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| gauraveca |
 Posted: Mon Mar 30, 2015 7:22 pm Post subject: Is Java Compute Node Singleton ? |
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Newbie
Joined: 15 Jan 2015
Posts: 5
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Hi
I am new to broker. We have a use case where we need to use java compute node for some transformation.
I need to know whether the class for my java compute node is a singleton ? For every incoming request a new instance of the class is created ?
I tried searching but couldn't find an answer to this.
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| Vitor |
| Posted: Tue Mar 31, 2015 4:29 am Post subject: Re: Is Java Compute Node Singleton ? |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| gauraveca wrote: |
I tried searching but couldn't find an answer to this.
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I'm suprised the searching didn't turn up the InfoCenter piece on the Java Compute Node.
| gauraveca wrote: |
| I need to know whether the class for my java compute node is a singleton ? For every incoming request a new instance of the class is created ? |
Why? I'm by no means the Java guy, but isn't the point of a singleton that there's only one of it between multiple instances?
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Honesty is the best policy.
Insanity is the best defence. |
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| mqjeff |
| Posted: Tue Mar 31, 2015 4:41 am Post subject: Re: Is Java Compute Node Singleton ? |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| Vitor wrote: |
| gauraveca wrote: |
I tried searching but couldn't find an answer to this.
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I'm suprised the searching didn't turn up the InfoCenter piece on the Java Compute Node. |
| Quote: |
| Only one instance of the JavaCompute node is created regardless of the number of threads that are running against the flow (either as a result of extra instances or multiple input nodes). |
The most important skill you can have when working wtih any technology is understanding how to use the documentation it provides.
The second most important skill is how to convince the maintainers to ensure the documentation is useful... |
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| mapa |
| Posted: Tue Mar 31, 2015 5:24 am Post subject: Re: Is Java Compute Node Singleton ? |
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Master
Joined: 09 Aug 2001
Posts: 257
Location: Malmö, Sweden
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| Vitor wrote: |
I'm suprised the searching didn't turn up the InfoCenter piece on the Java Compute Node.
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Why read about how the JCN works when you can post a question here? 
The link Vitor provided clearly express how it works if you read it.
However it does not mention Singleton (which is a design pattern) but if you know how the Singleton pattern works in Java you will know if the JCN is one or not if you read about it. |
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| kimbert |
| Posted: Tue Mar 31, 2015 5:28 am Post subject: |
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Jedi Council
Joined: 29 Jul 2003
Posts: 5542
Location: Southampton
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@mqjeff:
Arguably, this
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| Only one instance of the JavaCompute node is created |
...could be interpreted in terms of the node, and not the Java class that implements the user's transformation logic.
You and I know that it's talking about the latter, but it's not necessarily obvious.
@gauraveca:
There is sometimes a need to have a singleton class ( a common reason is to implement a process-wide cache for all message flows. Can be useful for storing session state, reference data etc. ). As mapa points out, you can easily implement one ( but make sure that you do some research on Java best practices first - it is easy to get it wrong ).
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| kimbert |
| Posted: Tue Mar 31, 2015 5:31 am Post subject: |
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Jedi Council
Joined: 29 Jul 2003
Posts: 5542
Location: Southampton
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...and before somebody else points it out, you may want to investigate using the global cache ( genuinely global ) before implementing a cache that can only be accessed from one OS process/execution group/integration server.
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| gauraveca |
| Posted: Tue Mar 31, 2015 9:24 pm Post subject: |
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Newbie
Joined: 15 Jan 2015
Posts: 5
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Thank you all for your replies. Apologies i didn't checked out the documentation in details. I did checked out the documentation and have some confusion or it might be my lack of experience in broker and java as i am just starting out.
This page says
http://www-01.ibm.com/support/knowledgecenter/SSMKHH_9.0.0/com.ibm.etools.mft.doc/ac20805_.htm
"Only one instance of the JavaCompute node is created regardless of the number of threads that are running against the flow (either as a result of extra instances or multiple input nodes). Therefore, all of your user Java code must be threadsafe and reentrant."
And this one says
http://www-01.ibm.com/support/knowledgecenter/SSMKHH_9.0.0/com.ibm.etools.mft.doc/ac01541_.htm?lang=en
In the message flow execution environment, the message flow is thread-safe. You can run message flows concurrently on many operating system threads, without having to consider serialization issues. Each input message that passes through a message flow for processing by a series of nodes executes on a single thread; it is processed only by the thread that received it.
The confusion is in the first article it asks the user to write the java code which is thread safe, however in the second article it says that the message flow itself is thread safe. So if the message flow is thread safe why do i need to explicitly write thread safe java code ? |
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| mqjeff |
| Posted: Wed Apr 01, 2015 4:32 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| gauraveca wrote: |
| So if the message flow is thread safe why do i need to explicitly write thread safe java code ? |
Because only one instance of your JavaComputeNode class is created, and so all message flow threads will call it. |
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| Vitor |
| Posted: Wed Apr 01, 2015 4:55 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| gauraveca wrote: |
| The confusion is in the first article it asks the user to write the java code which is thread safe, however in the second article it says that the message flow itself is thread safe. So if the message flow is thread safe why do i need to explicitly write thread safe java code ? |
The message flow is thread safe in that a message, once consumed by a given thread instance of the flow, will only be processed by that thread and flow artifacts (such as the Environment tree) are not shared / cross contaminated / locked by other thread instances of the same flow. The ESQL and the rest of the inbuilt functionality provide this thread safety by design.
To preserve this flow level thread safety it's essential that user written Java code is equally thread safe, as Java is the only part of the flow where it's physically possible to break the thread safe model; you simply can't write thread crossing ESQL, the language doesn't support or allow it.
You'll find the same requirement for thread safe code in the InfoCenter pieces about user defined nodes and user defined parsers, for the same reason. But you'll write Java Compute Nodes much, much more frequently.
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Insanity is the best defence. |
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| kimbert |
| Posted: Wed Apr 01, 2015 5:25 am Post subject: |
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Jedi Council
Joined: 29 Jul 2003
Posts: 5542
Location: Southampton
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| Quote: |
| you simply can't write thread crossing ESQL, the language doesn't support or allow it |
You can, if you declare SHARED variables in your ESQL.
Vitor knows this, of course. He just chose not to say it. And I only chose to say in order to annoy Vitor 
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| mqjeff |
| Posted: Wed Apr 01, 2015 5:34 am Post subject: |
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Grand Master
Joined: 25 Jun 2008
Posts: 17447
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| kimbert wrote: |
| Quote: |
| you simply can't write thread crossing ESQL, the language doesn't support or allow it |
You can, if you declare SHARED variables in your ESQL. |
Only the data crosses the threads, not the code... |
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| Vitor |
| Posted: Wed Apr 01, 2015 6:04 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| kimbert wrote: |
| Quote: |
| you simply can't write thread crossing ESQL, the language doesn't support or allow it |
You can, if you declare SHARED variables in your ESQL.
Vitor knows this, of course. He just chose not to say it. And I only chose to say in order to annoy Vitor |
This I assume to be the 2nd part of your cunning plan, the 1st part being to have one of your minions sabotage the coffee machine.....
....I echo the comments of yourself and our most worthy associate.
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Honesty is the best policy.
Insanity is the best defence. |
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| gauraveca |
| Posted: Thu Apr 02, 2015 10:27 pm Post subject: |
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Newbie
Joined: 15 Jan 2015
Posts: 5
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Thank you all for the help. I understand it now.
 kudos to the community here. |
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