fix(macOS): fix race condition in webview handler

[linw1995]

tauri-apps/tauri#5519 (comment)

[github-actions]

Package Changes Through 48e31fa

There are 1 changes which include wry with minor

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
wry	0.47.2	0.48.0

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[FabianLars]

Does this really help? We already check this 2 instructions above in check_webview_id_valid 🤔

[linw1995]

Does this really help? We already check this 2 instructions above in check_webview_id_valid 🤔

work like a charm.

  14:        0x103430874 - core::panicking::panic_fmt::ha4b80a05b9fff47a
                               at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/core/src/panicking.rs:74:14
  15:        0x102fa8054 - objc2::__macro_helpers::declared_ivars::get_initialized_ivar_ptr::h92376258763b2729
                               at /Users/linw1995/.cargo/registry/src/index.crates.io-6f17d22bba15001f/objc2-0.5.2/src/__macro_helpers/declared_ivars.rs:403:17
  16:        0x102f9dc44 - objc2::top_level_traits::DeclaredClass::ivars_mut::h2f3cb44ff3ce2dab
                               at /Users/linw1995/.cargo/registry/src/index.crates.io-6f17d22bba15001f/objc2-0.5.2/src/top_level_traits.rs:355:34
  17:        0x102fa0474 - wry::wkwebview::class::wry_web_view::WryWebView::remove_custom_task_key::hd2a6c5fea7c15784
                               at /Users/linw1995/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wry-0.47.1/src/wkwebview/class/wry_web_view.rs:149:5

Simply performing checks is not enough; it needs to be locked to prevent race conditions.

[pewsheen]

I think this will mitigate the problem, however it could still happen if the webview is closed just before calling remove_custom_task_key.

MacOS expects us to capture the NSExecption to tell if the task is dead, but that's impossible for now. The async command will be unreliable on MacOS until Objc2 can bubble up an NSException instead of panicking so that we can remove those weird checks.