Claim check pattern implementation

Hi
I would like to know how do we support this pattern via OSB.
http://camel.apache.org/claim-check.html
I am thinking of using Java callout in the message flow and use Stax parser to get a value for the unique key and then store the payload in a store.
I am relying on stax parser because the size of the message will be huge.
Is the java callout the only way to do this or i can use Xquery and Xpath to achieve what i want and if i do go through the simpler Xquery route will it give me memory error.
regards
Edited by: 899881 on Feb 25, 2013 8:03 AM

Can you not do this from SE19? If you know the BADI definition name just do an F4 on the implementation, and put in the definition name, and select Active Only option, and you should see the list.
Albert

Similar Messages

Design patterns implemented in java API

Hi,
I have some questions on design patterns implemented in core java class or in general in java API.
1)Whether
java.util.Collections, the checkedXXX(), synchronizedXXX() and unmodifiableXXX() methods.
can be considered as a decorator pattern?
2) Whether
LinkedHashMap(LinkedHashSet<K>, List<V>) which returns an unmodifiable linked map which doesn't clone the items, but uses them
can be considered as a Bridge pattern?
3) Whether Facade pattern is implemented in java ? If so which API uses it?
4) Whether
•     All non-abstract methods of java.io.InputStream, java.io.OutputStream, java.io.Reader and java.io.Writer.
•     All non-abstract methods of java.util.AbstractList, java.util.AbstractSet and java.util.AbstractMap
can be considered as a Template method pattern?
5) Whether
•     java.util.Comparator#compare(), executed by among others Collections#sort()
can be considered as a Stratergy pattern?
6)
Whether State pattern is implemented in java ? If so which API uses it?
7)
All implementations of java.lang.Runnable are considered as a Command pattern.
8)
Whether
•     java.io.InputStreamReader(InputStream) (returns a Reader)
•     java.io.OutputStreamWriter(OutputStream) (returns a Writer)
can be considered as an Adapter pattern?
Please clarify.
Thanks.

What do you think, and why?

Check active implementation in badi

Hi Expert,
Pl's let me know how to I check active implementation in badi in ECC6.0.
I have tried to find the solution by using call function 'SXC_EXIT_CHECK_ACTIVE' , as used in previous version of the server.
But this is not helping me out.
Kindly let me know if there exists a way to check the active implementations in badi.
Tx
Kshitija

Can you not do this from SE19? If you know the BADI definition name just do an F4 on the implementation, and put in the definition name, and select Active Only option, and you should see the list.
Albert

27" iMac Windows XP Green Checker Pattern Flashes

I just loaded Windows XP on my new 27" iMac with Boot Camp 3.1 and started noticing a green checker pattern flashing on the screen about every minute or so. Some times is would fill the screen or just flash on part of it. Has anyone had this problem or have a solution? Any help would be appreciated.

I'm having an almost identical issue but with different OS, only I seem to have even more issues. I first tried installing Windows 7 Pro 64bit -- the computer would just hang on a blank/shutdown screen forever. So Windows 7, 64Bit a no-go. I tried again with Windows 7 Home Premium, after removing the partition, recreating the partition and formatting, again. Same situation, blank/shutdown screen forever, but the computer is clearly still running -- HDD was still being accessed. Then after about 10 minutes, nothing except the fans. I tried BOTH versions in 32Bit following same pattern... no luck.
I tried one more time with just Windows Vista Home 32Bit -- recreated the partition, reformatted, and at first the same thing happened -- I rebooted in safe mode and it worked. Then I rebooted in normal and it didn't work. I eventually got it to boot -- then I installed BootCamp -- the Video drivers would not install, the audio drivers didn't seem to work, the Network drivers never loaded. Many, many issues.
Apple, I need you to help us out here, please. I need this machine to run Windows. I am going to wait for the BootCamp updates and hope that the new i7 machines are thoroughly tested.
By the way, 2 things: 1) Yes, all my Windows OS installations are bought and paid for legitimately. 2) these new Apple iMac 27" i7 machines are AWESOME!
Take care and best wishes to all encountering these issues,
Quark

Check on Implementation being used in a class

Hi Al,
We have a requirement of using one method of using one implimentation of a class but we have two implementations available .Is ther any check where in we can specify the usage of one implementation and ignoring the other
One way of doing it is to inactivate the implementation not needed but is there any other way of doing it.
It's urgent any help is highly appreciated.
Regards,
Rajashree

Using the below FM:
SUSR_USER_AUTH_FOR_OBJ_GET
EFG_USER_AUTH_FOR_OBJ_GET
You can get all the autority check available for a user.
Regards,
Prakash.

Bug in xs:pattern implementation when calling schemaValidate?

