Could Buffer replace the Queue in Producer/Consumer Design Pattern

Hello,
I have a question that the task of Buffer is to store the data and the queue is also of the same so could we use the Buffer inplace of queue in a Producer/Consumer Design Pattern.
Solved!
Go to Solution.

No, those buffer examples are not nearly equal to a queue and will never ever "replace" queues in producer/consumer.
The most important advantage of queues for producer/consumer (which none of the other buffer mechanics share) is that it works eventbased to notify the reader that data is available. So if you would simply replace the queue by overly elaborate buffer mechanics as you attached to your last post, you will lose a great deal of the the purpose using producer/consumer.
So, to compare both mechanics:
- Queue works eventbased, whereas the buffer example does not.
- Queue has to allocate memory during runtime if more elements are written to the queue than dequeued. This is also true for the buffer (it has to be resized).
- Since the buffer is effectively simply an array with overhead, memory management is getting slow and messy with increasing memory fragmentation. Queues perform way better here (but have their limits there too).
- The overhead for the buffer (array handling) has to be implemented manually. Queue functions encapsulate all necessary functionality you will ever need. So queues do have a simple API, whereas the buffer has not.
- Since the buffer is simply an array, you will have a hard time sharing the content in two parallel running loops. You will need to either implement additional overhead using data value references to manage the buffer or waste lots of memory by using mechanics like variables. In addition to wasting memory, you will presumably run into race conditions so do not even think about this.
So this leads to four '+' for the queue and only one point where "buffer" equals the queue.
i hope, this clears things up a bit.
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

Similar Messages

Producer consumer design pattern

Hello,
I am trying to build a simple program that does the following:
1. when program starts, the indicator is initialized to -999
2. when Measure button is clicked, the indicator shows random number continuously.
3. when Save button is clicked, the indicator shows 1
I use the event-based producer-consumer design pattern and it works great. However, I cannot find a way to allow the CONTINUOUSLY generating of random number when Measure is clicked. Can someone shed a light on it? Thanks a lot for the help.
Attachments:
CommandList.ctl ‏6 KB
Untitled 1.vi ‏25 KB

One simple way to do it is to use the Timeout event case. You can modify the timeout value based on what events have occurred. See attached mod.
Not saying this is the best way. Kind of depends on where the program goes from here.
Attachments:
Untitled 1-2 MOD.vi ‏27 KB

Producer/Consumer Design Pattern + DAQmx + Event Structure

Dear community users,
at the moment I try to implement the Producer/Consumer Design Pattern into my current project. For this purpose I am trying to make a "minimal-example" in which I use the Producer/Consumer Design Pattern for the data acquisition and analysis (display in GraphXY, calculation etc..) process. In the Producer Loop I perform the data readings via DAQmxRead.VI and in the Consumer Loop, in this example only, I display the data in a GraphXY. At the same time I want to control the data acquisition via an Event Structure, for example Start Measurement/Stop Measurement Buttons. To configure the measurement time, for example if the user only wants to measure 150 sec, I use the Time Out Event of the Event Structure. This is a technique which is often used, when data acquisition and Event Structures are used at the same time (Excuse me if this is wrong!). Due to understand the Producer/Consumer Design Pattern I looked up in the Template\Framework of LabVIEW.
In the attachment you will find my "minimal-example", which -sadly-, not working. What should I do ?
Thank you.
Best regards,
tugrul öztürk
Attachments:
daqEngine_PCP.vi ‏35 KB

