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  • java.util.concurrent.ThreadPoolExecutor strange logic

    - by rodrigoap
    Look ath this method of ThreadPoolExcecutor: public void execute(Runnable command) { ... if (runState == RUNNING && workQueue.offer(command)) { if (runState != RUNNING || poolSize == 0) ensureQueuedTaskHandled(command); } ... } It check that runState is RUNNING and then the oposite. As I'm trying to do some tuning on a SEDA like model I wanted to understand the internals of the thread pool. Do you think this code is correct?

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  • Can Ruby Fibers be Concurrent?

    - by Jesse J
    I'm trying to get some speed up in my program and I've been told that Ruby Fibers are faster than threads and can take advantage of multiple cores. I've looked around, but I just can't find how to actually run different fibers concurrently. With threads you can dO this: threads = [] threads << Thread.new {Do something} threads << Thread.new {Do something} threads.each {|thread| thread.join} I can't see how to do something like this with fibers. All I can find is yield and resume which seems like just a bunch of starting and stopping between the fibers. Is there a way to do true concurrency with fibers?

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  • Python XMLRPC with concurrent requests

    - by MattB
    I'm looking for a way to prevent multiple hosts from issuing simultaneous commands to a Python XMLRPC listener. The listener is responsible for running scripts to perform tasks on that system that would fail if multiple users tried to issue these commands at the same time. Is there a way I can block all incoming requests until the single instance has completed?

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  • Multiple Concurrent Postbacks when using UpdatePanels

    - by d4nt
    Here's an example app that I built to demonstrate my problem. A single aspx page with the following on it: <form id="form1" runat="server"> <asp:ScriptManager runat="server" /> <asp:Button runat="server" ID="btnGo" Text="Go" OnClick="btnGo_Click" /> <asp:UpdatePanel runat="server"> <ContentTemplate> <asp:TextBox runat="server" ID="txtVal1" /> </ContentTemplate> </asp:UpdatePanel> </form> Then, in code behind, we have the following: protected void btnGo_Click(object sender, EventArgs e) { Thread.Sleep(5000); Debug.WriteLine(string.Format("{0}: {1}", DateTime.Now.ToString("HH:MM:ss.fffffff"), txtVal1.Text)); txtVal1.Text = ""; } If you run this and click on the "Go" button multiple times you will see multiple debug statements on the "Output" window showing that multiple requests have been processed. This appears to contradict the documented behaviour of update panels (i.e. If you make a request while one is processing, the first requests gets terminated and the current one is processed). Anyway, the point is I want to fix it. The obvious option would be to use Javascript to disable the button after the first press, but that strikes me as hard to maintain, we potentially have the same issue on a lot of screens it could be easily broken if someone renames a button. Do you have any suggestions? Perhaps there is something I could do in BeginRequest in Global.asax to detect a duplicate request? Is there some setting or feature on the UpdatePanel to stop it doing this, or maybe something in the AjaxControlToolkit that will prevent it?

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  • New programming jargon you coined?

    - by jdk
    What programming terms have you coined that have taken off in your own circles? (i.e. have heard others repeating it?) It might be within your own team, workplace or garnered greater popularity on the Internet. Define your programming term, word or phrase in bold followed by an explanation, citation and/or usage example so we can use it in appropriate context. This question serves in the spirit of communication among programmers through sharing of terminology with each other, to benefit us by its propagation within our own teams and environments. Please no repeats of common jargon already ingrained in the programming culture like: "kludge", "automagically", "cruft", etc. (unless you coined it). Stealing from the comments: A shared vocabulary is the basis of communication, not just among programmers, Note: This Programming question has been reworded/reorganized to phrase a real question and remove ambiguity, vagueness and rhetorical device. It is not difficult to know what is being asked & question can be reasonably answered (see answers below).

