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Details

Type: Bug
Resolution: Done
Priority: P1: Critical
Fix Version/s: 5.15.1, 6.0
Affects Version/s: 5.6.3, 5.9.9, 5.12.6, 5.14.0, 5.14.1, 5.15.0 Beta2
Component/s: QML: Declarative and Javascript Engine
Labels:
- qmlnext
Environment:
WIndows 10 Pro, Intel Xeon E5-1650 v3 and AMD Ryzen 3900X, 32GB RAM, Qt Creator 4.11.2, Qt 5.6.3, Qt 5.9.6, Qt 5.12.6, Qt 5.14.0, Qt 5.14.1, Qt 5.15 beta 2

Platform/s:

Windows
Commits:
6de0287d7c3aa4251fe6eb4f970d73ce11cf07fc (qt/qtdeclarative/dev) 5d6c671232ca466a929cc23ee8ae92de2ce9ca8d (qt/qtdeclarative/5.15)

Description

QML components having a StateMachine with an “onTriggered” signal handler leak memory when destroyed.

The attached QML file has a Repeater with Rectangles containing a StateMachine. One of the States has a “trigger” signal handler in a SignalTransition. If the Repeater is repopulated rapidly, the memory usage for the process (measured using Windows Task Manager) grows continually. If the “onTriggered” signal handler is commented out, memory usage does not grow.

To reproduce:

Build and run the attached project
Open Windows Task Manager to the “Processes” tab and find the “QML Scene Viewer” (or "QmlScene", depends on Qt version)

Observe that under the Memory column, the memory usage grows by about 100 MB a minute

Close the app window
Edit the DsmMemoeryLeak.qml file to comment-out line 44: "onTriggered: root.canceled()"
Build and run the project again
On the Task Manager “Processes” tab, find the “QML Scene Viewer”

Observe that under the Memory column, memory usage stabilizes around 65-105MB (depends on Qt version) and does not grow.

Here's the content of the file:

// DsmMemoryLeak.qml
import QtQuick 2.6
import QtQuick.Window 2.2
import QtQml.StateMachine 1.0 as DSM

Window {
    visible: true
    width: 600
    height: 80
    title: qsTr("DSM Memory Leak")

    Row {
        id: row
        property int count: 1
        anchors.verticalCenter: parent.verticalCenter
        spacing: 1

        Repeater {
            model: row.count

            delegate: Rectangle {
                id: root

                signal bumped()
                signal canceled()

                width: 9; height: 20
                color: "green"

                DSM.StateMachine {
                    initialState: s1
                    running: true

                    DSM.State {
                        id: s1
                        DSM.SignalTransition {
                            targetState: s3
                            signal: root.bumped
                        }
                    }

                    DSM.State {
                        id: s2
                        DSM.SignalTransition {
                            targetState: s1; signal: root.bumped

                            // comment out line below to stop leak
                            onTriggered: root.canceled()
                        }
                    }

                    DSM.State {
                        id: s3
                        DSM.TimeoutTransition {
                            targetState: s1
                            timeout: 500
                        }
                    }
                }
            }
        }
    }
    Timer {
        interval: 1
        running: true
        repeat: true
        onTriggered: row.count = (row.count == 60) ? 0 : 60
    }
}