[Xamarin.Android.Build.Tasks] Dispose DirectoryAssemblyResolver instances

Context: https://bugzilla.xamarin.com/show_bug.cgi?id=44529

Commit 1d65825 bumped to Cecil 0.10.0-beta1-v2 and
Java.Interop/a1d3ecc8, which likewise uses Cecil 0.10.0-beta1-v2.

Among the various API changes in Cecil 0.10.x vs. Cecil 0.9.x is a
change to `Mono.Cecil.IAssemblyResolver`, implemented by
`Java.Interop.Tools.Cecil.DirectoryAssemblyResolver`, to implement the
`IDisposable` interface.

Java.Interop/a1d3ecc8 added a `DirectoryAssemblyResolver.Dispose()`
method, but this method didn't *do* anything.

Cecil 0.10.0-beta1-v2 also has a *semantic* change vs. Cecil 0.9.x:
`AssemblyDefinition` is no longer a "purely in-memory" construct.
Instead, it holds a `System.IO.Stream` to the assembly it's reading
(unless `Mono.Cecil.ReaderParameters.InMemory` is `true`).

This semantic change means that an assembly can't be read from and
written to at the same time via different mechanisms, so long as there
is an `AssemblyDefinition` instance to that file.

Which brings us to (private) Bug #44529, in which an `IOException` is
thrown from the `<StripEmbeddedLibraries/>` task:

	Error executing task StripEmbeddedLibraries: System.IO.IOException: Sharing violation on path .../obj/Release/linksrc/Xamarin.Android.NUnitLite.dll
	  at System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.Boolean anonymous, System.IO.FileOptions options) [0x0025f] in <253a3790b2c44512bbca8669ecfc1822>:0
	  at System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share) [0x00000] in <253a3790b2c44512bbca8669ecfc1822>:0
	  at (wrapper remoting-invoke-with-check) System.IO.FileStream:.ctor (string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare)
	  at Mono.Cecil.ModuleDefinition.GetFileStream (System.String fileName, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share) [0x00007] in :0
	  at Mono.Cecil.ModuleDefinition.Write (System.String fileName, Mono.Cecil.WriterParameters parameters) [0x00007] in :0
	  at Mono.Cecil.AssemblyDefinition.Write (System.String fileName, Mono.Cecil.WriterParameters parameters) [0x00001] in :0
	  at Xamarin.Android.Tasks.StripEmbeddedLibraries.Execute () [0x0034a] in <3d5202a5d4874a76a99388021bf1ab1a>:0

The underlying cause of the `IOException` is twofold:

1. `AssemblyDefinition` instances now hold a `FileStream` to the file
    they're reading from (and optionally writing to), and this
    `FileStream` will be kept open until
    `AssemblyDefinition.Dispose()` is called.

2. Nothing in `Xamarin.Android.Build.Tasks` calls
    `AssemblyDefinition.Dispose()`.

Nor should anything in `Xamarin.Android.Build.Tasks` call
`AssemblyDefinition.Dispose()`! (Almost) All `AssemblyDefinition`
instances are *cached* within `DirectoryAssemblyResolver` instances,
and nothing calls `DirectoryAssemblyResolver.Dispose()` either!
(Not that this matters *too* much, becuase
`DirectoryAssemblyResolver.Dispose()` is currently a no-op.)

There is no sane reasoning here: so long as we're using
`DirectoryAssemblyResolver`, we're going to have more files open
(compared to when Cecil 0.9.x was used), which can result in file
sharing problems and the above `IOException`.

The way foward is:

1. `Java.Interop.Tools.Cecil.DirectoryAssemblyResolver` needs to be
    updated so that
    [`DirectoryAssemblyResolver.Dispose()` is useful][0], i.e. that it
    will `Dispose()` of all held `AssemblyDefinition` instances.

2. The Java.Interop subproject reference needs to be updated to pick
    up (1).

    TODO: do this. ;-)

3. `Xamarin.Android.Build.Tasks.dll` needs to be updated so that
    `DirectoryAssemblyResolver.Dispose()` is used.

