[RFC][icedtea-web] Fix for single instance service with applets using jnlp_href

[Danesh Dadachanji]

On 12/03/12 06:42 AM, Jiri Vanek wrote:
> On 01/31/2012 09:07 PM, Danesh Dadachanji wrote:
>> Hi,
>>
> I must confess I can not guess motivation for this and not even find
> 100% what is it doing and why.
> Can you please write little bit (..much...;) ) more about background of
> this patch?
>
> My current thoughts - when two completely same appelts are on the page,
> they are not lunched - correct? Why this restriction?
>

Yeah, it was a confusing service to wrap my head around. :S

Right now, SingleInstanceService is available to use from 
applets/applications run by javaws. I am trying to port this over to the 
plugin so that when jnlp_href is used, applets have access to it.

The point of the service itself is to only let one instance of an applet 
run at a time. There's a catch to running another instance of the applet 
though. While the first one is running, it is setup with a listener for 
later instances to use. The idea is that the second instance can 
communicate with the running instance, passing along some args to be 
handled by the listener, and then exit. When you run another instance of 
the applet, icedtea-web is supposed to recognize this as the second 
instance and pass on a list of arguments provided by the dev. See the 
API for SingleInstanceListener[1] for the methods. I think the following 
signleapp example[2] might help you too.

Here's an example run path:

1. Start single instance app. The dev has set it up to handle params 
accordingly, say to spit it out on the screen to log.
2. IcedTea-Web sets up a single instance server to keep track of the 
instance running.
3. The second app is run, args are passed in by the dev again. Let's say 
they are the current date/time.
4. IcedTea-Web notices the second app is a second instance of the first 
one and checks that the first one's server is still running, then denies 
init of the second applet. The second instance's args are taken and 
passed along to the first instance's newActivation(String[] args) method.
5. Dev's newActivation method reacts accordingly.

I hope the example[2] helps clear up any doubts I have not covered but 
please ask if it doesn't!

>> Attached is a patch to fix SingleInstanceService to work when applets
>> use jnlp_href.
>>
>> If a single instance exists, it'll throw a fatal exception for the
>> second applet and stop running it. The applet passes the args along
>> while checking. However, proprietary documentation is unclear about
>> which args are passed so for now I have left it as a FIXME until
>> that's cleared up.
> I believe applets parameters inside tag/jnlp descriptor are correct way.

These args I was referring to are from the second instance being run so 
we're talking about different things here. =) Please see above.

>>
>> ChangeLog:
>> +2012-01-31 Danesh Dadachanji <ddadacha at redhat.com>
>> +
>> + Fixed SingleInstanceService to work with jnlp_href.
>> + * netx/net/sourceforge/jnlp/Launcher.java
>> + (launchApplication): Print existing single instance in debug mode.
>> + (launchApplet): Added check for single instance, throws launchError if
>> + single instance already exists.
>> + (getApplet): Same as above.
>> + (launchInstaller): Added TODO reminder for when it is implemented.
>> + * netx/net/sourceforge/jnlp/resources/Messages.properties:
>> + Added LSingleInstanceExists.
>> + * netx/net/sourceforge/jnlp/services/XSingleInstanceService.java
>> + (initializeSingleInstance): Modified to always initialize if the
>> applet is
>> + being run by the plugin.
>> + (checkSingleInstanceRunning): Modified args passed to
>> SingleInstanceListener.
>> + Marked applets' args as FIXME, for now it passes an empty args array.
>> +
>>
>> Okay for HEAD?
>>
>> Cheers,
>> Danesh
>>
>>
>> single-instance-service-01.patch
>>
>>
>> diff --git a/netx/net/sourceforge/jnlp/Launcher.java
>> b/netx/net/sourceforge/jnlp/Launcher.java
>> --- a/netx/net/sourceforge/jnlp/Launcher.java
>> +++ b/netx/net/sourceforge/jnlp/Launcher.java
>> @@ -536,6 +536,9 @@ public class Launcher {
>> try {
>> ServiceUtil.checkExistingSingleInstance(file);
>> } catch (InstanceExistsException e) {
>> + if (JNLPRuntime.isDebug()) {
>> + System.out.println("Single instance application is already running.");
>
> *
>
>> + }
>> return null;
>> }
>>
>> @@ -653,11 +656,17 @@ public class Launcher {
>> throw launchError(new LaunchException(file, null, R("LSFatal"),
>> R("LCClient"), R("LNotApplet"), R("LNotAppletInfo")));
>>
>> try {
>> + ServiceUtil.checkExistingSingleInstance(file);
>> AppletInstance applet = createApplet(file, enableCodeBase, cont);
>> applet.initialize();
>>
>> applet.getAppletEnvironment().startApplet(); // this should be a
>> direct call to applet instance
>> return applet;
>> + } catch (InstanceExistsException ieex) {
>> + if (JNLPRuntime.isDebug()) {
>> + System.out.println("Single instance applet is already running.");
>
> *
>
>> + }
>> + throw launchError(new LaunchException(file, ieex, R("LSFatal"),
>> R("LCLaunching"), R("LCouldNotLaunch"), R("LSingleInstanceExists")));
>> } catch (LaunchException lex) {
>> throw launchError(lex);
>> } catch (Exception ex) {
>> @@ -673,9 +682,17 @@ public class Launcher {
>> throw launchError(new LaunchException(file, null, R("LSFatal"),
>> R("LCClient"), R("LNotApplet"), R("LNotAppletInfo")));
>>
>> try {
>> + ServiceUtil.checkExistingSingleInstance(file);
>> +
>> AppletInstance applet = createApplet(file, enableCodeBase, cont);
>> applet.initialize();
>> return applet;
>> +
>> + } catch (InstanceExistsException ieex) {
>> + if (JNLPRuntime.isDebug()) {
>> + System.out.println("Single instance applet is already running.");
>
> * Why not also stacktraces?
>

The thing is this service uses exceptions as a means of telling 
icedtea-web that it shouldn't run the second applet. It's not really an 
exception that something went wrong, it's more of a means to check that 
there is a current single instance running. I figured that while 
debugging, it would be useful to have though. Also, the other thread 
throws the exception IIRC later on so it would really just be the same 
one being printed twice.

Please ask more questions if I was unclear!

[1] 
http://docs.oracle.com/javase/7/docs/jre/api/javaws/jnlp/javax/jnlp/SingleInstanceListener.html
[2] http://pscode.org/jws/api.html