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  • What is the difference between the add and offer methods in a queue?

    - by Finbarr
    Take the PriorityQueue for example http://java.sun.com/j2se/1.5.0/docs/api/java/util/PriorityQueue.html#offer(E) According to the Collection API entry http://java.sun.com/j2se/1.5.0/docs/api/java/util/Collection.html the add method will often seek to ensure that an element exists within the Collection rather than adding duplicates. So my question is, what is the difference between the add and offer methods? Is it that the Offer method will add duplicates regardless? (I doubt that it is because if a Collection should only have distinct elements this would circumvent that).

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  • How can I manage a FIFO-queue in an database with SQL?

    - by Jonas
    I have two tables in my database, one for In and one for Out. They have two columns, Quantity and Price. How can I write a SQL-query that selects the correct price? In example: If I have 3 items in for 75 and then 3 items in for 80. Then I have two out for 75, and the third out should be for 75 (X) and the fourth out should be for 80 (Y). How can I write the price query for X and Y? They should use the price from the third and forth row. In example, is there any way to SELECT the third row in the In-table? I can not use auto_increment as identifier for i.e. "third" row, because the tables will contain post for other items too. The rows will not be deleted, they will be saved for accountability reasons. SELECT Price FROM In WHERE ...? NEW database design: +----+ | In | +----+------+-------+ | Supply_ID | Price | +-----------+-------+ | 1 | 75 | | 1 | 75 | | 1 | 75 | | 2 | 80 | | 2 | 80 | +-----------+-------+ +-----+ | Out | +-----+-------+-------+ | Delivery_ID | Price | +-------------+-------+ | 1 | 75 | | 1 | 75 | | 2 | X | <- ? | 3 | Y | <- ? +-------------+-------+ OLD database design: +----+ | In | +----+------+----------+-------+ | Supply_ID | Quantity | Price | +-----------+----------+-------+ | 1 | 3 | 75 | | 2 | 3 | 80 | +-----------+----------+-------+ +-----+ | Out | +-----+-------+----------+-------+ | Delivery_ID | Quantity | Price | +-------------+----------+-------+ | 1 | 2 | 75 | | 2 | 1 | X | <- ? | 3 | 1 | Y | <- ? +-------------+----------+-------+

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  • How can manage a FIFO-queue in an database with SQL?

    - by Jonas
    I have two tables in my database, one for In and one for Out. They have two columns, Quantity and Price. How can I write a SQL-query that selects the correct price? In example: If I have 3 items in for 75 and then 3 items in for 80. Then I have two out for 75, and the third out should be for 75 (X) and the fourth out should be for 80 (Y). How can I write the price query for X and Y? They should use the price from the third and forth row. In example, is there any way to SELECT the third row in the In-table? I can not use auto_increment as identifier for i.e. "third" row, because the tables will contain post for other items too. The rows will not be deleted, they will be saved for accountability reasons. SELECT Price FROM In WHERE ...? NEW database design: +----+ | In | +----+------+-------+ | Supply_ID | Price | +-----------+-------+ | 1 | 75 | | 1 | 75 | | 1 | 75 | | 2 | 80 | | 2 | 80 | +-----------+-------+ +-----+ | Out | +-----+-------+-------+ | Delivery_ID | Price | +-------------+-------+ | 1 | 75 | | 1 | 75 | | 2 | X | <- ? | 3 | Y | <- ? +-------------+-------+ OLD database design: +----+ | In | +----+------+----------+-------+ | Supply_ID | Quantity | Price | +-----------+----------+-------+ | 1 | 3 | 75 | | 2 | 3 | 80 | +-----------+----------+-------+ +-----+ | Out | +-----+-------+----------+-------+ | Delivery_ID | Quantity | Price | +-------------+----------+-------+ | 1 | 2 | 75 | | 2 | 1 | X | <- ? | 3 | 1 | Y | <- ? +-------------+----------+-------+

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  • Any way to add an observer to the head of the queue using Element#observe?

    - by Josh
    This might not be possible but before I rewrite part of my application I wanted to ask... I have a JavaScript app which creates a submit <input> and observes that input's click event using Prototype's Element#observe function. For a few particular pages on one particular site which uses this app, I need to apply some additional business logic before the code which executes normally when the button is clicked. Is there any way I can use Elemen#observe to add my new event handler before the existing event handler, so I can stop the event if these new conditions aren't met? If not I'll probably solve this the "proper" way by having the application fire a specific beforeTakingAction event and add a listener for that which prevents the application from taking it's action, but that's more complicated than this simple problem requires, and requires rewriting part of a shared application for just one user...

