[Microsoft.Android.Build.BaseTasks] retry when copying files (#245)

Context: dotnet/android#9133
Context: https://learn.microsoft.com/visualstudio/msbuild/copy-task?view=vs-2022

We sometimes get collisions between the Design-Time-Build (or
AntiVirus) and our main build.  This can result in errors such as:

	Error (active)	XALNS7019	System.UnauthorizedAccessException: Access to the path 'D:\Projects\MauiApp2\obj\Debug\net9.0-android\android\assets\armeabi-v7a\MauiApp2.dll' is denied.
	   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
	   at System.IO.File.InternalDelete(String path, Boolean checkHost)
	   at Microsoft.Android.Build.Tasks.Files.CopyIfChanged(String source, String destination) in /Users/runner/work/1/s/xamarin-android/external/xamarin-android-tools/src/Microsoft.Android.Build.BaseTasks/Files.cs:line 125
	   at Xamarin.Android.Tasks.MonoAndroidHelper.CopyAssemblyAndSymbols(String source, String destination) in /Users/runner/work/1/s/xamarin-android/src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs:line 344
	   at Xamarin.Android.Tasks.LinkAssembliesNoShrink.CopyIfChanged(ITaskItem source, ITaskItem destination) in /Users/runner/work/1/s/xamarin-android/src/Xamarin.Android.Build.Tasks/Tasks/LinkAssembliesNoShrink.cs:line 161
	   at Xamarin.Android.Tasks.LinkAssembliesNoShrink.RunTask() in /Users/runner/work/1/s/xamarin-android/src/Xamarin.Android.Build.Tasks/Tasks/LinkAssembliesNoShrink.cs:line 76
	   at Microsoft.Android.Build.Tasks.AndroidTask.Execute() in /Users/runner/work/1/s/xamarin-android/external/xamarin-android-tools/src/Microsoft.Android.Build.BaseTasks/AndroidTask.cs:line 25	MauiApp2 (net9.0-android)	C:\Program Files\dotnet\packs\Microsoft.Android.Sdk.Windows\34.99.0-preview.6.340\tools\Xamarin.Android.Common.targets	1407

If we look at the [MSBuild `<Copy/>` task][0] we see that it has a
retry system in the cases of `UnauthorizedAccessException` or
`IOException` when the code is `ACCESS_DENIED` or
`ERROR_SHARING_VIOLATION`.  The `<Copy/>` task also has public
`Retries` and `RetryDelayMilliseconds` properties to control behavior.

Duplicate that kind of logic into our `Files.Copy*IfChanged()` helper
methods.  This should give our builds a bit more resiliency to these
kinds of issues.

Instead of adding new `Files.Copy*IfChanged()` method overloads which
accept "retries" and "retryDelay" parameters, we instead use
environment variables to allow overriding these values:

  * `DOTNET_ANDROID_FILE_WRITE_RETRY_ATTEMPTS`: The number of times
    to try to retry a copy operation; corresponds to the
    `Copy.Retries` MSBuild task property.

    The default value is 10.

  * `DOTNET_ANDROID_FILE_WRITE_RETRY_DELAY_MS`: The amount of time,
    in milliseconds, to delay between attempted copies; corresponds
    to the `Copy.RetryDelayMilliseconds` MSBuild task property.

    The default value is 1000 ms.

[0]: https://github.com/dotnet/msbuild/blob/main/src/Tasks/Copy.cs#L897

src/Microsoft.Android.Build.BaseTasks/Files.cs

@@ -9,11 +9,25 @@
 using System.Text;
 using Xamarin.Tools.Zip;
 using Microsoft.Build.Utilities;
+using System.Threading;
+using System.Reflection.Metadata;
+using System.Runtime.InteropServices;
+using System.Collections;
 
 namespace Microsoft.Android.Build.Tasks
 {
 	public static class Files
 	{
+		const int ERROR_ACCESS_DENIED = -2147024891;
+		const int ERROR_SHARING_VIOLATION = -2147024864;
+
+		const int DEFAULT_FILE_WRITE_RETRY_ATTEMPTS = 10;
+
+		const int DEFAULT_FILE_WRITE_RETRY_DELAY_MS = 1000;
+
+		static int fileWriteRetry = -1;
+		static int fileWriteRetryDelay = -1;
+
 		/// <summary>
 		/// Windows has a MAX_PATH limit of 260 characters
 		/// See: https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#maximum-path-length-limitation
@@ -28,6 +42,37 @@ public static class Files
 		public static readonly Encoding UTF8withoutBOM = new UTF8Encoding (encoderShouldEmitUTF8Identifier: false);
 		readonly static byte[] Utf8Preamble = Encoding.UTF8.GetPreamble ();
 
