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Running SWT based, cross-platform jar properly on a Mac

Answer 1

A:

SWT (like any other UI framework) has a "UI thread". That is usually the main thread (i.e. the one that executed main(String[] args). All calls to UI methods must happen in this thread.

If you need to call a UI method from a non-UI thread, you must wrap it:

Display.getDefault().asyncExec( new Runnable() { 
    public void run() {
         //ui call here
    }
} );

If you need to wait for the result, you can use syncExec()

Aaron Digulla 2010-10-20 09:39:19

Well the theory makes sense, but I am confused as to why it becomes a problem specific to Mac environment. Besides as I wasn't the one who coded the GUI, I have no clue as to where in the software there might be "calls to UI methods from a non-UI thread" which makes the problem all the more complicated.

posdef 2010-10-20 09:45:14

Answer 2

+2 A:

Yes, you will definitely need -XstartOnFirstThread to get this working on Mac OS X. Since it's a VM parameter, you can only specify it when launching your application, so detecting the OS from you code and setting it if it's Mac OS X is not possible. The solution on the Eclipse site creates a proper Mac OS X My Application.app, which is platform specific and, again, not feasible in your case.

However, I just tried running an Eclipse RCP application on Windows XP with the -XstartOnFirstThread argument specified, and it didn't complain at all. This means that you can specify this argument in your JNLP file and presumably it will be ignored on all other platforms and picked up on Mac OS X.

UPDATE: If for some reason -XstartOnFirstThread causes trouble on any platform, or you just want to Do The Right Thing, there is another possible solution. You could detect the user's OS in the browser — assuming that the application is launched from a web page —, and supply a different JNLP for Mac OS X and other platforms.

UPDATE 2: As pointed out in the comments, there is a tutorial on deploying SWT applications with Java Web Start. I simply launched the JNLP on Mac OS X (10.6.x), and it worked. Looking at the example JNPL I found the following:

<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0+"
    codebase="http://www.eclipse.org/swt/jws/"
    href="controlexample.jnlp">
<information>
      <title>Control Example</title>
      <vendor>eclipse.org</vendor>
      <homepage href="http://www.eclipse.org/swt/jws/" />
      <description>A demonstration of SWT Widgets</description>
      <description>Control Example</description>
</information>

<security>
    <all-permissions />
</security>

<resources>
    <extension href="swt.jnlp"/>
    <jar href="controlexample.jar" />
</resources>

<application-desc main-class="org.eclipse.swt.examples.controlexample.ControlExample" />
</jnlp>

Note the <extension href="swt.jnlp"/> line towards the end, pointing to the platform-specific SWT JNLP file (some parts omitted here):

<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0+"
    codebase="http://www.eclipse.org/swt/jws/"
    href="swt.jnlp">
<information>
      <title>SWT</title>
      <vendor>eclipse.org</vendor>
      <homepage href="http://www.eclipse.org/swt/jws/" />
      <description>SWT</description>
</information>

<security>
    <all-permissions />
</security>

<resources os="Windows" arch="x86">
    <j2se version="1.4+" />
    <jar href="swt-win32-windows-x86.jar" />
</resources>

...

<resources os="Mac\ OS\ X">
    <j2se version="1.5*" java-vm-args="-XstartOnFirstThread"/>
    <jar href="swt-carbon-osx-universal.jar" />
</resources>

<component-desc/>
</jnlp>

There it is towards the end of the file: the Mac OS X specific -XstartOnFirstThread argument.

Zsolt Török 2010-10-20 09:55:41

your suggestion (specifying in the JNLP file) sounds cool, could anyone deny or confirm it??

posdef 2010-10-20 10:40:53

answering my own question here; `-XstartOnFirstThread` argument is apparently an unrecognized option on linux64 (sun-jdk-1.6.0) which results in failed execution:> java -jar -XstartOnFirstThread dist/test.jar Unrecognized option: -XstartOnFirstThreadCould not create the Java virtual machine.[2]+ Killed java -jar dist/test.jar

posdef 2010-10-20 11:33:32

@posdef: interesting, apparently the Windows 32-bit VM is less picky than the Linux 64-bit version. Anyhow, this means you have to have two different JNLPs, as suggested above.

Zsolt Török 2010-10-20 12:32:21

@Zsolt: hmm, how about checking the OS in the JNLP file and passing arguments accordingly, as written here (http://www.eclipse.org/swt/jws/)? It should work right? Note that they use the OS-check for another reason.

posdef 2010-10-20 13:01:47

@posdef: great find, looking into the referenced swt.jnlp revealed that you can indeed do that. See updated answer.

Zsolt Török 2010-10-20 13:29:49

@Zsolt: I dont get the extension part, why two different files?

posdef 2010-10-20 13:59:24

@posdef: if I understood correctly you don't have to split the SWT specific stuff into a separate JNLP, but for whatever reason they did. Try this two-file approach first to verify that it works and then you can try to combine them if you like. Also note that swt.jnlp adds platform-specific JARs, be sure to replicate that.

Zsolt Török 2010-10-20 14:14:33

@Zsolt: well I have already sorted out the different libraries thing, as I have mentioned in the original post. At this stage what I need to do is to pass the `-XstartOnFirstThread` argument, conditioned on the OS

posdef 2010-10-20 14:26:40

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Running SWT based, cross-platform jar properly on a Mac

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