Second half of fix to dotnet/fsharp#106

FSharp.Compiler.Service contained a more complete fix for
dotnet/fsharp#106, which relates to the
memory leaks that can arise if type provider instance objects are kept live.
Historically the memory leaks have happened if a type provider registers
itself to listen to file system events (or other notifications), but for some
reason doesn't disconnect those listeners when the type provider is disposed.
This keeps the type provider instance alive - which is a bug in the type
provider - but even worse it can keep '00s MB of data associated with the
compiler state alive as well.

The missing part of the fix is to disconnect the "TypeProviderConfig" callback
when the type providers are disposed, so that even if a type provider instance
hangs on to a reference to the TypeProviderConfig, that doesn't cause the entire
object graph for the compilation session to be retained in memory.

After type provider disposal, any TypeProviderConfig objects provided to the
type provider will now raise ObjectDisposedException when the
SystemRuntimeContainsType method is called.

closes dotnet/fsharp#591
fixes dotnet/fsharp#106

commit d3b2f0e1b7f117de84feadcddc085a3cba307c09
Author: Don Syme <donsyme@fastmail.fm>
Date:   Fri Aug 14 14:35:53 2015 +0100

    testing for 2nd half of 106

commit adebe18e0291935d1b7eebd362abfef4b2dacc49
Author: Don Syme <donsyme@fastmail.fm>
Date:   Fri Aug 14 14:09:51 2015 +0100

    Second half of fix to dotnet/fsharp#106

Author: dsyme

src/fsharp/CompileOps.fs

@@ -3837,10 +3837,19 @@ type TcImports(tcConfigP:TcConfigProvider, initialResolutions:TcAssemblyResoluti
                    referencedAssemblies   = [| for r in resolutions.GetAssemblyResolutions() -> r.resolvedPath |]
                    temporaryFolder        = Path.GetTempPath() }
 
+            // The type provider should not hold strong references to disposed
+            // TcImport objects.  So the callbacks provided in the type provider config
+            // dispatch via a thunk which gets set to a non-resource-capturing 
+            // failing function when the object is disposed. 
+            let systemRuntimeContainsType =  
+                let systemRuntimeContainsTypeRef = ref tcImports.SystemRuntimeContainsType  
+                tcImports.AttachDisposeAction(fun () -> systemRuntimeContainsTypeRef := (fun _ -> raise (System.ObjectDisposedException("The type provider has been disposed"))))  
+                fun arg -> systemRuntimeContainsTypeRef.Value arg  
+
             let providers = 
                 [ for assemblyName in providerAssemblies do
                       yield ExtensionTyping.GetTypeProvidersOfAssembly(fileNameOfRuntimeAssembly, ilScopeRefOfRuntimeAssembly, assemblyName, typeProviderEnvironment, 
-                                                                       tcConfig.isInvalidationSupported, tcConfig.isInteractive, tcImports.SystemRuntimeContainsType, systemRuntimeAssemblyVersion, m) ]
+                                                                       tcConfig.isInvalidationSupported, tcConfig.isInteractive, systemRuntimeContainsType, systemRuntimeAssemblyVersion, m) ]
             let providers = providers |> List.concat
 
             // Note, type providers are disposable objects. The TcImports owns the provider objects - when/if it is disposed, the providers are disposed.

vsintegration/src/unittests/Resources.MockTypeProviders/DummyProviderForLanguageServiceTesting/DummyProviderForLanguageServiceTesting.fs

@@ -115,15 +115,25 @@ module internal TPModule =
 module GlobalCounters = 
     let mutable creations = 0
     let mutable disposals = 0
+    let mutable configs = ([]: TypeProviderConfig list)
     let GetTotalCreations() = creations
     let GetTotalDisposals() = disposals
+    let CheckAllConfigsDisposed() = 
+        for c in configs do 
+            try 
+                c.SystemRuntimeContainsType("System.Object") |> ignore
+                failwith "expected configuration object to be disposed"
+            with :? System.ObjectDisposedException -> 
+                ()
+
 
 
 [<TypeProvider>]
-type HelloWorldProvider() = 
+type HelloWorldProvider(config: TypeProviderConfig) = 
     inherit TypeProviderForNamespaces(TPModule.namespaceName,TPModule.types)
     do GlobalCounters.creations <- GlobalCounters.creations + 1                         
     let mutable disposed = false
+    do GlobalCounters.configs <- config :: GlobalCounters.configs
     interface System.IDisposable with 
         member x.Dispose() = 
             System.Diagnostics.Debug.Assert(not disposed)

vsintegration/src/unittests/Tests.LanguageService.Script.fs

@@ -1628,6 +1628,8 @@ type ScriptTests() as this =
         Assert.IsNotNull(totalCreationsMeth, "totalCreationsMeth should not be null")
         let totalDisposalsMeth = providerCounters.GetMethod("GetTotalDisposals")
         Assert.IsNotNull(totalDisposalsMeth, "totalDisposalsMeth should not be null")
+        let checkConfigsMeth = providerCounters.GetMethod("CheckAllConfigsDisposed")
+        Assert.IsNotNull(checkConfigsMeth, "checkConfigsMeth should not be null")
 
         let providerCounters2 = providerAssembly.GetType("Microsoft.FSharp.TypeProvider.Emit.GlobalCountersForInvalidation")
         Assert.IsNotNull(providerCounters2, "provider counters #2 module should not be null")
@@ -1638,6 +1640,7 @@ type ScriptTests() as this =
 
         let totalCreations() = totalCreationsMeth.Invoke(null, [| |]) :?> int
         let totalDisposals() = totalDisposalsMeth.Invoke(null, [| |]) :?> int
+        let checkConfigsDisposed() = checkConfigsMeth.Invoke(null, [| |]) |> ignore
         let totalInvaldiationHandlersAdded() = totalInvaldiationHandlersAddedMeth.Invoke(null, [| |]) :?> int
         let totalInvaldiationHandlersRemoved() = totalInvaldiationHandlersRemovedMeth.Invoke(null, [| |]) :?> int
 
@@ -1693,6 +1696,7 @@ type ScriptTests() as this =
         ClearLanguageServiceRootCachesAndCollectAndFinalizeAllTransients(this.VS)
         Assert.IsTrue(countDisposals() = 50, "Check6b, at end, countDisposals() = 50 after explicit clearing")
         Assert.IsTrue(countInvaldiationHandlersAdded() - countInvaldiationHandlersRemoved() = 0, "Check6b2, at end, all invalidation handlers removed after explicit cleraring")
+        checkConfigsDisposed()
 
     [<Test>]
     [<Category("TypeProvider")>]