Setting WMS Simultaneous connections to 1 makes JOSM unusable

[josm@…]

What steps will reproduce the problem?

1. Set preference WMS/TMS -> Settings -> WMS settings -> Simultaneous connections = "1" (cache.jcs.max_threads = 1)
2. Restart
3. Try to access Preferences (F12) or try to open download map data window.

What is the expected result?

Get access to preferences window, or download form OSM window.

What happens instead?

Exception or silent error eg. "Could not initialize class org.openstreetmap.josm.data.cache.JCSCachedTileLoaderJob" and nothing happens, or JOSM opens empty unusable download data from OSM window. I have also reproduced this error with default settings. It taked me a while to find which changed option caused this behaviour. Cannot access preferences window to change "Simultaneous connections" to something greater than 1. Beginner may not know what caused this, and may be forced to deleting his preferences. Finally, I have edited preferences.xml manually. Setting cache.jcs.max_threads to value greater than 1 resolved problem. I had temporarily very limited internet bandwidth 64 kbps/s after excessing provider quota, and I tried setting "Simultaneous connections" to "1" to not overload internet connection.

Thank you for your work on JOSM.

Please provide any additional information below. Attach a screenshot if possible.

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-06-04 17:28:58 +0200 (Sat, 04 Jun 2016)
Build-Date:2016-06-04 15:31:27
Revision:10327
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10327 pl) Windows 8.1 64-Bit
Memory Usage: 485 MB / 910 MB (415 MB allocated, but free)
Java version: 1.8.0_91-b15, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM


Last errors/warnings:
- E: java.net.SocketTimeoutException: Read timed out
- E: java.lang.ExceptionInInitializerError. Przyczyna: java.lang.IllegalArgumentException

java.lang.ExceptionInInitializerError
	at org.openstreetmap.josm.gui.preferences.imagery.WMSSettingsPanel.<init>(WMSSettingsPanel.java:45)
	at org.openstreetmap.josm.gui.preferences.imagery.ImageryPreference.<init>(ImageryPreference.java:82)
	at org.openstreetmap.josm.gui.preferences.imagery.ImageryPreference.<init>(ImageryPreference.java:76)
	at org.openstreetmap.josm.gui.preferences.imagery.ImageryPreference$Factory.createPreferenceSetting(ImageryPreference.java:91)
	at org.openstreetmap.josm.gui.preferences.PreferenceTabbedPane.buildGui(PreferenceTabbedPane.java:473)
	at org.openstreetmap.josm.gui.preferences.PreferenceDialog.build(PreferenceDialog.java:81)
	at org.openstreetmap.josm.gui.preferences.PreferenceDialog.<init>(PreferenceDialog.java:48)
	at org.openstreetmap.josm.actions.PreferencesAction.run(PreferencesAction.java:106)
	at org.openstreetmap.josm.actions.PreferencesAction.actionPerformed(PreferencesAction.java:101)
	at javax.swing.SwingUtilities.notifyAction(Unknown Source)
	at javax.swing.JComponent.processKeyBinding(Unknown Source)
	at javax.swing.KeyboardManager.fireBinding(Unknown Source)
	at javax.swing.KeyboardManager.fireKeyboardAction(Unknown Source)
	at javax.swing.JComponent.processKeyBindingsForAllComponents(Unknown Source)
	at javax.swing.JComponent.processKeyBindings(Unknown Source)
	at javax.swing.JComponent.processKeyEvent(Unknown Source)
	at java.awt.Component.processEvent(Unknown Source)
	at java.awt.Container.processEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
	at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
	at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
	at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
	at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
	at java.awt.Component.dispatchEventImpl(Unknown Source)
	at java.awt.Container.dispatchEventImpl(Unknown Source)
	at java.awt.Window.dispatchEventImpl(Unknown Source)
	at java.awt.Component.dispatchEvent(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$500(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.lang.IllegalArgumentException
	at java.util.concurrent.ThreadPoolExecutor.<init>(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.<init>(Unknown Source)
	at org.openstreetmap.josm.data.cache.JCSCachedTileLoaderJob.<clinit>(JCSCachedTileLoaderJob.java:73)
	... 48 more

[wiktorn]

In 10408/josm:

Set core pool size to 1, so minimum number of thread can be 1.

Closes: #12971