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  • Configuring external SMTP server on Azure VM - messages staying in queue

    - by Steph Locke
    I have an external SMTP provider: auth.smtp.1and1.co.uk I am trying to send SQL Server Reporting Services emails via this on an Windows 2012 Azure VM. It is configured sufficiently correctly for emails to be generated, but I've not configured something or mis-configured something as the emails then stay in the queue. Setup details Configured SMTP Virtual Server General: IP Address: Fixed value Access: Access Control: Authentication: ticked Anonymous access Access: Connection Control: All except the list below (which is empty) Access: relay restrictions: Only the list below (which contains 127.0.0.1), ticked 'allow all..' option Delivery: Outbound Security...:Basic Authentication with username and password completed, ticked TLS encryption Delivery: Outbound connections...:TCP port=587 Delivery: Advanced: FQDN=ServerName, smarthost=auth.smtp.1and1.co.uk I then set the following SSRS rsreportserver.config values: <SMTPServer>100.92.192.3</SMTPServer> <SendUsing>2</SendUsing> <SMTPServerPickupDirectory> c:\inetpub\mailroot\pickup </SMTPServerPickupDirectory> <From>[email protected]</From> Tried so far 1) turning the smtp service off and on again (just in case) 2) run SMTPDiag with no errors (also no emails) 3) tried turning off the firewall for the ports (and more generally to see if it made a difference) 4) tried generation from powershell which resulted with message in queue 5) added 25 and 857 as endpoint 6) perused the event log and found some warnings that appear to be about the recipient Message delivery to the remote domain 'gmail.com' failed for the following reason: Unable to bind to the destination server in DNS. Message delivery to the host '212.227.15.179' failed while delivering to the remote domain 'gmail.com' for the following reason: The remote server did not respond to a connection attempt. 7) tried pinging but this appears to be blocked on azure 8) tried more powershell sending on different domains variants (localhost, boxname, internal ip used in smtp properties, 127.0.0.1) - none resulting in success 9) tried adding a remote domain - no change Could anyone recommend what step 10 should be in fixing this issue please?

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  • 1 document pending in printer queue in System Tray that won't go away

    - by White Phoenix
    Edit: I didn't want to do it, but I restarted my computer - cleared the problem right away. Though if I were running a Windows 2003/2008 server, I would hate to have to restart the domain controller just to get rid of this irritating problem. If I run into this problem again, I'm going to try that remove printer/reinstall printer thing. Thanks for your help @Psychogeek. Points for your attempt. Running Windows 7, 32-bit Professional. My printer is an HP OfficeJet Wireless 8500. It's connected to my network wirelessly through TCP/IP as a standalone device. I was having some print problems awhile back and had to do some print spooler stuff as part of my troubleshooting (stopping the Print Spooler service, clearing the print spooler files from C:\Windows\System32\spool\PRINTERS and then restarting the service). I've finally narrowed it down to it being application specific, so that's that. However, as a leftover from all that troubleshooting, my printer icon is stuck in the tray - when I mouseover the icon, Windows says that there is 1 document(s) pending for my username. However, when I open up that printer's queue, there's nothing in there. I restarted the Printer Spooler service and also checked C:\Windows\System32\spool\PRINTERS if there's anything in there - nothing. I did a quick Google search and an answer from one of those "reps" at the Microsoft Socialnet site says for me to uninstall and reinstall the printer. The funny thing is, when I send print jobs, they print just fine - that 1 mystery document stuck in queue isn't stopping anything from happening. Short of having to do that, are there any other quick troubleshooting steps I may be missing?

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  • iis7 large worker process request queue creating process blocking aspnet.config & machine.config amended (bottleneck)