Hi all,
I have a schema with a pattern <xs:pattern value="(0?[1-9]|1[0-2])"/> that is supposed to validate the digits 01-09, 1-9, 10, 11, 12. When validating XML against the schema, values such as '12' fail. If the xs:pattern in re-written "(1[0-2]|0?[1-9])", i.e. the parts either side of the | are swapped, the xs:pattern works as expected, i.e. '12' validates as correct. The pattern itself works as expected with validators such as with Eclipse, and the RE seems to work as expected in PL/SQL
Is this a bug with the XML parser used in "Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production", or is there another parser I can configure 10g to use? I have a number of xml schemas and patterns to check, and want to be sure that they work as expected.
thanks
Paul
-- A simple example demonstrating the problem.
declare
vSchemaName varchar(100);
xmldoc XMLType;
vReturn boolean;
vResult int;
begin
vSchemaName := 'test.xsd';
-- Remove the old schema, if it exists.
if (dbms_xdb.existsResource('/' || vSchemaName)) then
dbms_xdb.deleteResource('/' || vSchemaName);
end if;
select count(1)
into vResult
from sys.DBA_XML_SCHEMAS
where SCHEMA_URL = vSchemaName;
if (vResult = 1) then
dbms_XMLSchema.deleteSchema(vSchemaName, DELETE_OPTION => dbms_xmlschema.DELETE_CASCADE_FORCE);
end if;
vReturn := dbms_xdb.createResource(
'/' || vSchemaName
, XMLType('
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
<xs:element name="Document_Creation_Date" type="Date_Mandatory"/>
     <xs:simpleType name="Date_Mandatory">
          <xs:restriction base="xs:string">


<xs:pattern value="(0?[1-9]|1[0-2])"/>
          </xs:restriction>
     </xs:simpleType>
</xs:schema>')
-- Register the schema
dbms_XMLSchema.registerSchema( schemaUrl => vSchemaName, schemaDoc => sys.UriFactory.getUri('/' || vSchemaName), GENTYPES => false, GENTABLES => false);
-- Sample XML to validate
xmldoc := XMLType('<Document_Creation_Date>12</Document_Creation_Date>').createSchemaBasedXML('test.xsd');
xmldoc.schemaValidate();
commit;
end;
/

Please patch one fo your machines to 10.2.0.3 and then try and duplicate. You do not have to go through the complete registration of the XSD process thoguh you can check and see if the c based parser will validate on the command line using the
schema executible under your oracle_home bin directory.
schema 1.xml 1.xsd
for example
if it dupes in 10.2.0.3 open a TAR with support so that we may bug it.
regards
Coby

Value Object pattern implementation problem

Hi All!
I try to implement value object pattern in my bean as follows:
/* Simplified code */
public class Value implements Serializable {
private String s;
public setS(String value){
s = value
public getS(){return s}
bean class:
public class Bean extends Value implemets EntityBean {
public Value getValue(){return this}
Now question.
When I try run this code I get next message
org.omg.CORBA.MARSHAL: minor code: 0 completed: No
org.omg.CORBA.portable.InputStream com.visigenic.vbroker.orb.GiopStubDelegate.invoke(org.omg.CORBA.Object, org.omg.CORBA.portable.OutputStream, org.omg.CORBA.StringHolder, org.omg.CORBA.Context, org.omg.CORBA.ContextList)
org.omg.CORBA.portable.InputStream com.visigenic.vbroker.orb.GiopStubDelegate.invoke(org.omg.CORBA.Object, org.omg.CORBA.portable.OutputStream, org.omg.CORBA.StringHolder)
org.omg.CORBA.portable.InputStream com.inprise.vbroker.CORBA.portable.ObjectImpl._invoke(org.omg.CORBA.portable.OutputStream, org.omg.CORBA.StringHolder)
com.retailpro.cms.common.InventoryValue com.retailpro.cms.ejb._st_Inventory.getValue()
void com.retailpro.cms.inventory.SetInventory._jspService(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void oracle.jsp.runtime.HttpJsp.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void oracle.jsp.app.JspApplication.dispatchRequest(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void oracle.jsp.JspServlet.doDispatch(oracle.jsp.app.JspRequestContext)
void oracle.jsp.JspServlet.internalService(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void oracle.jsp.JspServlet.service(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
void javax.servlet.http.HttpServlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
void oracle.lite.web.JupServlet.service(oracle.lite.web.JupRequest, oracle.lite.web.JupResponse)
void oracle.lite.web.MimeServletHandler.handle(oracle.lite.web.JupApplication, java.lang.String, int, oracle.lite.web.JupRequest, oracle.lite.web.JupResponse)
void oracle.lite.web.JupApplication.service(oracle.lite.web.JupRequest, oracle.lite.web.JupResponse)
void oracle.lite.web.JupHandler.handle(oracle.lite.web.JupRequest, oracle.lite.web.JupResponse)
void oracle.lite.web.HTTPServer.process(oracle.lite.web.JupRequest, oracle.lite.web.JupResponse)
boolean oracle.lite.web.HTTPServer.handleRequest(oracle.lite.web.JupInputStream, oracle.lite.web.JupOutputStream)
boolean oracle.lite.web.JupServer.handle(oracle.lite.web.JupInputStream, oracle.lite.web.JupOutputStream)
void oracle.lite.web.SocketListener.process(java.net.Socket)
void oracle.lite.web.SocketListener$ReqHandler.run()
Seems like object can't be serialized.
But when I change my getValue() to next
public Value getValue(){
Value result = new Value();
result.setS(s);
return result;
Everything goes fine!
Can anybody comments this situation?
Any information will be appreciated!
Mike
null