4. All code, in particular `Xamarin.Andorid.Build.Tasks.dll`, needs to
    be reviewed to ensure it doesn't do anything "stupid" with
    `AssemblyDefinition` instances and/or `DirectoryAssemblyResolver.`

    Examples of "stupid" things include:

    * `Dispose()`ing of the return value from
      `DirectoryAssemblyResolver.Load()`:

            resolver.Load (assemblyName).Dispose();

    * Treating `AssemblyDefinition` instances in a manner inconsistent
      with how `DirectoryAssemblyResolver` loads them.
      `DirectoryAssemblyResolver` will be getting a new constructor
      overload which takes an `Mono.Cecil.ReaderParameters` parameter;
      the default will be the default Cecil behavior, which is for
      read-only behavior. Thus, trying to use the `AssemblyDefinition`
      in a "write" context will fail:

            var r = new DirectoryAssemblyResolver (...);
            var a = r.Load (assemblyName);
            a.Write ();   // BOOM

[0]: dotnet/java-interop#88

Author: jonpryor

src/Xamarin.Android.Build.Tasks/Tasks/BuildApk.cs

@@ -444,30 +444,31 @@ void AddRuntimeLibraries (ZipArchive apk, string supportedAbis)
 		void AddNativeLibrariesFromAssemblies (ZipArchive apk, string supportedAbis)
 		{
 			var abis = supportedAbis.Split (new char[] { ',', ';' }, StringSplitOptions.RemoveEmptyEntries);
-			var res = new DirectoryAssemblyResolver (Console.WriteLine, loadDebugSymbols: false);
+			using (var res = new DirectoryAssemblyResolver (Console.WriteLine, loadDebugSymbols: false)) {
 			foreach (var assembly in EmbeddedNativeLibraryAssemblies)
 				res.Load (assembly.ItemSpec);
-			foreach (var assemblyPath in EmbeddedNativeLibraryAssemblies) {
-				var assembly = res.GetAssembly (assemblyPath.ItemSpec);
-				foreach (var mod in assembly.Modules) {
-					var ressozip = mod.Resources.FirstOrDefault (r => r.Name == "__AndroidNativeLibraries__.zip") as EmbeddedResource;
-					if (ressozip == null)
-						continue;
-					var data = ressozip.GetResourceData ();
-					using (var ms = new MemoryStream (data)) {
-						using (var zip = ZipArchive.Open (ms)) {
-							foreach (var e in zip.Where (x => abis.Any (a => x.FullName.Contains (a)))) {
-								if (e.IsDirectory)
-									continue;
-								var key = e.FullName.Replace ("native_library_imports", "lib");
-								if (apk.Any(k => k.FullName  == key)) {
-									Log.LogCodedWarning ("4301", "Apk already contains the item {0}; ignoring.", key);
-									continue;
-								}
-								using (var s = new MemoryStream ()) {
-									e.Extract (s);
-									s.Position = 0;
-									apk.AddEntry (s.ToArray (),key);
+				foreach (var assemblyPath in EmbeddedNativeLibraryAssemblies) {
+					var assembly = res.GetAssembly (assemblyPath.ItemSpec);
+					foreach (var mod in assembly.Modules) {
+						var ressozip = mod.Resources.FirstOrDefault (r => r.Name == "__AndroidNativeLibraries__.zip") as EmbeddedResource;
+						if (ressozip == null)
+							continue;
+						var data = ressozip.GetResourceData ();
+						using (var ms = new MemoryStream (data)) {
+							using (var zip = ZipArchive.Open (ms)) {
+								foreach (var e in zip.Where (x => abis.Any (a => x.FullName.Contains (a)))) {
+									if (e.IsDirectory)
+										continue;
+									var key = e.FullName.Replace ("native_library_imports", "lib");
+									if (apk.Any (k => k.FullName == key)) {
+										Log.LogCodedWarning ("4301", "Apk already contains the item {0}; ignoring.", key);
+										continue;
+									}
+									using (var s = new MemoryStream ()) {
+										e.Extract (s);
+										s.Position = 0;
+										apk.AddEntry (s.ToArray (), key);
+									}
 								}
 							}
 						}

src/Xamarin.Android.Build.Tasks/Tasks/CheckTargetFrameworks.cs

@@ -23,9 +23,8 @@ public class CheckTargetFrameworks : Task
 		public string ProjectFile { get; set; } 
 
 		Dictionary<ITaskItem, int> apiLevels = new Dictionary<ITaskItem, int> ();
-		DirectoryAssemblyResolver res;
 
