py4j-users

[Py4j-users] Starting/stopping py4j server from within python?

[Thomas N. <tom...@gm...>]

Hello,

What would be the best way for me to start and stop the py4j server from 
within python? I know I could use

 > os.system("java ...")

to start the server. I guess I would need a subprocess for that not to 
block. Then to stop it I could send it a kill signal. Is this the best 
way to do it? Is there a way for me to do this in a less 
directly-managed fashion? This is okay for me, but the users of what I'm 
making probably would have trouble...

Cheers,
Thomas

Re: [Py4j-users] Starting/stopping py4j server from within python?

[Barthelemy D. <bar...@in...>]

Hi,

it depends on your use case. Most of the examples start a server in
the Java main method so if you do gateway.shutdown() on the Python
side, it will (1) send a shutdown signal on the Java side, (2) the
Java server will stops, and (3) because there are no more active
threads, the JVM will exit.

You can even do something harsher from Python:

gateway.jvm.System.exit(0)

Does that help?

Barthelemy

On Mon, Dec 8, 2014 at 3:46 PM, Thomas Nyberg <tom...@gm...> wrote:
> Hello,
>
> What would be the best way for me to start and stop the py4j server from
> within python? I know I could use
>
>  > os.system("java ...")
>
> to start the server. I guess I would need a subprocess for that not to
> block. Then to stop it I could send it a kill signal. Is this the best
> way to do it? Is there a way for me to do this in a less
> directly-managed fashion? This is okay for me, but the users of what I'm
> making probably would have trouble...
>
> Cheers,
> Thomas
>
> ------------------------------------------------------------------------------
> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server
> from Actuate! Instantly Supercharge Your Business Reports and Dashboards
> with Interactivity, Sharing, Native Excel Exports, App Integration & more
> Get technology previously reserved for billion-dollar corporations, FREE
> http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
> _______________________________________________
> Py4j-users mailing list
> Py4...@li...
> https://lists.sourceforge.net/lists/listinfo/py4j-users

Re: [Py4j-users] Starting/stopping py4j server from within python?

[Thomas N. <tom...@gm...>]

Great that's a nice way to avoid sending any explicit kill signals. Also 
that's probably easy enough for my users to manage.

What would be really nice is if there could be some sort of garbage 
collector hook that would send the shutdown signal automatically. That 
way you could maybe create a class that automatically started the server 
and then when whatever you're using goes out of scope, your hook could 
shutdown the server. I'm sure something like this is theoretically 
possible, but I've never worked with that sort of thing. Then maybe on 
init one could check if the port is in use (i.e. by another py4j server) 
and choose a different port in that case.

This is all probably overkill though. Your method is great for now. Thanks!

On 12/08/2014 04:09 PM, Barthelemy Dagenais wrote:
> Hi,
>
> it depends on your use case. Most of the examples start a server in
> the Java main method so if you do gateway.shutdown() on the Python
> side, it will (1) send a shutdown signal on the Java side, (2) the
> Java server will stops, and (3) because there are no more active
> threads, the JVM will exit.
>
> You can even do something harsher from Python:
>
> gateway.jvm.System.exit(0)
>
> Does that help?
>
> Barthelemy
>
> On Mon, Dec 8, 2014 at 3:46 PM, Thomas Nyberg <tom...@gm...> wrote:
>> Hello,
>>
>> What would be the best way for me to start and stop the py4j server from
>> within python? I know I could use
>>
>>   > os.system("java ...")
>>
>> to start the server. I guess I would need a subprocess for that not to
>> block. Then to stop it I could send it a kill signal. Is this the best
>> way to do it? Is there a way for me to do this in a less
>> directly-managed fashion? This is okay for me, but the users of what I'm
>> making probably would have trouble...
>>
>> Cheers,
>> Thomas
>>
>> ------------------------------------------------------------------------------
>> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server
>> from Actuate! Instantly Supercharge Your Business Reports and Dashboards
>> with Interactivity, Sharing, Native Excel Exports, App Integration & more
>> Get technology previously reserved for billion-dollar corporations, FREE
>> http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
>> _______________________________________________
>> Py4j-users mailing list
>> Py4...@li...
>> https://lists.sourceforge.net/lists/listinfo/py4j-users
>
> ------------------------------------------------------------------------------
> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server
> from Actuate! Instantly Supercharge Your Business Reports and Dashboards
> with Interactivity, Sharing, Native Excel Exports, App Integration & more
> Get technology previously reserved for billion-dollar corporations, FREE
> http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
> _______________________________________________
> Py4j-users mailing list
> Py4...@li...
> https://lists.sourceforge.net/lists/listinfo/py4j-users
>

Re: [Py4j-users] Starting/stopping py4j server from within python?

