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System.GC F# snippets (#7624)
* GC F# snippets * related type snippet refs
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‎samples/snippets/fsharp/System/GC/CancelFullGCNotification/Program.fs

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// <Snippet1>
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// <Snippet2>
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open System
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open System.Threading
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// Variable for continual checking in the
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// While loop in the WaitForFullGCProc method.
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let mutable checkForNotify = false
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// Variable for suspending work
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// (such servicing allocated server requests)
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// after a notification is received and then
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// resuming allocation after inducing a garbage collection.
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let mutable bAllocate = false
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// Variable for ending the example.
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let mutable finalExit = false
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// Collection for objects that simulate the server request workload.
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let load = ResizeArray<byte []>()
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// <Snippet9>
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let redirectRequests () =
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// Code that sends requests
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// to other servers.
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// Suspend work.
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bAllocate <- false
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let finishExistingRequests () =
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// Code that waits a period of time
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// for pending requests to finish.
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// Clear the simulated workload.
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load.Clear()
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let acceptRequests () =
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// Code that resumes processing
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// requests on this server.
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// Resume work.
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bAllocate <- true
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// </Snippet9>
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// <Snippet5>
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let onFullGCApproachNotify () =
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printfn "Redirecting requests."
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// Method that tells the request queuing
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// server to not direct requests to this server.
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redirectRequests ()
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// Method that provides time to
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// finish processing pending requests.
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finishExistingRequests ()
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// This is a good time to induce a GC collection
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// because the runtime will induce a full GC soon.
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// To be very careful, you can check precede with a
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// check of the GC.GCCollectionCount to make sure
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// a full GC did not already occur since last notified.
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GC.Collect()
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printfn "Induced a collection."
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// </Snippet5>
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// <Snippet6>
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let onFullGCCompleteEndNotify () =
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// Method that informs the request queuing server
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// that this server is ready to accept requests again.
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acceptRequests ()
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printfn "Accepting requests again."
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// </Snippet6>
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// <Snippet8>
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let waitForFullGCProc () =
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let mutable broken = false
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while not broken do
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let mutable broken = false
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// CheckForNotify is set to true and false in Main.
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while checkForNotify && not broken do
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// <Snippet3>
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// Check for a notification of an approaching collection.
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match GC.WaitForFullGCApproach() with
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| GCNotificationStatus.Succeeded ->
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printfn "GC Notification raised."
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onFullGCApproachNotify ()
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// <Snippet4>
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// Check for a notification of a completed collection.
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match GC.WaitForFullGCComplete() with
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| GCNotificationStatus.Succeeded ->
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printfn "GC Notification raised."
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onFullGCCompleteEndNotify ()
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| GCNotificationStatus.Canceled ->
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printfn "GC Notification cancelled."
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broken <- true
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| _ ->
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// Could be a time out.
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printfn "GC Notification not applicable."
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broken <- true
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// </Snippet4>
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| GCNotificationStatus.Canceled ->
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printfn "GC Notification cancelled."
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broken <- true
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| _ ->
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// This can occur if a timeout period
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// is specified for WaitForFullGCApproach(Timeout)
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// or WaitForFullGCComplete(Timeout)
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// and the time out period has elapsed.
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printfn "GC Notification not applicable."
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broken <- true
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// </Snippet3>
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Thread.Sleep 500
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// FinalExit is set to true right before
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// the main thread cancelled notification.
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if finalExit then broken <- true
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// </Snippet8>
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try
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// Register for a notification.
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GC.RegisterForFullGCNotification(10, 10)
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printfn "Registered for GC notification."
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checkForNotify <- true
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bAllocate <- true
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// Start a thread using WaitForFullGCProc.
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let thWaitForFullGC = Thread(ThreadStart waitForFullGCProc)
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thWaitForFullGC.Start()
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// While the thread is checking for notifications in
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// WaitForFullGCProc, create objects to simulate a server workload.
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try
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let mutable lastCollCount = 0
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let mutable newCollCount = 0
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let mutable broken = false
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while not broken do
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if bAllocate then
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load.Add(Array.zeroCreate<byte> 1000)
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newCollCount <- GC.CollectionCount 2
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if newCollCount <> lastCollCount then
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// Show collection count when it increases:
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printfn $"Gen 2 collection count: {GC.CollectionCount(2)}"
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lastCollCount <- newCollCount
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// For ending the example (arbitrary).
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if newCollCount = 500 then
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finalExit <- true
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checkForNotify <- false
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broken <- true
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with :? OutOfMemoryException -> printfn "Out of memory."
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// <Snippet7>
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finalExit <- true
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checkForNotify <- false
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GC.CancelFullGCNotification()
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// </Snippet7>
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with :? InvalidOperationException as invalidOp ->
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printfn $"GC Notifications are not supported while concurrent GC is enabled.\n{invalidOp.Message}"
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// </Snippet2>
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// </Snippet1>