Have you tried using our Business Components for Java framework to assist in developing your EJB components. BC4J is a design pattern framework that implements the J2EE Blueprints design patterns out of the box:
[list][*]Session-Entity Fagade
[*]Paged-List
[*]Unified Data Access & Logic
[*]Value Object
[*]Model View Controller
[list]
and more...
So many things you don't have to code yourself when you use BC4J to turbocharge your development... Also, using BC4J insulates you from having to choose once and for all at the beginning of your project that you ARE USING EJB AT ALL COSTS on your project.
Many projects discover that they don't require a distributed objects configuration, but end up paying for it in architectural complexity and EJB's assumption that all beans might be located on remote VM's.
With BC4J, you can build an app, deploy to EJB if you need EJB for a given project, or deploy to CORBA, or just to simple Java classes for improved performance without the remoting overheads. All without touching your application code.
Pretty cool, I think. But of course, I'm biased :-)
Steve Muench
Lead Product Manager for BC4J and Lead XML Evangelist, Oracle Corp
Author, Building Oracle XML Applications

Negative Consumption Checking when Implementing Installation Groups

Hello,
I would like to Implement Installation Groups and I want to check for a negative consumption.
I didn't find any possibilities to make it through Custumising.
Maybe you know how to do it ?
Thank you very much in advance,
Michael.

Hi,
You can define Grouping types for Installation Groups as part of Master Data configuration.. You can do the same
Mater Data -> Utility Installation -> Define Grouping Types for Installation Groups..
You can control negetive consumption check here as well..
Have look at the doucument in SPRO pertaining to this for understanding.
Thanks
Vinod

Display checker pattern

I have a G-5 PowerMac (PPC) with 23" cinema display both circa fall 2003. The display just began overlaying a checkered/plaid looking pattern to the entire screen. The checker blocks are turquoise on a white background and red on a black background. The computer otherwise functions normally. I have tried changing display color settings and changing resolutions - the pattern stays, enlarging or shrinking with the resolution changes.
Anyone know how to fix this?
Thanks in advance.

Hi Ira,
Sounds like a Video Card problem or Heat issue, two things to try...
Get Temperature Monitor to see if it's heat related...
http://www.macupdate.com/info.php/id/12381/temperature-monitor
And/or iStat Pro...
http://www.islayer.com/apps/istatpro/
If you have any temps in the 70°C/160°F range, that's likely it, especially the Graphic Proccessor.
One way to test is to Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, is the screen still messed up in Safe Mode...
PS. Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive
Reboot, test again.
If it only does it in Regular Boot, then it could be some hardware problem like Video card, (Quartz is turned off in Safe Mode).

Using public views to check function implementation

Hi All,
I'm trying to use some public views to check whether the repositories of Development, Acceptance and Production are in sync.
In order to check the functions and procedures, I came up with the following query to have a simple comparison mechanism:
SELECT f.function_type
, f.schema_name
, f.function_name
, LENGTH(i.SCRIPT) script_length
FROM all_iv_functions f
, all_iv_function_impls i
WHERE f.FUNCTION_ID = i.FUNCTION_ID
Unfortunatly I get an error message:
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at "OWB_OWNER.OWM_VIEW_UTILITIES", line 572
ORA-06502: PL/SQL: numeric or value error: character string buffer too small
The same error occurs when I try to view data of all_iv_function_impls in TOAD.
Checked the viewdef, it selects (among others) the following:
OWM_VIEW_UTILITIES.FUNCTION_SCRIPT(im.elementid) AS script.
Of course the package body is wrapped so no way to see what's happening in there.
I tried a search on this problem, no result.
I did a general search on OWM_VIEW_UTILITIES, but no results.
Checked Metalink, only Note 237082.1 mentions this package but doesn't clarify the situation.
Any suggestions?
Cheers, Patrick

Hi,
You may try powershell, here are two PowerShell scripts that use
SMLets to reveal interesting information about user roles in SCSM, please refer to it:
https://gallery.technet.microsoft.com/Service-Manager-SCSM-User-ebcdfcd6
Regards,
Yan Li
Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact [email protected]

ADFC-0619: Authorization check failed implementing popup through taskflow

Hi All,
I receive the error ADFC-0619: Authorization check failed: '/WEB-INF/main-task-flow-template.xml#main-task-flow-template' 'VIEW'. when accessing the taskflow that will show as a popup as described in this blog: http://andrejusb.blogspot.com/2013/03/reusable-adf-region-with-dialog.html. I created a sample application and I have it working as expected. The sample app has no security configured. When I put the functionality into our main app the error occurs. I have checked the jazn-data.xml and have granted a role to both the task flow and the web page.
Our app is setup where I have a task flow template that most taskflows inherit from. The calling page is inherited from the template which uses page fragments. The taskflow for the popup is not inherited from the template and does not use page fragments.
I am using 11.1.1.6. The error happens when deploying to the Integrated server as well as a local WLS. I read a few forum posts on this subject and some folks removed the anonymous role. I have this role defined but is is only used for my login page so I don't want to remove it from there.
Appreciate the help as this is blocking me from working on the functionality within the popup.
Thank you - Rudy