Your VI will never stop due to the Ok Button that stops the producer loop is read OUTSIDE of the loop. Add an event case for it.
Move the Start and the Ok Button inside of their respective event cases. This will allow the latch to reset when they are read.
Change the Ok Button to a stop button.
Use a Greater Or Equal instead of Equal for the measurement time comparison. What if somebody randomly changes it to 0 on you? Again, you will never stop.
Is the DAQ only supposed to read for "Measurement Time". Right now, it constantly reads. So if you don't use the DAQmx Read, you will get a buffer overflow error. You need to put the DAQmx Start Task inside of the Start event case and then the Stop DAQmx Task inside of the Timeout event case when the measurement time is exceeded. You should also perform the read regardless inside of the Timeout event case.
I HATE telling the consumer loop to stop by destroying the queue. You can look data that way. Instead, send something an empty array. In the consumer, check for an empty array. If it is empty, stop. Destroy the queue only AFTER BOTH LOOPS HAVE COMPLETED.
You should also report your errors in some way. Simple Error Handler at the minimum.
Since you are using Continous Samples, don't limit the buffer. Leave the Samples per Channel unwired on the DAQmx Timing VI.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions
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Producer/Consumer Design Pattern with Classes

I'm starting a new project which involves acquiring data from various pieces of equipment using a GPIB port. I thought this would be a good time to start using Classes. I created a GPIB class which contains member data of: Address, Open State, Error; with member vis such as Set Address, Get Address, Open, Close...general actions that all GPIB devices need to do. I then created a child class for a specific instrument (Agilent N1912 Power Meter for this example) which inherits from the GPIB class but also adds member data such as Channel A power and Channel B power and the associated Member Functions to obtain the data from the hardware. This went fine and I created a Test vi for verfication utilizing a typical Event Structure architecture.
However, in other applications (without classes) I typically use the Producer/Consumer Design Pattern with Event Structure so that the main loop is not delayed by any hardware interaction. My queue data is a cluster of an "action" enum and a variant to pass data. Is it OK to use this pattern with classes? I created a vi and it works fine and attached is a png (of 1 case) of it.
Are there any problems doing it this way?
Jason

JTerosky wrote:
I'm starting a new project which involves acquiring data from various pieces of equipment using a GPIB port. I thought this would be a good time to start using Classes. I created a GPIB class which contains member data of: Address, Open State, Error; with member vis such as Set Address, Get Address, Open, Close...general actions that all GPIB devices need to do. I then created a child class for a specific instrument (Agilent N1912 Power Meter for this example) which inherits from the GPIB class but also adds member data such as Channel A power and Channel B power and the associated Member Functions to obtain the data from the hardware. This went fine and I created a Test vi for verfication utilizing a typical Event Structure architecture.
However, in other applications (without classes) I typically use the Producer/Consumer Design Pattern with Event Structure so that the main loop is not delayed by any hardware interaction. My queue data is a cluster of an "action" enum and a variant to pass data. Is it OK to use this pattern with classes? I created a vi and it works fine and attached is a png (of 1 case) of it.
Are there any problems doing it this way?
Including the error cluster as part of the private data is something I have never seen done and ... well I'll have to think about that one.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Register event in producer consumer design pattern

Hello wire workers,
I am fairly green when it comes to dynamic event registration, so my understanding of it is probably quite flawed, but what I have implemented seems to work fine.
Assuming a fairly typical queued producer/consumer state machine architecture.
Up till now, I have done the dynamic event registration outside (i.e. to the left of) the UI loop, so all events get registered before the UI loop starts to run.
My question is:
How can I register events from inside one of the consumer loops? I cannot wire it...
Maybe an example will make my scenario more clear.
I have a DAQ loop (queued state machine). In the init state of this loop I want to register a digital input such that changes on a line are handled by my main event structure (in the totally separate UI loop). Is this possible?
I look forward to hearing positive answers
nrp
CLA

The best way to send data from the Consumer Loop to the Producer Loop is through User Events. What you will want to do is create a User Event whose data type is the registered DAQmx event refnum. Then when you register the DAQmx event in the Consumer Loop, fire the User Event with that new refnum and update the registration in the Producer Loop. That's probably hard to wrap your head around in words, so I'll attach a dummy example and pic below. Hope this helps!
VI Saved in LV85.
Message Edited by Jarrod S. on 04-21-2008 12:54 PM
Jarrod S.
National Instruments
Attachments:
DAQmx Event.vi ‏30 KB
DAQmx Event Pic.PNG ‏38 KB