‎samples/snippets/fsharp/System/GC/CancelFullGCNotification/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="Program.fs" />
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</ItemGroup>
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</Project>

‎samples/snippets/fsharp/System/GC/Collect/Program.fs

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module Program
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//<Snippet1>
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open System
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GC.Collect(2, GCCollectionMode.Optimized)
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// </Snippet1>

‎samples/snippets/fsharp/System/GC/Collect/class1.fs

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module class1
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// <Snippet1>
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open System
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let maxGarbage = 1000
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let makeSomeGarbage () =
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// Create objects and release them to fill up memory with unused objects.
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for _ = 1 to maxGarbage do
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Version() |> ignore
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// Put some objects in memory.
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makeSomeGarbage()
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printfn $"Memory used before collection: {GC.GetTotalMemory false:N0}"
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// Collect all generations of memory.
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GC.Collect()
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printfn $"Memory used after full collection: {GC.GetTotalMemory true:N0}"
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// The output from the example resembles the following:
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// Memory used before collection: 79,392
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// Memory used after full collection: 52,640
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// </Snippet1>

‎samples/snippets/fsharp/System/GC/Collect/collect4.fs

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module collect4
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open System
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open System.Runtime
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let createObjects () =
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Array.init 10000 (fun i ->
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let s1= "word1"
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let s2 = "word2"
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s1 + " " + s2 )
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|> ignore
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createObjects ()
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printfn $"Memory allocated before GC: {GC.GetTotalMemory false:N0}"
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// <Snippet1>
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GCSettings.LargeObjectHeapCompactionMode <- GCLargeObjectHeapCompactionMode.CompactOnce
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GC.Collect(2, GCCollectionMode.Forced, true, true)
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// </Snippet1>
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printfn $"Memory allocated after GC: {GC.GetTotalMemory false:N0}"

‎samples/snippets/fsharp/System/GC/Collect/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="lohcompactionmode1.fs" />
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<Compile Include="class1.fs" />
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<Compile Include="Program.fs" />
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<Compile Include="collect4.fs" />
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</ItemGroup>
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</Project>

‎samples/snippets/fsharp/System/GC/Collect/lohcompactionmode1.fs

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module lohcompactionmode1
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open System
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open System.Runtime
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// <Snippet1>
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GCSettings.LargeObjectHeapCompactionMode <- GCLargeObjectHeapCompactionMode.CompactOnce
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GC.Collect()
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// </Snippet1>

‎samples/snippets/fsharp/System/GC/EndNoGCRegion/endnogcregion1.fs

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open System
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open System.Runtime
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// <Snippet1>
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if GCSettings.LatencyMode = GCLatencyMode.NoGCRegion then
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GC.EndNoGCRegion()
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// </Snippet1>

‎samples/snippets/fsharp/System/GC/EndNoGCRegion/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="endnogcregion1.fs" />
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</ItemGroup>
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</Project>

‎samples/snippets/fsharp/System/GC/GetGeneration/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="systemgcgetgenerationweak.fs" />
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</ItemGroup>
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</Project>

‎samples/snippets/fsharp/System/GC/GetGeneration/systemgcgetgenerationweak.fs

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//<snippet1>
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open System
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let maxGarbage = 1000
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[<AllowNullLiteral>]
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type MyGCCollectClass() =
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member _.MakeSomeGarbage() =
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for i = 1 to maxGarbage do
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// Create objects and release them to fill up memory
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// with unused objects.
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Version() |> ignore
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// Create a strong reference to an object.
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let mutable myGCCol = MyGCCollectClass()
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// Put some objects in memory.
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myGCCol.MakeSomeGarbage()
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// Get the generation of managed memory where myGCCol is stored.
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printfn $"The object is in generation: {GC.GetGeneration myGCCol}"
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// Perform a full garbage collection.
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// Because there is a strong reference to myGCCol, it will
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// not be garbage collected.
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GC.Collect()
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// Get the generation of managed memory where myGCCol is stored.
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printfn $"The object is in generation: {GC.GetGeneration myGCCol}"
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// Create a WeakReference to myGCCol.
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let wkref = WeakReference myGCCol
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// Remove the strong reference to myGCCol.
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myGCCol <- null
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// Get the generation of managed memory where wkref is stored.
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printfn $"The WeakReference to the object is in generation: {GC.GetGeneration wkref}"
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// Perform another full garbage collection.
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// A WeakReference will not survive a garbage collection.
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GC.Collect()
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// Try to get the generation of managed memory where wkref is stored.
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// Because it has been collected, an exception will be thrown.
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try
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printfn $"The WeakReference to the object is in generation: {GC.GetGeneration wkref}"
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stdin.Read() |> ignore
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with e ->
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printfn $"The WeakReference to the object has been garbage collected: '{e}'"
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stdin.Read() |> ignore
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//</snippet1>

‎samples/snippets/fsharp/System/GC/KeepAlive/fs.fsproj

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="gckeepalive.fs" />
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</ItemGroup>
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</Project>

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