+		/// <summary>
+		/// Checks for the environment variable DOTNET_ANDROID_FILE_WRITE_RETRY_ATTEMPTS to
+		/// see if a custom value for the number of times to retry writing a file has been 
+		/// set.
+		/// </summary>
+		/// <returns>The value of DOTNET_ANDROID_FILE_WRITE_RETRY_ATTEMPTS or the default of DEFAULT_FILE_WRITE_RETRY_ATTEMPTS</returns>
+		public static int GetFileWriteRetryAttempts ()
+		{
+			if (fileWriteRetry == -1) {
+				var retryVariable = Environment.GetEnvironmentVariable ("DOTNET_ANDROID_FILE_WRITE_RETRY_ATTEMPTS");
+				if (string.IsNullOrEmpty (retryVariable) || !int.TryParse (retryVariable, out fileWriteRetry))
+					fileWriteRetry = DEFAULT_FILE_WRITE_RETRY_ATTEMPTS;
+			}
+			return fileWriteRetry;
+		}
+
+		/// <summary>
+		/// Checks for the environment variable DOTNET_ANDROID_FILE_WRITE_RETRY_DELAY_MS to
+		/// see if a custom value for the delay between trying to write a file has been 
+		/// set.
+		/// </summary>
+		/// <returns>The value of DOTNET_ANDROID_FILE_WRITE_RETRY_DELAY_MS or the default of DEFAULT_FILE_WRITE_RETRY_DELAY_MS</returns>
+		public static int GetFileWriteRetryDelay ()
+		{
+			if (fileWriteRetryDelay == -1) {
+				var delayVariable = Environment.GetEnvironmentVariable ("DOTNET_ANDROID_FILE_WRITE_RETRY_DELAY_MS");
+				if (string.IsNullOrEmpty (delayVariable) || !int.TryParse (delayVariable, out fileWriteRetryDelay))
+					fileWriteRetryDelay = DEFAULT_FILE_WRITE_RETRY_DELAY_MS;
+			}
+			return fileWriteRetryDelay;
+		} 
 		/// <summary>
 		/// Converts a full path to a \\?\ prefixed path that works on all Windows machines when over 260 characters
 		/// NOTE: requires a *full path*, use sparingly
@@ -111,6 +156,33 @@ public static bool ArchiveZip (string target, Action<string> archiver)
 		}
 
 		public static bool CopyIfChanged (string source, string destination)
+		{
+			int retryCount = 0;
+			int attempts = GetFileWriteRetryAttempts ();
+			int delay = GetFileWriteRetryDelay ();
+			while (retryCount <= attempts) {
+				try {
+					return CopyIfChangedOnce (source, destination);
+				} catch (Exception e) {
+					switch (e) {
+						case UnauthorizedAccessException:
+						case IOException:
+							int code = Marshal.GetHRForException (e);
+							if ((code != ERROR_ACCESS_DENIED && code != ERROR_SHARING_VIOLATION) || retryCount == attempts) {
+								throw;
+							};
+							break;
+						default:
+							throw;
+					} 
+				}
+				retryCount++;
+				Thread.Sleep (delay);
+			}
+			return false;
+		}
+
+		public static bool CopyIfChangedOnce (string source, string destination)
 		{
 			if (HasFileChanged (source, destination)) {
 				var directory = Path.GetDirectoryName (destination);
@@ -157,6 +229,33 @@ public static bool CopyIfBytesChanged (byte[] bytes, string destination)
 		}
 
 		public static bool CopyIfStreamChanged (Stream stream, string destination)
+		{
+			int retryCount = 0;
+			int attempts = GetFileWriteRetryAttempts ();
+			int delay = GetFileWriteRetryDelay ();
+			while (retryCount <= attempts) {
+				try {
+					return CopyIfStreamChangedOnce (stream, destination);
+				} catch (Exception e) {
+					switch (e) {
+						case UnauthorizedAccessException:
+						case IOException:
+							int code = Marshal.GetHRForException (e);
+							if ((code != ERROR_ACCESS_DENIED && code != ERROR_SHARING_VIOLATION) || retryCount >= attempts) {
+								throw;
+							};
+							break;
+						default:
+							throw;
+					} 
+				}
+				retryCount++;
+				Thread.Sleep (delay);
+			}
+			return false;
+		}
+
+		public static bool CopyIfStreamChangedOnce (Stream stream, string destination)
 		{
 			if (HasStreamChanged (stream, destination)) {
 				var directory = Path.GetDirectoryName (destination);

src/Microsoft.Android.Build.BaseTasks/Microsoft.Android.Build.BaseTasks.csproj

@@ -9,6 +9,7 @@
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
     <AssemblyName>$(VendorPrefix)Microsoft.Android.Build.BaseTasks$(VendorSuffix)</AssemblyName>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

tests/Microsoft.Android.Build.BaseTasks-Tests/FilesTests.cs

@@ -6,6 +6,8 @@
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
 using Xamarin.Tools.Zip;
 using Microsoft.Android.Build.Tasks;
 
@@ -436,6 +438,34 @@ public void CopyIfStreamChanged_CasingChange ()
 			}
 		}
 
+		[Test]
+		public async Task CopyIfChanged_LockedFile ()
+		{
+			var dest = NewFile (contents: "foo", fileName: "foo_locked");
+			var src = NewFile (contents: "foo0", fileName: "foo");
+			using (var file = File.OpenWrite (dest)) {
+				Assert.Throws<IOException> (() => Files.CopyIfChanged (src, dest));
+			}
+			src = NewFile (contents: "foo1", fileName: "foo");
+			Assert.IsTrue (Files.CopyIfChanged (src, dest));
+			src = NewFile (contents: "foo2", fileName: "foo");
+			dest = NewFile (contents: "foo", fileName: "foo_locked2");
+			var ev = new ManualResetEvent (false);
+			var task = Task.Run (async () => {
+				var file = File.Open (dest, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read);
+				try {
+					ev.Set ();
+					await Task.Delay (2500);
+				} finally {
+					file.Close();
+					file.Dispose ();
+				}
+			});
+			ev.WaitOne ();
+			Assert.IsTrue (Files.CopyIfChanged (src, dest));
+			await task;
+		}
+
 		[Test]
 		public void ExtractAll ()
 		{