Fix crash in relation reference test

[troopa81]

Description

Fix flaky test in relation reference widget test.

QgsFeatureFilterModel needs to wait for the mGatherer to be complety finished. Even if the collectedValues signal emitting is the last instruction, there is no garantie run is over when we delete it (I can reproduce the issue every time by adding a sleep just after the signal emitting).

[elpaso]

Just hit this one myself, I believe the source of the issue was f39f5db#diff-bee409cb02c75d3272f877c88ea1e86eR345

[troopa81]

@elpaso Thanks for noticing.

@obrix Is the fix looks fine to you?

[obrix]

@troopa81 Thanks for this one. I was trying to fix a crash in updateCompleter (see #34581 ), It made the situation a bit better but it still did not fix the issue completely. Maybe your commit will fix this once and for all. Still not convinced that everything make sense in the way the thread is handled here though.

[troopa81]

We have a talk with @obrix on the subjet.

We think the first issue was not due to a signal order but because of the latency between the emitting of collectedValues and finished signal. As a consequence, updateCompleter could have triggered another reload and created another mGatherer object while the finished signal was not emitted and received yet. This ends in mGatherer being deleted while updateCompleter needs it.

The fix of @obrix fix this and this PR adds a wait to be sure the thread is completely finished. So it should be fine now.

[qgis-bot]

The backport to release-3_10 failed:

The process 'git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-3_10 release-3_10
# Navigate to the new working tree
cd .worktrees/backport-release-3_10
# Create a new branch
git switch --create backport-34818-to-release-3_10
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick fa6958fb650fb7fc6eac81be97c57391fd9def69
# Push it to GitHub
git push --set-upstream origin backport-34818-to-release-3_10
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_10

Then, create a pull request where the base branch is release-3_10 and the compare/head branch is backport-34818-to-release-3_10.

[qgis-bot]

The backport to release-3_12 failed:

The process 'git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-3_12 release-3_12
# Navigate to the new working tree
cd .worktrees/backport-release-3_12
# Create a new branch
git switch --create backport-34818-to-release-3_12
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick fa6958fb650fb7fc6eac81be97c57391fd9def69
# Push it to GitHub
git push --set-upstream origin backport-34818-to-release-3_12
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-3_12

Then, create a pull request where the base branch is release-3_12 and the compare/head branch is backport-34818-to-release-3_12.