[Xamarin.Android.Build.Tasks] close XAAssemblyResolvers by jonathanpeppers · Pull Request #9531 · dotnet/android (original) (raw)

Context: https://discord.com/channels/732297728826277939/732297916680765551/1308554103206580244
Fixes: #9133
Context: 86260ed

Various customers have been reporting UnauthorizedAccessExceptions in incremental builds, which seems to be a new problem in .NET 9. We were not able to reproduce the issue locally, but with the number of reports it seems to be a real issue.

One customer shared a MSBuild.dmp file (while the file was locked), where I could observe the objects in memory:

MemoryMappedViewStream	132
    Mono.Cecil.PE.Image	100
        Mono.Cecil.ModuleDefinition	100
            Mono.Cecil.TypeDefinition	100
                Mono.Cecil.TypeDefinition[]	100
                    List<Mono.Cecil.TypeDefinition>	1
                        Xamarin.Android.Tasks.NativeCodeGenState [Static variable Xamarin.Android.Tasks.NativeCodeGenState.<Template>k__BackingField]	1

Then realized the problem was:

• We opened some .dll files with Mono.Cecil.
• They were never closed.
• Future incremental build attempts would fail on various operations of the same .dll files.

We were also storing some static state (NativeCodeGenState) to be shared across multiple MSBuild tasks:

public static NativeCodeGenState? Template { get; set; }

NativeCodeGenState also holds a XAAssemblyResolver in a Resolver property. This means this XAAssemblyResolver instance would also be kept alive.

It appears we only use the static Template property for a bool flag, so I changed the property to a bool instead.

After this change, we can safely dispose Resolver instances. I looped over the NativeCodeGenState instances disposing of each Resolver at the end of the <GenerateJavaStubs/> MSBuild task.