Fix VirtualFlow performance regression in ListView scrolling

[youngledo]

The commit 1b12c8a introduced two performance issues in VirtualFlow:

1. Calling requestLayout() on all cells in the pile on every layout pass This causes unnecessary layout calculations for 50-100 recycled cells per frame during scrolling.

2. Using sheetChildren.removeAll(pile) which has O(n*m) time complexity This becomes extremely slow with large cell pools.

These changes caused severe scrolling lag in ListView/TableView with many items (e.g., 100+ items, even less). The fix removes both problematic code blocks while preserving the getViewportBreadth() visibility change needed by TableRowSkinBase.

Tested with ListView containing 1000 items - scrolling is now smooth again, matching JavaFX 24 performance.

The sample project has been uploaded:
demo-javafx.zip

My system environment is:

• Apple M1
• macOS 26.2

Installed and used JDKs from the following vendors via SDKMAN:

• 25.0.1-graalce
• 25.0.1.fx-nik
• 25.0.1-tem

Without exception, the lists are all somewhat laggy when scrolling. But if I downgrade the FX version to 24, only "25.0.1.fx-nik" still shows lag — the other two are very smooth!

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
         http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo-javafx</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>JavaFX ListView Demo</name>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>25</java.version>
        <javafx.version>25</javafx.version>
        <javafx.maven.plugin.version>0.0.8</javafx.maven.plugin.version>
    </properties>

    <dependencies>
        <!-- JavaFX Controls -->
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-controls</artifactId>
            <version>${javafx.version}</version>
        </dependency>

        <!-- JavaFX FXML -->
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-fxml</artifactId>
            <version>${javafx.version}</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- Maven Compiler Plugin -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.11.0</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>

            <!-- JavaFX Maven Plugin -->
            <plugin>
                <groupId>org.openjfx</groupId>
                <artifactId>javafx-maven-plugin</artifactId>
                <version>${javafx.maven.plugin.version}</version>
                <configuration>
                    <mainClass>com.example.javafx.MainApp</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

package com.example.javafx.controller;

import javafx.beans.property.IntegerProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.scene.control.ListView;

public class MainController {
    
    @FXML
    private ListView<DataItem> dataListView;
    
    private ObservableList<DataItem> dataItems;
    
    @FXML
    public void initialize() {
        dataItems = FXCollections.observableArrayList();
        
        generateTestData();

        dataListView.setItems(dataItems);
    }
    
    private void generateTestData() {
        for (int i = 1; i <= 1000; i++) {
            DataItem item = new DataItem(
                i,
                "item " + i,
                "this is " + i
            );
            dataItems.add(item);
        }
    }

    public static class DataItem {

        private final IntegerProperty id;
        private final StringProperty name;
        private final StringProperty description;

        public DataItem(int id, String name, String description) {
            this.id = new SimpleIntegerProperty(id);
            this.name = new SimpleStringProperty(name);
            this.description = new SimpleStringProperty(description);
        }

        @Override
        public String toString() {
            return String.format("[ID:%d] %s - %s", id.get(), name.get(), description.get());
        }
    }
}

---

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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jfx.git pull/2030/head

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[youngledo]

I discovered that version 25 has performance issues locally, and it works fine when rolling back to version 24. I don't have sufficient permissions and also don't have a place to report this issue. The current workaround is to roll back to version 24. However, I'm not sure if this is a destructive change.

[youngledo]

@Maran23 Hello, I noticed you've made contributions to this area before. Could you help me review this issue?

A relatively complete code example has been provided above. If you need a directly usable attachment, I can provide it.

[johanvos]

@Maran23 Hello, I noticed you've made contributions to this area before. Could you help me review this issue?

A relatively complete code example has been provided above. If you need a directly usable attachment, I can provide it.

Hi @youngledo , thanks for reporting this. To follow the normal procedure, can you please file a bug in https://bugs.java.com/bugreport/ ?
When doing that, there is (after manual triage) machinery going on behind the scenes that facilitates the whole flow between bug report, discussions, PR, release docs etc.

I believe there is a fair chance indeed that the code you mention can lead to regression in a number of situations. Your code sample would be helpful, but is best provided after you report the bug. I notice there are @FXML refs but I don't see an FXML file, so I suggest you upload a zip file (once the issue is in JBS).

[youngledo]

@Maran23 Hello, I noticed you've made contributions to this area before. Could you help me review this issue?
A relatively complete code example has been provided above. If you need a directly usable attachment, I can provide it.

Hi @youngledo , thanks for reporting this. To follow the normal procedure, can you please file a bug in https://bugs.java.com/bugreport/ ? When doing that, there is (after manual triage) machinery going on behind the scenes that facilitates the whole flow between bug report, discussions, PR, release docs etc.

I believe there is a fair chance indeed that the code you mention can lead to regression in a number of situations. Your code sample would be helpful, but is best provided after you report the bug. I notice there are @FXML refs but I don't see an FXML file, so I suggest you upload a zip file (once the issue is in JBS).

@johanvos
Sorry, I forgot to mention that since I'm just a regular user, I couldn't figure out how to become a member. Could you help me submit the issue, or what should I do instead?

The sample project has been uploaded:
demo-javafx.zip

[Maran23]

I forgot to mention that since I'm just a regular user, I couldn't figure out how to become a member

You are an Author, so you should be able to login to https://bugs.openjdk.org/issues/?filter=39543.
See also the message from @bridgekeeper

Welcome back youngledo

Without checking your example, simply removing both lines of code is certainly not the right fix. This was implemented to fix problems, so I'm pretty sure this will lead to regressions.

Also note that you should check if applying #1945 fixes your problem, as this is an issue that could lead to many unnecessary relayouts right now.

Note that I believe that the performance of the VirtualFlow can be improved a lot, but I'm not sure this is the right approach / the right place.
Example: the removeAll should not be triggered that often and the pile should not be that big. If it is, we may need to check out why this is first.

[youngledo]

@Maran23 Thank you for your reply. I don't have a JBS account yet, so I can't make edits. I am still in the application process.

Yes, you're right that deleting the code isn't appropriate, but I tried using the published version 24 locally and it worked fine.

Moreover, the sample code provided above is very simple, and it shouldn't be this laggy even when generating only a few entries.

I forgot to mention, my system environment is:

• Apple M1
• macOS 26.2

Installed and used JDKs from the following vendors via SDKMAN:

• 25.0.1-graalce
• 25.0.1.fx-nik
• 25.0.1-tem

Without exception, the lists are all somewhat laggy when scrolling. But if I downgrade the FX version to 24, only "25.0.1.fx-nik" still shows lag — the other two are very smooth!

[Maran23]

Also note that you need to enable your Github Actions on your fork: https://github.com/youngledo/jfx/actions.