EGL context cannot be shared between threads

[blasten]

If context is current to some other thread, or if either draw or read are bound to contexts in another thread, an EGL_BAD_ACCESS error is generated.
https://www.khronos.org/registry/EGL/sdk/docs/man/html/eglMakeCurrent.xhtml

This affects hybrid mode because the raster and the platform thread need to be merged. We might need to make a separate EGL context for the platform thread.

[blasten]

This is required for #58291

[blasten]

We also need to determinate if the raster task queue is running on the platform thread to decide where to dispatch these messages:

1. https://github.com/flutter/engine/blob/db4801c1e8895e10ebcbb394dbf66860e696a6a1/shell/platform/android/platform_view_android.cc#L127-L132

2. https://github.com/flutter/engine/blob/db4801c1e8895e10ebcbb394dbf66860e696a6a1/shell/platform/android/platform_view_android.cc#L94-L100

3. https://github.com/flutter/engine/blob/db4801c1e8895e10ebcbb394dbf66860e696a6a1/shell/platform/android/platform_view_android.cc#L112-L117

[blasten]

This is blocked as dynamic thread merging isn't ready. From @cyanglaz:

deadlock in shell::OnPlatformViewDestroy

[cyanglaz]

#57067 is the issue blocking thread merging

[chinmaygarde]

This was cross referenced from #63585. Can this just be reworded to "Enable dynamic thread merging on Android." to better reflect the action item? Can you comment on the priority? This seems like a blocker to the platform views work.

[blasten]

@chinmaygarde priority looks good. I will update this issue in a bit as I'm currently debugging this issue.

[blasten]

This issue is fixed by clearing the context before the context switch. For instance, in the raster thread before it is made current on the platform thread. However, a single context switch appears to cause significant frame drops. I haven’t identified the cause.

@cyanglaz I initially thought that resetting the context on every frame was the cause, but I have verified that the slow down occurs after a single reset. So, it might not be related to the context reset. I’m still investigating.

[cyanglaz]

I haven't tried this yet but: does context switching without thread merging also cause performance issues?

[blasten]

does context switching without thread merging also cause performance issues?

No

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