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• java distributed cache for low latency, high availability

  - by Shahbaz

  I've never used distributed caches/DHTs like memcached, jboss cache, ehcache, etc. I'm wondering which, if any, is appropriate for my use. First, I'm not doing web applications (as most of these project seem to be geared towards web apps). I write servers (Order Management Systems actually) for financial trading firms. The servers themselves are not too complicated. They need to receive information (market data, orders, executions, etc.) rout them to their destination while possibly transforming some of these messages. I am looking at these products to solve the following problems: * Safe repository of the state of the server. I'd rather build the logic of my application as a bunch of transformers (similar to Apache Camel) and store the state in a 'safe' place * This repository should be distributed: in case one of these data stores crashes, one or two more should be up and I should be able to switch to them seamlessly * This repository should be fast. Single digits milliseconds count here, in other words, systems which consume/process this data are automated systems, not humans clicking on links. This system needs to have high-throughput and low latency. By sending my data outside the process, I am necessarily slowing performance, but I am trying to balance absolute raw speed and absolute protection of data. * This repository should be safe. Similar to the point about several on-line backups, this system needs to write data to disk (potentially more than one disk). I'd really like to stop writing my own 'transaction servers.' Am I correct to be looking into projects such as jboss cache, ehcache, etc.? Thanks

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• Can't write the SysWow64 value to registry with vbscript for Screensaver

  - by Valentein

  Scripts, registries, screen-savers, oh my! I'm trying to use a screen-saver on a Windows XP 64 bit machine which uses a .NET app which makes an interop call which relies on some x86 Shockwave Dlls (some Shockwave animation). Everything should be in the %systemroot%\WINNT\SysWOW64 directory. When the timeout for the screensaver occurs, the process should looks like this: Screensaver.scr - .NET app - shockwave animation. During installation I want a vbscript to my screen-saver file to copy the Screensaver.scr to the SysWow64 directory and then set the proper registry key to this file for Windows to launch the screen-saver. The code is something like this: Dim sScreenSaver, tScreenSaver sScreenSaver = "C:\SourceFiles\bin\ScreenSaver.scr" 'screensaver tScreenSaver = "C:\winnt\SysWOW64\" Set WshShell = WScript.CreateObject("WScript.Shell") 'script shell to run objects Set FSO = createobject("scripting.filesystemobject") 'file system object 'copy screensaver FSO.CopyFile sScreenSaver, tScreenSaver, True 'set screen saver Dim p1 p1 = "HKEY_CURRENT_USER\Control Panel\Desktop\" WshShell.RegWrite p1 & "SCRNSAVE.EXE", (tScreenSaver & "ScreenSaver.scr") After installation, I can verify the the Screensaver exists in the correct directory. (It actually seems to be in both the system32 and the sysWOW64 directories---whether that's the install script or something I did post-install I'm in the process of verifying.) However, the registry entry is not correct. In both the 32 and 64 bit regedit I see the HKCU\ControlPanel\Desktop\SCRNSAVE.EX is set to: C:\WINNT\system32\Screensaver.scr This isn't right. The screen-saver won't run from this directory. It only runs from SysWOW64. If I manually edit the registry with regedit to the correct SysWOW64 path everything works fine. Is this a problem with using the script or is this a Windows registry redirection, or filesystem redirection problem? You'd think this would be simple...

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• Can't debug Java Windows Services with jhat, jps, jstack

  - by Matthew McCullough

  I frequently showcase the jhat, jps, and jstack tool set to developers on Linux and Mac. However, a developer recently indicated that these are unusable in Windows if the Java app in question is running as a Windows Service. A Sun-filed bug says something very similar, but was closed due to inactivity. I have tested this out for myself, and indeed it appears true, though I can hardly believe it. Here is the setup: Tomcat or similar running as a Windows service with the "Log On As" == "Local System" A user with Admin privileges logged in to the same Windows machine. Admin opens Windows Task Manager, can see java.exe running Admin opens console, types "jps", gets back a list of processes that does not include Tomcat's java service process. As a brute force attempt, get the PID of tomcat as a service from Windows Task Manager. Type jstack < pid . Get a reply: < pid no such process This appears reproducible under Windows XP, Windows 2003 Server, and Windows 7. Java versions 1.5 and 1.6 yield the same outcome. Is there a way from the terminal, even though logged in as Admin, to "sudo up" to get JPS and the other tools to see the java service?

