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• How to solve "java.io.IOException: error=12, Cannot allocate memory" calling Runtime#exec()?

  - by Andrea Francia

  On my system I can't run a simple Java application that start a process. I don't know how to solve. Could you give me some hints how to solve? The program is: [root@newton sisma-acquirer]# cat prova.java import java.io.IOException; public class prova { public static void main(String[] args) throws IOException { Runtime.getRuntime().exec("ls"); } } The result is: [root@newton sisma-acquirer]# javac prova.java && java -cp . prova Exception in thread "main" java.io.IOException: Cannot run program "ls": java.io.IOException: error=12, Cannot allocate memory at java.lang.ProcessBuilder.start(ProcessBuilder.java:474) at java.lang.Runtime.exec(Runtime.java:610) at java.lang.Runtime.exec(Runtime.java:448) at java.lang.Runtime.exec(Runtime.java:345) at prova.main(prova.java:6) Caused by: java.io.IOException: java.io.IOException: error=12, Cannot allocate memory at java.lang.UNIXProcess.<init>(UNIXProcess.java:164) at java.lang.ProcessImpl.start(ProcessImpl.java:81) at java.lang.ProcessBuilder.start(ProcessBuilder.java:467) ... 4 more Configuration of the system: [root@newton sisma-acquirer]# java -version java version "1.6.0_0" OpenJDK Runtime Environment (IcedTea6 1.5) (fedora-18.b16.fc10-i386) OpenJDK Client VM (build 14.0-b15, mixed mode) [root@newton sisma-acquirer]# cat /etc/fedora-release Fedora release 10 (Cambridge) EDIT: Solution This solves my problem, I don't know exactly why: echo 0 /proc/sys/vm/overcommit_memory Up-votes for who is able to explain :) Additional informations, top output: top - 13:35:38 up 40 min, 2 users, load average: 0.43, 0.19, 0.12 Tasks: 129 total, 1 running, 128 sleeping, 0 stopped, 0 zombie Cpu(s): 1.5%us, 0.5%sy, 0.0%ni, 94.8%id, 3.2%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 1033456k total, 587672k used, 445784k free, 51672k buffers Swap: 2031608k total, 0k used, 2031608k free, 188108k cached Additional informations, free output: [root@newton sisma-acquirer]# free total used free shared buffers cached Mem: 1033456 588548 444908 0 51704 188292 -/+ buffers/cache: 348552 684904 Swap: 2031608 0 2031608

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• Mysql Algorithm for Determining Closest Colour Match

  - by buggedcom

  I'm attempting to create a true mosaic application. At the moment I have one mosaic image, ie the one the mosaic is based on and about 4000 images from my iPhoto library that act as the image library. I have already done my research and analysed the mosaic image. I've converted it into 64x64 slices each of 8 pixels. I've calculated the average colour for each slice and assertain the r, g, b and brightness (Luminance (perceived option 1) = (0.299*R + 0.587*G + 0.114*B)) value. I have done the same for each of the image library photos. The mosaic slices table looks like so. slice_id, slice_image_id, slice_slice_id, slice_image_column, slice_image_row, slice_colour_hex, slice_rgb_red, slice_rgb_blue, slice_rgb_green, slice_rgb_brightness The image library table looks like so. upload_id, upload_file, upload_colour_hex, upload_rgb_red, upload_rgb_green, upload_rgb_blue, upload_rgb_brightness So basically I'm reading the image slices from the slices table into PHP and then pulling out the appropriate images from the library table based on the colour hexs. My trouble is that I've been on this too long and probably had too many energy drinks so am not concentrating properly, I can't figure out the way to pick out the nearest colour neighbor if the appropriate hex code doesn't exist. Any ideas on the perfect query? NB: I know pulling out the slices one by one is not ideal however the mosaic is only rebuilt periodically so a sudden burst in the mysql load doesn't really bother me, however if there us a way to pull the images out all at once that would also be a massive bonus.

