Fix possible result update issue for plugins with IResultUpdate interface #3115
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📝 WalkthroughWalkthroughThe changes in this pull request primarily focus on the Changes
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Actionable comments posted: 1
🧹 Outside diff range and nitpick comments (2)
Flow.Launcher/ViewModel/MainViewModel.cs (2)
1475-1476: Fix typo in error message comment- // Plugin with IResultUpdate interface can somtimes throw this exception - // Collection was modified; enumeration operation may not execute + // Plugin with IResultUpdate interface can sometimes throw this exception + // Collection was modified; enumeration operation may not execute
1450-1478: Consider implementing proper synchronization mechanismsThe current implementation could benefit from proper synchronization mechanisms to handle concurrent access to shared collections.
Consider these architectural improvements:
- Use a synchronization mechanism (like
lockorSemaphoreSlim) when accessing shared collections- Implement the producer-consumer pattern using
BlockingCollection<T>for thread-safe queuing of results- Consider using immutable collections (
ImmutableList<T>) to prevent modification during enumeration- Add documentation about thread-safety requirements for plugin developers implementing
IResultUpdateWould you like me to provide example implementations for any of these approaches?
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I do not know why I have caught exception in Seems that Solution 2 fails to work. So I reverted fix in |
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Actionable comments posted: 2
🧹 Outside diff range and nitpick comments (2)
Plugins/Flow.Launcher.Plugin.WebSearch/Main.cs (2)
Line range hint
88-95: Add cancellation check before raising eventThe event is raised without checking the cancellation token, which could cause unnecessary work when cancellation is requested.
+ token.ThrowIfCancellationRequested(); ResultsUpdated?.Invoke(this, new ResultUpdatedEventArgs { Results = results.ToList(), Query = query });
Line range hint
15-24: Consider improving thread-safety and separation of concernsThe class manages shared state (
_settings,_viewModel) without apparent thread-safety mechanisms while implementing multiple interfaces. This could lead to race conditions under concurrent access.Consider these architectural improvements:
- Implement the Repository pattern for thread-safe settings access
- Use a dedicated event aggregator for result updates
- Split the class into smaller, focused components:
- SearchService (core search logic)
- ResultAggregator (result collection and event handling)
- SettingsManager (thread-safe settings access)
Would you like me to provide a detailed implementation proposal for any of these improvements?
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Plugins/Flow.Launcher.Plugin.WebSearch/Main.cs(1 hunks)
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Plugins/Flow.Launcher.Plugin.WebSearch/Main.cs (1)
Line range hint 27-91: Verify alignment with PR objectives
The PR description mentions implementing solution #2 (error handling with try-catch), but the changes show implementation of solution #1 (defensive copy). Additionally, the comments indicate ongoing exceptions despite error handling.
Let's verify the presence of error handling in the codebase:
Please clarify which solution is being implemented and ensure the changes align with the chosen approach.
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However, what I am confused is that IResultsUpdate should only append a job to the channel Flow.Launcher/Flow.Launcher/ViewModel/MainViewModel.cs Lines 229 to 241 in 304f98e and then the consumer should be a single thread? Flow.Launcher/Flow.Launcher/ViewModel/MainViewModel.cs Lines 188 to 215 in 304f98e I want to understand the root courses of this synchronization problem. |
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on the other hand looks like you didn't commit the correct change? |
Sorry, I don not know your meaning. |
Here I describe my finding about the issue of |
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Sorry that I am not quite familiar with such synchronization problem and I just happen to find it. |
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Oh now I understand what's going wrong. The ResultsUpdateEvent didn't return a new list, which causes issue when the plugin is modifying the same underlying list. |
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A better solution is to create a copy here |
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Now the only change of this PR is all about |
Let me have a try. |
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@taooceros Now handle the copy operation in |
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🧹 Outside diff range and nitpick comments (1)
Flow.Launcher/ViewModel/MainViewModel.cs (1)
236-240: Consider enhancing thread safety with ConcurrentBag.While creating a defensive copy works, consider implementing Solution 3 from the PR objectives by using
ConcurrentBag<Result>forResultUpdatedEventArgs. This would provide stronger thread-safety guarantees and potentially better performance by avoiding list copying.Example implementation:
- var resultsCopy = e.Results.ToList(); + var resultsCopy = new ConcurrentBag<Result>(e.Results);
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Flow.Launcher/ViewModel/MainViewModel.cs(1 hunks)
🔇 Additional comments (1)
Flow.Launcher/ViewModel/MainViewModel.cs (1)
236-240: Good implementation of defensive copying to prevent concurrent modification.
The implementation correctly addresses the concurrency issue by creating a defensive copy of the results list before updating the view model. This prevents the race condition where the plugin might modify the same list that's being processed by the main view model.
However, let's verify that this change is consistently applied across all result update paths:
#!/bin/bash
# Description: Check for other potential places where results list might be modified
# Look for patterns where Results collection is modified without defensive copying
# Search for direct result list modifications
rg -A 5 'Results\.(Add|Clear|Remove)'
# Search for result list assignments
ast-grep --pattern 'Results = $_'
Issue
This issue could happen when calling
ResultsUpdated.Invokeevent inIResultUpdateinterface so fast that main view model cannot complete update event (still execute foreach sentence).Example
Take
WebSearchplugin for example, I change itsQueryAsyncfunction to this:And I can catch the exception in
UpdateResultViewfunction ofMainViewModel:Solution
The key of the problem is that this plugin has not tell the developer to do thread-safe operation in
QueryAsync(like return a copy of the list as theResultsinResultUpdatedEventArgs). So the developer will possibly return the sameListto theResultUpdatedEventArgsand the result of theQueryAsyncfunction. I think there are two solutions for this.Solution 1
Update the
IResultUpdatedocuments and ask developers to return the copy of the list as the parameter ofResultUpdatedEventArgs.Take the above example, I can change its
QueryAsyncfunction to this:Solution 2
Wrap the update codes in
UpdateResultViewwith try catch, it is what my PR does.Solution 3
For example, you can change the definition of the
ResultUpdatedEventArgsso that developer won't return the sameListlike this: