Flex and concurrent access

I am going to work on a new project. This project is a real time scanning processing monitor. The application would launch from an html wrapper. Also a few more processes will also start from there using JavaScript code:
oReadfromScanner1 = new ActiveXObject("comportreader.classname");
oReadfromScanner2 = new ActiveXObject("comportreader.classname");
I am going to have up to 10 scanner readers which will update Flex client screen.
There will be many times when readers try to update the client in exact same time. What is a design pattern to manage simultaneous access to Flex? Or there will be no problem at all?
Thanks

Thanks for the feedback. This is still bothering me,
yes I could have a static RandomAccessFile and
synchronise on this, but I really want concurrent
access.
I've implemented a locking mechanism to prevent
different RandomAccessFile instances updating the
same record - is this not a waste if only one
RandomAccessFile can write to the file anyway?
Or is there another Java class I can use to access
the file in this way?
Thanks for the help.Hi,
if the intention of using multiple instanced of RandamAccessFile is concurrent access, then i feel your locking mechanism doesnt achieve the purpose..
also, at any case, you may not plan for full concurrency in updating a file....
it is more prone to malfunctions..
probably, to enhance performance, you can lock only the part your code that actually writes to the file, like io.write() , in this way you can perform all business logic with respect to writing and serialize only the actual file writing...
even in this case, you must be sure that writing to different part of the file, doesnt really impact other parts of the file which might be manipulated by other threads..
i have one more thought on this,
if updating different parts of the file doesnt affect content of other parts of the file,
then can you think of having different files itself?
if using different files is not a good idea, then
probably think of using some buffering mechanism, like collect all data concurrently and periodically update the actual file from the buffer.. just a raw idea but all depends on your system needs & requirements.. ..

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Hi Meendar,
1. I interpret your "set" as "insert" or "put", that is, inserting key/data pairs into db.
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Hello Christian
Here is an example that shows that the static attributes of a class are not shared between two reports that are linked via SUBMIT statement.
*& Report ZUS_SDN_OO_STATIC_ATTRIBUTES
REPORT zus_sdn_oo_static_attributes.
DATA:
gt_list TYPE STANDARD TABLE OF abaplist,
go_static TYPE REF TO zcl_sdn_static_attributes.
* CONSTRUCTOR method of class ZCL_SDN_STATIC_ATTRIBUTES:
**METHOD constructor.
*** define local data
** DATA:
** ld_msg TYPE bapi_msg.
** ADD id_count TO md_count.
**ENDMETHOD.
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PARAMETERS:
p_called(1) TYPE c DEFAULT ' ' NO-DISPLAY.
START-OF-SELECTION.
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syst-index = 0.
WRITE: / syst-index, '. object: static counter=',
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DO 5 TIMES.
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 syst-index = 3 ).
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Regards
Uwe

Concurrent access

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Hello,
Before the call to your BAPI, call the function module ENQUEUE_<name of the lock object> and pass the parameters to locjk the specific entry. Now all your BAPI amd once done unlock the entry by call the function module DEQUEUE_<name of the lock object>.
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Concurrent access in Diadem

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And if they want to write on the same report?
Thanks

Hi condor31,
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Brad Turpin
DIAdem Product Support Engineer
National Instruments

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I need advice which strategy to use with lazy loading.
My project is based on Spring, Struts 2 and Hibernate JPA. I have enough OneToMany and ManyToMany relationships and it's reasonable to use lazy loading. It seems very convenient to load data in Struts Actions with OpenEntityManagerInViewFilter in such way like:
Style style = user.getStyle()
But to avoid LazyLoadException I have to use:
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I've found this issue when tried to make quick sequential page reloading which call some selects and got:
java.sql.SQLException: You can't operate on a closed Statement!!!
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Hi
Do you have the link to the "lazy loading content"?
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The "Set cost controls" concurrent program is used in R12 to mass update the cost control fields on item costs.
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Concurrent Access for Crystal Reports for eclipse

Hi,
May i know is there any concurrent access limitation when viewing the reports in web using JRC?