-		int ExtractApiLevel(ITaskItem ass)
+		int ExtractApiLevel(DirectoryAssemblyResolver res, ITaskItem ass)
 		{
 			Log.LogDebugMessage (ass.ItemSpec);
 			foreach (var ca in res.GetAssembly (ass.ItemSpec).CustomAttributes) {
@@ -51,13 +50,14 @@ public override bool Execute ()
 			Log.LogDebugMessage ("  ProjectFile: {0}", ProjectFile);
 			Log.LogDebugTaskItems ("  ResolvedUserAssemblies: {0}", ResolvedAssemblies);
 
-			res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false);
-			foreach (var assembly in ResolvedAssemblies) {
-				res.Load (Path.GetFullPath (assembly.ItemSpec));
-				var apiLevel = ExtractApiLevel (assembly);
-				if (apiLevel > 0) {
-					Log.LogDebugMessage ("{0}={1}", Path.GetFileNameWithoutExtension (assembly.ItemSpec), apiLevel);
-					apiLevels.Add (assembly, apiLevel);
+			using (var res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false)) {
+				foreach (var assembly in ResolvedAssemblies) {
+					res.Load (Path.GetFullPath (assembly.ItemSpec));
+					var apiLevel = ExtractApiLevel (res, assembly);
+					if (apiLevel > 0) {
+						Log.LogDebugMessage ("{0}={1}", Path.GetFileNameWithoutExtension (assembly.ItemSpec), apiLevel);
+						apiLevels.Add (assembly, apiLevel);
+					}
 				}
 			}
 

src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs

@@ -79,7 +79,11 @@ public override bool Execute ()
 			Log.LogDebugMessage ("  ApplicationJavaClass: {0}", ApplicationJavaClass);
 
 			try {
-				Run ();
+				// We're going to do 3 steps here instead of separate tasks so
+				// we can share the list of JLO TypeDefinitions between them
+				using (var res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: true)) {
+					Run (res);
+				}
 			}
 			catch (XamarinAndroidException e) {
 				Log.LogCodedError (string.Format ("XA{0:0000}", e.Code), e.MessageWithoutCode);
@@ -90,17 +94,13 @@ public override bool Execute ()
 			return !Log.HasLoggedErrors;
 		}
 
-		void Run ()
+		void Run (DirectoryAssemblyResolver res)
 		{
 			PackageNamingPolicy pnp;
 			JniType.PackageNamingPolicy = Enum.TryParse (PackageNamingPolicy, out pnp) ? pnp : PackageNamingPolicyEnum.LowercaseHash;
 			var temp = Path.Combine (Path.GetTempPath (), Path.GetRandomFileName ());
 			Directory.CreateDirectory (temp);
 
-			// We're going to do 3 steps here instead of separate tasks so
-			// we can share the list of JLO TypeDefinitions between them
-			var res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols:true);
-			
 			var selectedWhitelistAssemblies = new List<string> ();
 
 			// Put every assembly we'll need in the resolver

src/Xamarin.Android.Build.Tasks/Tasks/GenerateResourceDesigner.cs

@@ -106,23 +106,24 @@ public override bool Execute ()
 			var assemblyNames = new List<string> ();
 			if (IsApplication && References != null && References.Any ()) {
 				// FIXME: should this be unified to some better code with ResolveLibraryProjectImports?
-				var resolver = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false);
-				foreach (var assemblyName in References) {
-					var suffix = assemblyName.ItemSpec.EndsWith (".dll") ? String.Empty : ".dll";
-					string hintPath = assemblyName.GetMetadata ("HintPath").Replace (Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
-					string fileName = assemblyName.ItemSpec + suffix;
-					resolver.Load (Path.GetFullPath (assemblyName.ItemSpec));
-					if (!String.IsNullOrEmpty (hintPath) && !File.Exists (hintPath)) // ignore invalid HintPath
-						hintPath = null;
-					string assemblyPath = String.IsNullOrEmpty (hintPath) ? fileName : hintPath;
-					if (MonoAndroidHelper.IsFrameworkAssembly (fileName) && !MonoAndroidHelper.FrameworkEmbeddedJarLookupTargets.Contains (Path.GetFileName (fileName)))
-						continue;
-					Log.LogDebugMessage ("Scan assembly {0} for resource generator", fileName);
-					assemblyNames.Add (assemblyPath);
+				using (var resolver = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false)) {
+					foreach (var assemblyName in References) {
+						var suffix = assemblyName.ItemSpec.EndsWith (".dll") ? String.Empty : ".dll";
+						string hintPath = assemblyName.GetMetadata ("HintPath").Replace (Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
+						string fileName = assemblyName.ItemSpec + suffix;
+						resolver.Load (Path.GetFullPath (assemblyName.ItemSpec));
+						if (!String.IsNullOrEmpty (hintPath) && !File.Exists (hintPath)) // ignore invalid HintPath
+							hintPath = null;
+						string assemblyPath = String.IsNullOrEmpty (hintPath) ? fileName : hintPath;
+						if (MonoAndroidHelper.IsFrameworkAssembly (fileName) && !MonoAndroidHelper.FrameworkEmbeddedJarLookupTargets.Contains (Path.GetFileName (fileName)))
+							continue;
+						Log.LogDebugMessage ("Scan assembly {0} for resource generator", fileName);
+						assemblyNames.Add (assemblyPath);
+					}
+					var assemblies = assemblyNames.Select (assembly => resolver.GetAssembly (assembly));
+					new ResourceDesignerImportGenerator (Namespace, resources)
+						.CreateImportMethods (assemblies);
 				}
-				var assemblies = assemblyNames.Select (assembly => resolver.GetAssembly (assembly));
-				new ResourceDesignerImportGenerator (Namespace, resources)
-					.CreateImportMethods (assemblies);
 			}
 