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• How to display NotifyIcon and SSDP Service running during AutoLogon

  - by Paul Farry

  I've got an application (that is targetting .Net Framework 2.0) that is running on startup of the System, and I'm trying to get a NotifyIcon to display. When my program starts up when a user either Runs it normally or is started as a child process after the system has already logged on everything is fine. If my application starts up as the system is performing an AutoLogon using POSReady2009 (basically XP with Single User set). Then the NotifyIcon never becomes active. If you subsequently check (in a timer) the .Visible of the Icon at any point later it always reports that it is visible = true. If you disable the SSDPSrv and restart the Computer, the Icon displays correctly. I have a sneaking suspicion this is related to .Net 3.5sp1 installed over the top of a .Net 2 system. Is there some process that I should be following to ensure that my NotifyIcon is always available to the user. I have setup RegisterWindowMessage("TaskbarCreated") but I don't get this message called, except when you forcilbly Kill Explorer.exe and restart it. Even so, a NotifyIcon interally registers for these notifications anyway, so it shouldn't be required. I'm happy to stall the startup of my program, but once the program starts up, I expect that the icon shows correctly. If there is a KB article that I cannot find detailing this I'd be happy with that too.

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• How can I make a server log file available via my ASP.NET MVC website?

  - by Gary McGill

  I have an ASP.NET MVC website that works in tandem with a Windows Service that processes file uploads. For easy maintenance of the site, I'd like the log file for the Windows Service to be accessible (to me, only) via the website, so that I can hit http://myserver/logs/myservice to view the contents of the log file. How can I do that? At a guess, I could either have the service write its log file in a "Logs" folder at the top level of the site, or I could leave it where it is and set up a virtual directory to point to it. Which of these is better - or is there another, better way? Wherever the file is stored, I can see that there's going to be another problem. I tried out the first option (Logs folder in my website), but when I try to access the file via HTTP I get an error: The process cannot access the file 'foo' because it is being used by another process. Now, I know from experience that my service keeps the file locked for writing while it's running, but that I can still open the file in Notepad to view the current contents. (I'm surprised that IIS insists on write access, if that's what's happening). How can I get around that? Do I really have to write a handler to read the file and serve it to the browser myself? Or can I fix this with configuration or somesuch? PS. I'm using IIS7 if that helps.

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• Some general C questions.

  - by b-gen-jack-o-neill

  Hello. I am trying to fully understand the process pro writing code in some language to execution by OS. In my case, the language would be C and the OS would be Windows. So far, I read many different articles, but I am not sure, whether I understand the process right, and I would like to ask you if you know some good articles on some subjects I couldn´t find. So, what I think I know about C (and basically other languages): C compiler itself handles only data types, basic math operations, pointers operations, and work with functions. By work with functions I mean how to pass argument to it, and how to get output from function. During compilation, function call is replaced by passing arguments to stack, and than if function is not inline, its call is replaced by some symbol for linker. Linker than find the function definition, and replace the symbol to jump adress to that function (and of course than jump back to program). If the above is generally true and I get it right, where to final .exe file actually linker saves the functions? After the main() function? And what creates the .exe header? Compiler or Linker? Now, additional capabilities of C, today known as C standart library is set of functions and the declarations of them, that other programmers wrote to extend and simplify use of C language. But these functions like printf() were (or could be?) written in different language, or assembler. And there comes my next question, can be, for example printf() function be written in pure C without use of assembler? I know this is quite big question, but I just mostly want to know, wheather I am right or not. And trust me, I read a lots of articles on the web, and I would not ask you, If I could find these infromation together on one place, in one article. Insted I must piece by piece gather informations, so I am not sure if I am right. Thanks.

