RFC: Netx - Implement SingeInstanceService

[Deepak Bhole]

* Omair Majid <omajid at redhat.com> [2009-06-23 10:28]:
> Hi,
>
> Updated patch attached.
>

One very minor nitpick:

In SingleInstanceLock::getPort(), if an exception occurs, port is set to 
Integer.MIN_VALUE. It should probably be set to INVALID_PORT, since such 
a variable has already been defined and is used in comparison elsewhere.

Other than that, looks good to me!

Cheers,
Deepak

> Andrew Haley wrote:
>> Omair Majid wrote:
>>> Hi,
>>>
>>> Andrew Haley wrote:
>>>> Omair Majid wrote:
>>>>
>>>>> The attached patch adds support for SingleInstanceService to Netx.
>>>>>
>>>>> It creates a lock file under ~/.netx/locks/ once an application adds a
>>>>> SingleInstanceListener to the SingleInstanceService. A second instance
>>>>> of the application sees this lock file, sends it's arguments to the
>>>>> first instance and shuts down.
>>>> Do you know that the first instance is connected to the same X server?
>>> Just to be clear, even though the file names begin with X, they dont
>>> have much to do with the X server. All Linux implementations of jnlp
>>> services are prefixed with X in Netx.
>>>
>>> To answer the question: no. This patch enforces a single instance per
>>> user rather than per X session. Many other applications (such as
>>> Firefox) do the same thing.
>>
>> I am aware of that, of course: it's a famous longstanding Firefox bug.
>> What I don't know is whether jnlp is supposed to behave the same way;
>> I can't tell from the javadoc.  If it really is supposed to do that, fine.
>>
> The updated patch enforces a single instance per X session.
>
>>>> What happens if a stale lock file is left behind by some earlier event?
>>> This patch never cleans up the lock files. Each lock file contains a
>>> port number where first instance of the application is listening. If no
>>> application is listening at the port, then the file is assumed to be
>>> stale and ignored/overwritten.
>>
>> Sounds good.
>>
>>>> Is it good to use NFS for the lock file?  Would something in /tmp work
>>>> better?
>>
>>> Honestly, I have no clue. Fwiw, Sun's JRE creates lock files under
>>> ~/.java/ . I have no issues with using /tmp if you think that would work
>>> better.
>>
>> It probably is better, yes.
>
> Done. Netx now puts locks under /tmp/$USER/netx/locks.
>
> ChangeLog:
> 2009-06-23  Omair Majid  <omajid at redhat.com>
>
>     *rt/net/sourceforge/jnlp/Launcher.java
>     (launchApplication): Check for any existing single instance.
>     Dont start a second instance.
>     *rt/net/sourceforge/jnlp/resources/Messages.properties: Add
>     RNoLockDir.
>     *rt/net/sourceforge/jnlp/runtime/JNLPRuntime.java:
>     Added USER, TMP_DIR, and changed LOCKS_DIR
>     *rt/net/sourceforge/jnlp/services/ExtendedSingleInstanceService.java
>     New file.
>     *rt/net/sourceforge/jnlp/services/InstanceExistsException.java: New
>     file.
>     *rt/net/sourceforge/jnlp/services/ServiceUtil.java
>     (getSingleInstanceService): New function.
>     (checkExistingSingleInstance): New function.
>     *rt/net/sourceforge/jnlp/services/SingleInstanceLock.java: New
>     file.
>     *rt/net/sourceforge/jnlp/services/XServiceManagerStub.java: Add
>     SingleInstanceService to serviceNames. Create a new instance of
>     XSingleInstanceService as a privileged proxy.
>     *rt/net/sourceforge/jnlp/services/XSingleInstanceService.java: New
>     file.
>
> Cheers,
> Omair