 			AdjustConstructor (isFSharp, resources);

src/Xamarin.Android.Build.Tasks/Tasks/GetAdditionalResourcesFromAssemblies.cs

@@ -363,28 +363,29 @@ public override bool Execute ()
 				? CachePath
 				: Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.LocalApplicationData), CacheBaseDir);
 
-				var resolver = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false);
-				foreach (var assemblyItem in Assemblies) {
-					string fullPath = Path.GetFullPath (assemblyItem.ItemSpec);
-					if (assemblies.Contains (fullPath)) {
-						LogDebugMessage ("  Skip assembly: {0}, it was already processed", fullPath);
-						continue;
-					}
-					assemblies.Add (fullPath);
-					resolver.Load (fullPath);
-					// Append source file name (without the Xamarin. prefix or extension) to the base folder
-					// This would help avoid potential collisions.
-					foreach (var ca in resolver.GetAssembly (assemblyItem.ItemSpec).CustomAttributes) {
-						switch (ca.AttributeType.FullName) {
-						case "Android.IncludeAndroidResourcesFromAttribute":
-							AddAttributeValue (androidResources, ca, "XA5206", "{0}. Android resource directory {1} doesn't exist.", true, fullPath);
-							break;
-						case "Java.Interop.JavaLibraryReferenceAttribute":
-							AddAttributeValue (javaLibraries, ca, "XA5207", "{0}. Java library file {1} doesn't exist.", false, fullPath);
-							break;
-						case "Android.NativeLibraryReferenceAttribute":
-							AddAttributeValue (nativeLibraries, ca, "XA5210", "{0}. Native library file {1} doesn't exist.", false, fullPath);
-							break;
+				using (var resolver = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false)) {
+					foreach (var assemblyItem in Assemblies) {
+						string fullPath = Path.GetFullPath (assemblyItem.ItemSpec);
+						if (assemblies.Contains (fullPath)) {
+							LogDebugMessage ("  Skip assembly: {0}, it was already processed", fullPath);
+							continue;
+						}
+						assemblies.Add (fullPath);
+						resolver.Load (fullPath);
+						// Append source file name (without the Xamarin. prefix or extension) to the base folder
+						// This would help avoid potential collisions.
+						foreach (var ca in resolver.GetAssembly (assemblyItem.ItemSpec).CustomAttributes) {
+							switch (ca.AttributeType.FullName) {
+							case "Android.IncludeAndroidResourcesFromAttribute":
+								AddAttributeValue (androidResources, ca, "XA5206", "{0}. Android resource directory {1} doesn't exist.", true, fullPath);
+								break;
+							case "Java.Interop.JavaLibraryReferenceAttribute":
+								AddAttributeValue (javaLibraries, ca, "XA5207", "{0}. Java library file {1} doesn't exist.", false, fullPath);
+								break;
+							case "Android.NativeLibraryReferenceAttribute":
+								AddAttributeValue (nativeLibraries, ca, "XA5210", "{0}. Native library file {1} doesn't exist.", false, fullPath);
+								break;
+							}
 						}
 					}
 				}

src/Xamarin.Android.Build.Tasks/Tasks/LinkAssemblies.cs

@@ -75,8 +75,16 @@ public override bool Execute ()
 			Log.LogDebugMessage ("  DumpDependencies: {0}", DumpDependencies);
 			Log.LogDebugMessage ("  LinkOnlyNewerThan: {0}", LinkOnlyNewerThan);
 
