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  • handling Concurrency in SQL SERVER 2005

    - by sameer
    Hi, I have one question for you, if you can answer and refer resource it will be great help. I have a scenario where i need to create a appointment slot and a serial no for each slot memberwise. ex: Member Id |App Slot # 1|1 1|2 2|1 2|2 1|3 what im doing is take the Max slot number,increamenting it and insert it memberwise. but the problem is concurrent user can create a slot when i take the max slot after that if any other user insert the slot the value that im working with is no more valid, how to over come this problem Thanks & Regards, Sameer

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  • Keeping a large volume of data in Session - Suggestions / alternatives?

    - by Fishcake
    I'm developing a web app for which the client wants us to query their data as little as possible. The data will be coming from a Microsoft CRM instance. So we've agreed that data will only be queried as and when it is needed, therefore if a web user wants to see a list of contacts (for example) that list is fetched into a local DataTable. Then if a new contact is created on the website the new contact is sent to CRM and added to the local DataTable at the same time. Likewise for edits. If the user then looks at their contacts again the data will just come from the local DataTable. At the moment local data is being kept in Session but my concern is that too much memory will start being used up. However traffic is expected to be pretty small, perhaps no more than 20 concurrent users so am I worrying about nothing or is there a better way you can suggest to handle this?

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  • java tool for debugging

    - by user269723
    Hi experts, Currently we are studying the java based tool which is primararily Reporting tool.It was developed in 2000/2001 period and uses many open source libraries like Apache Avalon/Mx4J.Adaptor/edu.Oswego(java concurrent package) etc. Tool uses jdk 1.3.1 and goal is to upgrade to jdk 1.5.We have also been asked to remove these 'outdated' packages and replace by standard java packages if possible. Unfortunately we have the code available for study but lacks any documentation and really difficult to track the flow(Total number of classes written might be more than 1000) during debugging. Whats the best way to understand this kind of tool? any Graphical tool to see the relationship between the classes? Thanks SR

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  • How to generate a good random seed to pass to srand()?

    - by zr
    Hi, I am writing a C++ program which needs to create a temporary file for its internal usage. I would like to allow concurrent executions of the program by running multiple proccesses, so the temporary file name needs to be randomized, that way each spawned process will generate a unique temporary file name for its own use. I am using rand() to generate random characters for part of the file name, so i need to initialize the random number generator's seed using srand(). What options are there for passing a good argument to srand() such that two processes will not be initialized with the same seed value? My code needs to work both on Windows and pn Linux TIA.

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  • Server-side technology for a game

    - by Soonts
    We’re creating a massively-multiplayer social game. We expect up to 1 million concurrent users. The game is not real-time, instead it’s turn-based. We need reliable messaging between our clients and the server, preferably over HTTP protocol. Besides the multiplayer functionality, we’ll also need a content delivery service. Could you please recommend a server-side technology for us, so we’ll start searching for the right people to hire? Is it correct assumption that no single server will hold that amount of load so it must scale horizontally? Will Windows Azure do the job? Thanks in advance.

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  • net c# lock statement in data access layer

    - by Pedro Rivera
    I saw a code where they have the data access layer like this: public class CustomerDA{ private static readonly object _sync = new object(); private static readonly CustomerDA _mutex = new CustomerDA(); private CustomerDA(){ } public CustomerDA GetInstance(){ lock(_sync){ return _mutex; } } public DataSet GetCustomers(){ //database SELECT //return a DataSet } public int UpdateCustomer(some parameters){ //update some user } } public class CustomerBO{ public DataSet GetCustomers(){ //some bussiness logic return CustomerDA.GetInstance().GetCustomers(); } } I was using it, but start thinking... "and what if had to build a facebook like application where there are hundreds of thousands of concurrent users? would I be blocking each user from doing his things until the previous user ends his database stuff? and for the Update method, is it useful to LOCK THREADS in the app when database engines already manage concurrency at database server level?" Then I started to think about moving the lock to the GetCustomers and UpdateCustomer methods, but think again: "is it useful at all?"