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• SqlBulkCopy causes Deadlock on SQL Server 2000.

  - by megatoast

  I have a customized data import executable in .NET 3.5 which the SqlBulkCopy to basically do faster inserts on large amounts of data. The app basically takes an input file, massages the data and bulk uploads it into a SQL Server 2000. It was written by a consultant who was building it with a SQL 2008 database environment. Would that env difference be causing this? SQL 2000 does have the bcp utility which is what BulkCopy is based on. So, When we ran this, it triggered a Deadlock error. Error details: Transaction (Process ID 58) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction. I've tried numerous ways to try to resolve it. like temporarily setting the connection string variable MultipleActiveResultSets=true, which wasn't ideal, but it still gives a Deadlock error. I also made sure it wasn't a connection time out problem. here's the function. Any advice? /// <summary> /// Bulks the insert. /// </summary> public void BulkInsert(string destinationTableName, DataTable dataTable) { SqlBulkCopy bulkCopy; if (this.Transaction != null) { bulkCopy = new SqlBulkCopy ( this.Connection, SqlBulkCopyOptions.TableLock, this.Transaction ); } else { bulkCopy = new SqlBulkCopy ( this.Connection.ConnectionString, SqlBulkCopyOptions.TableLock | SqlBulkCopyOptions.UseInternalTransaction ); } bulkCopy.ColumnMappings.Add("FeeScheduleID", "FeeScheduleID"); bulkCopy.ColumnMappings.Add("ProcedureID", "ProcedureID"); bulkCopy.ColumnMappings.Add("AltCode", "AltCode"); bulkCopy.ColumnMappings.Add("AltDescription", "AltDescription"); bulkCopy.ColumnMappings.Add("Fee", "Fee"); bulkCopy.ColumnMappings.Add("Discount", "Discount"); bulkCopy.ColumnMappings.Add("Comment", "Comment"); bulkCopy.ColumnMappings.Add("Description", "Description"); bulkCopy.BatchSize = dataTable.Rows.Count; bulkCopy.DestinationTableName = destinationTableName; bulkCopy.WriteToServer(dataTable); bulkCopy = null; }

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• Custom Database integration with MOSS 2007

  - by Bob

  Hopefully someone has been down this road before and can offer some sound advice as far as which direction I should take. I am currently involved in a project in which we will be utilizing a custom database to store data extracted from excel files based on pre-established templates (to maintain consistency). We currently have a process (written in C#.Net 2008) that can extract the necessary data from the spreadsheets and import it into our custom database. What I am primarily interested in is figuring out the best method for integrating that process with our portal. What I would like to do is let SharePoint keep track of the metadata about the spreadsheet itself and let the custom database keep track of the data contained within the spreadsheet. So, one thing I need is a way to link spreadsheets from SharePoint to the custom database and vice versa. As these spreadsheets will be updated periodically, I need tried and true way of ensuring that the data remains synchronized between SharePoint and the custom database. I am also interested in finding out how to use the data from the custom database to create reports within the SharePoint portal. Any and all information will be greatly appreciated.

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• Locking a table for getting MAX in LINQ

  - by Hossein Margani

  Hi Every one! I have a query in LINQ, I want to get MAX of Code of my table and increase it and insert new record with new Code. just like the IDENTITY feature of SQL Server, but here my Code column is char(5) where can be alphabets and numeric. My problem is when inserting a new row, two concurrent processes get max and insert an equal Code to the record. my command is: var maxCode = db.Customers.Select(c=>c.Code).Max(); var anotherCustomer = db.Customers.Where(...).SingleOrDefault(); anotherCustomer.Code = GenerateNextCode(maxCode); db.SubmitChanges(); I ran this command cross 1000 threads and each updating 200 customers, and used a Transaction with IsolationLevel.Serializable, after two or three execution an error occured: using (var db = new DBModelDataContext()) { DbTransaction tran = null; try { db.Connection.Open(); tran = db.Connection.BeginTransaction(IsolationLevel.Serializable); db.Transaction = tran; . . . . tran.Commit(); } catch { tran.Rollback(); } finally { db.Connection.Close(); } } error: Transaction (Process ID 60) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction. other IsolationLevels generates this error: Row not found or changed. Please help me, thank you.