State Machine and producer consumer design patterns

Hi!
In my application I am using state machine(for top level VI) and producer consumer(for subVIs) design patterns throught out.
If there is no activity on the front panel for 1min then the ideal state is invoked. Following are the situation of the ideal state:
1. It checks for any hardware present on the network . If no hardware is found on the network within 1 min then the application and LabVIEW exits.
2. While the ideal state checks for the hardware, and user clicks on any front panel button then it should exit the ideal state. The control
should be in the respective button state.
I am able to achive the point#1 mentioned above but could not get the point #2 to work. I am including the snap shot of
the state machine(default case) and prouducer consumer(deafualt state).
Each screen has the concept of the ideal state. The only additional step in the subVIs is that when the ideal state is reached and the time has expired then it will close the subVIfront panel.It will go to the exit state of the Main(top level) VI. Thus closing the application and quitting LabVIEW.
Any ideas or suggestions. Will multithreading and notifiers help?
TIA
Rachana
Attachments:
Sanpshot_Of_Design.zip ‏75 KB

Hi Rachana,
I was thinking about using event structures wherein there would an event case that would handle any value change event for any of the buttons on the front panel. But before suggesting that, I would need to know more about the Ideal State subvi( more specifically, how is it checking for any hardware present on the network and where is the one minute wait coming from?).
Please feel free to respond to this post with your questions/comments.
Regards,
Ankita A.

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lindsay242,
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No water damage will show up to Apple you have voided any warranty you may have

Producer/ Consumer Design error?

I am learning labview as I go and little errors keep stumping me. I set up the producer/consumer design and it reads the two while loops like I want. However, when I stop the program to save it to the write to measure it gives me an error saying invalid input and highlights the dequeue. I have to queues running (one for a button and one for data) and they both do this. I tried connecting it different ways but its always the same error. Any ideas?
Attachments:
2whlloopprgrm.vi ‏392 KB

Dublicate post
Stick to one post at a time. Do not post the same question on two different threads.

The search for a perfect design pattern

The search for a perfect design pattern
I am searching tip to upgrade a labview program used. I am looking for the best approach to make
my program more robust and scalable.Software and hardware.
Today the system consists of :
GPS, weather station, ultrasound wind sensor, echosounder and a webcamera, all connected to a computer.
The computer OS is XP pro with Labview version 2009 installed. Except for the webcamera all peripherals have serial communication interface.
The webcamera interface is ethernet.
Device                           Data type                 Interval                    Interface
GPS                                NMEA string                1 second                   Serial rs232
Ultrasound wind sensor   NMEA string                1 second                   Serial rs232
Weather, temp,humid     NMEA string               35 seconds                 Serial rs232
Echosounder                  NMEA string               500ms-5 seconds       Serial rs232
                                                                      (depending of depth)
Webcamera                    Jpg                           Snapshot on demand Ethernet
The tasks to be solved
All the data have to be stored.
All the data have to be displayed in real time.
Weather history data must be buffered to be plotted in a graph (pop-up windows).
Absolute wind speed and direction have to be calculated.
Option to send navigation data attached to email at desired time intervals.
Image snapshot at desired time intervals.
The data wich streams into the serial ports are not synchronized and vary in intervals . Would it be a good idea to put all the serial peripherals into a serial device server. Is it possible to let the server place a event in my software, to trigger reading of the data, from the the server. Or how could that be done in other ways?
The perfect design pattern
In version one of the software I use 4 parallel loops to read data at the serial ports, inside these loops the data was separated and outputted to a datasocket server. I used datasocked read in other loops to present and store data. But it did not look good, and yes it was a mess, a really rat nest. I am looking for a better design pattern.
Could some kind of producer/ consumer pattern be the way to go?
Comments and tips are wanted.
TIK