    - by scott_lotus
    ASP.net 2.0 app .net 2.0 framework IIS7 I am seeing a large queue of "requests" appear under the "worker process" option. State recorded appear to be Authenticate Request and Execute Request Handles more than anything else. I have amended aspnet.config in C:\Windows\Microsoft.NET\Framework64\v2.0.50727 (32 bit path and 64 bit path) to include: maxConcurrentRequestsPerCPU="50000" maxConcurrentThreadsPerCPU="0" requestQueueLimit="50000" I have amended machine.config in C:\Windows\Microsoft.NET\Framework64\v2.0.50727\CONFIG (32 bit and 64 bit path) to include: autoConfig="true" maxIoThreads="100" maxWorkerThreads="100" minIoThreads="50" minWorkerThreads="50" minFreeThreads="176" minLocalRequestFreeThreads="152" Still i get the issue. The issue manifestes itself as a large number of processes in the Worker Process queue. Number of current connections to the website display 500 when this issue occurs. I dont think i have seen concurrent connections over 500 without this issue occurring. Web application slows as the request block. Refreshing the app pool resolves for a while (as expected) as the load is spread between the two pools. Application pool in question FIXED REQUEST have been set to refresh on 50000. Thank you for any help. Scott quick edit to say hmm, my develeopers are telling me the project was built with .net 3.5 framework. Looking at C:\Windows\Microsoft.NET\Framework64\v3.5 there does not appear to be a ASPNET.CONFIG or a MACHINE.CONFIG .... is there a 3.5 equivalent ? after a little searching apparenetly 3.5 uses the 2.0 framework files that 3.5 is missing. So back to the original question , where is my bottleneck ?

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  • Using AT on Ubuntu to Background Downloads (w/ Queue)

    - by Nicholas Yost
    I am writing a PHP script, but I want to use the AT command in Ubuntu to fetch a remote file via WGET. I'm basically looking to background the process, so PHP can finish fairly quickly. I cannot find any questions on here about how to use both, but I basically want to do the following pseudo-code: <?php exec('at now -q queuename wget http://path.to/remote/file.ext'); ?> Additionally, I'd like to queue this between providers. I'd like to have each path.to have its own queue, so I only download one file from each provider at a time. Meaning: <?php exec('at now -q remote wget http://path.to/remote/file.ext /local/path'); exec('at now -q vendorone wget http://vendor.one/remote/file.ext /local/path'); exec('at now -q vendortwo wget http://vendor.two/remote/file.ext /local/path'); exec('at now -q vendorone wget http://vendor.one/remote/file.ext /local/path'); ?> This should download the files from path.to, vendor.one, vendor.two immediately, and when the first file is finished downloading from vendor.one, it starts the second file. Does that make sense? I can't find anything like this anywhere on the web, much less on SO/SF. If we can use the crontab to run a one-off wget command, thats fine too.

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  • 2 Printers 1 Queue

    - by Shazburg
    My issue: When an order is processed, the same document needs to be printed on two printers. My proposed solution: Create a single queue in CUPS with a backend script that spits the job out to the two real printers queues. My problem: Documentation. Maybe I'm looking at every ring around the bullseye, but I can't find anything that lays out the rules for writing a CUPS backend script. In the end, I have several questions: Is there already an option to do this in CUPS that I've missed? The line I use to add my queue is "lpadmin -p MultiPass -E -v multipass -P Generic PostScript Printer". But DeviceURI is bad unless I specify a directory like "-v multipass:/tmp". Why is this? For testing, my script does nothing but capture ARGV and write it out to a text file one line per argument. Problem is, I'm getting nothing. Logs show the job as successful, but I'm pretty sure my meager attempt at a backend isn't even being run. I've tried to keep this question brief, so please ask for more info as I'm sure I've left out the most important part in all this. Honestly, I'm just done chasing my own tail. Thank you for your time.

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  • Print job leaves queue but document isn't printed

    - by midnightstar
    I'm dealing with an HP Deskjet F380 All-in-One printer. It's connected via USB to a desktop running Windows 7 Enterprise x64. If I attempt to print something like a web page or a word document, the print job will show up in the print queue and the printer would stir. By stir, I mean, it would seem to prepare itself to print. However, the print job would then leave queue (I'm thinking the computer sees it as completed) and the printer would never actually print anything. However I went into Printers and Devices under the Windows start menu, into printer properties, and print a test page, the test page would print out successfully. I attempted to uninstall and re-install the printer drivers for the printer, but the printer would continue the same behavior afterwards. I also connected the printer to another computer and the printer will print just about anything. I also checked to make sure that the computer the printer needs to be connected to was update to date as far as the OS. The machine is fully up to date. I played with the way the computer handles printer spooling. Under the printer properties, under the "Advanced" tab, I had the print job print directly to the printer. In all these instances, the same behavior continues. I've restarted the printer spooling service. I've also gone under C:\Windows\System32\spool\PRINTERS and deleted files that were sitting in the folder. I have ran SFC /scannnow and the system found no errors in the system's integrity. I had the computer and printer make a cold reboot individually. The only lead I really have going for me is that since the printer prints on other PCs, I can only assume that there is something wrong with the way the PC is configured.