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  • For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue?

    - by Jonathan Allen
    For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue? Concerns: * My goal is to pull up to 100 items at a time and send them as a batch to the next step. * If I use a ConcurrentQueue, I have to manually cause it to go asleep when there is no work to be done. Otherwise I waste CPU cycles on spinning. * If I use a BlockingQueue and I only have 99 work items, it could indefinitely block until there the 100th item arrives. http://msdn.microsoft.com/en-us/library/system.collections.concurrent.aspx

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  • Service injection into Controller (Spring MVC)

    - by ThaSaleni
    Hi I have a Spring web application, I have built it up to the controller stage and I could inject my Daos, into my Services fine. Now when I want to inject my Service into my controller i get an error for dependency with the Dao and further down the sessionFactory. I don't want to inject these again cause this will ultimately lead me to eventually create a data source but I have my Daos for data access and they already know about sessionFactory. Am I missing something here? here's the sample code snippets My Service: @Service("productService") @Transactional public class ProductServiceImpl implements ProductService { private ProductDao productDao; @Autowired public void setDao(ProductDao productDao) { this.productDao = productDao; } My Controller @Controller @WebServlet(name="controllerServlet", loadOnStartup= urlPatterns=...}) public class ControllerServlet extends HttpServlet { boolean isUserLogedIn =false; @Autowired private ProductService productService; public void setProductService(ProductService productService){ this.productService = productService; } Servlet-context Stack trace javax.servlet.ServletException: Servlet.init() for servlet mvcServlet threw exception org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999) org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java: 565) org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1812) java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) java.lang.Thread.run(Thread.java:662) root cause org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'controllerServlet': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.phumzile.acme.services.ProductService com.phumzile.acme.client.web.controller.ControllerServlet.productService; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.phumzile.acme.services.ProductService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)} org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.p ostProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:287) org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106) org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517) org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456) org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294) org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225) SERVLET-CONTEXT <context:component-scan base-package="com.phumzile.acme.client" /> <!-- Enables the Spring MVC @Controller programming model --> <mvc:annotation-driven /> </beans> APP-CONFIG <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations"> <list> <value>configuration.properties</value> </list> </property> </bean> <context:annotation-config/> <context:component-scan base-package="com.phumzile.acme" /> <import resource="db-config.xml" /> </beans> DB-CONFIG <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close"> <property name="idleConnectionTestPeriod" value="10800"/> <property name="maxIdleTime" value="21600"/> <property name="driverClass"> <value>${jdbc.driver.className}</value> </property> <property name="jdbcUrl"> <value>${jdbc.url}</value> </property> <property name="user"> <value>${jdbc.username}</value> </property> <property name="password"> <value>${jdbc.password}</value> </property> </bean> <bean id="sessionFactory" class="org.springframework.orm.hibernate3.a nnotation.AnnotationSessionFactoryBean"> <property name="dataSource"> <ref bean="dataSource" /> </property> <property name="annotatedClasses"> <list> <!-- Entities --> <value>com.phumzile.acme.model.User</value> <value>com.phumzile.acme.model.Person</value> <value>com.phumzile.acme.model.Company</value> <value>com.phumzile.acme.model.Product</value> <value>com.phumzile.acme.model.Game</value> <value>com.phumzile.acme.model.Book</value> <!-- Entities --> </list> </property> <property name="packagesToScan" value="com.phumzile.acme" /> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect">${jdbc.hibernate.dialect </prop> <prop key="hibernate.hbm2ddl.auto">validate</prop> <prop key="hibernate.show_sql">true</prop> </props> </property> </bean> <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"> <property name="sessionFactory"> <ref bean="sessionFactory" /> </property> </bean> <tx:annotation-driven /> </beans> CONFIGURATION.PROPERTIES jdbc.driver.className=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql://localhost:3306/mydb jdbc.username=root jdbc.password=root jdbc.hibernate.dialect=org.hibernate.dialect.MySQLDialect