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  • Using SQL dB column as a lock for concurrent operations in Entity Framework

    - by Sid
    We have a long running user operation that is handled by a pool of worker processes. Data input and output is from Azure SQL. The master Azure SQL table structure columns are approximated to [UserId, col1, col2, ... , col N, beingProcessed, lastTimeProcessed ] beingProcessed is boolean and lastTimeProcessed is DateTime. The logic in every worker role is: public void WorkerRoleMain() { while(true) { try { dbContext db = new dbContext(); // Read foreach (UserProfile user in db.UserProfile .Where(u => DateTime.UtcNow.Subtract(u.lastTimeProcessed) > TimeSpan.FromHours(24) & u.beingProcessed == false)) { user.beingProcessed = true; // Modify db.SaveChanges(); // Write // Do some long drawn processing here ... ... ... user.lastTimeProcessed = DateTime.UtcNow; user.beingProcessed = false; db.SaveChanges(); } } catch(Exception ex) { LogException(ex); Sleep(TimeSpan.FromMinutes(5)); } } // while () } With multiple workers processing as above (each with their own Entity Framework layer), in essence beingProcessed is being used a lock for MutEx purposes Question: How can I deal with concurrency issues on the beingProcessed "lock" itself based on the above load? I think read-modify-write operation on the beingProcessed needs to be atomic but I'm open to other strategies. Open to other code refinements too.

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  • Design patterns for Agent / Actor based concurrent design.

    - by nso1
    Recently i have been getting into alternative languages that support an actor/agent/shared nothing architecture - ie. scala, clojure etc (clojure also supports shared state). So far most of the documentation that I have read focus around the intro level. What I am looking for is more advanced documentation along the gang of four but instead shared nothing based. Why ? It helps to grok the change in design thinking. Simple examples are easy, but in a real world java application (single threaded) you can have object graphs with 1000's of members with complex relationships. But with agent based concurrency development it introduces a whole new set of ideas to comprehend when designing large systems. ie. Agent granularity - how much state should one agent manage - implications on performance etc or are their good patterns for mapping shared state object graphs to agent based system. tips on mapping domain models to design. Discussions not on the technology but more on how to BEST use the technology in design (real world "complex" examples would be great).

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  • Get number of concurrent users online - ASP.NET

    - by Srikanth
    I would like to know the number of users logged into my ASP.NET 2.0 application. Points to be considered: 1) Simplest way would be to use Application or Cache object to have the counts on Session start or end. However this would fail if there is a worker process recycle. Wouldn't it? 2) Should't make a difference whether the session is inproc/state server managed/ or SQL server managed. 3) Should preferably be seamless to a web-farm architecture.

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  • Preventing concurrent data modification in Web based app

    - by Manoj
    Hi, I am building a web app in Silverlight which allows users to view and edit a database. In order to prevent multiple users from editing the same data, I was thinking of implementing a lock and key mechanism, so that other users are made to wait when one particular user is editing the data. Is there any way in which we can have variable(flag specifying if a user is editing data) in the server which can be shared across multiple clients? Is there a better way to manage this type of conurrent data access issues?

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  • Oracle (PL/SQL): Is UPDATE RETURNING concurrent?

    - by Jaap
    I'm using table with a counter to ensure unique id's on a child element. I know it is usually better to use a sequence, but I can't use it because I have a lot of counters (a customer can create a couple of buckets and each of them needs to have their own counter, they have to start with 1 (it's a requirement, my customer needs "human readable" keys). I'm creating records (let's call them items) that have a prikey (bucket_id, num = counter). I need to guarantee that the bucket_id / num combination is unique (so using a sequence as prikey won't fix my problem). The creation of rows doesn't happen in pl/sql, so I need to claim the number (btw: it's not against the requirements to have gaps). My solution was: UPDATE bucket SET counter = counter + 1 WHERE id = param_id RETURNING counter INTO num_forprikey; PL/SQL returns var_num_forprikey so the item record can be created. Question: Will I always get unique num_forprikey even if the user concurrently asks for new items in a bucket?

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  • High concurrent request server in ruby

    - by WedTM
    I'm trying to write a simple server that will grab an mp3 file from rackspace cloudfiles, and stream it to a client over HTTP. The server must be able to stream to multiple clients simultaneously, however, I'm finding it difficult to come up with a viable solution. Anyone have some ideas?

