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• Programmatically open an email from a POP3 and extract an attachment

  - by Josh

  We have a vendor that sends CSV files as email attachments. These CSV files contain statuses that are imported into our application. I'm trying to automate the process end-to-end, but it currently depends on someone opening an email, saving the attachment to a server share, so the application can use the file. Since I cannot convince the vendor to change their process, such as offering an FTP location or a Web Service, I'm stuck with trying to automate the existing process. Does anyone know of a way to programmatically open an email from a POP3 account and extract an attachment? The preferred solution would reside on a Windows 2003 server, be written VB.NET and secure. The application can reside on the same server as the POP3 server, for example, we could setup the free POP3 server that comes with Windows Server and pull against the mail file stored on the file system. BTW, we are willing to pay for an off-the-shelf solution, if one exists. Note: I did look at this question but the answer points to a CodeProject solution that doesn't deal with attachments.

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• Web Start Application built on NetBeans Platform doesn't create desktop shortcut & start menu item

  - by rudolfv

  I've created a NetBeans Platform application that is launched using Java Web Start. I built the WAR file using the 'Build JNLP Application'-command in Netbeans. I've added a desktop shortcut and menu item to the JNLP file, but for some reason, these are not created when the application is launched. However, when I go to: Control Panel - Java - Temporary Internet Files - View - Select my application Click 'Install shortcuts to the selected application' the desktop and menu shortcuts are created correctly. Also, in the Java Console, the Shortcut Creation option is set to the following (the default, I presume): Prompt user if hinted Below is a snippet of my JNLP file: <jnlp spec="6.0+" codebase="$$codebase"> <information> <title>${app.title}</title> <vendor>SomeVendor (Pty) Ltd</vendor> <description>Some description</description> <icon href="${app.icon}"/> <shortcut online="true"> <desktop/> <menu submenu="MyApp"/> </shortcut> </information> ... I'm stumped. Does anybody have an explanation for this? Thanks PS This is on both Windows XP and Windows 7. NetBeans version: 6.8

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• How to wrap a thirdparty library COM class for notifications in a C++ project

  - by geocoin

  A thirdparty vendor has provided a COM interface as an external API to their product, and for sending instructions to it, it's fine with the mechanism of generating class wrappers with visual studio by importing from the dll, then creating instances of the created classes, calling their CreateDispatch(), using the access functions and releasing when done. For return notifications, I'd normally create an EventsListener class derived from IDispatch using the Invoke function to handle events returning from the interface. This vendor has created an Events lass which I have to wrap and expose, then explicitly tell the installation where to look. all the example are given is C# where it's really easy, but I'm struggling on how to do it in C++ in the C# example, the interop dll provided is simply added as a reference and derived into a class like so: using System; using System.Runtime.InteropServices; using System.Windows.Forms; using System.Text; using <THIER INTEROP LIB> namespace some.example.namespace { [ComVisible(true)] public class EventViewer : IEvents //where IEvents is their events class { public void OnEvent(EventID EventID, object pData) //overridden function { //event handled here } } } In broad terms I assume that I must create a COM interface, since they require a ProgID from me to instantiate, but how do I derive that's been wrapped by the import and then expose the created class to COM I'm just not sure where to even start, as all the tutorials I've seen so far talk in terms of creating brand new classes not wrapping a third party one

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• Deadlock in ThreadPoolExecutor