-			var res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false);
-			
+			var rp = new ReaderParameters {
+				InMemory    = true,
+			};
+			using (var res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false /* TODO, rp */)) {
+				return Execute (res);
+			}
+		}
+
+		bool Execute (DirectoryAssemblyResolver res)
+		{
 			// Put every assembly we'll need in the resolver
 			foreach (var assembly in ResolvedAssemblies) {
 				res.Load (Path.GetFullPath (assembly.ItemSpec));

src/Xamarin.Android.Build.Tasks/Tasks/ResolveAssemblies.cs

@@ -42,17 +42,21 @@ public class ResolveAssemblies : Task
 		[Output]
 		public string[] ResolvedDoNotPackageAttributes { get; set; }
 
-		DirectoryAssemblyResolver     resolver;
-
 		public override bool Execute ()
+		{
+			using (var resolver = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false)) {
+				return Execute (resolver);
+			}
+		}
+
+		bool Execute (DirectoryAssemblyResolver resolver)
 		{
 			Log.LogDebugMessage ("ResolveAssemblies Task");
 			Log.LogDebugMessage ("  ReferenceAssembliesDirectory: {0}", ReferenceAssembliesDirectory);
 			Log.LogDebugMessage ("  I18nAssemblies: {0}", I18nAssemblies);
 			Log.LogDebugMessage ("  LinkMode: {0}", LinkMode);
 			Log.LogDebugTaskItems ("  Assemblies:", Assemblies);
 
-			resolver  = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false);
 			foreach (var dir in ReferenceAssembliesDirectory.Split (new char[] { ';' }, StringSplitOptions.RemoveEmptyEntries))
 				resolver.SearchDirectories.Add (dir);
 
@@ -80,14 +84,14 @@ public override bool Execute ()
 			}
 			try {
 				foreach (var assembly in topAssemblyReferences)
-					AddAssemblyReferences (assemblies, assembly, true);
+					AddAssemblyReferences (resolver, assemblies, assembly, true);
 			} catch (Exception ex) {
 				Log.LogError ("Exception while loading assemblies: {0}", ex);
 				return false;
 			}
 
 			// Add I18N assemblies if needed
-			AddI18nAssemblies (assemblies);
+			AddI18nAssemblies (resolver, assemblies);
 
 			ResolvedAssemblies = assemblies.Select (a => new TaskItem (a)).ToArray ();
 			ResolvedSymbols = assemblies.Select (a => a + ".mdb").Where (a => File.Exists (a)).Select (a => new TaskItem (a)).ToArray ();
@@ -100,13 +104,13 @@ public override bool Execute ()
 			Log.LogDebugTaskItems ("  [Output] ResolvedFrameworkAssemblies:", ResolvedFrameworkAssemblies);
 			Log.LogDebugTaskItems ("  [Output] ResolvedDoNotPackageAttributes:", ResolvedDoNotPackageAttributes);
 
-			return true;
+			return !Log.HasLoggedErrors;
 		}
 
 		readonly List<string> do_not_package_atts = new List<string> ();
 		int indent = 2;
 
-		private void AddAssemblyReferences (ICollection<string> assemblies, AssemblyDefinition assembly, bool topLevel)
+		void AddAssemblyReferences (DirectoryAssemblyResolver resolver, ICollection<string> assemblies, AssemblyDefinition assembly, bool topLevel)
 		{
 			var fqname = assembly.MainModule.FullyQualifiedName;
 
@@ -130,7 +134,7 @@ private void AddAssemblyReferences (ICollection<string> assemblies, AssemblyDefi
 			// Recurse into each referenced assembly
 			foreach (AssemblyNameReference reference in assembly.MainModule.AssemblyReferences) {
 				var reference_assembly = resolver.Resolve (reference);
-				AddAssemblyReferences (assemblies, reference_assembly, false);
+				AddAssemblyReferences (resolver, assemblies, reference_assembly, false);
 			}
 			indent -= 2;
 		}
@@ -147,7 +151,7 @@ static LinkModes ParseLinkMode (string linkmode)
 			return mode;
 		}
 