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  • Inconsistency in java.util.concurrent.Future?

    - by loganj
    For the sake of argument, let's say I'm implementing Future for a task which is not cancelable. The Java 6 API doc says: After [cancel()] returns, subsequent calls to isDone() will always return true. [cancel()] returns false if the task could not be cancelled, typically because it has already completed normally It also says: [isDone()] returns true if this task completed. But what if my cancellation fails not because the task is already completed, but because it simply cannot be cancelled? Is there a way out of this contradiction (other than making my uncancelable task cancelable and sidestepping it altogether)?

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  • What is your favourite programming-related lolcat picture?

    - by DR
    In the spirit of these questions... http://stackoverflow.com/questions/234075/what-is-your-best-programmer-joke http://stackoverflow.com/questions/354686/programming-related-songs http://stackoverflow.com/questions/517897/anyone-know-any-programming-related-poetry ... I wonder: What is your favourite programming-related lolcat picture? Please add one answer per picture.

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  • Java: Making concurrent MySQL queries from multiple clients synchronised

    - by Misha Gale
    I work at a gaming cybercafe, and we've got a system here (smartlaunch) which keeps track of game licenses. I've written a program which interfaces with this system (actually, with it's backend MySQL database). The program is meant to be run on a client PC and (1) query the database to select an unused license from the pool available, then (2) mark this license as in use by the client PC. The problem is, I've got a concurrency bug. The program is meant to be launched simultaneously on multiple machines, and when this happens, some machines often try and acquire the same license. I think that this is because steps (1) and (2) are not synchronised, i.e. one program determines that license #5 is available and selects it, but before it can mark #5 as in use another copy of the program on another PC tries to grab that same license. I've tried to solve this problem by using transactions and table locking, but it doesn't seem to make any difference - Am I doing this right? Here follows the code in question: public LicenseKey Acquire() throws SmartLaunchException, SQLException { Connection conn = SmartLaunchDB.getConnection(); int PCID = SmartLaunchDB.getCurrentPCID(); conn.createStatement().execute("LOCK TABLE `licensekeys` WRITE"); String sql = "SELECT * FROM `licensekeys` WHERE `InUseByPC` = 0 AND LicenseSetupID = ? ORDER BY `ID` DESC LIMIT 1"; PreparedStatement statement = conn.prepareStatement(sql); statement.setInt(1, this.id); ResultSet results = statement.executeQuery(); if (results.next()) { int licenseID = results.getInt("ID"); sql = "UPDATE `licensekeys` SET `InUseByPC` = ? WHERE `ID` = ?"; statement = conn.prepareStatement(sql); statement.setInt(1, PCID); statement.setInt(2, licenseID); statement.executeUpdate(); statement.close(); conn.commit(); conn.createStatement().execute("UNLOCK TABLES"); return new LicenseKey(results.getInt("ID"), this, results.getString("LicenseKey"), results.getInt("LicenseKeyType")); } else { throw new SmartLaunchException("All licenses of type " + this.name + "are in use"); } }

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  • Is there a concurrent container library for C++

    - by Lirik
    I'm looking for implementations of lock-free containers: Blocking Queue Blocking Stack Hash Map etc... Are there any good libraries out there? I would like to refrain from writing these data structures... I would much rather use something that has been tested by the community.

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  • Java Download Concurrent Data

    - by xger86x
    Hi, i'm developing an app which download map tiles around different places in a city. To do this, i have one thread for each place in which i select the tiles and create a thread to download each. Well, the question is how to avoid creating a thread for a tile that already exists in the thread pool. Should not just check if the file exists, since it is possible that the thread for that tile already exists (other place already need that tile) but the file has not been created- Any idea? Thanks

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  • NoSQL for concurrent reads/writes

    - by Mickael Marrache
    After getting some performance issues for an application using a MySQL database, I'm thinking of using NoSQL solutions. My architecture is as follows: One application receives messages from the network at a high throughput (i.e. 50000 messages/sec). Each message is stored in the DB, so it's important for the write rate to be as fast as the arrival rate. Then, I also have some PHP pages that accesses the DB to get the data stored by the other application. It's important for me that the retrieved data is as relevant as possible (i.e. not old data, let's say not more than 5 seconds old). Also, the data is not critical, so I don't need any security mechanism to avoid losing the data. I see there are a lot of NoSQL solutions, but I don't know if they are all relevant. Could you please provide me some directions. Thanks