  - by Vitaly

  Encountered a situation when ThreadPoolExecutor is parked in execute(Runnable) function while all the ThreadPool threads are waiting in getTask func, workQueue is empty. Does anybody have any ideas? The ThreadPoolExecutor is created with ArrayBlockingQueue, corePoolSize == maximumPoolSize = 4 [Edit] To be more precise, the thread is blocked in ThreadPoolExecutor.exec(Runnable command) func. It has the task to execute, but doesn't do it. [Edit2] The executor is blocked somewhere inside the working queue (ArrayBlockingQueue). [Edit3] The callstack: thread = front_end(224) at sun.misc.Unsafe.park(Native methord) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:778) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1114) at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:186) at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:262) at java.util.concurrent.ArrayBlockingQueue.offer(ArrayBlockingQueue.java:224) at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:653) at net.listenThread.WorkersPool.execute(WorkersPool.java:45) at the same time the workQueue is empty (checked using remote debug) [Edit4] Code working with ThreadPoolExecutor: public WorkersPool(int size) { pool = new ThreadPoolExecutor(size, size, IDLE_WORKER_THREAD_TIMEOUT, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(WORK_QUEUE_CAPACITY), new ThreadFactory() { @NotNull private final AtomicInteger threadsCount = new AtomicInteger(0); @NotNull public Thread newThread(@NotNull Runnable r) { final Thread thread = new Thread(r); thread.setName("net_worker_" + threadsCount.incrementAndGet()); return thread; } }, new RejectedExecutionHandler() { public void rejectedExecution(@Nullable Runnable r, @Nullable ThreadPoolExecutor executor) { Verify.warning("new task " + r + " is discarded"); } }); } public void execute(@NotNull Runnable task) { pool.execute(task); } public void stopWorkers() throws WorkersTerminationFailedException { pool.shutdownNow(); try { pool.awaitTermination(THREAD_TERMINATION_WAIT_TIME, TimeUnit.SECONDS); } catch (InterruptedException e) { throw new WorkersTerminationFailedException("Workers-pool termination failed", e); } } }

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• WCF Callback Contract InvalidOperationException: Collection has been modified

  - by mrlane

  We are using a WCF service with a Callback contract. Communication is Asynchronous. The service contract is defined as: [ServiceContract(Namespace = "Silverlight", CallbackContract = typeof(ISessionClient),SessionMode = SessionMode.Allowed)] public interface ISessionService With a method: [OperationContract(IsOneWay = true)] void Send(Message message); The callback contract is defined as [ServiceContract] public interface ISessionClient With methods: [OperationContract(IsOneWay = true, AsyncPattern = true)] IAsyncResult BeginSend(Message message, AsyncCallback callback, object state); void EndSend(IAsyncResult result); The implementation of BeginSend and EndSend in the callback channel are as follows: public void Send(ActionMessage actionMessage) { Message message = Message.CreateMessage(_messageVersion, CommsSettings.SOAPActionReceive, actionMessage, _messageSerializer); lock (LO_backChannel) { try { _backChannel.BeginSend(message, OnSendComplete, null); } catch (Exception ex) { _hasFaulted = true; } } } private void OnSendComplete(IAsyncResult asyncResult) { lock (LO_backChannel) { try { _backChannel.EndSend(asyncResult); } catch (Exception ex) { _hasFaulted = true; } } } We are getting an InvalidOperationException: "Collection has been modified" on _backChannel.EndSend(asyncResult) seemingly randomly, and we are really out of ideas about what is causing this. I understand what the exception means, and that concurrency issues are a common cause of such exceptions (hence the locks), but it really doesn't make any sense to me in this situation. The clients of our service are Silverlight 3.0 clients using PollingDuplexHttpBinding which is the only binding available for Silverlight. We have been running fine for ages, but recently have been doing a lot of data binding, and this is when the issues started. Any help with this is appreciated as I am personally stumped at this time.

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• Boost::Mutex & Malloc

  - by M. Tibbits

  Hi all, I'm trying to use a faster memory allocator in C++. I can't use Hoard due to licensing / cost. I was using NEDMalloc in a single threaded setting and got excellent performance, but I'm wondering if I should switch to something else -- as I understand things, NEDMalloc is just a replacement for C-based malloc() & free(), not the C++-based new & delete operators (which I use extensively). The problem is that I now need to be thread-safe, so I'm trying to malloc an object which is reference counted (to prevent excess copying), but which also contains a mutex pointer. That way, if you're about to delete the last copy, you first need to lock the pointer, then free the object, and lastly unlock & free the mutex. However, using malloc to create a boost::mutex appears impossible because I can't initialize the private object as calling the constructor directly ist verboten. So I'm left with this odd situation, where I'm using new to allocate the lock and nedmalloc to allocate everything else. But when I allocate a large amount of memory, I run into allocation errors (which disappear when I switch to malloc instead of nedmalloc ~ but the performance is terrible). My guess is that this is due to fragmentation in the memory and an inability of nedmalloc and new to place nice side by side. There has to be a better solution. What would you suggest?