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• What is the relationship between Turing Machine & Modern Computer ? [closed]

  - by smwikipedia

  I heard a lot that modern computers are based on Turing machine. I just cannot build a bridge between a conceptual Turing Machine and a modern computer. Could someone help me build this bridge? Below is my current understanding. I think the computer is a big general-purpose Turing machine. Each program we write is a small specific-purpose Turing machine. The classical Turing machine do its job based on the input and its current state inside and so do our programs. Let's take a running program (a process) as an example. We know that in the process's address space, there's areas for stack, heap, and code. A classical Turing machine doesn't have the ability to remember many things, so we borrow the concept of stack from the push-down automaton. The heap and stack areas contains the state of our specific-purpose Turing machine (our program). The code area represents the logic of this small Turing machine. And various I/O devices supply input to this Turing machine.

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• when long polling, Why are my other requests taking so long?

  - by Pascal

  The client makes 2 concurrent requests. (1 which takes 60 seconds - long polling) and another which is NOT long polling - supposed to return right away. It does return right away when I'm not doing long polling. But as soon as I start doing long polling with the other thread, the other one takes forever to execute. Firebug shows that the request is waiting for 10-50 seconds. On the server, I profiled ALL requests from the moment the php script starts to the time it goes back to the client, and it shows that each one only took 300ms or less. This problem started about the same time I started doing long polling (with the other XHR requests). I'm using jquery for both requests. The server shows that it is under very light load. CPU and memory less then 2%. 8 processes running out of a pool of 15. (it doesn't seem to deviate much from that number 8, even when I run more ajax requests). I guess each process can run multiple ajax threads concurrently. I made sure to EXIT from all processes as soon as their done executing. I don't see how the process pool has run out, if there are still 7 unused processes listed under prstat -J. Also, the problem happens somewhat intermittently. Firefox should be able to handle 2 concurrent ajax requests. i dont get what the problem is.

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• Can I use RegFree Com with an application written in Excel VBA?

  - by Steven

  I have an application that is written in Excel VBA, myApp.xls. Currently we use InstallShield to distribute the application. Since we are moving to Windows Vista, I need to be able to install the application as a standard user. This does not allow for me to update the registry during the install process. In addition to the excel application we also have several VB6 applications. In order to install those applications, I was able to use RegFree com and Make My Manifest (MMM) as suggested by people on this forum (I greatly appreciate the insight btw!). This process, although a bit tedious, worked well. I then packaged the output from MMM in a VS '05 installer project and removed the UAC prompt on the msi using msiinfo.exe. Now I am faced with installing an application that basically lives in an Excel file. I modified a manifest that MMM created for me for one of my VB6 apps and tried to run the excel file through that, but I did not have much luck. Does anybody know of a way to do this? Does RegFree com work with VBA? Any thoughts or suggestions would be much appreciated. Thanks, Steve

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• Running custom JAXB2 plugins using Maven JAXB 2.x Plugin

