Blazor: Running Module.malloc too early?

[kg]

Describe the bug

Blazor appears to be potentially invoking emscripten/mono APIs before mono has actually loaded - there's some logic being executed in preRun that chains some callbacks that can call malloc, which will assert and fail. I'm seeing it in my local execution environment. It could have something to do with the fact that I'm testing a newer build of mono, but there aren't any changes that would cause this problem and it appears that blazor is doing something incorrect.

To Reproduce

Steps to reproduce the behavior:

1. Follow the directions at https://docs.microsoft.com/en-us/aspnet/core/tutorials/build-your-first-blazor-app?view=aspnetcore-3.0
2. Replace the mono.js + mono.wasm with a recent from-source build

Expected behavior

Something mostly functions

I think the correct behavior here is for the malloc call (and other calls out to emscripten/mono APIs) to be queued to occur after mono has actually started. I'm a little surprised that these callbacks could run this early but I suppose there's no reason they couldn't (unless this is a violation of some obscure promise ordering spec)

Screenshots

Additional context

kate@reeir-debian2:~/Projects/blazortest$ dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview9-014004
 Commit:    8e7ef240a5

Runtime Environment:
 OS Name:     debian
 OS Version:  10
 OS Platform: Linux
 RID:         debian.10-x64
 Base Path:   /usr/share/dotnet/sdk/3.0.100-preview9-014004/

Host (useful for support):
  Version: 3.0.0-preview9-19423-09
  Commit:  2be172345a

.NET Core SDKs installed:
  2.2.402 [/usr/share/dotnet/sdk]
  3.0.100-preview9-014004 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.2.7 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.2.7 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview9.19424.4 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.2.7 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview9-19423-09 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

[kg]

Can confirm that with a release mono.js/mono.wasm built from the same source, the app starts - probably because the assertions are stripped in release mode. 🙃

[pranavkm]

We understand that @lewing is going to suggest some changes to Blazor wasm's startup. This should ensure Blazor works better with mono's startup.

[mkArtakMSFT]

@SteveSandersonMS not sure this is just a tracking issue or not, so assigning to you to do what's necessary here.