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• How can a program be detected as running?

  - by ryeguy

  I have written a program that is sort of an unofficial, standalone plugin for an application. It allows customers to get a service that is a lower priced alternative then the vendor-owned one. My program is not illegal, against any kind of TOS, and is certainly not a virus, adware, or anything like that. That being said, the vendor of course is not happy about me taking his competition, and is trying to block my application from running. He has already tried some tactics to stop people from running my app alongside his. He makes it so if it is detected, his app throws a fake error. First, he checked to see if my program was running by looking for an open window with the right title. I countered this by randomizing the program title at startup. Next, he looked for the running process name. I countered this by making the app copy itself when it is started as [random string].exe and then running that. Anyways, my question is this: what else can he do to detect if my program running? I know that you can read window text (ie status bar, labels). I'm prepared to counter this by replacing the labels with images (ugh, any other way?). But what else is there? Can you detect what .dlls a program has loaded? If so, could this be solved by randomizing the dll names before loading them? I know that it's possible to get a program's signature in memory and track it that way (like a virus scanner), but the chances of him doing that probably aren't good because that sounds pretty advanced. Even though this is kinda crappy of him to be doing, its kind of fun. It's like a nerdy fist fight. EDIT: When I said it's a plugin, that is just the (incorrect) term I used. It's a standalone EXE. The "API" between my program and the other is mine is simply entering data into the controls (like textboxes, etc).

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• Creating a desktop icon using JWS JNLP for a JavaFX app.

  - by Sleepycat

  I am trying to get a custom destop icon to be displayed for my app but for some reason no matter what I do the same default java icon shows up. I have tried everything I can think of and gone and compared my jnlp file with others whose icons seem to work ok. According to everything I have read the following should work fine. But of course, it doesn't: <information> <title>MikesApp</title> <vendor>Mike</vendor> <homepage href="http://www.mikesapp.com/"/> <description>Mikes App.</description> <icon kind="shortcut" href="res/icon64x64.png" width="64" height="64"/> <offline-allowed/> <shortcut> <desktop/> </shortcut> </information> Any ideas would be greatly appreciated.

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• JMX - MBean automated registration on application deployment

  - by Gadi

  Hi All, I need some direction with JMX and J2EE. I am aware (after few weeks of research) that the JMX specification is missing as far as deployment is concerned. There are few vendor specific implementations for what I am looking for but none are cross vendor. I would like to automate the deployment of MBeans and registration with the Server. I need the server to load and register my MBeand when the application is deployed and remove when the application is un-deployed. I develop with: NetBean 6.7.1, GlassFish 2.1, J2EE5, EJB3 More specific, I need a way to manage timer service runs. My application need to run different archiving agents and batch reporting. I was hoping the JMX will give me remote access to create and manage the timer services and enable the user to create his own schedule. If the JMX is auto registered on application deployment the user can immediately connect and manage the schedule. On the other hand, how can an EJB connect/access an MBean? Many thanks in advance. Gadi.