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  • C++ Class Templates (Queue of a class)

    - by Dalton Conley
    Ok, so I have my basic linked Queue class with basic functions such as front(), empty() etc.. and I have transformed it into a template. Now, I also have a class called Student. Which holds 2 values: Student name and Student Id. I can print out a student with the following code.. Student me("My Name", 2); cout << me << endl; Here is my display function for student: void display(ostream &out) const { out << "Student Name: " << name << "\tStudent Id: " << id << "\tAddress: " << this << endl; } Now it works fine, you can see the basic output. Now I'm declaring a queue like so.. Queue<Student> qstu; Storing data in this queue is fine, I can add new values and such.. now what I'm trying to do is print out my whole queue of students with: cout << qstu << endl; But its simply returning an address.. here is my display function for queues. void display(ostream & out) const { NodePointer ptr; ptr = myFront; while(ptr != NULL) { out << ptr->data << " "; ptr = ptr->next; } out << endl; } Now, based on this, I assume ptr-data is a Student type and I would assume this would work, but it doesn't. Is there something I'm missing? Also, when I Try: ptr->data.display(out); (Making the assumtion ptr-data is of type student, it does not work which tells me I am doing something wrong. Help on this would be much appreciated!

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  • Does add() on LinkedBlockingQueue notify waiting threads?

    - by obvio171
    I have a consumer thread taking elements from a LinkedBlockingQueue, and I make it sleep manually when it's empty. I use peek() to see if the queue empty because I have to do stuff because sending the thread to sleep, and I do that with queue.wait(). So, when I'm in another thread and add()an element to the queue, does that automatically notify the thread that was wait()ing on the queue?

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  • What happens differently when you add a task Asynchronously on GAE?

    - by Ben Grunfeld
    Google's doc on async tasks assumes knowledge of the difference between regular and asynchronously added tasks. add_async(task, transactional=False, rpc=None) Asynchronously add a Task or a list of Tasks to this Queue. How is adding tasks asynchronously different to adding them regularly. I.e. what is the difference between using add(task, transactional=False) and add_async(task, transactional=False, rpc=None) I've heard that adding tasks regularly blocks certain things. Any explanation of what it blocks and how, and how async tasks don't block would be greatly appreciated.

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  • What are some good, simple examples for queues?

    - by Michael Ekstrand
    I'm teaching CS2 (Java and data structures), and am having some difficulty coming up with good examples to use when teaching queues. The two major applications I use them for are multithreaded message passing (but MT programming is out of scope for the course), and BFS-style algorithms (and I won't be covering graphs until later in the term). I also want to avoid contrived examples. Most things that I think of, if I were actually going to solve them in a single-threaded fashion I would just use a list rather than a queue. I tend to only use queues when processing and discovery are interleaved (e.g. search), or in other special cases like length-limited buffers (e.g. maintaining last N items). To the extent practical, I am trying to teach my students good ways to actually do things in real programs, not just toys to show off a feature. Any suggestions of good, simple algorithms or applications of queues that I can use as examples but that require a minimum of other prior knowledge?

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  • Serialization of Queue type- Serialization not working; C#

    - by Soham
    Hi All, Consider this piece of code: private Queue Date=new Queue(); //other declarations public DateTime _Date { get { return (DateTime)Date.Peek();} set { Date.Enqueue(value); } } //other properties and stuff.... public void UpdatePosition(...) { //other code IFormatter formatter = new BinaryFormatter(); Stream Datestream = new MemoryStream(); formatter.Serialize(Datestream, Date); byte[] Datebin = new byte[2048]; Datestream.Read(Datebin,0,2048); //Debug-Bug Console.WriteLine(Convert.ToString(this._Date)); Console.WriteLine(BitConverter.ToString(Datebin, 0, 3)); //other code } The output of the first writeline is perfect. I.e to check if really the Queue is initialised or not. It is. The right variables are stored and et. all [I inserted a value in that Q, that part of the code is not shown] But the second writeline is not giving the right expected answer: It serializes the entire Queue to 00-00-00. Want some serious help! Soham

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  • Choosing between .NET Service Bus Queues vs Azure Queue Service

