Generate Jni marshal methods spec

[radekdoulik]

We are now able to generate the Jni marshal methods by jnimarshalmethod-gen.exe. The usage of those can be enabled by AndroidGenerateJniMarshalMethods property. (added in 106a621)

This specs describes how to also generate the methods by our build process when AndroidGenerateJniMarshalMethods is true.

Generating the methods

We will generate these just before linking the application/library, by executing jnimarshalmethod-gen.exe, similar to this:

<Target Name="_GenerateJniMarshalMethods"
  Condition="'$(AndroidGenerateJniMarshalMethods)' == 'True' And '$(AndroidLinkMode)' != 'None'"
  DependsOnTargets="_GetReferenceAssemblyPaths"
  Inputs="@(ResolvedUserAssemblies->'$(MonoAndroidLinkerInputDir)%(Filename)%(Extension)')"
  Outputs="$(_AndroidJniMarshalMethodsFlag)">

    <Exec
       Command="MONO_PATH=$(_XATargetFrameworkDirectories) $(MonoAndroidBinDirectory)\mono $(MonoAndroidBinDirectory)\..\jnimarshalmethod-gen.exe --jvm=$(AndroidJvmPath) -v @(ResolvedUserAssemblies->'$(MonoAndroidLinkerInputDir)%(Filename)%(Extension)', ' ')"
    />
    <Exec
       Command="MONO_PATH=$(_XATargetFrameworkDirectories) $(MonoAndroidBinDirectory)\mono $(MonoAndroidBinDirectory)\..\jnimarshalmethod-gen.exe --jvm=$(AndroidJvmPath) --types $(MonoAndroidMarshalMethodTypes) @(ResolvedAssemblies->'$(MonoAndroidLinkerInputDir)%(Filename)%(Extension)')"
       Condition=" '%(ResolvedAssemblies.Filename)' == 'Mono.Android' "
    />
    <Touch Files="$(_AndroidJniMarshalMethodsFlag)" AlwaysCreate="True" />

</Target>

It will generate the methods for user assemblies and also for Mono.Android.dll.

AndroidJvmPath

We will need to know the AndroidJvmPath value. We will get it by adding new JdkInfo task to https://github.com/xamarin/xamarin-android/tree/master/src/Xamarin.Android.Build.Tasks/Tasks and it will use the JdkInfo class (https://github.com/xamarin/xamarin-android-tools/blob/master/src/Xamarin.Android.Tools.AndroidSdk/JdkInfo.cs)

Mono.Android.dll start-up types

To avoid long builds by generating complete marshal methods for the whole Mono.Android.dll, we will generate it for only few types, used during application startup. The file containing the list of types will be passed as $(MonoAndroidMarshalMethodTypes) property and might be overridden

Current list:

# XA template startup, Mono.Android
#
Android.Runtime.UncaughtExceptionHandler
Java.Interop.TypeManager\+JavaTypeManager
Android.Views.View\+IOnClickListenerImplementor

# XForms template, Mono.Android
#
Android.Animation.ValueAnimator\+IAnimatorUpdateListenerImplementor
Java.Lang.Thread\+RunnableImplementor

Tests

To test the feature, we will enable it when building runtime and Xamarin.Forms test in Release and AOT configurations. This will also give use performance plots of the feature on regular basis.

[radekdoulik]

In the end we end up generating the marshal methods for everything and didn't introduce the MonoAndroidMarshalMethodTypes property.

The initial integration is implemented by #2153

[grendello]

jnimarshalmethods-gen was superseded by marshal methods (commit 8bc7a3e and others)