[hot_reload] Calling a method for the first time after an update crashes the app

[pavelsavara]

If a hot reload delta is applied to a method M that has never been called before, and then that method is called for the first time after the update, the runtime will assert.

A common variant of this is doing a browser refresh of a Blazor WebAssembly app that had some changes applied. When the runtime restarts, dotnet watch replays the deltas on a fresh runtime, and after that calling any of the updated methods will cause a crash.

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Original report:

with dotnet.6.0.0-rc.1.21411.2.js

• Create new app with dotnet new blazorwasm
• Replace Pages\Index.razor with https://gist.github.com/pavelsavara/52bf2a7e3625bdbb747473fb6b2ba432
• run dotnet new watch
• open chrome dev console
• click 'Test'
• change Pages\Index.razor to https://gist.github.com/pavelsavara/06ca4d3d420ff72ec526bd59721c7210 & save
• click 'Test'
• reload web page via browser button
• click 'Test'
• observe the error in console log

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Issue Details

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with dotnet.6.0.0-rc.1.21411.2.js

• Create new app with dotnet new blazorwasm
• Replace Pages\Index.razor with https://gist.github.com/pavelsavara/52bf2a7e3625bdbb747473fb6b2ba432
• run dotnet new watch
• open chrome dev console
• click 'Test'
• change Pages\Index.razor to https://gist.github.com/pavelsavara/06ca4d3d420ff72ec526bd59721c7210 & save
• click 'Test'
• reload web page
• click 'Test'
• observe the error in console log

Author:	pavelsavara
Assignees:	-
Labels:	arch-wasm
Milestone:	-

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[lambdageek]

The interesting thing about "ctrl-R" is that it is like we're in a cold-start situation.

We start the runtime. Immediately apply an update to a method we never called before. We indirectly try to call it.

So we're on some "let's interpret this method for the first time" path.

[lambdageek]

Some assertions that may be hit:

• [wasm][hot-reload] * Assertion at /__w/1/s/src/mono/mono/component/hot_reload.c:869, condition ' not met`
• * Assertion at /Users/alklig/work/dotnet-runtime/runtime/src/mono/mono/metadata/metadata.c:1321, condition idx >= 0' not met`

Can happen in the "src/mono/samples/mbr/console" sample, too - just change the main Program.cs code to apply the update before calling the test method.

[lambdageek]

FYI @danroth27

[pavelsavara]

When you are talking about applying deltas, It seems to me that we expect that the state of the browser is in sync with state of the server ? I guess I could have many browser tabs of different age-of-last-reload.

[lambdageek]

When you are talking about applying deltas, It seems to me that we expect that the state of the browser is in sync with state of the server ? I guess I could have many browser tabs of different age-of-last-reload.

I believe dotnet watch handles that - for each websocket session they keep track of what's been sent over.