e.SignalTime}"
+
+// Create a timer and set a two second interval.
+let aTimer = new Timer()
+aTimer.Interval <- 2000
+
+// Hook up the Elapsed event for the timer. 
+aTimer.Elapsed.AddHandler onTimedEvent
+
+// Have the timer fire repeated events (true is the default)
+aTimer.AutoReset <- true
+
+// Start the timer
+aTimer.Enabled <- true
+
+printfn "Press the Enter key to exit the program at any time... "
+stdin.ReadLine() |> ignore
+
+// The example displays output like the following: 
+//       Press the Enter key to exit the program at any time... 
+//       The Elapsed event was raised at 5/20/2015 8:48:58 PM 
+//       The Elapsed event was raised at 5/20/2015 8:49:00 PM 
+//       The Elapsed event was raised at 5/20/2015 8:49:02 PM 
+//       The Elapsed event was raised at 5/20/2015 8:49:04 PM 
+//       The Elapsed event was raised at 5/20/2015 8:49:06 PM 
+// </Snippet1>

snippets/fsharp/System.Timers/ElapsedEventArgs/Overview/timer2a.fs

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+module timer2a
+
+// <Snippet2>
+open System
+open System.Timers
+
+let onTimedEvent source (e: ElapsedEventArgs) =
+    printfn $"""The Elapsed event was raised at {e.SignalTime.ToString "HH:mm:ss.fff"}"""
+
+// Create a timer with a two second interval.
+let aTimer = new Timer 2000
+// Hook up the Elapsed event for the timer. 
+aTimer.Elapsed.AddHandler onTimedEvent
+aTimer.AutoReset <- true
+aTimer.Enabled <- true
+
+printfn "\nPress the Enter key to exit the application...\n"
+printfn $"""The application started at {DateTime.Now.ToString "HH:mm:ss.fff"}"""
+stdin.ReadLine() |> ignore
+aTimer.Stop()
+aTimer.Dispose()
+
+printfn "Terminating the application..."
+
+// The example displays output like the following:
+//       Press the Enter key to exit the application...
+//
+//       The application started at 09:40:29.068
+//       The Elapsed event was raised at 09:40:31.084
+//       The Elapsed event was raised at 09:40:33.100
+//       The Elapsed event was raised at 09:40:35.100
+//       The Elapsed event was raised at 09:40:37.116
+//       The Elapsed event was raised at 09:40:39.116
+//       The Elapsed event was raised at 09:40:41.117
+//       The Elapsed event was raised at 09:40:43.132
+//       The Elapsed event was raised at 09:40:45.133
+//       The Elapsed event was raised at 09:40:47.148
+//
+//       Terminating the application...
+// </Snippet2>

snippets/fsharp/System.Timers/ElapsedEventHandler/Overview/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="source.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.Timers/ElapsedEventHandler/Overview/source.fs

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+// <Snippet1>
+// To avoid confusion with other Timer classes, this sample always uses the fully-qualified
+// name of System.Timers.Timer instead of a using statement for System.Timers.
+module Example
+
+let mutable aTimer = new System.Timers.Timer()
+
+let onTimedEvent source (e: System.Timers.ElapsedEventArgs) =
+    printfn $"The Elapsed event was raised at {e.SignalTime}"
+
+[<EntryPoint>]
+let main _ =
+    // Normally, the timer is declared at the class level, so that it stays in scope as long as it
+    // is needed. If the timer is declared in a long-running method, KeepAlive must be used to prevent
+    // the JIT compiler from allowing aggressive garbage collection to occur before the method ends.
+    // You can experiment with this by commenting out the class-level declaration and uncommenting
+    // the declaration below then uncomment the GC.KeepAlive(aTimer) at the end of the method.
+    //System.Timers.Timer aTimer
+
+    // Set a two second interval.
+    aTimer.Interval <- 2000
+
+    // Alternate method: create a Timer with an interval argument to the constructor.
+    //aTimer = new System.Timers.Timer(2000)
+
+    // Create a timer with a two second interval.
+    aTimer <- new System.Timers.Timer(2000)
+
+    // Hook up the Elapsed event for the timer.
+    aTimer.Elapsed.AddHandler onTimedEvent
+
+    // Have the timer fire repeated events (true is the default)
+    aTimer.AutoReset <- true
+
+    // Start the timer
+    aTimer.Enabled <- true
+
+    printfn "Press the Enter key to exit the program at any time... "
+    stdin.ReadLine() |> ignore
+
+    // If the timer is declared in a long-running method, use KeepAlive to prevent garbage collection
+    // from occurring before the method ends.
+    //GC.KeepAlive(aTimer)
+    0
+
+// This example displays output like the following:
+//       Press the Enter key to exit the program at any time...
+//       The Elapsed event was raised at 5/20/2015 8:48:58 PM
+//       The Elapsed event was raised at 5/20/2015 8:49:00 PM
+//       The Elapsed event was raised at 5/20/2015 8:49:02 PM
+//       The Elapsed event was raised at 5/20/2015 8:49:04 PM
+//       The Elapsed event was raised at 5/20/2015 8:49:06 PM
+
+// </Snippet1>

snippets/fsharp/System.Timers/Timer/AutoReset/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="source.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.Timers/Timer/AutoReset/source.fs