  - by nadouani

  I would like to generate JAXB Java classes using the Maven JAXB 2.x plugin http://static.highsource.org/mjiip/maven-jaxb2-plugin/generate-mojo.html To declare the custom JAXB plugins I would execute during the generate process, I used the "args" element like below: <plugin> <groupId>org.jvnet.jaxb2.maven2</groupId> <artifactId>maven-jaxb2-plugin</artifactId> <version>0.7.4</version> <executions> <execution> <goals> <goal>generate</goal> </goals> </execution> </executions> <configuration> <extension>true</extension> <args> <arg>-Xinheritance</arg> <arg>-XtoString</arg> </args> ... </configuration> ... </plugin> The issue is that the maven generate process is failing with the following error: Failed to execute goal org.jvnet.jaxb2.maven2:maven-jaxb2-plugin:0.7.4:generate (default) on project was: Error parsing the command line [[Ljava.lang.String;@1ad4a1ae] Any idea on how to specify the args values? Thanks

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• There's a black hole in my server (TcpClient, TcpListener)

  - by Matías

  Hi, I'm trying to build a server that will receive files sent by clients over a network. If the client decides to send one file at a time, there's no problem, I get the file as I expected, but if it tries to send more than one I only get the first one. Here's the server code: I'm using one Thread per connected client public void ProcessClients() { while (IsListening) { ClientHandler clientHandler = new ClientHandler(listener.AcceptTcpClient()); Thread thread = new Thread(new ThreadStart(clientHandler.Process)); thread.Start(); } } The following code is part of ClientHandler class public void Process() { while (client.Connected) { using (MemoryStream memStream = new MemoryStream()) { int read; while ((read = client.GetStream().Read(buffer, 0, buffer.Length)) > 0) { memStream.Write(buffer, 0, read); } if (memStream.Length > 0) { Packet receivedPacket = (Packet)Tools.Deserialize(memStream.ToArray()); File.WriteAllBytes(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.DesktopDirectory), Guid.NewGuid() + receivedPacket.Filename), receivedPacket.Content); } } } } On the first iteration I get the first file sent, but after it I don't get anything. I've tried using a Thread.Sleep(1000) at the end of every iteration without any luck. On the other side I have this code (for clients) . . client.Connect(); foreach (var oneFilename in fileList) client.Upload(oneFilename); client.Disconnect(); . . The method Upload: public void Upload(string filename) { FileInfo fileInfo = new FileInfo(filename); Packet packet = new Packet() { Filename = fileInfo.Name, Content = File.ReadAllBytes(filename) }; byte[] serializedPacket = Tools.Serialize(packet); netStream.Write(serializedPacket, 0, serializedPacket.Length); netStream.Flush(); } netStream (NetworkStream) is opened on Connect method, and closed on Disconnect. Where's the black hole? Can I send multiple objects as I'm trying to do? Thanks for your time.

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• Identifying and Resolving Oracle ITL Deadlock

  - by Allan

  I have an Oracle DB package that is routinely causing what I believe is an ITL (Interested Transaction List) deadlock. The relevant portion of a trace file is below. Deadlock graph: ---------Blocker(s)-------- ---------Waiter(s)--------- Resource Name process session holds waits process session holds waits TM-0000cb52-00000000 22 131 S 23 143 SS TM-0000ceec-00000000 23 143 SX 32 138 SX SSX TM-0000cb52-00000000 30 138 SX 22 131 S session 131: DID 0001-0016-00000D1C session 143: DID 0001-0017-000055D5 session 143: DID 0001-0017-000055D5 session 138: DID 0001-001E-000067A0 session 138: DID 0001-001E-000067A0 session 131: DID 0001-0016-00000D1C Rows waited on: Session 143: no row Session 138: no row Session 131: no row There are no bit-map indexes on this table, so that's not the cause. As far as I can tell, the lack of "Rows waited on" plus the "S" in the Waiter waits column likely indicates that this is an ITL deadlock. Also, the table is written to quite often (roughly 8 insert or updates concurrently, as often as 240 times a minute), so and ITL deadlock seems like a strong possibility. I've increased the INITRANS parameter of the table and it's indexes to 100 and increased the PCT_FREE on the table from 10 to 20 (then rebuilt the indexes), but the deadlocks are still occurring. The deadlock seems to happen most often during an update, but that could just be a coincidence, as I've only traced it a couple of times. My questions are two-fold: 1) Is this actually an ITL deadlock? 2) If it is an ITL deadlock, what else can be done to avoid it?