Nice Project! Congratulations ;-)
I am not an expert for large applications. But your project looks nice and manageable. Here my straightforward ideas:
I would build a GUI, with menu bar, pop-up graph display thing.
THen low level tasks with each one handling a RS232 device and feeding queues or fireing notifications.
Maybe handle the snapshots in an event structure on the GUI blockdiagramm.
When GUI and producer tasks are running, close the gap with a middle layer which captures the data and actualizes GUI by reference. For instance the graph-thing-dialogue triggers a "flush queue" and displays the last 200 entries of the array of data.
I often run into issues when having defined too many userevent structures. I guess i am too stupid for that. Thats why i rather use queues (when i dont want to loose data) or notifiers (data is up-to-date). Nevertheless I like a "stop-all-tasks" user event...traditionally.
My team is actually developing a large application. We are using LabVIEW classes and objects.
So have fun!
Yours
RZM

Releasing Queue in Producer Consumer model

I am having a VI which reads data from ethernet,writes to disk,processes and displays. Since lot of processing and displays are there, I am converting it to a Producer- Consumer model so that no data is lost.
I am using 2 loops. IN the Producer I am doing the UDP read and Write to disk functions.and use the enqueing also.In the Consumer loop I am dequeing it and do all the processing and displays.My idea is to avoid any data loss in UDP reception and file writing.
My confusion- where to use the release queue?from the Producer or Consumer ? In a third loop ? Should it be in a sequence structure ?
How to set the loops stop conditions ?
My requirements for stopping - when I press the stop button the program should stop completely(the Consumer loop should stop only after dequeing and processing all the data in the queue). If i don't press the stop button the whole program should run continuously (if data does not arrive for some time it should wait without time out-i am using -1 for the time out condition in UDP read.)

Here is the ultimate Producer-Consumer loop. It queues a stop command when the stop button is pressed. This ensures that every element is dequeued and processed before the bottom loop stops. The last queue data to get processed is the stop command because after you press the stop button, the top loop stops enqueueing more elements.
If your data type is other than a string, you can create something to represent stop, like NaN for a numeric.
Notice the shift registers. This is good practice. Every loop starts with an error out of the previous loop. If an error occurs, it is passed on to the next loop iteration. Also, if an error occurs in the consumer loop, the loop stops. It is good practice to put shift registers on the queue reference also, but not necessary in this case. If you use a For loop, and the loop iterates 0 times, the output of the queue reference would be a null reference, and the Release Queue would not release the queue. With While loops, they always iterate at least once, so it isn't necessary. Its just good practice to make a habit of using shift registers so you don't forget when using For loops.
Notice also that the error in to the Release Queue is not wired. If there were an error, the Release would not take place. All errors are merged at the end to report exactly where an error occured. A timeout is included in case an error prevents the stop command from being enqueued or dequeued.
- tbob
Inventor of the WORM Global
Attachments:
ProducerConsumer.vi ‏53 KB