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• Finding most efficient transmission size in varying network latency scenarios

  - by rwmnau

  I'm building a .NET remoting client/server that will be transmitting thousands of files, of varying sizes (everything from a few bytes to hundreds of MB), and I'm curious about a general method for finding the appropriate transmission size. As I see it, there's the following tradeoff: Serialize entire file into a transmission object and transmit at once, regardless of size. This would be the fastest, but a failure during tranmission requires that the whole file be re-transmitted. If the file size is larger than something small (like 4KB), break it into 4KB chunks and transmit those, re-assembling on the server. In addition to the complexity of this, it's slower because of continued round-trips and acknowledgements, though a failure of any one piece doesn't waste much time. The ideal transmission method (when taking into account negotiation latency vs. failure rate) is somewhere in between, and I'm wondering about how to find out the best size for that particular client. Do I have some dynamic tuning step in my transmission that looks at the current bytes/second average, and then raises the transmission size until the speed starts to drop (failures overwhelm negotiation cost)? Or is there some other method for determining ideal transmission size? The application will be multi-threaded, so number of threads also factors in to the calculation. I'm not looking for a formula (though I'll take one if you've got it), but just what to consider as I create this process.

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• Metaprogramming - self explanatory code - tutorials, articles, books

  - by elena

  Hello everybody, I am looking into improving my programming skils (actually I try to do my best to suck less each year, as our Jeff Atwood put it), so I was thinking into reading stuff about metaprogramming and self explanatory code. I am looking for something like an idiot's guide to this (free books for download, online resources). Also I want more than your average wiki page and also something language agnostic or preferably with Java examples. Do you know of such resources that will allow to efficiently put all of it into practice (I know experience has a lot to say in all of this but i kind of want to build experience avoiding the flow bad decisions - experience - good decisions)? EDIT: Something of the likes of this example from the Pragmatic Programmer: ...implement a mini-language to control a simple drawing package... The language consists of single-letter commands. Some commands are followed by a single number. For example, the following input would draw a rectangle: P 2 # select pen 2 D # pen down W 2 # draw west 2cm N 1 # then north 1 E 2 # then east 2 S 1 # then back south U # pen up Thank you!

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• Open source GIS tools

  - by TRV_SQL

  Hi I’ve been looking at Open Source GIS tools. In particular MapServer and GeoServer. The problem I’m seeing is that to actually deploy these to the public you can’t use a regular $5/ month (or free) hosting service because you have to install these services on the server in ways that are not accessible in the average hosting scheme. So you either have to use a host that has MapServer installed (many of which look unreliable) or have a dedicated server or VPS. All of these options have a significant cost barrier ($30 - $200/month). I’m just doing this for fun. Are there any free or inexpensive ways to have your GIS services hosted? Or are there any products that install in a way that you don’t need to access the root structure of the server? I have tried OpenLayers and GeoExt but I don’t think a client side option will work for me because of the size of the datasets I am using. My base data will be vector data not WMS data (or something similar). I haven’t tried Google maps yet, but I will be looking into it. Also, any thought on using SVG for GIS purposes? Thanks

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• django+uploadify - don't working

