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  • C programming getting back into it - the red pill

    - by JavaRocky
    Can someone provide recommended reading, website resources or best practices to follow when programming with C. I am a proficient software developer with strong skills in Java and PHP. Is there standard libraries these days which people use? Like what spring is to java? And standard design patterns for managing memory or even standard libraries for that fact? I want to write solid, maintainable C programs. GO THE RED PILL! :P

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  • Should we denormalize database to improve performance?

    - by Groo
    We have a requirement to store 500 measurements per second, coming from several devices. Each measurement consists of a timestamp, a quantity type, and several vector values. Right now there is 8 vector values per measurement, and we may consider this number to be constant for needs of our prototype project. We are using HNibernate. Tests are done in SQLite (disk file db, not in-memory), but production will probably be MsSQL. Our Measurement entity class is the one that holds a single measurement, and looks like this: public class Measurement { public virtual Guid Id { get; private set; } public virtual Device Device { get; private set; } public virtual Timestamp Timestamp { get; private set; } public virtual IList<VectorValue> Vectors { get; private set; } } Vector values are stored in a separate table, so that each of them references its parent measurement through a foreign key. We have done a couple of things to ensure that generated SQL is (reasonably) efficient: we are using Guid.Comb for generating IDs, we are flushing around 500 items in a single transaction, ADO.Net batch size is set to 100 (I think SQLIte does not support batch updates? But it might be useful later). The problem Right now we can insert 150-200 measurements per second (which is not fast enough, although this is SQLite we are talking about). Looking at the generated SQL, we can see that in a single transaction we insert (as expected): 1 timestamp 1 measurement 8 vector values which means that we are actually doing 10x more single table inserts: 1500-2000 per second. If we placed everything (all 8 vector values and the timestamp) into the measurement table (adding 9 dedicated columns), it seems that we could increase our insert speed up to 10 times. Switching to SQL server will improve performance, but we would like to know if there might be a way to avoid unnecessary performance costs related to the way database is organized right now. [Edit] With in-memory SQLite I get around 350 items/sec (3500 single table inserts), which I believe is about as good as it gets with NHibernate (taking this post for reference: http://ayende.com/Blog/archive/2009/08/22/nhibernate-perf-tricks.aspx). But I might as well switch to SQL server and stop assuming things, right? I will update my post as soon as I test it.

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  • Built in Analyzer in Xcode 3.1.4

    - by Mustafa
    Hi all, I wonder if the built in Analyzer in Xcode 3.1.4 makes it redundant to use LLVM/Clang Static Analyzer separately? Please refer to the original article here: Finding memory leaks with the LLVM/Clang Static Analyzer Thanks.

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  • how to create partition on windows CE device

    - by mack369
    Is there any tool to create a new partition on windows CE device? Device has a NAND flash memory and initially there were two partitions. Using Storage manager in Control Panel I was able to delete one partition but when I want to create it again, I get an error message: "Unable to create partition".

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  • Filtering Attributes with Weka

    - by hrzafer
    Hi eveyone! I have a simple question about filtering attributes in WEKA. Let's say I have 500 attributes 30 classes and 100 samples for each class which equals 3000 rows and 500 columns. This causes time and memory problems a you can guess. How do I filter attributes that occur only once or twice (or n times) in 3000 rows. And is it a good idea? Thank you

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  • Java Garbage Collection

    - by pietervn
    I was wondering about the garbage collection that takes place in Java. Is it really able to handle all objects that aren't used and free up the most possible memory? I also want to know how does the Java garbage collection compare to another language like lets say C#? And then, how does the automatic garbage collection measure up against manual collection from a language like C?

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  • Char* vs std::string

    - by Lockyer
    Is there any advantage to using char*'s instead of std::string? I know char*'s are usually defined on the stack, so we know exactly how much memory we'll use, is this actually a good argument for their use? Or is std::string better in every way?

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  • What would be the best .NET 2.0 type to represent .NET 3.5 HashSet<T>?

    - by Will Marcouiller
    I'm writing myself a class library to manage Active Directory. I have an interface: Public Interface ISourceAnnuaire(Of T as {IGroupe, ITop, IUniteOrganisation, IUtilisateur}) Readonly Property Changements As Dictionary(Of T, HashSet(Of String)) End Interface This Changements property is used to save in memory the changes that occur on a particular element that is part of the source. However, I am stuck with .NET Framework 2.0. What would be the closest .NET 2.0 for HashSet(Of String)?

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  • How do access a secure website within a sharepoint webpart?