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  • PHP Launch Execute Files Concurrently

    - by Ozzy
    Hi all. Basically, I was doing some testing using apache bench. The file i was testing takes 2 seconds to execute (its optimised, it connects to an external server hence the slowdown) Basically I found that the more concurrent useres i emulated, the more executions of the file i could do per second. Is there anyway that i can do something like this in php? : <?php execute_file('file.php'); execute_file('file.php'); execute_file('file.php'); execute_file('file.php'); execute_file('file.php'); ?> That would execute the file 5 times but would NOT wait for the files to finish downloading so the above example would quickly call the 5 functions then exit. Im assuming somesort of timeout would be used?

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  • What is the best way to make a schedule in MFC

    - by Vanwaril
    I have a list of items that are each associated with a start and end time and date. What I want to do is, given a time and date range, display only the items that fall within that window, even partially. What I'm doing is creating a CListCtrl with all the items in it and the CListCtrl is sorted by start time by default. But given a time range, I don't know how to search for the first item that is within the range. Another problem with the list control is it displays as a list, whereas it would be nice if there was a control that could also show things that are concurrent side by side. I'm doing this within a dialog application.

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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  • how to store dynamically generated pages in html?

    - by Dharmik Bhandari
    I'm working on ASP.net MVC3 Web application that is facing scalability issue. For improving performance I want to store dynamically generated pages in html and serve them from generated html directly rather then querying database for each page request. I'm sure this will dramatically increase performance. Can any one share any hint / example / tutorial on how to do it? And what are challenges? I would also like to know how others are handling performance issue for large e-commerce sites with at-least thousand categories and 200k products with at least 200-500 concurrent visitors? What are the best approaches? Thanks in advance.

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  • HBase as web app backend

    - by NathanD
    Can anyone advise if it is a good idea to have HBase as primary data source for web-based application? My primary concern is HBase's response time to queries. Is it possible to have sub-second response? edit: more details about the app itself. Amount of data: ~500GB of text data, expect to reach 1TB soon Number of concurrent users using the app: up to 50 The app will be used to present reports about data stored in HBase, like how many times keyword "X" occured in last 24h. For ~80% of requests from that app I will know the exact key, 20% will be scans (I'm looking into HBase schema design related topics to make it run fast)

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  • Algorithm to select groups of similar items in 2d array

    - by mafutrct
    There is a 2d array of items (in my case they are called Intersections). A certain item is given as a start. The task is to find all items directly or indirectly connected to this item that satisfy a certain function. So the basic algorithm is like this: Add the start to the result list. Repeat until no modification: Add each item in the array that satisfies the function and touches any item in the result list to the result list. My current implementation looks like this: private IList<Intersection> SelectGroup ( Intersection start, Func<Intersection, Intersection, bool> select) { List<Intersection> result = new List<Intersection> (); Queue<Intersection> source = new Queue<Intersection> (); source.Enqueue (start); while (source.Any ()) { var s = source.Dequeue (); result.Add (s); foreach (var neighbour in Neighbours (s)) { if (select (start, neighbour) && !result.Contains (neighbour) && !source.Contains (neighbour)) { source.Enqueue (neighbour); } } } Debug.Assert (result.Distinct ().Count () == result.Count ()); Debug.Assert (result.All (x => select (x, result.First ()))); return result; } private List<Intersection> Neighbours (IIntersection intersection) { int x = intersection.X; int y = intersection.Y; List<Intersection> list = new List<Intersection> (); if (x > 1) { list.Add (GetIntersection (x - 1, y)); } if (y > 1) { list.Add (GetIntersection (x, y - 1)); } if (x < Size) { list.Add (GetIntersection (x + 1, y)); } if (y < Size) { list.Add (GetIntersection (x, y + 1)); } return list; } (The select function takes a start item and returns true iff the second item satisfies.) This does its job and turned out to be reasonable fast for the usual array sizes (about 20*20). However, I'm interested in further improvements. Any ideas? Example (X satisfies in relation to other Xs, . does never satisfy): .... XX.. .XX. X... In this case, there are 2 groups: a central group of 4 items and a group of a single item in the lower left. Selecting the group (for instance by starting item [2, 2]) returns the former, while the latter can be selected using the starting item and sole return value [0, 3]. Example 2: .A.. ..BB A.AA This time there are 4 groups. The 3 A groups are not connected, so they are returned as separate groups. The bigger A and B groups are connected, but A does not related to B so they are returned as separate groups.