Resolved. Our Application is setup as described by Jobinesh in the book "Oracle ADF Real World Developer's Guide". In this case we have a separate application called "Common", within that we have projects for the ADFFrameWorkExtension, CommonModel, CommonUtilities and CommonUI. The CommonUI project contains the main-task-flow-template and errorPage.jsff as well as the MainTemplate.jspx. Each of these projects are deployed as a jar and imported into the main project.
In the jazn-data.xml under Resource Grants, Resource Type = Task Flow, check the option to "Show task flows imported from ADF libraries". This showed the main-task-flow-template which I granted the anonymous-role view action.
When I run it now shows the popup.

IPhone 5 grid/checker pattern

'm seeing a grid pattern on my iPhone 5 screen when solid, dark colors or the screen is off/black. Is this a screen defect?

While the phone is on and in the "black screen", press and hold the home button and the power button at the same time until you see the Apple logo appear. Then release them. This resolved my issue I was having with this problem. Good luck.

Checker patterned

Can anyone help me understand what is happening to their shirts in this image? When zoomed out (30% or so), the blue checkered shirts appear wavy and out of sorts, but that effect disappears when I zoom in to 100%. More importantly, can anyone tell me how to fix it? And can anyone tell me how to avoid this?
Thank you in advanceQ

See that video:
http://www.youtube.com/watch?v=diO_Lak5ftE
You have 'moiré' when the resolution of your display is not enough to show small details.

Dummy PI serviceinterfaces can be used in BPM scenarios and how?

Hi Experts,
We have a requirement where SAP ECC(Async system) is sending the file to HSM tool(sync system) through PI and sends the response from HSM tool to bank system(Async system) through PI. Entire flow is the passthrough interface.
Firstly we thought of developing the Adapter module to send the received HSM response to bank and it's very complex to implement. We are planning to implement the BPM here.
But the question is how we can use the dummy interfaces in BPM. Is it possible to implement in such a way.
Suggestions are welcome.
Thanks in advance.
Regards,
Jaya

Hi Jaya,
I suppose with dummy interfaces you mean interfaces where the content that "flows through it" at runtime does not match the definition in ESR, Messages of that type are supported by ccBPM in PI Double Stack through an implementation detail - as long as you do not access the payload through XPaths, you can route messages through an integration process. So if you are asking for an answer for ccBPM, then the approach is to just define a dummy interface (data structure does not matter, a very simple one suffices), but do not define any XPath-accesses in the process definition (no condition expressions, no correlations). You can use all step types that work on complete messages, like receive, send or transformation steps or container operations appending messages to lists.
If you are talking about NW BPM as part of NW Process Orchestration 7.31 / 7.4, then you need to apply other concepts, such as using Claim Check pattern. Refer to https://help.sap.com/saphelp_nw74/helpdata/en/7f/984c062f3a4579b97602e48fd17cc8/content.htm?frameset=/de/b5/0a32b8ef0545…
Regards,
Tobias

