Avoid reentrancy issues when dropping AppHost #19296
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lhecker
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carlos-zamora
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Aug 29, 2025
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Is there an issue this is linked to or that it closes? |
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No, this is going off of a hunch. It's related to a slight rise in crashes as reported by watson. |
carlos-zamora
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Aug 29, 2025
DHowett
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Sep 5, 2025
tl;dr: ~Apphost() may pump the message loop. That's no bueno. See comments in the diff. Additionally, this PR enables `_assertIsMainThread` in release to trace down mysterious crashes in those builds. **BACKPORT NOTES** I returned the `_assertIsMainThread` check to debug-only to remove the assertion risk from production builds. (cherry picked from commit 8d41ace) Service-Card-Id: PVTI_lADOAF3p4s4AxadtzgebmmE Service-Version: 1.23
DHowett
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Sep 5, 2025
tl;dr: ~Apphost() may pump the message loop. That's no bueno. See comments in the diff. Additionally, this PR enables `_assertIsMainThread` in release to trace down mysterious crashes in those builds. (cherry picked from commit 8d41ace) Service-Card-Id: PVTI_lADOAF3p4s4BBcTlzgeJeYA Service-Version: 1.24
DHowett
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Sep 29, 2025
The previous fix in #19296 moved the _destruction_ of AppHost into the tail end after we manipulate the `_windows` vector; however, it kept the part which calls into XAML (`Close`) before the `erase`. I suspect that we still had some reentrancy issues, where we cached an iterator before the list was modified by another window close event. That is: ```mermaid sequenceDiagram Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (a) AppHost->>XAML: Close XAML-->>Emperor: pump loop Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (b) AppHost->>XAML: Close XAML-->>Emperor: pump loop AppHost->>-Emperor: Closed Emperor->>Emperor: erase(b) AppHost->>-Emperor: Closed Emperor->>Emperor: erase(a) ``` Moving the `Close()` to after the `erase` ensures that there are no cached iterators that survive beyond XAML pumping the message loop. Fixes 8d41ace
DHowett
added a commit
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Sep 30, 2025
The previous fix in #19296 moved the _destruction_ of AppHost into the tail end after we manipulate the `_windows` vector; however, it kept the part which calls into XAML (`Close`) before the `erase`. I suspect that we still had some reentrancy issues, where we cached an iterator before the list was modified by another window close event. That is: ```mermaid sequenceDiagram Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (a) AppHost->>XAML: Close XAML-->>Emperor: pump loop Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (b) AppHost->>XAML: Close XAML-->>Emperor: pump loop AppHost->>-Emperor: Closed Emperor->>Emperor: erase(b) AppHost->>-Emperor: Closed Emperor->>Emperor: erase(a) ``` Moving the `Close()` to after the `erase` ensures that there are no cached iterators that survive beyond XAML pumping the message loop. Fixes 8d41ace
DHowett
added a commit
that referenced
this pull request
Oct 8, 2025
The previous fix in #19296 moved the _destruction_ of AppHost into the tail end after we manipulate the `_windows` vector; however, it kept the part which calls into XAML (`Close`) before the `erase`. I suspect that we still had some reentrancy issues, where we cached an iterator before the list was modified by another window close event. That is: ```mermaid sequenceDiagram Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (a) AppHost->>XAML: Close XAML-->>Emperor: pump loop Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (b) AppHost->>XAML: Close XAML-->>Emperor: pump loop AppHost->>-Emperor: Closed Emperor->>Emperor: erase(b) AppHost->>-Emperor: Closed Emperor->>Emperor: erase(a) ``` Moving the `Close()` to after the `erase` ensures that there are no cached iterators that survive beyond XAML pumping the message loop. Fixes 8d41ace (cherry picked from commit 5976de1) Service-Card-Id: PVTI_lADOAF3p4s4AxadtzgfScoo Service-Version: 1.23
DHowett
added a commit
that referenced
this pull request
Oct 8, 2025
The previous fix in #19296 moved the _destruction_ of AppHost into the tail end after we manipulate the `_windows` vector; however, it kept the part which calls into XAML (`Close`) before the `erase`. I suspect that we still had some reentrancy issues, where we cached an iterator before the list was modified by another window close event. That is: ```mermaid sequenceDiagram Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (a) AppHost->>XAML: Close XAML-->>Emperor: pump loop Emperor->>Emperor: Close Window Emperor->>+AppHost: Close (b) AppHost->>XAML: Close XAML-->>Emperor: pump loop AppHost->>-Emperor: Closed Emperor->>Emperor: erase(b) AppHost->>-Emperor: Closed Emperor->>Emperor: erase(a) ``` Moving the `Close()` to after the `erase` ensures that there are no cached iterators that survive beyond XAML pumping the message loop. Fixes 8d41ace (cherry picked from commit 5976de1) Service-Card-Id: PVTI_lADOAF3p4s4BBcTlzgfScpM Service-Version: 1.24
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tl;dr: ~Apphost() may pump the message loop.
That's no bueno. See comments in the diff.
Additionally, this PR enables
_assertIsMainThreadinrelease to trace down mysterious crashes in those builds.