The performance does get better after the initialization of the JRC application. Because it is a pure java application without any reliances on servers for processing power, it will rely on the speed of the application server. In the initialization, all of the libraries get loaded in to the classpath so this does take some time. Generally speaking the performance will get better after this because everything has been loaded in to memory; that is until you restart the application server.
The JRC will be a bit slower when rendering a large report. Depending on the size of that report, you may be looking at between a few seconds and several minutes in processing time.
Whether or not you use the JRC will depend on the number of users you anticipate having at any given time for your application as well as the general size of your reports.
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Unexpected error occurred :concurrent access to HashMap attempted

While runnig the ALBPM 5.7 we got this error. This looks like the ALBPM workflow engine is using HashMap in a unsynchronized way. is this a known issue and is there a work around for this?
This error happened shortly after a possible blip in the database server, with exception message which said:
Message:
The connectivity to the BEA AquaLogic™ BPM Server database has been successful restablished.
Any thoughts/insight/past experience....
Looks like we should be using Hashtable instead of a HashMap (or atleast a Synchronized HashMap)
This is best done at creation time, to prevent accidental unsynchronized access to the map:
Map m = Collections.synchronizedMap(new HashMap(...));
See Exception message below
Message:
An unexpected error occurred while running an automatic item.
Details: Connector [ffmaeng_ENGINE_DB_FUEGOLABS_ARG:SQL:Oracle (ALI)] caused an exception when getting a resource of type [0].
Detail:Connector [ffmaeng_ENGINE_DB_FUEGOLABS_ARG:SQL:Oracle (ALI)] caused an exception when getting a resource of type [0].
Caused by: concurrent access to HashMap attempted by Thread[ET(49),5,Execution Thread Pool]
fuego.connector.ConnectorException: Connector [ffmaeng_ENGINE_DB_FUEGOLABS_ARG:SQL:Oracle (ALI)] caused an exception when getting a resource of type [0].
Detail:Connector [ffmaeng_ENGINE_DB_FUEGOLABS_ARG:SQL:Oracle (ALI)] caused an exception when getting a resource of type [0].
at fuego.connector.ConnectorException.exceptionOnGetResource(ConnectorException.java:95)
at fuego.connector.ConnectorTransaction.getResource(ConnectorTransaction.java:285)
at fuego.connector.JDBCHelper.getConnection(JDBCHelper.java:43)
at fuego.server.service.EngineConnectorService.getConnection(EngineConnectorService.java:260)
at fuego.server.service.EngineConnectorService.getEngineConnection(EngineConnectorService.java:160)
at fuego.transaction.TransactionAction.getEngineHandle(TransactionAction.java:180)
at fuego.server.execution.EngineExecutionContext.getEngineHandle(EngineExecutionContext.java:352)
at fuego.server.execution.EngineExecutionContext.persistInstances(EngineExecutionContext.java:1656)
at fuego.server.execution.EngineExecutionContext.persist(EngineExecutionContext.java:1010)
at fuego.transaction.TransactionAction.beforeCompletion(TransactionAction.java:133)
at fuego.connector.ConnectorTransaction.beforeCompletion(ConnectorTransaction.java:654)
at fuego.connector.ConnectorTransaction.commit(ConnectorTransaction.java:330)
at fuego.transaction.TransactionAction.commit(TransactionAction.java:303)
at fuego.transaction.TransactionAction.startBaseTransaction(TransactionAction.java:470)
at fuego.transaction.TransactionAction.startTransaction(TransactionAction.java:540)
at fuego.transaction.TransactionAction.start(TransactionAction.java:213)
at fuego.server.execution.DefaultEngineExecution.executeImmediate(DefaultEngineExecution.java:118)
at fuego.server.execution.DefaultEngineExecution.executeAutomaticWork(DefaultEngineExecution.java:58)
at fuego.server.execution.EngineExecution.executeAutomaticWork(EngineExecution.java:42)
at fuego.server.execution.ToDoItem.executeAutomaticWork(ToDoItem.java:264)
at fuego.server.execution.ToDoItem.run(ToDoItem.java:531)
at fuego.component.ExecutionThread.processMessage(ExecutionThread.java:754)
at fuego.component.ExecutionThread.processBatch(ExecutionThread.java:734)
at fuego.component.ExecutionThread.doProcessBatch(ExecutionThread.java:140)
at fuego.component.ExecutionThread.doProcessBatch(ExecutionThread.java:132)
at fuego.fengine.ToDoQueueThread$PrincipalWrapper.processBatch(ToDoQueueThread.java:432)
at fuego.component.ExecutionThread.work(ExecutionThread.java:818)
at fuego.component.ExecutionThread.run(ExecutionThread.java:397)
Caused by: java.util.ConcurrentModificationException: concurrent access to HashMap attempted by Thread[ET(49),5,Execution Thread Pool]
at java.util.HashMap.onExit(HashMap.java:226)
at java.util.HashMap.transfer(HashMap.java:690)
at java.util.HashMap.resize(HashMap.java:676)
at java.util.HashMap.addEntry(HashMap.java:1049)
at java.util.HashMap.put(HashMap.java:561)
at fuego.lang.cache.CacheStatistic.lock(CacheStatistic.java:246)
at fuego.lang.cache.TimedMultiValuatedCache.getLocked(TimedMultiValuatedCache.java:282)
at fuego.lang.cache.TimedPool.get(TimedPool.java:80)
at fuego.connector.impl.BaseJDBCPooledConnector.getConnection(BaseJDBCPooledConnector.java:140)
at fuego.connector.impl.BaseJDBCConnector.getResource(BaseJDBCConnector.java:222)
at fuego.connector.ConnectorTransaction.getResource(ConnectorTransaction.java:280)
... 26 more