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• Lua Alien Module - Trouble using WriteProcessMemory function, unsure on types (unit32)

  - by jefferysanders

  require "alien" --the address im trying to edit in the Mahjong game on Win7 local SCOREREF = 0x0744D554 --this should give me full access to the process local ACCESS = 0x001F0FFF --this is my process ID for my open window of Mahjong local PID = 1136 --function to open proc local op = alien.Kernel32.OpenProcess op:types{ ret = "pointer", abi = "stdcall"; "int", "int", "int"} --function to write to proc mem local wm = alien.Kernel32.WriteProcessMemory wm:types{ ret = "long", abi = "stdcall"; "pointer", "pointer", "pointer", "long", "pointer" } local pRef = op(ACCESS, true, PID) local buf = alien.buffer("99") -- ptr,uint32,byte arr (no idea what to make this),int, ptr print( wm( pRef, SCOREREF, buf, 4, nil)) --prints 1 if success, 0 if failed So that is my code. I am not even sure if I have the types set correctly. I am completely lost and need some guidance. I really wish there was more online help/documentation for alien, it confuses my poor brain. What utterly baffles me is that it WriteProcessMemory will sometimes complete successfully (though it does nothing at all, to my knowledge) and will also sometimes fail to complete successfully. As I've stated, my brain hurts. Any help appreciated.

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• Business Layer Pattern on Rails? MVCL

  - by Fabiano PS

  That is a broad question, and I appreciate no short/dumb asnwers like: "Oh that is the model job, this quest is retarded (period)" PROBLEM Where I work at people created a system over 2 years for managing the manufacture process over demand in the most simplified still broad as possible, involving selling, buying, assemble, The system is coded over Ruby On Rails. The result has been changed lots of times and the result is a mess on callbacks (some are called several times), 200+ models, and fat controllers: Total bad. The QUESTION is, if there is a gem, or pattern designed to handle Rails large app logic? The logic whould be able to fully talk to models (whose only concern would be data format handling and validation) What I EXPECT is to reduce complexity from various controllers, and hard to track callbacks into files with the responsibility to handle a business operation logic. In some cases there is the need to wait for a response, in others, only validation of the input is enough and a bg process would take place. ie: -- Sell some products (need to wait the operation to finish) 1. Set a View able to get the products input 2. Controller gets the product list inputed by employee and call the logic Logic::ExecuteWithResponse('sell', 'products', :prods => @product_list_with_qtt, :when => @date, :employee => current_user() ) This Logic would handle buying order, assemble order, machine schedule, warehouse reservation, and others

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• segmentation fault on Unix - possible stack corruption

  - by bob

  hello, i'm looking at a core from a process running in Unix. Usually I can work my around and root into the backtrace to try identify a memory issue. In this case, I'm not sure how to proceed. Firstly the backtrace only gives 3 frames where I would expect alot more. For those frames, all the function parameters presented appears to completely invalid. There are not what I would expect. Some pointer parameters have the following associated with them - Cannot access memory at address Would this suggest some kind of complete stack corruption. I ran the process with libumem and all the buffers were reported as being clean. umem_status reported nothing either. so basically I'm stumped. What is the likely causes? What should I look for in code since libumem appears to have reported no errors. Any suggestions on how I can debug furhter? any extra features in mdb I should consider? thank you.

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• How can I turn a column name into a result value in SQL Server?

  - by Brennan

  I have a table which has essentially boolean values in a legacy database. The column names are stored as string values in another table so I need to match the column names of one table to a string value in another table. I know there has to be a way to do this directly with SQL in SQL Server but it is beyond me. My initial thought was to use PIVOT but it is not enabled by default and enabling it would likely be a difficult process with pushing that change to the Production database. I would prefer to use what is enabled by default. I am considering using COALESCE to translate the boolean value to the string that value that I need. This will be a manual process. I think I will also use a table variable to insert the results of the first query into that variable and use those results to do the second query. I still have the problem that the columns are on a single row so I wish I could easily pivot the values to put the column names in the result set as strings. But if I could easily do that I could easily write the query with a sub-select. Any tips are welcome.