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• strange behavior in python

  - by fsm

  The tags might not be accurate since I am not sure where the problem is. I have a module where I am trying to read some data from a socket, and write the results into a file (append) It looks something like this, (only relevant parts included) if __name__ == "__main__": <some init code> for line in file: t = Thread(target=foo, args=(line,)) t.start() while nThreads > 0: time.sleep(1) Here are the other modules, def foo(text): global countLock, nThreads countLock.acquire() nThreads += 1 countLock.release() """connect to socket, send data, read response""" writeResults(text, result) countLock.acquire() nThreads -= 1 countLock.release() def writeResults(text, result): """acquire file lock""" """append to file""" """release file lock""" Now here's the problem. Initially, I had a typo in the function 'foo', where I was passing the variable 'line' to writeResults instead of 'text'. 'line' is not defined in the function foo, it's defined in the main block, so I should have seen an error, but instead, it worked fine, except that the data was appended to the file multiple times, instead of being written just once, which is the required behavior, which I got when I fixed the typo. My question is, 1) Why didn't I get an error? 2) Why was the writeResults function being called multiple times?

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• Update a PDF to include an encrypted, hidden, unique identifier?

  - by Dave Jarvis

  Background The idea is this: Person provides contact information for online book purchase Book, as a PDF, is marked with a unique hash Person downloads book PDF passwords are annoying and extremely easy to circumvent. The ideal process would be something like: Generate hash based on contact information Store contact information and hash in database Acquire book lock Update an "include" file with hash text Generate book as PDF (using pdflatex) Apply hash to book Release book lock Send email with book download link Technologies The following technologies can be used (other programming languages are possible, but libraries will likely be limited to those supplied by the host): C, Java, PHP LaTeX files PDF files Linux Question What programming techniques (or open source software) should I investigate to: Embed a unique hash (or other mark) to a PDF Create a collusion-attack resistant mark Develop a non-fragile (e.g., PDF -> EPS -> PDF still contains the mark) solution Research I have looked at the following possibilities: Steganography Natural Language Processing (NLP) Convert blank pages in PDF to images; mark those images; reassemble PDF LaTeX watermark package ImageMagick Steganograhy requires keeping a master copy of the images, and I'm not sure if the watermark would survive PDF -> EPS -> PDF, or other types of conversion. LaTeX creates an image cache, so any steganographic process would have to intercept that process somehow. NLP introduces grammatical errors. Inserting blank pages as images is immediately suspect; it is easy to replace suspicious blank pages. The LaTeX watermark package draws visible marks. ImageMagick draws visible marks. What other solutions are possible? Related Links http://www.tcpdf.org/ invisible watermarks in images Thank you!

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• What is the fastest collection in c# to implement a prioritizing queue?

  - by Nathan Smith

  I need to implement a queue for messages on a game server so it needs to as fast as possible. The queue will have a maxiumem size. I need to prioritize messages once the queue is full by working backwards and removing a lower priority message (if one exists) before adding the new message. The appliation is asynchronous so access to the queue needs to be locked. I'm currently implementing it using a LinkedList as the underlying storage but have concerns that searching and removing nodes will keep it locked for too long. Heres the basic code I have at the moment: public class ActionQueue { private LinkedList<ClientAction> _actions = new LinkedList<ClientAction>(); private int _maxSize; /// <summary> /// Initializes a new instance of the ActionQueue class. /// </summary> public ActionQueue(int maxSize) { _maxSize = maxSize; } public int Count { get { return _actions.Count; } } public void Enqueue(ClientAction action) { lock (_actions) { if (Count < _maxSize) _actions.AddLast(action); else { LinkedListNode<ClientAction> node = _actions.Last; while (node != null) { if (node.Value.Priority < action.Priority) { _actions.Remove(node); _actions.AddLast(action); break; } } } } } public ClientAction Dequeue() { ClientAction action = null; lock (_actions) { action = _actions.First.Value; _actions.RemoveFirst(); } return action; } }

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• Delphi: Alternative to using Reset/ReadLn for text file reading