Double Factory pattern purposal as replacement for Double Check #2

Hi All,
Here is the code for the pattern proposal, its intended as a replacement for double checked locking, which was proved to be broken in 2001. Here is the code...
public class DoubleFactory {
   private static Object second_reference = null;
   public static Object getInstance() {
      Object toRet = second_reference;
         if (toRet == null) {
            second_reference = CreationFactory.createInstance();
            toRet = second_reference;
      return toRet;
   private DoubleFactory() {}
public class CreationFactory {
   private static Object instance = null;
   public static synchronized Object createInstance() {
      if (instance == null) {
         instance = new Object();
      return instance;
}Also I have spent several months discussing this with Peter Haggar, who believes that this code is not guaranteed to work. However I have been unable to discern from his message why he believes this will not be guaranteed to work, and I am posting this here to attempt to find a clearer explanation or confirmation that the pattern I am purposing (Double Factory) is guaranteed to work.
Thanks,
Scott
---------------------------- Original Message ----------------------------
Subject: Re: [Fwd: Double Factory replacement for Double Check #2] From:
"Scott Morgan" <[email protected]>
Date: Fri, January 25, 2008 10:36 pm
To: "Peter Haggar" <[email protected]>
Hi Peter,
I appologize if my last response came accross as rude or something. If
my code is not guaranteed to work ok, can you help me understand why. I
am after all looking for a solution for all of us.
If my solution is wrong as you say because the member variables of the
singleton are not up to date. I understand this to mean that the
second_reference pointer is assigned to the memory where the instance
object will get created before the instance object even starts the
creation process (when the jvm allocates memory and then enters the
constructor method of the Singleton). This doesn't seem possible to me.
Can you refrase your statments, to help me understand your points?
If not I am happy to turn to the original wiki for discussion.
Thanks for your effort,
Scott
Thanks for asking my opinion, many times, then telling me I'm
wrong...wonderful. You are a piece of work my friend. For what it'sworth, your email below shows you still don't understand these issues
or what I was saying in my emails. I've been more than patient.
>
All the best. And by the way, your code is not guaranteed to work. It's not just me that's "wrong", it's also the engineers at Sun who
designed Java, the JVM, and the memory model, and countless people who
have studied it. I'm glad you have it all figured out.
>
Peter
"Scott Morgan" <[email protected]>
01/18/2008 12:47 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
Thanks I understand your position now. However am I still believe that
it will work and be safe;
1) the Singleton you show would be fully constructed (having exited theSingleton() method) before the createInstance() method would have
returned.
2) The second_reference could not be assigned until the createInstance()
method returns.
3) So by the time second_reference points to Singleton all of the valueswill be set.
>
>
I do understand that if the createInstance method was not synchronized(at the CreationFactory class level) that my logic would be flawed, but
since there is synchronization on that method these points are true, and
your comments about up-to-date values are not accurate.
>
Cheers,
Scott
>In your listing from your latest email T2 does encounter a sync block
on createInstance.
>>>>
No. T2 will call getInstance and see second_reference as non-null.second_reference was made non-null by T1.
>>
>>>>
What are you exactly are you refering to with the phrase 'up-to-datevalues'?
>>>>
Assume my singleton ctor is thus:
public class Singleton
private int i;
private long l;
private String str;
public Singleton()
i = 5;
l = 10;
str = "Hello";
T2 will get a reference to the Singleton object. However, because youaccess second_reference without synchronization it may not see i as 5,
l as 10 and str as "Hello". It may see any of them as 0 or null. This
is not the out of order write problem, but is a general visibility
problem because you are accessing a variable without proper
synchronization.
>>
Peter
"Scott Morgan" <[email protected]>
01/16/2008 11:38 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
In your listing from your latest email T2 does encounter a sync blockon createInstance.
>>
What are you exactly are you refering to with the phrase 'up-to-datevalues'?
In this code the Singleton should also be
A) non mutable (as in the instance of class Object in the example).
If the singleton was more complex then the code to populate it'svalues
would go inside the sync of createInstance().
B) mutable with synchronization on it's mutator methods.
In your article you mention out of order writes, which doesn't occurin
this code.
Cheers,
Scott
You read it wrong.
- T1 calls getInstance which in turn calls createInstance.
- T1 constructs the singleton in createInstance and returns to
getInstance.
- T1 sets second_reference to the singleton returned in getInstance. -T1 goes about its business.
- T2 calls createInstance.
- T2 sees second_reference as non-null and returns it
- Since T2 accessed second_reference without sync, there is noguarantee
that T2 will see the up-to-date values for what this object refers to.
- Therefore the code is not guaranteed to work.
>>>
If this is not clear:
- Re-read my email below
- Re-read my article
- If still not clear, google on Double Checked Locking and readanything
from Brian Goetz or Bill Pugh.
Peter
"Scott Morgan" <[email protected]>
01/13/2008 05:26 AM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
Thanks for the reply, I don't see how T2 would see the a referenceto
a
partialy initialized object before the createInstance() method had
returned. If T1 was in createInstance() when T2 entered
getInstance(), T2 would wait on the CreationFactory's class monitor to
wait to enter createInstance().
Or in other words in the line of code ....
second_reference = CreationFactory.createInstance();
The pointer second_reference couldn't be assigned to the singleton
instance when the synchronized createInstance() had fully constructed,initialized and returned the singleton instance. Before that the the
second_reference pointer would always be assigned to null. So any
thread entering getInstance() before createInstance() had returned
(for the first time) would wait on the CreationFactory's class monitor
and enter the createInstance() method.
>>>
So T2 will wait for T1.
Cheers,
Scott
PS I think I am writing requirements for my next project :)
Sorry for the delay...been in all day meetings this week.
You are correct...I had been reading your code wrong, my apologies.
My explanations, although correct, did not exactly correspond to your
code.
However, the code is still not guaranteed to work. Here's why:
Assume T1 calls getInstance() which calls createInstance() and returnsthe
singelton. It then sets second_reference to refer to that singleton.
So
far, so good. Now, T2 executes and calls getInstance(). It can see
second_reference as non-null, so it simply returns it. But, there
was
no
synchronization in T2's code path. So there's no guarantee that even
if
T2 sees an up-to-date value for the reference, that it will seeup-to-date
values for anything else, ie what the object refers to...it's