    - by Bill
    How do access a secure website within a sharepoint webpart? The following code works fine as a console application but if you run it in a webpart, you will get a access violation WebRequest request = WebRequest.Create("https://somesecuresite.com"); WebResponse firstResponse = null; try { firstResponse = request.GetResponse(); } catch (WebException ex) { writer.WriteLine("Error: " + ex.ToString()); return; } if you access a non secure site, it also works. Any ideas? Error: System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive. --- System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. at System.Net.UnsafeNclNativeMethods.NativePKI.CertVerifyCertificateChainPolicy(IntPtr policy, SafeFreeCertChain chainContext, ChainPolicyParameter& cpp, ChainPolicyStatus& ps) at System.Net.PolicyWrapper.VerifyChainPolicy(SafeFreeCertChain chainContext, ChainPolicyParameter& cpp) at System.Net.Security.SecureChannel.VerifyRemoteCertificate(RemoteCertValidationCallback remoteCertValidationCallback) at System.Net.Security.SslState.CompleteHandshake() at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest) at System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult) at System.Net.TlsStream.CallProcessAuthentication(Object state) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result) at System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size) at System.Net.ConnectStream.WriteHeaders(Boolean async) --- End of inner exception stack trace --- at System.Net.HttpWebRequest.GetResponse()

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  • Squid: The request or reply is too large

    - by Ueli
    I have done a reverse proxy with an Apache in the background (on the same server). All works great but I can't open one page. I get the error "The request or reply is too large." In my cache.log contains: 2010/12/09 15:28:29| WARNING: http.c:971: HTTP header too large 2010/12/09 15:29:03| ctx: enter level 0: 'http://server/admin/cms/nav' 2010/12/09 15:29:03| httpProcessReplyHeader: Too large reply header 2010/12/09 15:29:03| ctx: exit level 0 In my squid.conf i disabled the limitations of the request and reply header, without success: reply_body_max_size 0 allow all request_body_max_size 0 Does someone know why that don't work? Thank you very much. Squid Version: Squid Cache: Version 2.7.STABLE3 configure options: '--prefix=/usr' '--exec_prefix=/usr' '--bindir=/usr/sbin' '--sbindir=/usr/sbin' '--libexecdir=/usr/lib/squid' '--sysconfdir=/etc/squid' '--localstatedir=/var/spool/squid' '--datadir=/usr/share/squid' '--enable-async-io' '--with-pthreads' '--enable-storeio=ufs,aufs,coss,diskd,null' '--enable-linux-netfilter' '--enable-arp-acl' '--enable-epoll' '--enable-removal-policies=lru,heap' '--enable-snmp' '--enable-delay-pools' '--enable-htcp' '--enable-cache-digests' '--enable-underscores' '--enable-referer-log' '--enable-useragent-log' '--enable-auth=basic,digest,ntlm,negotiate' '--enable-negotiate-auth-helpers=squid_kerb_auth' '--enable-carp' '--enable-follow-x-forwarded-for' '--with-large-files' '--with-maxfd=65536' 'amd64-debian-linux' 'build_alias=amd64-debian-linux' 'host_alias=amd64-debian-linux' 'target_alias=amd64-debian-linux' 'CFLAGS=-Wall -g -O2' 'LDFLAGS=' 'CPPFLAGS='

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  • lightweight publish/subscribe framework in java

    - by mdma
    Is there a good lightweight framework for java that provides the publish/subscribe pattern? Some ideal features Support for generics Registration of multiple subscribers to a publisher API primarily interfaces and some useful implementations purely in-memory, persistence and transaction guarantees not required. I know about JMS but that is overkill for my need. The publish/subscribed data are the result of scans of a file system, with scan results being fed to another component for processing, which are then processed before being fed to another and so on.

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  • How do you drop in substitute JRE classes?

    - by evilfred
    Hi, java.util.zip has well-known problems with native memory usage, so i'm trying to use a drop-in replacement called "jazzlib". unfortunately as is typical for sourceforge projects there is no documentation. If I add the jar to my classpath then Java freaks out and gives me "prohibited package name" errors because it replaced java.util.zip. How do I tell Java that this is what I want it to do?

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  • Performance tuning of a Hibernate+Spring+MySQL project operation that stores images uploaded by user

    - by Umar
    Hi I am working on a web project that is Spring+Hibernate+MySQL based. I am stuck at a point where I have to store images uploaded by a user into the database. Although I have written some code that works well for now, but I believe that things will mess up when the project would go live. Here's my domain class that carries the image bytes: @Entity public class Picture implements java.io.Serializable{ long id; byte[] data; ... // getters and setters } And here's my controller that saves the file on submit: public class PictureUploadFormController extends AbstractBaseFormController{ ... protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws Exception{ MutlipartFile file; // getting MultipartFile from the command object ... // beginning hibernate transaction ... Picture p=new Picture(); p.setData(file.getBytes()); pictureDAO.makePersistent(p); // this method simply calls getSession().saveOrUpdate(p) // committing hiernate transaction ... } ... } Obviously a bad piece of code. Is there anyway I could use InputStream or Blob to save the data, instead of first loading all the bytes from the user into the memory and then pushing them into the database? I did some research on hibernate's support for Blob, and found this in Hibernate In Action book: java.sql.Blob and java.sql.Clob are the most efficient way to handle large objects in Java. Unfortunately, an instance of Blob or Clob is only useable until the JDBC transaction completes. So if your persistent class defines a property of java.sql.Clob or java.sql.Blob (not a good idea anyway), you’ll be restricted in how instances of the class may be used. In particular, you won’t be able to use instances of that class as detached objects. Furthermore, many JDBC drivers don’t feature working support for java.sql.Blob and java.sql.Clob. Therefore, it makes more sense to map large objects using the binary or text mapping type, assuming retrieval of the entire large object into memory isn’t a performance killer. Note you can find up-to-date design patterns and tips for large object usage on the Hibernate website, with tricks for particular platforms. Now apparently the Blob cannot be used, as it is not a good idea anyway, what else could be used to improve the performance? I couldn't find any up-to-date design pattern or any useful information on Hibernate website. So any help/recommendations from stackoverflowers will be much appreciated. Thanks