-		private void AddI18nAssemblies (ICollection<string> assemblies)
+		void AddI18nAssemblies (DirectoryAssemblyResolver resolver, ICollection<string> assemblies)
 		{
 			var i18n = Linker.ParseI18nAssemblies (I18nAssemblies);
 			var link = ParseLinkMode (LinkMode);
@@ -156,25 +160,25 @@ private void AddI18nAssemblies (ICollection<string> assemblies)
 			if (i18n == Mono.Linker.I18nAssemblies.None)
 				return;
 
-			assemblies.Add (ResolveI18nAssembly ("I18N"));
+			assemblies.Add (ResolveI18nAssembly (resolver, "I18N"));
 
 			if (i18n.HasFlag (Mono.Linker.I18nAssemblies.CJK))
-				assemblies.Add (ResolveI18nAssembly ("I18N.CJK"));
+				assemblies.Add (ResolveI18nAssembly (resolver, "I18N.CJK"));
 
 			if (i18n.HasFlag (Mono.Linker.I18nAssemblies.MidEast))
-				assemblies.Add (ResolveI18nAssembly ("I18N.MidEast"));
+				assemblies.Add (ResolveI18nAssembly (resolver, "I18N.MidEast"));
 
 			if (i18n.HasFlag (Mono.Linker.I18nAssemblies.Other))
-				assemblies.Add (ResolveI18nAssembly ("I18N.Other"));
+				assemblies.Add (ResolveI18nAssembly (resolver, "I18N.Other"));
 
 			if (i18n.HasFlag (Mono.Linker.I18nAssemblies.Rare))
-				assemblies.Add (ResolveI18nAssembly ("I18N.Rare"));
+				assemblies.Add (ResolveI18nAssembly (resolver, "I18N.Rare"));
 
 			if (i18n.HasFlag (Mono.Linker.I18nAssemblies.West))
-				assemblies.Add (ResolveI18nAssembly ("I18N.West"));
+				assemblies.Add (ResolveI18nAssembly (resolver, "I18N.West"));
 		}
 
-		private string ResolveI18nAssembly (string name)
+		string ResolveI18nAssembly (DirectoryAssemblyResolver resolver, string name)
 		{
 			var assembly = resolver.Resolve (AssemblyNameReference.Parse (name));
 			return assembly.MainModule.FullyQualifiedName;

src/Xamarin.Android.Build.Tasks/Tasks/ResolveLibraryProjectImports.cs

@@ -71,7 +71,10 @@ public override bool Execute ()
 			var resolvedResourceDirectories   = new List<string> ();
 			var resolvedAssetDirectories      = new List<string> ();
 			var resolvedEnvironmentFiles      = new List<string> ();
-			Extract (jars, resolvedResourceDirectories, resolvedAssetDirectories, resolvedEnvironmentFiles);
+
+			using (var resolver = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false)) {
+				Extract (resolver, jars, resolvedResourceDirectories, resolvedAssetDirectories, resolvedEnvironmentFiles);
+			}
 
 			Jars                        = jars.ToArray ();
 			ResolvedResourceDirectories = resolvedResourceDirectories
@@ -133,6 +136,7 @@ static string GetTargetAssembly (ITaskItem assemblyName)
 
 		// Extracts library project contents under e.g. obj/Debug/[__library_projects__/*.jar | res/*/*]
 		void Extract (
+				DirectoryAssemblyResolver res,
 				ICollection<string> jars,
 				ICollection<string> resolvedResourceDirectories,
 				ICollection<string> resolvedAssetDirectories,
@@ -142,7 +146,6 @@ void Extract (
 			if (!outdir.Exists)
 				outdir.Create ();
 
-			var res = new DirectoryAssemblyResolver (Log.LogWarning, loadDebugSymbols: false);
 			foreach (var assembly in Assemblies)
 				res.Load (assembly.ItemSpec);
 

src/Xamarin.Android.Build.Tasks/Tasks/StripEmbeddedLibraries.cs

@@ -28,7 +28,13 @@ public override bool Execute ()
 			Log.LogDebugMessage ("StripEmbeddedLibraries Task");
 			Log.LogDebugTaskItems ("  Assemblies: ", Assemblies);
 
-			var res = new DirectoryAssemblyResolver (Log.LogWarning, true);
+			using (var res = new DirectoryAssemblyResolver (Log.LogWarning, true)) {
+				return Execute (res);
+			}
+		}
+
+		bool Execute (DirectoryAssemblyResolver res)
+		{
 			foreach (var assembly in Assemblies)
 				res.Load (Path.GetFullPath (assembly.ItemSpec));