instance data. If T2 used synchronization, it would ensure that it
read
up-to-date
values when it obtained the lock. Because it didn't, it could see
stale
values for the object's fields, which means it could see a partially
constructed object.
>>>>
In the typical double-checked locking, the mistake is to assume theworst
case is that two threads could race to initialize the object. But
the worst case is actually far worse -- that a thread uses an object
which
it
believes to be "fully baked" but which is in fact not.
Peter
"Scott Morgan" <[email protected]>
01/03/2008 06:33 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
Thanks for responding, I am still thinking that your mis
interpreting
the code so I have rewritten it here (Replacing
DoubleFactory.instance with DoubleFactory.second_reference for
clarity). If the T1 burps (gets interrupted) in the createInstance
method it wouldn't have returned so the second_reference pointer
would have never been
assigned
so T2 would just try again upon entering the getInstance method. Orif
it had already entered getInstance it would be waiting to enter
(until T1 releases the lock on CreationFactory.class ) on the
createInstance method.
>>>>
public class DoubleFactory {
private static Object second_reference = null;
public static Object getInstance() {
Object toRet = second_reference;
if (toRet == null) {
second_reference =
CreationFactory.createInstance();
toRet = second_reference;
return toRet;
private DoubleFactory() {}
public class CreationFactory {
private static Object instance = null;
public static synchronized Object createInstance() {
if (instance == null) {
instance = new Object();
return instance;
Does this clear up my idea at all?
second_reference should be always pointing to
null
or
a fully initialized Object
(also referenced by the pointer named 'instance' ), I don't see howit would end up partially initialized.
>>>>
Thanks Again,
Scott
"It" refers to T2.
Your createInstance method is identical to my Listing 2 and is fine
and
will work.
Yes, the problem with your code is in getInstance.
>I don't see how the DoubleFactory getInstance method could bereturning
a partially initialized object at this point. If CreationFactoryalways
returns a fully initialized object and DoubleFactory only assigns a
new
reference/pointer to it how could DoubleFactory getInstance return a
reference/pointer to partially initialized object?
>>>>>>>
>>>>>
The reason it is not guaranteed to work is explained in my previousemails
and in detail in the article. However, I'll try again. Anytime you
access shared variables from multiple threads without proper
synchronization, your code is not guaranteed to work. Threads are
allowed
to keep private working memory separate from main memory. There are
2
distinct points where private working memory is reconciled with main
memory:
- When using a synchronized method or block - on acquisition of thelock
and when it is released.
- If the variable is declared volatile - on each read or write of
that
volatile variable. (Note, this was broken in pre 1.5 JVMs which isthe
reason for the caveat I previously mentioned)
Your createInstance method uses synchronization, therefore, the
reconciliation happens on lock acquisition and lock release. T1 can
acquire the lock in createInstance, make some updates (ie create an
object, run it's ctor etc), but then get interrupted before exiting
createInstance and therefore before releasing the lock. Therefore,
T1
has
not released the lock and reconciled its private working memory withmain
memory. Therefore, you have ZERO guarantee about the state of mainmemory
from another threads perspective. Now, T2 comes along and accesses
"instance" from main memory in your getInstance method. What will
T2
see?
Since it is not properly synchronized, you cannot guarantee that T2sees
the values that T1 is working with since T1 may not have completely
flushed its private working memory back to main memory. Maybe it
did completely flush it, maybe it didn't. Since T1 still hold the
lock,
you
cannot guarantee what has transpired. Maybe your JVM is not usingprivate
working memory. However, maybe the JVM your code runs on does or
will
some day.
Bottom line: Your code is not properly synchronized and is notguaranteed
to work. I hope this helps.
Peter
"Scott Morgan" <[email protected]>
01/03/2008 12:49 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
Thanks for your response, I don't follow what 'it' refers to in
the
phrase 'It can see'. So for the same reason that you state that
example 2 from your article I believe this class CreationFactory to
work flawlessly when a client object calls the createInstance
method.
>>>>>
I see this CreationFactory code as identical to your example 2 doyou agree with this?
>>>>>
public class CreationFactory {
private static Object instance = null;
public static synchronized Object createInstance() {
if (instance == null) {
instance = new Object();
return instance;
}Then my rational in the DoubleFactory class is that it can obtain a
reference/pointer to the fully initialized object returned bycalling the above code. I believe you think that the problem with
my code is
in
the DoubleFactorys getInstance method, is this correct?
I don't see how the DoubleFactory getInstance method could bereturning
a partially initialized object at this point. If CreationFactory
always
returns a fully initialized object and DoubleFactory only assigns a
new
reference/pointer to it how could DoubleFactory getInstance return a
reference/pointer to partially initialized object?
>>>>>
Thanks again,
Scott
public static synchronized Singleton getInstance() //0
if (instance == null) //1
instance = new Singleton(); //2
return instance; //3
This above code is fine and will work flawlessly.
Annotating my paragraph:
T1 calls getInstance() and obtains the class lock at //0. T1 "sees"
instance as null at //1 and therefore executes: instance = new
Singleton() at //2. Now, instance = new Singleton() is made up of
several lines of non-atomic code. Therefore, T1 could be
interrupted
after Singleton is created but before Singleton's ctor isrun...somewhere
before all of //2 completes. T1 could also be interrupted after
//2 completes, but before exiting the method at //3. Since T1 has
not
exited
its synchronized block it has not flushed its cache. Now assume T2
then
calls getInstance().
All still true to this point. However, with your code the nextparagraph
is possible, with the code above, it's not. The reason is that T2
would
never enter getInstance() above at //0 because T1 holds the lock. T2will
block until T1 exits and flushes it's cache. Therefore, the code
above
is
properly thread safe.
It can "see" instance to be non-null and thus
return it. It will return a valid object, but one in which its ctor
has
not yet run or an object whose
values have not all been fully flushed since T1 has not exited itssync
block.
"Scott Morgan" <[email protected]>
01/02/2008 06:10 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
Thanks for the response I understand the rational for inventing
the
double check anti pattern, I am sorry I still don't understand the
difference between your solution #2 and my CreationFactory class.
>>>>>>
From your article figure 2.public static synchronized Singleton getInstance() //0
if (instance == null) //1
instance = new Singleton(); //2
return instance; //3
If I understand your email correctly this figure 2 is also flawed,since...
>>>>>>
T1 calls getInstance() and obtains the class lock at //0. T1 "sees"
instance as null at //1 and therefore executes: instance = new