  - by Ian Boyd

  i want to process a text file line by line. In the olden days i loaded the file into a StringList: slFile := TStringList.Create(); slFile.LoadFromFile(filename); for i := 0 to slFile.Count-1 do begin oneLine := slFile.Strings[i]; //process the line end; Problem with that is once the file gets to be a few hundred megabytes, i have to allocate a huge chunk of memory; when really i only need enough memory to hold one line at a time. (Plus, you can't really indicate progress when you the system is locked up loading the file in step 1). The i tried using the native, and recommended, file I/O routines provided by Delphi: var f: TextFile; begin Reset(f, filename); while ReadLn(f, oneLine) do begin //process the line end; Problem withAssign is that there is no option to read the file without locking (i.e. fmShareDenyNone). The former stringlist example doesn't support no-lock either, unless you change it to LoadFromStream: slFile := TStringList.Create; stream := TFileStream.Create(filename, fmOpenRead or fmShareDenyNone); slFile.LoadFromStream(stream); stream.Free; for i := 0 to slFile.Count-1 do begin oneLine := slFile.Strings[i]; //process the line end; So now even though i've gained no locks being held, i'm back to loading the entire file into memory. Is there some alternative to Assign/ReadLn, where i can read a file line-by-line, without taking a sharing lock? i'd rather not get directly into Win32 CreateFile/ReadFile, and having to deal with allocating buffers and detecting CR, LF, CRLF's. i thought about memory mapped files, but there's the difficulty if the entire file doesn't fit (map) into virtual memory, and having to maps views (pieces) of the file at a time. Starts to get ugly. i just want Reset with fmShareDenyNone!

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• Assigning a RecID field to Gridview TemplateField (Checbox column)

  - by user279521

  I want to assign a RecID to the checkbox column "cbPOID". The RecID field that is being returned in my dataset, but should not be displayed in the gridview. <asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="False" CellPadding="4" GridLines="None" Width="100%" AllowPaging="True" PageSize="20" onpageindexchanging="gvOrders_PageIndexChanging" ForeColor="#333333"> <Columns> <asp:TemplateField HeaderText="VerifiedComplete" > <ItemTemplate> <asp:CheckBox ID="cbPOID" runat="server"/> </ItemTemplate> </asp:TemplateField> <asp:BoundField DataField="PurchaseOrderID" HeaderText="PurchaseOrderID" HtmlEncode="False" ></asp:BoundField> <asp:BoundField DataField="VENDOR_ID" HeaderText="Vendor ID"></asp:BoundField> <asp:BoundField DataField="VENDOR_NAME" HeaderText="Vendor Name"></asp:BoundField> <asp:BoundField DataField="ITEM_DESC" HeaderText="Item Desc"></asp:BoundField> <asp:BoundField DataField="SYS_DATE" HeaderText="System Date"></asp:BoundField> </Columns> <FooterStyle CssClass="GridFooter" BackColor="#990000" Font-Bold="True" ForeColor="White" /> <PagerStyle CssClass="GridPager" ForeColor="#333333" BackColor="#FFCC66" HorizontalAlign="Center" /> <SelectedRowStyle BackColor="#FFCC66" Font-Bold="True" ForeColor="Navy" /> <HeaderStyle CssClass="GridHeader" BackColor="#990000" Font-Bold="True" ForeColor="White" /> <RowStyle CssClass="GridItem" BackColor="#FFFBD6" ForeColor="#333333" /> <AlternatingRowStyle CssClass="GridAltItem" BackColor="White" /> </asp:GridView>

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• How should I handle this Optimistic Concurrency error in this Entity Framework code, I have?

  - by Pure.Krome

  Hi folks, I have the following pseduo code in some Repository Pattern project that uses EF4. public void Delete(int someId) { // 1. Load the entity for that Id. If there is none, then null. // 2. If entity != null, then DeleteObject(..); } Pretty simple but I'm getting a run-time error:- ConcurrencyException: Store, Update, Insert or Delete statement affected an unexpected number of rows (0). Now, this is what is happening :- Two instances of EF4 are running inthe app at the same time. Instance A calls delete. Instance B calls delete a nano second later. Instance A loads the entity. Instance B also loads the entity. Instance A now deletes that entity - cool bananas. Instance B tries to delete the entity, but it's already gone. As such, the no-count or what not is 0, when it expected 1 .. or something like that. Basically, it figured out that the item it is suppose to delete, didn't delete (because it happened a split sec ago). I'm not sure if this is like a race-condition or something. Anyways, is there any tricks I can do here so the 2nd call doesn't crash? I could make it into a stored procedure.. but I'm hoping to avoid that right now. Any ideas? I'm wondering If it's possible to lock that row (and that row only) when the select is called ... forcing Instance B to wait until the row lock has been relased. By that time, the row is deleted, so when Instance B does it's select, the data is not there .. so it will never delete.