  - by Erico

  Hi, I'm trying to use an example posted on the "github" the link is http://github.com/tstone/django-uploadify. And I'm having trouble getting work. can you help me? I followed step by step, but does not work. Accessing the "URL" / upload / the only thing is that returns "True" part of settings.py import os PROJECT_ROOT_PATH = os.path.dirname(os.path.abspath(file)) MEDIA_ROOT = os.path.join(PROJECT_ROOT_PATH, 'media') TEMPLATE_DIRS = ( os.path.join(PROJECT_ROOT_PATH, 'templates')) urls.py from django.conf.urls.defaults import * from django.conf import settings from teste.uploadify.views import * from django.contrib import admin admin.autodiscover() urlpatterns = patterns('', (r'^admin/', include(admin.site.urls)), url(r'upload/$', upload, name='uploadify_upload'), ) views.py from django.http import HttpResponse import django.dispatch upload_received = django.dispatch.Signal(providing_args=['data']) def upload(request, *args, **kwargs): if request.method == 'POST': if request.FILES: upload_received.send(sender='uploadify', data=request.FILES['Filedata']) return HttpResponse('True') models.py from django.db import models def upload_received_handler(sender, data, **kwargs): if file: new_media = Media.objects.create( file = data, new_upload = True, ) new_media.save() upload_received.connect(upload_received_handler, dispatch_uid='uploadify.media.upload_received') class Media(models.Model): file = models.FileField(upload_to='images/upload/', null=True, blank=True) new_upload = models.BooleanField() uploadify_tags.py from django import template from teste import settings register = template.Library() @register.inclusion_tag('uploadify/multi_file_upload.html', takes_context=True) def multi_file_upload(context, upload_complete_url): """ * filesUploaded - The total number of files uploaded * errors - The total number of errors while uploading * allBytesLoaded - The total number of bytes uploaded * speed - The average speed of all uploaded files """ return { 'upload_complete_url' : upload_complete_url, 'uploadify_path' : settings.UPLOADIFY_PATH, # checar essa linha 'upload_path' : settings.UPLOADIFY_UPLOAD_PATH, } template - uploadify/multi_file_upload.html {% load uploadify_tags }{ multi_file_upload '/media/images/upload/' %} <script type="text/javascript" src="{{ MEDIA_URL }}js/swfobject.js"></script> <script type="text/javascript" src="{{ MEDIA_URL }}js/jquery.uploadify.js"></script> <div id="uploadify" class="multi-file-upload"><input id="fileInput" name="fileInput" type="file" /></div> <script type="text/javascript">// <![CDATA[ $(document).ready(function() { $('#fileInput').uploadify({ 'uploader' : '/media/swf/uploadify.swf', 'script' : '{% url uploadify_upload %}', 'cancelImg' : '/media/images/uploadify-remove.png/', 'auto' : true, 'folder' : '/media/images/upload/', 'multi' : true, 'onAllComplete' : allComplete }); }); function allComplete(event, data) { $('#uploadify').load('{{ upload_complete_url }}', { 'filesUploaded' : data.filesUploaded, 'errorCount' : data.errors, 'allBytesLoaded' : data.allBytesLoaded, 'speed' : data.speed }); // raise custom event $('#uploadify') .trigger('allUploadsComplete', data); } // ]]</script>

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• Sparse parameter selection using Genetic Algorithm

  - by bgbg

  Hello, I'm facing a parameter selection problem, which I would like to solve using Genetic Algorithm (GA). I'm supposed to select not more than 4 parameters out of 3000 possible ones. Using the binary chromosome representation seems like a natural choice. The evaluation function punishes too many "selected" attributes and if the number of attributes is acceptable, it then evaluates the selection. The problem is that in these sparse conditions the GA can hardly improve the population. Neither the average fitness cost, nor the fitness of the "worst" individual improves over the generations. All I see is slight (even tiny) improvement in the score of the best individual, which, I suppose, is a result of random sampling. Encoding the problem using indices of the parameters doesn't work either. This is most probably, due to the fact that the chromosomes are directional, while the selection problem isn't (i.e. chromosomes [1, 2, 3, 4]; [4, 3, 2, 1]; [3, 2, 4, 1] etc. are identical) What problem representation would you suggest? P.S If this matters, I use PyEvolve.

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• ProgrammingError when aggregating over an annotated & grouped Django ORM query

