GWT development mode issue - gwt

Question

I'm running a GWT app in a dev mode with a custom Jetty container. The app loads fine for the first time, however, if I refresh it, I get the following errors in the Development Mode window (paths changed):
00:16:44.854 [ERROR] Unable to create file 'C:\somePath\src\war\msjavaSnack\C4EA130FD0ED44BE513FEEDDE13614DA.cache.png'
java.io.FileNotFoundException: C:\somePath\src\war\msjavaSnack\C4EA130FD0ED44BE513FEEDDE13614DA.cache.png (The requested operation cannot be performed on a file with a user-mapped section open)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.<init>(FileOutputStream.java:194)
at java.io.FileOutputStream.<init>(FileOutputStream.java:145)
at com.google.gwt.core.ext.linker.impl.StandardLinkerContext.writeArtifactToFile(StandardLinkerContext.java:658)
at com.google.gwt.core.ext.linker.impl.StandardLinkerContext.produceOutputDirectory(StandardLinkerContext.java:595)
at com.google.gwt.dev.DevMode.produceOutput(DevMode.java:476)
at com.google.gwt.dev.DevModeBase.relink(DevModeBase.java:1131)
at com.google.gwt.dev.DevModeBase.access$000(DevModeBase.java:67)
at com.google.gwt.dev.DevModeBase$2.accept(DevModeBase.java:1076)
at com.google.gwt.dev.shell.ShellModuleSpaceHost$1.accept(ShellModuleSpaceHost.java:122)
at com.google.gwt.dev.shell.StandardRebindOracle$Rebinder.rebind(StandardRebindOracle.java:59)
at com.google.gwt.dev.shell.StandardRebindOracle.rebind(StandardRebindOracle.java:154)
at com.google.gwt.dev.shell.ShellModuleSpaceHost.rebind(ShellModuleSpaceHost.java:119)
at com.google.gwt.dev.shell.ModuleSpace.rebind(ModuleSpace.java:531)
at com.google.gwt.dev.shell.ModuleSpace.rebindAndCreate(ModuleSpace.java:414)
at com.google.gwt.dev.shell.GWTBridgeImpl.create(GWTBridgeImpl.java:39)
at com.google.gwt.core.client.GWT.create(GWT.java:98)
at com.extjs.gxt.ui.client.GXT.<clinit>(GXT.java:38)
at com.extjs.gxt.ui.client.widget.Component.<clinit>(Component.java:202)
at msjava.snack.gui.client.MSHeaderPanelViewport.<init>(MSHeaderPanelViewport.java:62)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.google.gwt.dev.shell.ModuleSpace.rebindAndCreate(ModuleSpace.java:422)
at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:361)
at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:185)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:380)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222)
at java.lang.Thread.run(Thread.java:662)
UPDATE
In the ProcessExplorer I can see that the JVM process hosting Jetty has an open handle to the file so this is probably the reason why the other JVM (hosting the dev mode) can't write to it. Any way to work it around?

Answer 1

It seems that two (open/close) (open/close) rutines over the same file happening too soon one after another causes this... Some developers suggest to call the gc. Check for closing correctly every i/o operation. Not to perform complete (open,loop(writes),close) too soon. It seems that when one operation it is going to be finished while the second request arrives and that throws the problem.

Answer 2

I found the solution on this page:
http://docs.codehaus.org/display/JETTY/Files+locked+on+Windows
EDIT:
The above URL is dead now.
Now it's quite easy to find the solution in Jetty's wiki:
Jetty provides a configuration switch in the webdefault.xml file for
the DefaultServlet that enables or disables the use of memory-mapped
files. If you are running on Windows and are having file-locking
problems, you should set this switch to disable memory-mapped file
buffers.
The default webdefault.xml file is in the lib/jetty.jar at
org/eclipse/jetty/webapp/webdefault.xml. Extract it to a convenient
disk location and edit it to change useFileMappedBuffer to false.
https://wiki.eclipse.org/Jetty/Howto/Deal_with_Locked_Windows_Files