Singleton() at //2. Now, instance = new Singleton() is made up ofseveral lines of non-atomic code. Therefore, T1 could be
interrupted
after Singleton is created but before Singleton's ctor isrun...somewhere
before all of //2 completes. T1 could also be interrupted after
//2 completes, but before exiting the method at //3. Since T1 has
not
exited
its synchronized block it has not flushed its cache. Now assume T2
then
calls getInstance(). It can "see" instance to be non-null and thus
return it. It will return a valid object, but one in which its
ctor
has
not yet run or an object whose
values have not all been fully flushed since T1 has not exited itssync
block.
So is #2 is also flawed for this reason?
If so please revise your article, since I interpreted #2 as a
plausible
solution recommended by you (which lead me to the DoubleFactory
idea).
If not please help me understand the difference between #2 and my
CreationFactory class.
>>>>>>
Thanks,
Scott
#2 is in Listing 2 in the article. What I meant was to forget the
DCL
idiom, and just synchronize the method...that's what listing 2
shows.
DCL
was invented to attempt to get rid of the synchronization for 99.9%
of
the
accesses.
The solution I outlined in my email is using the DCL idiom, but on
a
1.5
or later JVM and using volatile.
You solution is not guaranteed to work. Here's why:
public class DoubleFactory {
private static Object instance = null;
public static Object getInstance() {
Object toRet = instance;
if (toRet == null) {
instance =
CreationFactory.createInstance();
toRet = instance;
return toRet;
private DoubleFactory() {}
public class CreationFactory {
private static Object instance = null;
public static synchronized ObjectcreateInstance()
//1
if (instance == null) {
instance = new Object(); //2
return instance;
} //3
}T1 calls createInstance() and obtains the class lock at //1. T1"sees"
instance as null and therefore executes: instance = new Object() at//2.
Now, instance = new Object() is made up of several lines of
non-atomic
code. Therefore, T1 could be interrupted after Object is created
but
before Object's ctor is run...somewhere before all of //2
completes.
T1
could also be interrupted after //2 completes, but before exiting
the
method at //3. Since T1 has not exited its synchronized block ithas
not
flushed its cache. Now assume T2 then calls getInstance(). It can"see"
instance to be non-null and thus return it. It will return a
valid object, but one in which its ctor has not yet run or an
object
whose
values have not all been fully flushed since T1 has not exited itssync
block.
The bottom line is that if you are accessing shared variables
between
multiple threads without proper protection, you are open for aproblem.
Proper protection is defined as: proper synchronization pre 1.5,
and
proper synchronization or proper use of volatile 1.5 or after.
Therefore, if you must use the DCL idiom you have one option: -
Use DCL with volatile on a 1.5 or later JVM.
>>>>>>>
You can also forget about DCL and just use synchronization (listing2
in
my article) or use a static field (listing 10 in my article).
I hope this clears it up.
Peter
"Scott Morgan" <[email protected]>
01/02/2008 04:00 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
Re: [Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
I apologies for not understanding but I don't see what is
different
between the solution you purposed...
2) Don't use DCL but use synchronization
and the code that I am putting forward. Perhaps I do just notunderstand
but you seem to be contradicting yourself in this email?
I understand that you are saying in #2 that this will always 'work'
with
out any issues...
public static Object instance = null;
public static synchronized Object getInstance() {
if (instance == null) {
instance = new Object();
return instance;
But first you seem to say in the email that if T1 gets
interrupted
it
may leave the instance pointing to a partially initialized object?
So as far as I understand it the createInstance method in my
CreationFactory class should be successful (always retuning a
fully initialized object) for the same reason #2 is successful.
Please keep in mind that there are two different instancepointers
in
the code I sent you, one is part of the DoubleFactory class and
the other is part of the CreationFactory class.
>>>>>>>
Thanks for your time, just looking for better solutions!
Scott
Scott,
Your solution is not guaranteed to work for various reasons
outlined
in
the article. For example, you can still return from your code apartially
initialized object. This can occur if T1 gets interrupted beforeleaving
the synchronized method createInstance() and T2 calls
getInstance().
T2
can "see" toRet/instance as non-null but partially initialized
since
T1
has not fully flushed its values.
As of 1.5, Sun fixed various issues with the memory model that
were
broken. Double Checked Locking will still break unless you usevolatile
(which was fixed in 1.5). Therefore, the following code works:
volatile Helper helper;
Helper getHelper() {
if (helper == null)
synchronized(this) {
if (helper == null)
helper = new Helper();
return helper;
but the original DCL idiom will not work. So, your options are:
1) Use DCL with volatile (above)
2) Don't use DCL but use synchronization
3) Don't use DCL, but use a static field.
#2 and #3 are outlined in my article from 2002.
Hope this helps,
Peter
"Scott Morgan" <[email protected]>
12/26/2007 04:12 PM
Please respond to
[email protected]
To
Peter Haggar/Raleigh/IBM@IBMUS
cc
Subject
[Fwd: Double Factory replacement for Double Check #2]
Hi Peter,
Thanks for the article on the out of order write problem. Whatdo
you
think of this as a solution?
TIA,
Scott
---------------------------- Original Message----------------------------
Subject: Double Factory replacement for Double Check #2
From: "Scott Morgan" <[email protected]>
Date: Wed, December 26, 2007 2:55 pm
To: [email protected]
Hi Ward,
Here is a pattern submission
Double Factory
Lazy initialization of singletons in accepted for a while usingthe
double check pattern. However it has been discovered that the
double
check pattern isn't thread safe because of the out of order write
problem. This problem occurs when Threads entering the Singleton
Factory method return with a fully constructed, but partially
initialized, Singleton object.
>>>>>>>>
Therefore: It makes sense to look for a way to initializeSingletons
in
a Lazy and Thread Safe manor. The following illustrates a fairly
simple
solution...
package foo;
public class DoubleFactory {
private static Object instance = null;
public static Object getInstance() {
Object toRet = instance;
if (toRet == null) {
instance =
CreationFactory.createInstance();
toRet = instance;
return toRet;
private DoubleFactory() {}
public class CreationFactory {
private static Object instance = null;
public static synchronized ObjectcreateInstance()
if (instance == null) {
instance = new Object();
return instance;
This gets around the out of order write problem because all
Threads
waiting on the CreationFactory's Class monitor will have a fully
constructed and initialized instance when they actually exit the
createInstance method.
>>>>>>>>
>>>>>>>>
During runtime while the Singleton instance is getting created(constructed and initialized) there may be a few Threads waiting
on
the
CreationFactory Class's objects monitor. After that period all
the
Treads
accessing
the Singleton will have unsynchronized reads to the instance,
which
will
optimize execution.
References:
http://www.ibm.com/developerworks/java/library/j-dcl.html
Copyright 2007 Adligo Inc.