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  • Why avoid pessimistic locking in a version control system?

    - by raven
    Based on a few posts I've read concerning version control, it seems people think pessimistic locking in a version control system is a bad thing. Why? I understand that it prevents one developer from submitting a change while another has the file checked out, but so what? If your code files are so big that you constantly have more than one person working on them at the same time, I submit that you should reorganize your code. Break it up into smaller functional units. Integration of concurrent code changes is a tedious and error-prone process even with the tools a good version control system provides to make it easier. I think it should be avoided if at all possible. So, why is pessimistic locking discouraged?

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  • iPhone: One Object, One Thread

    - by GingerBreadMane
    On the iPhone, I would like to do some operations on an image in a separate thread. Rather than dealing with semiphores, locking, etc., I'd like to use the 'One Object, One Thread' method of safely writing this concurrent operation. I'm not sure what is the correct way to copy my object into a new thread so that the object is not accessed in the main thread. Do I use the 'copy' method? If so, do I do this before the thread or inside the thread? ... -(void)someMethod{ UIImage *myImage; [NSThread detachNewThreadSelector:@selector(getRotatedImage:) toTarget:self withObject:myImage]; } -(void)getRotatedImage:(UIImage *)image{ ... ... UIImage *copiedImage = [image copy]; ... ... }

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  • How to manage db connections on server?

    - by simpatico
    I have a severe problem with my database connection in my web application. Since I use a single database connection for the whole application from singleton Database class, if i try concurrent db operations (two users) the database rollsback the transactions. This is my static method used: All threads/servlets call static Database.doSomething(...) methods, which in turn call the the below method. private static /* synchronized*/ Connection getConnection(final boolean autoCommit) throws SQLException { if (con == null) { con = new MyRegistrationBean().getConnection(); } con.setAutoCommit(true); //TODO return con; } What's the recommended way to manage this db connection/s I have, so that I don't incurr in the same problem.

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  • Sort/Enumerate an NSArray from somewhere in the middle?

    - by Kenny Winker
    I have an NSArray, with objects ordered like so: a b c d e f I would like to enumerate through this array in this order: c d e f a b i.e. starting at some point that is not the beginning, but hitting all the items. I imagine this is a matter of sorting first and then enumerating the array, but I'm not sure if that's the best technique... or, frankly, how to sort the array like this. Edit Adding details: These will be relatively small arrays, varying from 3 to 10 objects. No concurrent access. I'd like to permanently alter the sort order of the array each time I do this operation.

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  • Why doesn't ConcurrentQueue<T>.Count return 0 when IsEmpty == true?

    - by DanTup - Danny Tuppeny
    I was reading about the new concurrent collection classes in .NET 4 on James Michael Hare's blog, and the page talking about ConcurrentQueue<T> says: It’s still recommended, however, that for empty checks you call IsEmpty instead of comparing Count to zero. I'm curious - if there is a reason to use IsEmpty instead of comparing Count to 0, why does the class not internally check IsEmpty and return 0 before doing any of the expensive work to count? E.g.: public int Count { get { // Check IsEmpty so we can bail out quicker if (this.IsEmpty) return 0; // Rest of "expensive" counting code } } It seems strange to suggest this if it could be "fixed" so easily with no side-effects?