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• E-Commerce Security: Only Credit Card Fields Encrypted?!

  - by bizarreunprofessionalanddangerous

  I'd like your opinions on how a major bricks-and-mortar company is running the security for its shopping Web site. After a recent update, when you are logged into your shopping account, the session is now not secured. No 'https', no browser 'lock'. All the personal contact info, shopping history -- and if I'm not mistaken submit and change password -- are being sent unencrypted. There is a small frame around the credit card fields that is https. There's a little notice: "Our website is secure. Our website uses frames and because of this the secure icon will not appear in your browser" On top of this the most prominent login fields for the site are broken, and haven't gotten fixed for a week or longer (giving the distinct impression they have no clue what's going on and can't be trusted with anything). Now is it just me -- or is this simply incomprehensible for a billion dollar company, significant shopping site, in the year 2010. No lock. "We use frames" (maybe they forget "Best viewed in IE4"). Customers complaining, as you can see from their FAQ "explaining" why you aren't seeing https. I'm getting nowhere trying to convince customer service that they REALLY need to do something about this, and am about to head for the CEO. But I just want to make sure this is as BIZARRE and unprofessional and dangerous a situation as I think it is. (I'm trying to visualize what their Web technical team consists of. I'm getting A) some customer service reps who were given a 3 hour training course on Web site maintenance, B) a 14 year old boy in his bedroom masquerading as a major technical services company, C) a guy in a hut in a jungle with an e-commerce book from 1996.)

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• DB2 Driver Connection Hanging in Glassfish Connection Pool

  - by Ant

  We have an intermittent issue around the DB2 used from a Glassfish connection pool. What happens is this: Under situations where the database (DB2 on ZOS) is under stress, our application (which is a multi-threaded application using connections to DB2 via a Glassfish connection pool) stops doing anything. The following are observed: 1) Looking at the server using JConsole, we can see a thread waiting indefinitely in the DB2 driver's getConnection() method. We can also see that it has gained a lock on a Vector within the driver. Several other threads are also calling the getConnection() method in the driver, and are hanging waiting for the lock on the Vector to be released. 2) Looking at the database itself, we can see that there are connections from the Glassfish server open and waiting to be used. It seems that there is some sort of mismatch between the connection pool on Glassfish and the connections actually open to DB2. Has anyone come across this issue before? Or something similar? If you need any more information that I haven't provided, then please let me know!

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• Heroku: bash: bundle: command not found

  - by Space Monkey

  My heroku deployment is crashing with following errors. 2012-12-12T17:16:18+00:00 app[web.1]: bash: bundle: command not found 2012-12-12T17:16:19+00:00 heroku[web.1]: Process exited with status 127 2012-12-12T17:16:19+00:00 heroku[web.1]: State changed from starting to crashed The Heroku documentation for this error is to set PATH and GEM variables as described in https://devcenter.heroku.com/articles/changing-ruby-version-breaks-path I tried that, however that too is not helping. ? heroku config:add PATH=bin:vendor/bundle/ruby/1.9.1/bin:/usr/local/bin:/usr/bin:/bin ? heroku config:add GEM_PATH=vendor/bundle/ruby/1.9.1 ? heroku run rake db:migrate Running rake db:migrate attached to terminal... up, run.7130 bash: bundle: command not found Next, I tried setting Ruby version in my Heroku app. This increased the slugsize. But app was still not up. Gemfile ruby "1.9.2" Pushed to Heroku -----> Using Ruby version: ruby-1.9.2 -----> Installing dependencies using Bundler version 1.2.2 heroku run "ruby -v" Running `ruby -v` attached to terminal... up, run.4483 ruby 1.9.2p320 (2012-04-20 revision 35421) [x86_64-linux] Can someone please advice