Still stuck with the same old producer consumer weight problem need help

Hello All,
This is the problem I am stuck with right now.
I have two array lists one producer array list and one consumer array list denoted by a and b
P1 P2 P3 P4 P5
5 6 7 8 9
C1 C2 C3 C4 C5
2 3 4 5 6
Now we find all those producer consumer pairs which satisfy the criteria Pi>=Ci
We have the following sets
(5,2)(6,2)(7,2),(8,2),(9,2)
(5,3)(6,3)(7,3),(8,3),(9,3)
(5,4)(6,4)(7,4),(8,4),(9,4)
(5,5)(6,5)(7,5),(8,5),(9,5)
(6,6)(7,6)(8,6),(9,6)
Let us done each of them with Si
so we have S1,S2,S3,S4,S5
we assign a third parameter called weight to each element in Si which has satisfied the condition Pi>=Ci;
so we we will have
(5,2,ai),(6,2,bi),(7,2,ci)....etc for S1
similarly for S2 and so on.
We need to find in each set Si the the pair which has the smallest weight.
if we have (5,2,3) and (6,2,4) then 5,2,3 should be chosen.We should make sure that there is only one pair in every set which is finally chosen on the basis of weight.
Suppose we get a pair (5,2,3) in S1 and (5,2,3) in S2 we should see that (5,2,3) is not used to compare to compare with any other elements in the same set S2,
Finally we should arrive at the best element pair in each set.They should be non repeating in other sets.
Given a problem
P0 P1 P2 P3 P4
9 5 2 2 8
6 5 4 5 3
C0 C1 C2 C3 C4
we have So as (P0,C0) and (P4,C0)
assuming that the one with the smaller index has lesser weight PO is selected.In the program I have used random weights.from set S1 we select the pair PO,CO
S1 =(P0,C1),(P1,C1) and (P4,C1)
since P0 and P4 are already used in previous set we dont use them for checking in S1 so we have (P1,C1) as best.
S2=(P0,C2),(P1,C2) and (P4,C2) so we dont use P0,C2 and P1 and C2 because PO and P1 are already used in S1.
So we choose P4,C2
in S3 and S4 ae have (P0,C3),(P1,C3),(P4,C3) so we dont choose anything
and same in S4 also.
So answer is
(P0,C0),(P1,C1) and (P4,C2).
My program is trying to assign weights and I am trying to print the weights along with the sets.It doesnt work fine.I need help to write this program to do this.
Thanks.
Regards.
NP
What I have tried till now.
I have one more question could you help me with this.
I have an array list of this form.
package mypackage1;
import java.util.*;
public class DD
private int P;
private int C;
private int weight;
public void set_p(int P1)
P=P1;
public void set_c(int C1)
C=C1;
public void set_weight(int W1)
weight=W1;
public int get_p()
return P;
public int get_c()
return C;
public int get_x()
return weight;
public static void main(String args[])
ArrayList a=new ArrayList();
ArrayList min_weights_int=new ArrayList();
ArrayList rows=new ArrayList();
ArrayList temp=new ArrayList();
Hashtable h=new Hashtable();
String v;
int o=0;
DD[] d=new DD[5];
for(int i=0;i<4;i++)
d=new DD();
for(int i=0;i<4;i++)
d[i].set_p(((int)(StrictMath.random()*10 + 1)));
d[i].set_c((int)(StrictMath.random()*10 + 1));
d[i].set_weight(0);
System.out.println("Producers");
for(int i=0;i<4;i++)
System.out.println(d[i].get_p());
System.out.println("Consumers");
for(int i=0;i<4;i++)
System.out.println(d[i].get_c());
System.out.println("Weights");
for(int i=0;i<4;i++)
System.out.println(d[i].get_x());
for(int i=0;i<4;i++ )
int bi =d[i].get_c();
ArrayList row=new ArrayList();
for(int j=0;j<4;j++)
if( d[j].get_p() >=bi)
d[j].set_weight((int)(StrictMath.random()*10 + 1));
row.add("(" + bi + "," + d[j].get_p() + "," +d[j].get_x() + ")");
else
d[j].set_weight(0);
row.add("null");
rows.add(row);
System.out.println(rows);
int f=0;
for(Iterator p=rows.iterator();p.hasNext();)
temp=(ArrayList)p.next();
String S="S" +f;
h.put(S,temp);
String tt=new String();
for(int j=0;j<4;j++)
if(temp.get(j).toString() !="null")
// System.out.println("In if loop");
//System.out.println(temp.get(j).toString());
String l=temp.get(j).toString();
System.out.println(l);
//System.out.println("Comma matches" + l.lastIndexOf(","));
//System.out.println(min_weights);
f++;
for(Enumeration e=h.keys();e.hasMoreElements();)
//System.out.println("I am here");
int ii=0;
int smallest=0;
String key=(String)e.nextElement();
System.out.println("key=" + key);
temp=(ArrayList)h.get(key);
System.out.println("Array List" + temp);
for( int j=0;j<4;j++)
String l=(temp.get(j).toString());
if(l!="null")
System.out.println("l=" +l);
[\code]

In your example you selected the pair with the greatest
distance from the first set, and the pair with the least
distance from the second. I don't see how the distance
function was used.
Also it's not clear to me that there is always a solution,
and, if there is, whether consistently choosing the
furthest or the closest pairs will always work.
The most obvious approach is to systematically try
all possibilities until the answer is reached, or there
are no possibilities left. This means backtracking whenever
a point is reached where you cannot continue. In this case
backtrack one step and try another possibility at this
step. After all possible choices of the previous step,
backtrack one more step and so on.
This seems rather involved, and it probably is.
Interestingly, if you know Prolog, it is ridiculously
easy because Prolog does all the backtracking for you.
In Java, you can implement the algorithm in much the same
way as Prolog implementations do it--keep a list of all the
choice points and work through them until success or there
are none left.
If you do know Prolog, you could generate lots of random
problems and see if there is always a solution.