Scott-Morgan wrote:
Hi All,
Thanks for your comments, here are some more....
jtahlborn you state that
the only way to guarantee that a (non-final) reference assignment is visible across threads is through the use of volatile and synchronized,
From the jvm spec
http://java.sun.com/docs/books/jls/third_edition/html/memory.html
17.4.1 Shared Variables
Memory that can be shared between threads is called shared memory or heap memory.
All instance fields, static fields and array elements are stored in heap memory.
Since both the second_reference and instance fields are both static, they are shared and visible across all threads.Yes, all these things are shared across threads, however, if you keep reading, there is a notion of "correct" sharing. obviously these values may be visible, that's why double-checked locking was used for so long before people realized it was broken. it worked most of the time, except when it didn't, and that's what i'm trying to show. that the only way to correctly share state between threads is via synchronization points, the most common being volatile and synchronized (there are a couple of other less used ones which don't apply here). The articles you linked to below from ibm cover the "visibility" in great depth, this is exactly what i am referring to.
You also state that volatile is a solution, but you seem to rebut your self in stating that the overhead for volatile is almost as great as synchronization.
This article illustrates the solution, and also comments on the overhead of volatile.
http://www.ibm.com/developerworks/library/j-jtp03304/
linked from
http://www.ibm.com/developerworks/java/library/j-dcl.html
volatile is a solution, in that it is correct, and you avoid the appearance of synchronization each time. however, since the semantics of volatile were strengthened in the new memory model, using volatile will perform practically (if not exactly) the same as simply synchronizing each time. the article you link to says exactly this under the heading "Does this fix the double-checked locking problem?".
Also could you be more specific about the example at the end of the jvm memory spec page, like a section number?It's the very last thing on the page, the "discussion" under 17.9, where it mentions that changes to "this.done" made by other threads may never be visible to the current thread.

Claim check pattern implementation

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