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+// <Snippet1>
+open System.Threading
+open System.Timers
+
+// Handle the Elapsed event.
+let onTimedEvent source e =
+    printfn "Hello World!"
+
+// Create a timer with a 1.5 second interval.
+let interval = 1500.
+let aTimer = new Timer(interval)
+
+// Hook up the event handler for the Elapsed event.
+aTimer.Elapsed.AddHandler(ElapsedEventHandler onTimedEvent)
+
+// Only raise the event the first time Interval elapses.
+aTimer.AutoReset <- false
+aTimer.Enabled <- true
+
+// Ensure the event fires before the exit message appears.
+Thread.Sleep(interval * 2. |> int)
+printfn "Press the Enter key to exit the program."
+stdin.ReadLine() |> ignore
+
+// This example displays the following output:
+//       Hello World!
+//       Press the Enter key to exit the program.
+// </Snippet1>

snippets/fsharp/System.Timers/Timer/Interval/fs.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="interval2.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System.Timers/Timer/Interval/interval2.fs

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+// What is the resolution of the system clock?
+
+// <Snippet1>
+open System
+open System.IO
+open System.Timers
+
+let aTimer = new Timer 5
+let eventlog = ResizeArray()
+let mutable nEventsFired = 0
+let mutable previousTime = DateTime()
+       
+let onTimedEvent source (e: ElapsedEventArgs) =
+    String.Format("Elapsed event at {0:HH':'mm':'ss.ffffff} ({1})", e.SignalTime, if nEventsFired = 0 then 0. else (e.SignalTime - previousTime).TotalMilliseconds)
+    |> eventlog.Add
+    nEventsFired <- nEventsFired + 1
+
+    previousTime <- e.SignalTime
+
+    if nEventsFired = 20 then
+        printfn "No more events will fire..."
+        aTimer.Enabled <- false
+
+[<EntryPoint>]
+let main _ =
+    use sr = new StreamWriter(@".\Interval.txt")
+    // Create a timer with a five millisecond interval.
+    aTimer.Elapsed.AddHandler onTimedEvent
+    // Hook up the Elapsed event for the timer. 
+    aTimer.AutoReset <- true
+    sr.WriteLine $"The timer should fire every {aTimer.Interval} milliseconds."
+    aTimer.Enabled <- true
+
+    printfn "Press the Enter key to exit the program... "
+    stdin.ReadLine() |> ignore
+    for item in eventlog do
+        sr.WriteLine item
+    printfn "Terminating the application..."
+    0
+
+// The example writes output like the following to a file:
+//       The timer should fire every 5 milliseconds.
+//       Elapsed event at 08:42:49.370344 (0)
+//       Elapsed event at 08:42:49.385345 (15.0015)
+//       Elapsed event at 08:42:49.400347 (15.0015)
+//       Elapsed event at 08:42:49.415348 (15.0015)
+//       Elapsed event at 08:42:49.430350 (15.0015)
+//       Elapsed event at 08:42:49.445351 (15.0015)
+//       Elapsed event at 08:42:49.465353 (20.002)
+//       Elapsed event at 08:42:49.480355 (15.0015)
+//       Elapsed event at 08:42:49.495356 (15.0015)
+//       Elapsed event at 08:42:49.510358 (15.0015)
+//       Elapsed event at 08:42:49.525359 (15.0015)
+//       Elapsed event at 08:42:49.540361 (15.0015)
+//       Elapsed event at 08:42:49.555362 (15.0015)
+//       Elapsed event at 08:42:49.570364 (15.0015)
+//       Elapsed event at 08:42:49.585365 (15.0015)
+//       Elapsed event at 08:42:49.605367 (20.002)
+//       Elapsed event at 08:42:49.620369 (15.0015)
+//       Elapsed event at 08:42:49.635370 (15.0015)
+//       Elapsed event at 08:42:49.650372 (15.0015)
+//       Elapsed event at 08:42:49.665373 (15.0015)
+// </Snippet1>