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• General SQL Server query performance

  - by Kiril

  Hey guys, This might be stupid, but databases are not my thing :) Imagine the following scenario. A user can create a post and other users can reply to his post, thus forming a thread. Everything goes in a single table called Posts. All the posts that form a thread are connected with each other through a generated key called ThreadID. This means that when user #1 creates a new post, a ThreadID is generated, and every reply that follows has a ThreadID pointing to the initial post (created by user #1). What I am trying to do is limit the number of replies to let's say 20 per thread. I'm wondering which of the approaches bellow is faster: 1 I add a new integer column (e.x. Counter) to Posts. After a user replies to the initial post, I update the initial post's Counter field. If it reaches 20 I lock the thread. 2 After a user replies to the initial post, I select all the posts that have the same ThreadID. If this collection has more than 20 items, I lock the thread. For further information: I am using SQL Server database and Linq-to-SQL entity model. I'd be glad if you tell me your opinions on the two approaches or share another, faster approach. Best Regards, Kiril

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• Long running transactions with Spring and Hibernate?

  - by jimbokun

  The underlying problem I want to solve is running a task that generates several temporary tables in MySQL, which need to stay around long enough to fetch results from Java after they are created. Because of the size of the data involved, the task must be completed in batches. Each batch is a call to a stored procedure called through JDBC. The entire process can take half an hour or more for a large data set. To ensure access to the temporary tables, I run the entire task, start to finish, in a single Spring transaction with a TransactionCallbackWithoutResult. Otherwise, I could get a different connection that does not have access to the temporary tables (this would happen occasionally before I wrapped everything in a transaction). This worked fine in my development environment. However, in production I got the following exception: java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction This happened when a different task tried to access some of the same tables during the execution of my long running transaction. What confuses me is that the long running transaction only inserts or updates into temporary tables. All access to non-temporary tables are selects only. From what documentation I can find, the default Spring transaction isolation level should not cause MySQL to block in this case. So my first question, is this the right approach? Can I ensure that I repeatedly get the same connection through a Hibernate template without a long running transaction? If the long running transaction approach is the correct one, what should I check in terms of isolation levels? Is my understanding correct that the default isolation level in Spring/MySQL transactions should not lock tables that are only accessed through selects? What can I do to debug which tables are causing the conflict, and prevent those tables from being locked by the transaction?

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• Synchronizing Access to a member of the ASP.NET session

  - by Sam

  I'm building a Javascript application and eash user has an individual UserSession. The application makes a bunch of Ajax calls. Each Ajax call needs access to a single UserSession object for the user. Each Ajax call needs a UserSession object. Data in the UserSession object is unique to each user. Originally, during each Ajax call I would create a new UserSession object and it's data members were stored in the ASP.NET Session. However, I found that the UserSession object was being instantiated a lot. To minimize the construction of the UserSession object, I wrapped it in a Singleton pattern and sychronized access to it. I believe that the synchronization is happening application wide, however I only need it to happen per user. I saw a post here that says the ASP.NET cache is synchronized, however the time between creating the object and inserting it into the cache another Thread could start construction it's another object and insert it into the cache. Here is the way I'm currently synchronizing access to the object. Is there a better way than using "lock"... should be be locking on the HttpContext.Session object? private static object SessionLock = new object(); public static WebSession GetSession { get { lock (SessionLock) { try { var context = HttpContext.Current; WebSession result = null; if (context.Session["MySession"] == null) { result = new WebSession(context); context.Session["MySession"] = result; } else { result = (WebSession)context.Session["MySession"]; } return result; } catch (Exception ex) { ex.Handle(); return null; } } } }

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Does complex JOINs causes high coupling and maintenance problems ?