Hi BalusC,
I forgot to tell one thing, the exception what I mentioned is coming very rarely. The application is in Production and they getting this Exception once in 3 months. Is there any way to re-produce the same exception number of times to check whether it has been fixed or not after installing the updates as you said. If you have any information regarding this exception please send me.
Thank You.

Working with Flex and Central

Hi,
I am new in Flex and Central and interested in working with
Flex and Central and I'm currently trying to run one of the samples
from the "Central Flex SDK", the HelloFlexCentral. I have an error
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not recognized.
I don't understand how to connect Flex and Central. My
questions are :
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kind of application or can I develop the application without a JRun
Environment ?
- Can I deploy my application on a IIS server for example
(and then all the users will install it in central by accessing
this webserver) ?
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avoid this error I encounter ?
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If you want three distinct notes, I suggest you cut it into three samples, then using flex pitch drag the notes to the pitches you desire. Keep in mind that the farther away a note is from it's actual sampled pitch, the worse it's quality will be.

Weak and concurrent hash map for caching

Hello,
I have written a very simple cache class with both weakness and concurrency benefits. This class is intended to be used as a weak cache in "hot redeploy" capable servers (JBoss or any other).
My implementation uses the (problematic) "double-check" pattern with a reentrant lock and encapsulates a WeakHashMap with WeakReference values (to avoid circular key/value references). Here is the code:
public interface ValueCreator<V> {
 public V create();
public class WeakCache<K, V> {
 private final Lock lock = new ReentrantLock();
 private final Map<K, WeakReference<V>> weakMap;
 public WeakCache() {
 this(16);
 public WeakCache(int initialCapacity) {
 this(initialCapacity, 0.75F);
 public WeakCache(int initialCapacity, float loadFactor) {
 weakMap = new WeakHashMap<K, WeakReference<V>>(initialCapacity, loadFactor);
 public V get(K key, ValueCreator<V> creator) {
 WeakReference<V> ref = weakMap.get(key);
 if (ref == null) {
 lock.lock();
 try {
 ref = weakMap.get(key);
 if (ref == null) {
 ref = new WeakReference<V>(creator.create());
 weakMap.put(key, ref);
 } finally {
 lock.unlock();
 return ref.get();
 }One usage of this cache is for session ejb3 lookup:
private static final WeakCache<Class, Object> LOOKUP_CACHE = new WeakCache<Class, Object>();
public static <T> T lookup(final Class<T> serviceClass) {
 T service = (T)LOOKUP_CACHE.get(serviceClass,
 new ValueCreator<Object>() {
 public T create() {
 String lookup = "myapp/" + serviceClass.getSimpleName() + "/local";
 try {
 return (T)(new InitialContext()).lookup(lookup);
 } catch (NamingException e) {
 throw new RuntimeException("Could not lookup EJB " + serviceClass + ": " + lookup, e);
 return service;
...2 questions:
1. Is there any issue with concurrent access to this cache ?
2. What happens exactly when the garbage collector wants to free memory with a map with both weak keys and values ?
Some limited tests show that the behavior of this cache fits my needs: the lookup cache is cleared on redeploy and it keeps its key/values pairs otherwise.
Thanks for any comments.
Message was edited by:
fwolff999