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  • CURL alternative - Design ideas

    - by Vincent
    All, I am looking for some web application design ideas here. I have a server X that hosts an SDK, which has the capacity to talk a piece of hardware. When I make an HTTPS request from an external PHP web application (hosted on Server Y) to Server X through curl, Server X gives JSON data as a response. I use this data to render my UI for the web app on Server Y. The above method seems to be slow and has a tendency to fail in production if there are too many concurrent requests. Can anybody let me know if there is an alternative to CURL or any other design people are using to pull data like this from servers? Thanks

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  • (win32) What to do when a file remains left open when a remote application crashes or forgets to clo

    - by Stephane R.
    Hi I have not worked so much with files: I am wondering about possible issues with accessing remote files on another computer. What if the distant application crashes and doesn't close the file ? My aim is to use this win32 function: HFILE WINAPI OpenFile(LPCSTR lpFileName, LPOFSTRUCT lpReOpenBuff, UINT uStyle); Using the flag OF_SHARE_EXCLUSIVE assures me that any concurrent access will be denied (because several machines are writing to this file from time to time). But what if the file is left open ? (application crash for example ?) How to put the file back to normal ?

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  • What database is a good progression from MS Access for Coldfusion?

    - by Saul
    All my (home) CF learning has so far been done using Access as a database, and as far as the DB goes I "get it". There's no database server, and no need to log on to the database or anything, and setting up table relationships is easy and visual. Oh and its essentially free to deploy. However, I'm now working on an application that's likely to be used across several businesses and probably up to 50 concurrent users. I've heard that Access really isn't up to multi user use or production use on an app. What would you recommend as more suitable, preferably easy to grasp, with minimal tweeking needed for my SQL (I used a tool to convert to MySQL and it certainly handles concatenation differently, I dont want to have to do too much debugging), visual interface available, scalable, backupable, and whatever else I need that I don't yet know I need!

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  • How bad is opening and closing a SQL connection for several times? What is the exact effect?

    - by Eren
    For example, I need to fill lots of DataTables with SQLDataAdapter's Fill() method: DataAdapter1.Fill(DataTable1); DataAdapter2.Fill(DataTable2); DataAdapter3.Fill(DataTable3); DataAdapter4.Fill(DataTable4); DataAdapter5.Fill(DataTable5); .... .... Even all the dataadapter objects use the same SQLConnection, each Fill method will open and close the connection unless the connection state is already open before the method call. What I want to know is how does unnecessarily opening and closing SQLConnections affect the performance of the application. How much does it need to scale to see the bad effects of this problem (100,000s of concurrent users?). In a mid-size website (daily 50000 users) does it worth bothering and searching for all the Fill() calls, keeping them together in the code and opening the connection before any Fill() call and closing afterwards?

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  • Script Speed vs Memory Usage

    - by Doug Neiner
    I am working on an image generation script in PHP and have gotten it working two ways. One way is slow but uses a limited amount of memory, the second is much faster, but uses 6x the memory . There is no leakage in either script (as far as I can tell). In a limited benchmark, here is how they performed: -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 65.626 | 540,036 | 200 Two | 20.207 | 3,269,600 | 200 -------------------------------------------- And here is the average of the previous numbers (if you don't want to do your own math): -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 0.328 | 540,036 | 1 Two | 0.101 | 3,269,600 | 1 -------------------------------------------- Which method should I use and why? I anticipate this being used by a high volume of users, with each user making 10-20 requests to this script during a normal visit. I am leaning toward the faster method because though it uses more memory, it is for a 1/3 of the time and would reduce the number of concurrent requests.

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  • While using ConcurrentQueue, trying to dequeue while looping through in parallel

    - by James Black
    I am using the parallel data structures in my .NET 4 application and I have a ConcurrentQueue that gets added to while I am processing through it. I want to do something like: personqueue.AsParallel().WithDegreeOfParallelism(20).ForAll(i => ... ); as I make database calls to save the data, so I am limiting the number of concurrent threads. But, I expect that the ForAll isn't going to dequeue, and I am concerned about just doing ForAll(i => { personqueue.personqueue.TryDequeue(...); ... }); as there is no guarantee that I am popping off the correct one. So, how can I iterate through the collection and dequeue, in a parallel fashion. Or, would it be better to use PLINQ to do this processing, in parallel?

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