  - by ento

  I'm trying to construct a query to get the "average, maximum, minimum number of items purchased by a single user". The data source is this simple sales record table: class SalesRecord(models.Model): id = models.IntegerField(primary_key=True) user_id = models.IntegerField() product_code = models.CharField() price = models.IntegerField() created_at = models.DateTimeField() A new record is inserted into this table for every item purchased by a user. Here's my attempt at building the query: q = SalesRecord.objects.all() q = q.values('user_id').annotate( # group by user and count the # of records count=Count('id'), # (= # of items) ).order_by() result = q.aggregate(Max('count'), Min('count'), Avg('count')) When I try to execute the code, a ProgrammingError is raised at the last line: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'FROM (SELECT sales_records.user_id AS user_id, COUNT(sales_records.`' at line 1") Django's error screen shows that the SQL is SELECT FROM (SELECT `sales_records`.`player_id` AS `player_id`, COUNT(`sales_records`.`id`) AS `count` FROM `sales_records` WHERE (`sales_records`.`created_at` >= %s AND `sales_records`.`created_at` <= %s ) GROUP BY `sales_records`.`player_id` ORDER BY NULL) subquery It's not selecting anything! Can someone please show me the right way to do this? Hacking Django I've found that clearing the cache of selected fields in django.db.models.sql.BaseQuery.get_aggregation() seems to solve the problem. Though I'm not really sure this is a fix or a workaround. @@ -327,10 +327,13 @@ # Remove any aggregates marked for reduction from the subquery # and move them to the outer AggregateQuery. + self._aggregate_select_cache = None + self.aggregate_select_mask = None for alias, aggregate in self.aggregate_select.items(): if aggregate.is_summary: query.aggregate_select[alias] = aggregate - del obj.aggregate_select[alias] + if alias in obj.aggregate_select: + del obj.aggregate_select[alias] ... yields result: {'count__max': 267, 'count__avg': 26.2563, 'count__min': 1}

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• Spikes in Socket Performance

  - by Harun Prasad

  We are facing random spikes in high throughput transaction processing system using sockets for IPC. Below is the setup used for the run: The client opens and closes new connection for every transaction, and there are 4 exchanges between the server and the client. We have disabled the TIME_WAIT, by setting the socket linger (SO_LINGER) option via getsockopt as we thought that the spikes were caused due to the sockets waiting in TIME_WAIT. There is no processing done for the transaction. Only messages are passed. OS used Centos 5.4 The average round trip time is around 3 milli seconds, but some times the round trip time ranges from 100 milli seconds to couple of seconds. Steps used for Execution and Measurement and output Starting the server $ python sockServerLinger.py /dev/null & Starting the client to post 1 million transactions to the server. And logs the time for a transaction in the client.log file. $ python sockClient.py 1000000 client.log Once the execution finishes the following command will show the execution time greater than 100 milliseconds in the format <line_number>:<execution_time>. $ grep -n "0.[1-9]" client.log | less Below is the example code for Server and Client. Server # File: sockServerLinger.py import socket, traceback,time import struct host = '' port = 9999 l_onoff = 1 l_linger = 0 lingeropt = struct.pack('ii', l_onoff, l_linger) s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) s.setsockopt(socket.SOL_SOCKET, socket.SO_LINGER, lingeropt) s.bind((host, port)) s.listen(1) while 1: try: clientsock, clientaddr = s.accept() print "Got connection from", clientsock.getpeername() data = clientsock.recv(1024*1024*10) #print "asdasd",data numsent=clientsock.send(data) data1 = clientsock.recv(1024*1024*10) numsent=clientsock.send(data) ret = 1 while(ret>0): data1 = clientsock.recv(1024*1024*10) ret = len(data) clientsock.close() except KeyboardInterrupt: raise except: print traceback.print_exc() continue Client # File: sockClient.py import socket, traceback,sys import time i = 0 while 1: try: st = time.time() s = socket.socket(socket.AF_INET,socket.SOCK_STREAM) while (s.connect_ex(('127.0.0.1',9999)) != 0): continue numsent=s.send("asd"*1000) response = s.recv(6000) numsent=s.send("asd"*1000) response = s.recv(6000) i+=1 if i == int(sys.argv[1]): break except KeyboardInterrupt: raise except: print "in exec:::::::::::::",traceback.print_exc() continue print time.time() -st

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• Looking for ideas for a simple pattern matching algorithm to run on a microcontroller