I know that DCL is broken under certain circumstances (but I have read it may work with modern JVM and the use of volatile variables for example).
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Hi All,
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of my Flex generated swf file - which is the debug directory of my
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than the entire directory.
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directory to allow a local Flex generated swf file access to the
internet? Also I cannot see the mms.cfg file in the
C:\windows\system32\Macromed\Flash directory as is described in the
Adobe Flex 3 Help chapter "Overview of permission controls".
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Regards
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really grateful for any suggestions

Flex and large real world b2b applications

Hi all.
I am new to Flex. I am acting in an architect capacity to
review the potential in Flex to become the client presentation
layer for a classic ASP?SQL application. I am seeking a
cross-browser, cross-platform, zero-installation,
just-in-time-delivery, rich user experience web application client.
I think I'm in the right place.
My aim in creating this post is to solicit feedback on
approaches and techniques on how to plan and execute a major-system
re-write into Flex, what is in-scope and what is not, etc. With the
Flex team putting the final touches into release 1.0, this might be
considered a bit too soon to ask these questions, but worthy of
response if Flex is to be take as anything more than
‘something to do with that flash games thing that my kids
play on’.
One of the key issues for my client company, which I believe
will be typical for many in the same situation, is to retain
current investment in the system by re-use of the business logic
and DB access layers. Basically the back-end is not broken and is
well prepared for generation of XML instead of HTML. What is
considered weak, by nature of the web browsers poor user interface
abilities, is the client side of the system.
The company has a small, loyal and technically able workforce
who are very familiar with the current system, which is written
using classic ASP and SQL Server , HTML and JavaScript. The company
is risk and runaway cost averse. It has held back from jumping into
.Net for fear of getting into a costly 5 year revision cycle as
.Net matures. The AJAX approach is another potentially fruitful
client-only route but is likely to be a painful way forward as
there is no major technology vendor leading the charge on
standards. A Java approach would meet the user interface
improvement needs but would require replacing or retraining the
current workforce and a paradigm shift in the technology losing all
of the middle-tier database logic.
The ideal is a stable zero-installation web-client that can
communicate with a server back-end consisting of the same, or
slightly modified or wrapped business logic and db configuration as
the current system and that could then run side-by-side during
switchover.
If this is possible then risk adverse organisations have a
way forward.
The problem is, that from several docs and articles on
Adobe's web site, there seems to be some careful but vague
positioning of the capability of Flex in terms of application
complexity and depth. Also, the demo's that are available seem to
be quite lightweight compared to real-world needs. These apps
‘seem’ to work in a mode where the entire application
is downloaded in one-hit at user initiation. The assumption is that
the user will be prepared to pay some wait time for a better UX,
but there must be a limit.
Question:: How does one go about crafting in Flex what would
have been a 300-page website when produced in HTML? Is this
practical? To create a download containing the drawing instructions
and page-logic for 300 pages would probably cause such a delay at
user-initiation that it would not be practical.
There are many further questions that span from here, but
lets see what we get back from the post so far.
Looking forward to reading responses.
J.