[Barthelemy D. <bar...@in...>]

Hi, here are a few pointers that may be useful to you:

1. The py4j.java_gateway.launch_gateway enables you to start a JVM and
kill it when the Python process dies.

2. It's possible to launch the Java server with port 0 (ephemeral
port): this takes the first accessible port. You then need a way to
communicate this port to the Python side (launch_gateway uses a pipe)

3. Py4J supports garbage collection: if a python reference to a Java
object is garbage collected, the reference to the Java object is
released. This uses the weakref.ref(obj, callback) method. You may
want to use something like that to know when to stop the Java server.
Please note that finalizers, as it is the case with most programming
languages, are not guaranteed to be called, but they are good enough
for most use cases.

Barthelemy

On Mon, Dec 8, 2014 at 4:19 PM, Thomas Nyberg <tom...@gm...> wrote:
> Great that's a nice way to avoid sending any explicit kill signals. Also
> that's probably easy enough for my users to manage.
>
> What would be really nice is if there could be some sort of garbage
> collector hook that would send the shutdown signal automatically. That
> way you could maybe create a class that automatically started the server
> and then when whatever you're using goes out of scope, your hook could
> shutdown the server. I'm sure something like this is theoretically
> possible, but I've never worked with that sort of thing. Then maybe on
> init one could check if the port is in use (i.e. by another py4j server)
> and choose a different port in that case.
>
> This is all probably overkill though. Your method is great for now. Thanks!
>
> On 12/08/2014 04:09 PM, Barthelemy Dagenais wrote:
>> Hi,
>>
>> it depends on your use case. Most of the examples start a server in
>> the Java main method so if you do gateway.shutdown() on the Python
>> side, it will (1) send a shutdown signal on the Java side, (2) the
>> Java server will stops, and (3) because there are no more active
>> threads, the JVM will exit.
>>
>> You can even do something harsher from Python:
>>
>> gateway.jvm.System.exit(0)
>>
>> Does that help?
>>
>> Barthelemy
>>
>> On Mon, Dec 8, 2014 at 3:46 PM, Thomas Nyberg <tom...@gm...> wrote:
>>> Hello,
>>>
>>> What would be the best way for me to start and stop the py4j server from
>>> within python? I know I could use
>>>
>>>   > os.system("java ...")
>>>
>>> to start the server. I guess I would need a subprocess for that not to
>>> block. Then to stop it I could send it a kill signal. Is this the best
>>> way to do it? Is there a way for me to do this in a less
>>> directly-managed fashion? This is okay for me, but the users of what I'm
>>> making probably would have trouble...
>>>
>>> Cheers,
>>> Thomas
>>>
>>> ------------------------------------------------------------------------------
>>> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server
>>> from Actuate! Instantly Supercharge Your Business Reports and Dashboards
>>> with Interactivity, Sharing, Native Excel Exports, App Integration & more
>>> Get technology previously reserved for billion-dollar corporations, FREE
>>> http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
>>> _______________________________________________
>>> Py4j-users mailing list
>>> Py4...@li...
>>> https://lists.sourceforge.net/lists/listinfo/py4j-users
>>
>> ------------------------------------------------------------------------------
>> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server
>> from Actuate! Instantly Supercharge Your Business Reports and Dashboards
>> with Interactivity, Sharing, Native Excel Exports, App Integration & more
>> Get technology previously reserved for billion-dollar corporations, FREE
>> http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
>> _______________________________________________
>> Py4j-users mailing list
>> Py4...@li...
>> https://lists.sourceforge.net/lists/listinfo/py4j-users
>>
>
> ------------------------------------------------------------------------------
> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server
> from Actuate! Instantly Supercharge Your Business Reports and Dashboards
> with Interactivity, Sharing, Native Excel Exports, App Integration & more
> Get technology previously reserved for billion-dollar corporations, FREE
> http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk
> _______________________________________________
> Py4j-users mailing list
> Py4...@li...
> https://lists.sourceforge.net/lists/listinfo/py4j-users