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• Forking in PHP on Windows

  - by Doug Kavendek

  We are running PHP on a Windows server (a source of many problems indeed, but migrating is not an option currently). There are a few points where a user-initiated action will need to kick off a few things that take a while and about which the user doesn't need to know if they succeed or fail, such as sending off an email or making sure some third-party accounts are updated. If I could just fork with pcntl_fork(), this would be very simple, but the PCNTL functions are not available in Windows. It seems the closest I can get is to do something of this nature: exec( 'php-cgi.exe somescript.php' ); However, this would be far more complicated. The actions I need to kick off rely on a lot of context that already will exist in the running process; to use the above example, I'd need to figure out the essential data and supply it to the new script in some way. If I could fork, it'd just be a matter of letting the parent process return early, leaving the child to work on a few more things. I've found a few people talking about their own work in getting various PCNTL functions compiled on Windows, but none seemed to have anything available (broken links, etc). Despite this question having practically the same name as mine, it seems the problem was more execution timeout than needing to fork. So, is my best option to just refactor a bit to deal with calling php-cgi, or are there other options? Edit: It seems exec() won't work for this, at least not without me figuring some other aspect of it, as it waits until the call returns. I figured I could use START, sort of like exec( 'start php-cgi.exe somescript.php' );, but it still waits until the other script finishes.

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• Memory mapped files and "soft" page faults. Unavoidable?

  - by Robert Oschler

  I have two applications (processes) running under Windows XP that share data via a memory mapped file. Despite all my efforts to eliminate per iteration memory allocations, I still get about 10 soft page faults per data transfer. I've tried every flag there is in CreateFileMapping() and CreateFileView() and it still happens. I'm beginning to wonder if it's just the way memory mapped files work. If anyone there knows the O/S implementation details behind memory mapped files I would appreciate comments on the following theory: If two processes share a memory mapped file and one process writes to it while another reads it, then the O/S marks the pages written to as invalid. When the other process goes to read the memory areas that now belong to invalidated pages, this causes a soft page fault (by design) and the O/S knows to reload the invalidated page. Also, the number of soft page faults is therefore directly proportional to the size of the data write. My experiments seem to bear out the above theory. When I share data I write one contiguous block of data. In other words, the entire shared memory area is overwritten each time. If I make the block bigger the number of soft page faults goes up correspondingly. So, if my theory is true, there is nothing I can do to eliminate the soft page faults short of not using memory mapped files because that is how they work (using soft page faults to maintain page consistency). What is ironic is that I chose to use a memory mapped file instead of a TCP socket connection because I thought it would be more efficient. Note, if the soft page faults are harmless please note that. I've heard that at some point if the number is excessive, the system's performance can be marred. If soft page faults intrinsically are not significantly harmful then if anyone has any guidelines as to what number per second is "excessive" I'd like to hear that. Thanks.

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• Wizard form in Struts

  - by Kuntal Basu

  I am creating a wizard in Struts. It cotains 4 steps. For Each step I have separate ActionClass say:- Step1Action.java Step2Action.java Step3Action.java Step4Action.java and in each class there are 2 methods input() and process(). input() method is for showing the page in input mode process() method is will be use for processing the submitted data (if validation is ok) I am carrying all data upto the last step in a session. And saving all of them in database in the last step Similaly 4 action tags in struts.xml like :- <action name="step1" class="com.mycomp.myapp.action.Step1Action1" method="input"> <result name="success" type="redirectAction">step2</result> <result name="input">/view/step1.jsp</result> </action> <action name="step2" class="com.mycomp.myapp.action.Step1Action2" method="input"> <result name="success" type="redirectAction">step3</result> <result name="input">/view/step2.jsp</result> </action> But I think I am going wrong. Please Tell me How will I handle This case?