    - by ChrisV
    Just a quick question regarding an Azure application. If I have a number of Web and Worker roles that need to communicate, documentation says to use the Azure Queue Service. However, I've just read that the new .NET Service Bus now also offers queues. These look to be more powerful as they appear to offer a much more detailed API. Whilst the .NSB looks more interesting it has a couple of issues that make me wary of using it in distributed application. (for example, Queue Expiration... if I cannot guarantee that a queue will be renewed on time I may lose it all!). Has anyone had any experience using either of these two technologies and could give any advice on when to choose one over the other. I suspect that whilst the service bus looks more powerful, as my use case is really just enabling Web/Worker roles to communicate between each other, that the Azure Queue Service is what I'm after. But I'm just really looking for confirmation of that before progamming myself in to a corner :-) Thanks in advance. UPDATE Have read up about the two systems over the break. It defo looks like .NET service bus is more specifically designed for integrating systems rather than providing a general purpose reliable messaging system. Azure Queues are distributed and so reliable and scalable in a way that .NSB queues are not and so more suitable for code hosted within Azure itself. Thanks for the responses.

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  • Producer/consumer in Grails?

    - by Mulone
    Hi all, I'm trying to implement a Consumer/Producer app in Grails, after several unsuccessful attempts at implementing concurrent threads. Basically I want to store all the events coming from a clients (through separate AJAX calls) in a single queue and then process such a queue in a linear way as soon as new events are added. This looks like a Producer/Consumer problem: http://en.wikipedia.org/wiki/Producer-consumer_problem How can I implement this in Grails (maybe with a timer or even better by generating an event 'process queue')? Basically I'd like to a have a singleton service waiting for new events in the queue and processing them linearly (even if the queue is loaded by several concurrent processes). Any hints? Cheers!

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  • Open Source Queuing Solutions for peek, mark as done and then remove

    - by user330114
    I am looking at open source queuing platforms that allow me do the following: I have multiple producers, multiple consumers putting data into a queue in a multithreaded environment with the specific use case: I want the ability for consumers to be able do the following Peek at a message from the queue(which should mark as the message as invisible on the queue so that other consumers cannot consume the same message) The consumer works on the message consumed and if it is able to do the work successfully, it marks the message as consumed which should permanently delete it from the queue. If the consumer dies abruptly after marking the message as consumed or fails to acknowledge successful consumption after a certain timeout, the message is made visible on the queue again so that another consumer can pick it up. I've been looking at RabbitMQ, hornetQ, ActiveMQ but I'm not sure I can get this functionality out of the box, any recommendations on a system that gives me this functionality?

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  • jms message not moving of the queue in websphere

    - by user271858
    I have a message driven bean that throws exception under certain conditions. When it throws an exception the message is not processed and put back on the queue. From what I understand with MQ and WAS (Websphere Application Server) the message should be marked as bad after x number of tries and removed from the queue. This is not happening and the message remains on the queue marked as bad. What part of the configuration in MQ and/or WAS have I missed to set correct? (The issue with the MDB throwing exceptions is NOT the point here) Thanks.

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  • Delete MSMQ Queue During Uninstall

    - by Todd Kobus
    Is it possible to delete a private message queue that was created by the service user? During uninstallation, we would like to clean up any message queues created by our application. For security purposes, access to these queues has been restricted to the current user (ServiceUser). During uninstall, we have admin privileges, but still get an access denied MessageQueueException when we attempt to delete the queue or modify the privs on the queue. Here is the cleanup code: public void DeleteAppQueues() { List<string> trash = new List<string>(); var machineQueues = MessageQueue.GetPrivateQueuesByMachine("."); foreach (var q in machineQueues) { if (IsAppQueue(q.QueueName)) { trash.Add(".\\" + q.QueueName); } q.Dispose(); } foreach (var queueName in trash) { try { using (MessageQueue delQueue = new MessageQueue(queueName)) { delQueue.SetPermissions("Everyone", MessageQueueAccessRights.FullControl, AccessControlEntryType.Allow); } MessageQueue.Delete(queueName); } catch (MessageQueueException ex) { // ex.Message is "Access to Message Queuing system is denied." } } }

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  • What happens if a message is rolled back in MQ?

    - by Manglu
    Hi, I receive a message from a WebSPhere MQ queue. I try to process and if i receive some exceptions i want to rollback the message to the MQ Queue. I have no problems in doing the same. What happens to the message? Does it go to the bottom of the queue? If i try and pull a message from the queue would i receive the same message that i rolledback? What is the behaviour likely to be? I want to know this behaviour typically in a high volume Queue scenario? Appreciate any inputs. Thanks, Manglu

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