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  • My Rails session is getting reset when I have concurrent requests

    - by alex_c
    I think I might be misunderstanding something about Rails sessions, so please bear with me, I might not be phrasing my question the best way. I'm working on an iPhone app with a Ruby on Rails backend. I have a web view which by default goes to the index action of one controller (and uses sessions), and in the background a bunch of API calls going to a different controller (and which don't need to use sessions). The problem is, the sessions set by my web view seem to be overwitten by the API calls. My staging server is pretty slow, so there's lots of time for the requests to overlap each other - what I see in the logs is basically this: Request A (first controller) starts. Session is empty. Request B (second controller) starts. Session is empty. Request A finishes. Request A has done authentication, and stored the user ID in the session. Session contains user ID. Request B finishes. Session is empty. Request C starts. Session is empty - not what I want. Now, the strange thing is that request B should NOT be writing anything to the session. I do have before and after filters which READ from the session - things like: user = User.find_by_id(session[:id]) or logger.debug session.inspect and if I remove all of those, then everything works as expected - session contents get set by request A, and they're still there when request C starts. So. I think I'm missing something about how sessions work. Why would reading from the session overwrite it? Should I be accessing it some other way? Am I completely on the wrong track and the problem is elsewhere? Thank you for any insights!

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  • Embedded programming books

    - by Velho Kerho
    What embedded programming/design books would you suggest? With embedded I mean near to hardware programming in ASM and C/C++. I'm looking something related to best practices in embedded programming/design. Operation system could be Linux, Real Time Linux or any other RTOS.

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  • Concurrent usage of table causing issues

    - by Sven
    Hello In our current project we are interfacing with a third party data provider. They need to insert data in a table of ours. This inserting can be frequent every 1 min, every 5min, every 30, depends on the amount of new data they need to provide. The use the isolation level read committed. On our end we have an application, windows service, that calls a webservice every 2 minutes to see if there is new data in this table. Our isolation level is repeatable read. We retrieve the records and update a column on these rows. Now the problem is that sometimes this third party provider needs to insert a lot of data, let's say 5000 records. They do this per transaction (5rows per transaction), but they don't close the connection. They do one transaction and then the next untill all records are inserted. This caused issues for our process, we receive a timeout. If this goes on for a long time the database get's completely unstable. For instance, they maybe stopped, but the table somehow still stays unavailable. When I try to do a select on the table, I get several records but at a certain moment I don't get any response anymore. It just says retrieving data but nothing comes anymore until I get a timeout exception. Only solution is to restart the database and then I see the other records. How can we solve this. What is the ideal isolation level setting in this scenario?

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  • Is programming overrated?

    - by aengine
    [Subjective and intended to be a community wiki] I am sorry for such an offensive question: But here are my arguments Most of the progress in "computing" has came from non-programming sources. i.e. People invented faster microprocessors and better routers and novel memory devices. I dont think on average people are writting more efficient programs than those written 10 years ago. And the newer and popular languages are infact slower than C. though speed is one of the lesser criterias. Most of the progress came from novel paradigms. Web, Internet, Cloud computing and Social networking are novel paradigms and did not involve progress in programming as such. Heck even facebook was written in PHP and not some extreme language. Though it did face scalability issues (same with twitter) but i believe money and better programmers (who came in much later) took care of that. Thus ideating capability trumped programming capability/ Even things like Map-Reduce, Column oriented database and Probablistic algorithms (E.g. bloom filters) came from hardcore Algorithms research, rather than some programming convention. Thus my final point is why programming skill is so overstressed? To point a recent example about how only 10% of programmers can "write code" (binary search) without debugging. Isnt it a bit hypocritical, considering your real successs lies in coming up with better algorithm or a novel feature rather than getting right first time???

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