Can anyone tell me what's wrong with my queue or producer consumer loop?

A Labview engineer helped me with the overall structure of my program, necessitated by the fast data sample rate and post processing requirements. He recommended the producer/consumer loop and using one of the example files (Cont Acq graph voltage - int clk) to do the actual data acquistion. So I put together the loop and go my two channels of data acq going in the producer loop. However, nothing's getting picked up in the consumer loop and none of my data gets displayed over there.
Anyone care to take a look at it and let me know what I'm doing wrong?
Solved!
Go to Solution.
Attachments:
P-C Yanmar Program.vi ‏296 KB

Your Enque Element should be inside the while loop where you aquire the data. As it is now, the data has to stop being aquired before you send the last set of aquired data.
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Could not create the queue connection

Hi,
I have successfully registered and retrieved the connection factory object from LDAP server..But when i try to make connection out of that connection factory object, it gives following issue[1]. My sample code is like;
          // get connection factory "test_queue_factory"
          QueueConnectionFactory qc_fact = (QueueConnectionFactory) connctx.lookup("cn=test_queue_factory");
          System.out.println("Factory look up success "+qc_fact.toString());
          QueueConnection QCon = qc_fact.createQueueConnection();
          System.out.println("Connection craeted " + QCon.toString());
and the error im getting is;
[1]
Factory look up success oracle.jms.AQjmsQueueConnectionFactory@126e85f
oracle.jms.AQjmsException: The Network Adapter could not establish the connection
     at oracle.jms.AQjmsDBConnMgr.checkForSecurityException(AQjmsDBConnMgr.java:939)
     at oracle.jms.AQjmsDBConnMgr.getConnection(AQjmsDBConnMgr.java:617)
     at oracle.jms.AQjmsDBConnMgr.<init>(AQjmsDBConnMgr.java:251)
     at oracle.jms.AQjmsConnection.<init>(AQjmsConnection.java:185)
     at oracle.jms.AQjmsQueueConnectionFactory.createQueueConnection(AQjmsQueueConnectionFactory.java:252)
     at OracleAQJNDIClient.get_Factory_from_LDAP(OracleAQJNDIClient.java:71)
     at OracleAQJNDIClient.main(OracleAQJNDIClient.java:79)
Caused by: java.sql.SQLException: The Network Adapter could not establish the connection
     at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:412)
     at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:531)
     at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:221)
     at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
     at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:503)
     at java.sql.DriverManager.getConnection(DriverManager.java:582)
     at java.sql.DriverManager.getConnection(DriverManager.java:154)
     at oracle.jms.AQjmsDBConnMgr.getConnection(AQjmsDBConnMgr.java:579)
     ... 5 more
Caused by: oracle.net.ns.NetException: The Network Adapter could not establish the connection
     at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:359)
     at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:422)
     at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:672)
     at oracle.net.ns.NSProtocol.connect(NSProtocol.java:237)
     at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1042)
     at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:301)
     ... 12 more
Caused by: java.net.ConnectException: Connection refused: connect
     at java.net.PlainSocketImpl.socketConnect(Native Method)
     at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
     at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
     at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
     at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
     at java.net.Socket.connect(Socket.java:529)
     at oracle.net.nt.TcpNTAdapter.connect(TcpNTAdapter.java:141)
     at oracle.net.nt.ConnOption.connect(ConnOption.java:123)
     at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:337)
     ... 17 more
Any help?
Thanks
-Ratha
Edited by: Ratha on Oct 3, 2011 1:56 AM

I solved it..my oracle service was down...

Could Buffer replace the Queue in Producer/Consumer Design Pattern

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