You're absolutely in the right place (IMO)...
Cynergy Systems can help you get started. We are a Flex
Alliance partner,
and have developed some extremely complex RIAs with Flex.
Contact our VP of Consulting - Dave Wolf for more info:
[email protected]
Paul Horan
Cynergy Systems, Inc.
Macromedia Flex Alliance Partner
http://www.cynergysystems.com
Office: 866-CYNERGY
"TKJames" <[email protected]> wrote in
message
news:[email protected]...
> Hi all.
>
> I am new to Flex. I am acting in an architect capacity
to review the
> potential
> in Flex to become the client presentation layer for a
classic ASP?SQL
> application. I am seeking a cross-browser,
cross-platform,
> zero-installation,
> just-in-time-delivery, rich user experience web
application client. I
> think I'm
> in the right place.
>
> My aim in creating this post is to solicit feedback on
approaches and
> techniques on how to plan and execute a major-system
re-write into Flex,
> what
> is in-scope and what is not, etc. With the Flex team
putting the final
> touches
> into release 1.0, this might be considered a bit too
soon to ask these
> questions, but worthy of response if Flex is to be take
as anything more
> than
> ?something to do with that flash games thing that my
kids play on?.
>
> One of the key issues for my client company, which I
believe will be
> typical
> for many in the same situation, is to retain current
investment in the
> system
> by re-use of the business logic and DB access layers.
Basically the
> back-end is
> not broken and is well prepared for generation of XML
instead of HTML.
> What is
> considered weak, by nature of the web browsers poor user
interface
> abilities,
> is the client side of the system.
>
> The company has a small, loyal and technically able
workforce who are very
> familiar with the current system, which is written using
classic ASP and
> SQL
> Server , HTML and JavaScript. The company is risk and
runaway cost
> averse. It
> has held back from jumping into .Net for fear of getting
into a costly 5
> year
> revision cycle as .Net matures. The AJAX approach is
another potentially
> fruitful client-only route but is likely to be a painful
way forward as
> there
> is no major technology vendor leading the charge on
standards. A Java
> approach
> would meet the user interface improvement needs but
would require
> replacing or
> retraining the current workforce and a paradigm shift in
the technology
> losing
> all of the middle-tier database logic.
>
> The ideal is a stable zero-installation web-client that
can communicate
> with a
> server back-end consisting of the same, or slightly
modified or wrapped
> business logic and db configuration as the current
system and that could
> then
> run side-by-side during switchover.
>
> If this is possible then risk adverse organisations have
a way forward.
>
> The problem is, that from several docs and articles on
Adobe's web site,
> there
> seems to be some careful but vague positioning of the
capability of Flex
> in
> terms of application complexity and depth. Also, the
demo's that are
> available
> seem to be quite lightweight compared to real-world
needs. These apps
> ?seem? to
> work in a mode where the entire application is
downloaded in one-hit at
> user
> initiation. The assumption is that the user will be
prepared to pay some
> wait
> time for a better UX, but there must be a limit.
>
>
Question:: How does one go about crafting in Flex what would
have
> been
> a 300-page website when produced in HTML? Is this
practical? To create a
> download containing the drawing instructions and
page-logic for 300 pages
> would
> probably cause such a delay at user-initiation that it
would not be
> practical.
>
> There are many further questions that span from here,
but lets see what we
> get
> back from the post so far.
>
> Looking forward to reading responses.
>
> J.
>
>

Segment fault in concurrent access to BDB

Hi, All
I am extending a single thread BDB application to allow concurrent
access to the DB from 2 threads, transaction is not needed.
The environment is opened with the flag (DB_CREATE | DB_INIT_MPOOL | DB_INIT_LOCK).
Then I open a new DB under the same directory in each thread, and
modify the DB simultaneously. my expectation was that each thread
will not conflict with each other and in turn improve the
throughput. While the program constantly crashed because of segment
fault in file (src/lock/lock.c:832, both threads crashed on this
line).
I inspected the back trace, the only suspecious thing I found is that
the 2 threads are using the same locker object[1], so I'm wondering if
anyone has similar experience implementing concurrent BDB
applications? And what's possible cause of my problem and possible
fixes? Thanks.
[1]
thread 1: #0 0x00002aaab3651a7f in __lock_get_internal (lt=0x13cbda0, sh_locker=0x2aab0119f258, flags=4, obj=0x1c55650, lock_mode=DB_LOCK_WRITE, timeout=0, lock=0x2aab449fe8a0)
at ../src/lock/lock.c:832
thread 2: #0 0x00002aaab3651a7f in __lock_get_internal (lt=0x13cbda0, sh_locker=0x2aab0119f258, flags=4, obj=0x13da640, lock_mode=DB_LOCK_WRITE, timeout=0, lock=0x2aab3ffc78a0)
at ../src/lock/lock.c:832

Hi, Mike
Thanks for the timely reply!
I referred to the Berkeley DB Transaction Guide, while the doc does not mention the consequence if you violate the scenario requirement.
1. I choose the default Data Store model, and my program will allow multiple writers, what's the expected behavior? 2 threads using the same locker compete different locks is supposed to segment fault? I'm also curious about how a put(key, data) correspond to a locker, keys in the memory page map to the same locker?
2. I try to enable concurrent reader & writer without transaction, while the guide assumes transaction is enable, is Data Store able to achieve this? Or at least Concurrent Data Store is required?
Thank you very much!

Flex and concurrent access

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