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  • Summary of the last decade of garbage collection?

    - by Ben Karel
    I've been reading through the Jones & Lin book on garbage collection, which was published in 1996. Obviously, the computing world has changed dramatically since then: multicore, out-of-order chips with large caches, and even larger main memory in desktops. The world has also more-or-less settled on the x86 and ARM microarchitectures for most consumer-facing systems. How has the field of garbage collection changed since the seminal book was published?

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  • Subclassing NSObject, can it cause problems?

    - by Sheehan Alam
    I have a very basic data class that is subclassed from NSObject. I declare a few strings, make sure they have properties (nonatomic, copy), and synthesize them. The only method I implemented was dealloc() which releases my strings. Can any memory problems arise from just this? Are there any other methods I need to implement?

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  • BigInteger.pow(BigInteger) ?

    - by PeterW
    I'm playing with numbers in Java, and want to see how big a number I can make. It is my understanding that BigInteger can hold a number of infinite size, so long as my computer has enough Memory to hold such a number, correct? My problem is that BigInteger.pow accepts only an int, not another BigInteger, which means I can only use a number up to 2,147,483,647 as the exponent. Is it possible to use the BigInteger class as such? BigInteger.pow(BigInteger) Thanks.

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  • Solr startup script problem

    - by Camran
    I have installed solr and it works finally... I have now problems setting it up to start automatically with a start command. I have followed a tutorial and created a file called solr in the /etc/init.d/solr dir... Here is that file: #!/bin/sh -e # SOLR auto-start # # description: auto-starts solr engine # processname: solr-production # pidfile: /var/run/solr-production.pid NAME="solr" PIDFILE="/var/run/solr-production.pid" LOG_FILE="/var/log/solr-production.log" SOLR_DIR="/etc/jetty" JAVA_OPTIONS="-Xmx1024m -DSTOP.PORT=8079 -DSTOP.KEY=stopkey -jar start.jar" JAVA="/usr/bin/java" start() { echo -n "Starting $NAME... " if [ -f $PIDFILE ]; then echo "is already running!" else cd $SOLR_DIR $JAVA $JAVA_OPTIONS 2> $LOG_FILE & sleep 2 echo `ps -ef | grep -v grep | grep java | awk '{print $2}'` > $PIDFILE echo "(Done)" fi return 0 } stop() { echo -n "Stopping $NAME... " if [ -f $PIDFILE ]; then cd $SOLR_DIR $JAVA $JAVA_OPTIONS --stop sleep 2 rm $PIDFILE echo "(Done)" else echo "can not stop, it is not running!" fi return 0 } case "$1" in start) start ;; stop) stop ;; restart) stop sleep 5 start ;; *) echo "Usage: $0 (start | stop | restart)" exit 1 ;; esac Whenever I do solr -start I get this error: "Error occurred during initialization of VM Could not reserve enough space for object heap" I think this is because of the file above... Also here is where I have solr installed: var/www/solr and here is the start.jar file located: var/www/start.jar Help me out if you know whats causing this. Thanks BTW: OS is ubuntu 9.10

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  • T-SQL query with date range

    - by Moo
    Hi, I have a fairly weird 'bug' with a simple query, and I vaguely remember reading the reason for it somewhere a long time ago but would love someone to refresh my memory. The table is a basic ID, Datetime table. The query is: select ID, Datetime from Table where Datetime <= '2010-03-31 23:59:59' The problem is that the query results include results where the Datetime is '2010-04-01 00:00:00'. The next day. Which it shouldn't. Anyone? Cheers Moo

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  • Help! I got a runaway PHP script. My server is down.

    - by gAMBOOKa
    I got a PHP script that is looping and will continue to do so for about another hour. How do I stop it. The script explicitly overrides the time out and the memory buffer. It's on a shared hosting server with cPanel installed. The entire website is down until the script completes. I had added a usleep(100000) statement, but it doesn't appear to work.

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  • What's holding up my PHP script?

    - by gAMBOOKa
    We've got a PHP crawler running on our web server. When the crawler is running, there are no cpu, memory or network bandwidth spikes. Everything is normal. But our website (also PHP), hosted on the same server, stops responding. Basically the crawler blocks any other php script from running. What could be the problem? EDIT: ** fsockopen is being used to download files to crawler! **

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