"Comparison method violates its general contract" when sorting a collection in Java 7

[mdk]

Simply open the attached file and start Validator. After validation (when moving the mouse ?) these error occurs.

First I found it in Revision 5950, but it is also in the latest version 5958:

Repository Root: http://josm.openstreetmap.de/svn
Build-Date: 2013-05-13 01:34:36
Last Changed Author: Don-vip
Revision: 5958
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
URL: http://josm.openstreetmap.de/svn/trunk
Last Changed Date: 2013-05-13 03:10:05 +0200 (Mon, 13 May 2013)
Last Changed Rev: 5958

Identification: JOSM/1.5 (5958 en) Linux Ubuntu 12.10
Memory Usage: 347 MB / 876 MB (79 MB allocated, but free)
Java version: 1.7.0_21, Oracle Corporation, OpenJDK Server VM
VM arguments: [-Djosm.home=/home/michael/.josm-latest, -Djava.net.useSystemProxies=true]
Dataset consistency test: No problems found

Plugin: ColumbusCSV (29500)
Plugin: FastDraw (29532)
Plugin: HouseNumberTaggingTool (29487)
Plugin: OpeningHoursEditor (29435)
Plugin: RoadSigns (29435)
Plugin: SimplifyArea (29435)
Plugin: buildings_tools (29435)
Plugin: contourmerge (1003)
Plugin: imagery_offset_db (29467)
Plugin: multipoly-convert (29435)
Plugin: poly (29435)
Plugin: public_transport (29435)
Plugin: reltoolbox (29535)
Plugin: reverter (29561)
Plugin: terracer (29509)
Plugin: turnrestrictions (29435)
Plugin: utilsplugin2 (29435)

java.lang.IllegalArgumentException: Comparison method violates its general contract!
	at java.util.TimSort.mergeLo(TimSort.java:747)
	at java.util.TimSort.mergeAt(TimSort.java:483)
	at java.util.TimSort.mergeCollapse(TimSort.java:410)
	at java.util.TimSort.sort(TimSort.java:214)
	at java.util.TimSort.sort(TimSort.java:173)
	at java.util.Arrays.sort(Arrays.java:659)
	at java.util.Collections.sort(Collections.java:217)
	at javax.swing.SortingFocusTraversalPolicy.enumerateAndSortCycle(SortingFocusTraversalPolicy.java:136)
	at javax.swing.SortingFocusTraversalPolicy.getFocusTraversalCycle(SortingFocusTraversalPolicy.java:110)
	at javax.swing.SortingFocusTraversalPolicy.getComponentAfter(SortingFocusTraversalPolicy.java:280)
	at javax.swing.LayoutFocusTraversalPolicy.getComponentAfter(LayoutFocusTraversalPolicy.java:106)
	at java.awt.Component.getNextFocusCandidate(Component.java:7860)
	at java.awt.Component.transferFocus(Component.java:7828)
	at java.awt.Component.hide(Component.java:1684)
	at java.awt.Component.show(Component.java:1653)
	at java.awt.Component.setVisible(Component.java:1603)
	at javax.swing.JComponent.setVisible(JComponent.java:2631)
	at org.openstreetmap.josm.gui.dialogs.ToggleDialog.eventDispatched(ToggleDialog.java:875)
	at java.awt.Toolkit$SelectiveAWTEventListener.eventDispatched(Toolkit.java:2434)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2326)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit$ToolkitEventMulticaster.eventDispatched(Toolkit.java:2325)
	at java.awt.Toolkit.notifyAWTEventListeners(Toolkit.java:2284)
	at java.awt.Component.dispatchEventImpl(Component.java:4757)
	at java.awt.Container.dispatchEventImpl(Container.java:2287)
	at java.awt.Component.dispatchEvent(Component.java:4687)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4505)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
	at java.awt.Container.dispatchEventImpl(Container.java:2273)
	at java.awt.Window.dispatchEventImpl(Window.java:2719)
	at java.awt.Component.dispatchEvent(Component.java:4687)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
	at java.awt.EventQueue.access$200(EventQueue.java:103)
	at java.awt.EventQueue$3.run(EventQueue.java:688)
	at java.awt.EventQueue$3.run(EventQueue.java:686)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
	at java.awt.EventQueue$4.run(EventQueue.java:702)
	at java.awt.EventQueue$4.run(EventQueue.java:700)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

[mdk]

Data to validate

[Don-vip]

Seems to be this Java bug, introduced in JDK7: ​javabug:6923200

[Don-vip]

Fix targeted to Java 8: ​javabug:7075600

Funny thing, Oracle almost fixed the bug in 7u6 before changing their mind (sic): ​javabug:2217231

[Don-vip]

Described here: ​http://www.oracle.com/technetwork/java/javase/compatibility-417013.html#jdk7

Area: API: Utilities
Synopsis: Updated sort behavior for Arrays and Collections may throw an IllegalArgumentException
Description: The sorting algorithm used by java.util.Arrays.sort and (indirectly) by java.util.Collections.sort has been replaced. The new sort implementation may throw an IllegalArgumentException if it detects a Comparable that violates the Comparable contract. The previous implementation silently ignored such a situation.
If the previous behavior is desired, you can use the new system property, java.util.Arrays.useLegacyMergeSort, to restore previous mergesort behavior.
Nature of Incompatibility: behavioral
RFE: 6804124

[mdk]

There are some other tickets, which seems to be related: #8335, #8453 and #8671

[Don-vip]

@mdk: you're right, the second one is exact duplicate. Other ones must be fixed on our side.

I'd be tempted to apply the workaround (setting system property java.util.Arrays.useLegacyMergeSort to true until we switch to Java 8 in many years), but not by default for local builds, because it will hide some bogus Comparators to developers too (like those that we must fix in #8335 and #8671).

So something like this:

        if (Main.pref.getBoolean("jdk.Arrays.useLegacyMergeSort", !Version.getInstance().isLocalBuild())) {
            System.setProperty("java.util.Arrays.useLegacyMergeSort", true);
        }

Dirk, your opinion about this ?

[stoecker]

Dirk, your opinion about this?

I can't see the java bug reports ălways telling me "This bug is not available.", but it sounds like a proper solution to me.

[Don-vip]

Sun bug tracker is live again if you want to look at the bugs first :)

[Don-vip]

In 5977/josm:

fix #8712 - workaround to "Comparison method violates its general contract" when sorting a collection in Java 7, disabled for local builds. Set new property jdk.Arrays.useLegacyMergeSort to true to enable the workaround for local builds.