  - by ashkan.kh.nazary

  Our project has ~40 tables with complex relations.A colleague believes in using long join queries which enforces me to learn about tables outside of my module but I think I should not concern about tables not directly related to my module and use data access functions (written by those responsible for other modules) when I need data from them. Let me clarify: I am responsible for the ContactVendor module which enables the customers to contact the vendor and start a conversation about some specific product. Products module has it's own complex tables and relations with functions that encapsulate details (for example i18n, activation, product availability etc ...). Now I need to show the product title of some product related to some conversation between the vendor and customers. I may either write a long query that retrieves the product info along with conversation stuff in one shot (which enforces me to learn about Product tables) OR I may pass the relevant product_id to the get_product_info(int) function. First approach is obviously demanding and introduces many bad practices and things I normally consider fault in programming. The problem with the second approach seems to be the countless mini queries these access functions cause and performance loss is a concern when a loop tries to fetch product titles for 100 products using functions that each perform a separate query. So I'm stuck between "don't code to the implementation, code to interface" and performance. What is the right way of doing things ? UPDATE: I'm specially concerned about possible future modifications to those tables outside of my module. What if the Products module decided to change the way they are doing things? or for some reason modify the schema? It means some other modules would break or malfunction until the change is integrated to them. The usual ripple effect problem.

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• Do complex JOINs cause high coupling and maintenance problems ?

  - by ashkan.kh.nazary

  Our project has ~40 tables with complex relations.A colleague believes in using long join queries which enforces me to learn about tables outside of my module but I think I should not concern about tables not directly related to my module and use data access functions (written by those responsible for other modules) when I need data from them. Let me clarify: I am responsible for the ContactVendor module which enables the customers to contact the vendor and start a conversation about some specific product. Products module has it's own complex tables and relations with functions that encapsulate details (for example i18n, activation, product availability etc ...). Now I need to show the product title of some product related to some conversation between the vendor and customers. I may either write a long query that retrieves the product info along with conversation stuff in one shot (which enforces me to learn about Product tables) OR I may pass the relevant product_id to the get_product_info(int) function. First approach is obviously demanding and introduces many bad practices and things I normally consider fault in programming. The problem with the second approach seems to be the countless mini queries these access functions cause and performance loss is a concern when a loop tries to fetch product titles for 100 products using functions that each perform a separate query. So I'm stuck between "don't code to the implementation, code to interface" and performance. What is the right way of doing things ? UPDATE: I'm specially concerned about possible future modifications to those tables outside of my module. What if the Products module decided to change the way they are doing things? or for some reason modify the schema? It means some other modules would break or malfunction until the change is integrated to them. The usual ripple effect problem.

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• Thread-safe data structure design

  - by Inso Reiges

  Hello, I have to design a data structure that is to be used in a multi-threaded environment. The basic API is simple: insert element, remove element, retrieve element, check that element exists. The structure's implementation uses implicit locking to guarantee the atomicity of a single API call. After i implemented this it became apparent, that what i really need is atomicity across several API calls. For example if a caller needs to check the existence of an element before trying to insert it he can't do that atomically even if each single API call is atomic: if(!data_structure.exists(element)) { data_structure.insert(element); } The example is somewhat awkward, but the basic point is that we can't trust the result of "exists" call anymore after we return from atomic context (the generated assembly clearly shows a minor chance of context switch between the two calls). What i currently have in mind to solve this is exposing the lock through the data structure's public API. This way clients will have to explicitly lock things, but at least they won't have to create their own locks. Is there a better commonly-known solution to these kinds of problems? And as long as we're at it, can you advise some good literature on thread-safe design? EDIT: I have a better example. Suppose that element retrieval returns either a reference or a pointer to the stored element and not it's copy. How can a caller be protected to safely use this pointer\reference after the call returns? If you think that not returning copies is a problem, then think about deep copies, i.e. objects that should also copy another objects they point to internally. Thank you.

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