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• wcf 4.0 service on IIS7

  - by Jan

  I am currently developing a service with wcf 4.0 (visual studio 2010 RC). When I try my service on the Visual Studio Development Server, it all works perfect. However, when I tree to run my service on IIS7 on a windows 7 machine, the service doesn't work anymore. (I already changed the framework version on my application pool). When I call an operation on the service, like the default operation GetData when I create a service, I get an error. I used the WCF test client to connect to the service. When I call the operation on the service, the Visual Studio Just-In-Time debugger shows the following message: An unhandled win32 exception occured in w3wp.exe The Just-In-Time debugger was launched without necessary security permissions. To debug this proces, the JIT debugger must be run as an administrator. Would you like to debug the proces? As far as I know, I am running Visual Studio as an administrator and this is probably the process that starts the JIT debugger. The only option I have is to debug the W3WP process, which is probably not the right thing to do. What can I do the make the Service to run on IIS7?

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• SQL (mySQL) update some value in all records processed by a select

  - by jdmuys

  I am using mySQL from their C API, but that shouldn't be relevant. My code must process records from a table that match some criteria, and then update the said records to flag them as processed. The lines in the table are modified/inserted/deleted by another process I don't control. I am afraid in the following, the UPDATE might flag some records erroneously since the set of records matching might have changed between step 1 and step 3. SELECT * FROM myTable WHERE <CONDITION>; # step 1 <iterate over the selected set of lines. This may take some time.> # step 2 UPDATE myTable SET processed=1 WHERE <CONDITION> # step 3 What's the smart way to ensure that the UPDATE updates all the lines processed, and only them? A transaction doesn't seem to fit the bill as it doesn't provide isolation of that sort: a recently modified record not in the originally selected set might still be targeted by the UPDATE statement. For the same reason, SELECT ... FOR UPDATE doesn't seem to help, though it sounds promising :-) The only way I can see is to use a temporary table to memorize the set of rows to be processed, doing something like: CREATE TEMPORARY TABLE workOrder (jobId INT(11)); INSERT INTO workOrder SELECT myID as jobId FROM myTable WHERE <CONDITION>; SELECT * FROM myTable WHERE myID IN (SELECT * FROM workOrder); <iterate over the selected set of lines. This may take some time.> UPDATE myTable SET processed=1 WHERE myID IN (SELECT * FROM workOrder); DROP TABLE workOrder; But this seems wasteful and not very efficient. Is there anything smarter? Many thanks from a SQL newbie.

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• Database INSERT does not take place

  - by reggie

  My code is as follows: <?php include("config.php"); $ip=$_SERVER['REMOTE_ADDR']; if($_POST['id']) { $id=$_POST['id']; $id = mysql_escape_String($id); $ip_sql=mysql_query("select ip_add from Voting_IP where mes_id_fk='$id' and ip_add='$ip'"); $count=mysql_num_rows($ip_sql); if($count==0) { $sql = "update Messages set up=up+1 where mes_id='$id'"; mysql_query($sql); $sql_in = "insert into Voting_IP (mes_id_fk,ip_add) values ('$id','$ip')"; mysql_query($sql_in) or die(mysql_error()); echo "<script>alert('Thanks for the vote');</script>"; } else { echo "<script>alert('You have already voted');</script>"; } $result=mysql_query("select up from Messages where mes_id='$id'"); $row=mysql_fetch_array($result); $up_value=$row['up']; echo "<img src='button.png' width='110' height='90'>"; echo $up_value; } ?> My problem is that the insert process does not take place at all. The script tags echos an alert box. Even the img tag is echoed to the web page. But the insert process does not take place. The config file is fine. Note: This code works on my local machine which has PHP 5.3 but it does not work on the server which has PHP 5.2. Any advice?

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