  - by pic_audio

  I'm working on a project to recognize simple audio patterns. I have two data sets, each made up of between 4 and 32 note/duration pairs. One set is predefined, the other is from an incoming data stream. The length of the two strongly correlated data sets is often different, but roughly the same "shape". My goal is to come up with some sort of ranking as to how well the two data sets correlate/match. I have converted the incoming frequencies to pitch and shifted the incoming data stream's pitch so that it's average pitch matches that of the predefined data set. I also stretch/compress the incoming data set's durations to match the overall duration of the predefined set. Here are two graphical examples of data that should be ranked as strongly correlated: http://s2.postimage.org/FVeG0-ee3c23ecc094a55b15e538c3a0d83dd5.gif (Sorry, as a new user I couldn't directly post images) I'm doing this on a 8-bit microcontroller so resources are minimal. Speed is less an issue, a second or two of processing isn't a deal breaker. It wouldn't surprise me if there is an obvious solution, I've just been staring at the problem too long. Any ideas? Thanks in advance...

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• Adding multiple star rating widgets to one page

  - by diglettpotato

  I am using this jQuery plugin for star ratings: http://orkans-tmp.22web.net/star_rating/ Everything is going great, including using AJAX, etc. The problem is that I need to have many per page and can't quite figure out how to work with the selectors to achieve this. I think this is probably very easy for someone who knows their jQuery... Here's some code below... There are multiple kids per page, and I need one rating widget for each kid. I can set up each #rat to be unique with a kid attached to it, like #1rat, #2rat, etc. But then how would I set up the function to be run on each of them independently? <script type="text/javascript"> $(function(){ var kidval=1; //this needs to be setup for each kid... not just 1 var uidval=1; $('#rat').children().not("select, #rating_title").hide(); var $caption = $('<div id="caption"/>'); $('#rat').stars({ inputType: "select", oneVoteOnly: false, callback: function(ui, type, value) { $("#"+kidval+"messages").text("Saving...").fadeIn(30); $.post("vote.php", {rate: value, kid: kidval, uid: uidval}, function(json) { $("#"+kidval+"messages").text("Average"); ui.select(Math.round(json.avg)); $caption.text(" (" + json.votes + " votes, " + json.avg + " avg)"); $("#"+kidval+"messages").text("Rated " + value + " Thanks!").stop().css("opacity", 1).fadeIn(30); setTimeout(function(){ $("#"+kidval+"messages").fadeOut(1000) }, 2000); }, "json"); } }); $('#rat').stars("selectID", -1); $caption.appendTo(#rat); $('<div id="'+kidval+'messages"/>').appendTo(#rat); });

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• Fast string suffix checking in C# (.NET 4.0)?

  - by ilitirit

  What is the fastest method of checking string suffixes in C#? I need to check each string in a large list (anywhere from 5000 to 100000 items) for a particular term. The term is guaranteed never to be embedded within the string. In other words, if the string contains the term, it will be at the end of the string. The string is also guaranteed to be longer than the suffix. Cultural information is not important. These are how different methods performed against 100000 strings (half of them have the suffix): 1. Substring Comparison - 13.60ms 2. String.Contains - 22.33ms 3. CompareInfo.IsSuffix - 24.60ms 4. String.EndsWith - 29.08ms 5. String.LastIndexOf - 30.68ms These are average times. [Edit] Forgot to mention that the strings also get put into separate lists, but this is not important. It does add to the running time though. On my system substring comparison (extracting the end of the string using the String.Substring method and comparing it to the suffix term) is consistently the fastest when tested against 100000 strings. The problem with using substring comparison though is that Garbage Collection can slow it down considerably (more than the other methods) because String.Substring creates new strings. The effect is not as bad in .NET 4.0 as it was in 3.5 and below, but it is still noticeable. In my tests, String.Substring performed consistently slower on sets of 12000-13000 strings. This will obviously differ between systems and implementations. [EDIT] Benchmark code: http://pastebin.com/smEtYNYN

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• Terrible DotNetNuke performance

  - by Peter Bridger

  I'm involved with a project using DotNetNuke version 05.01.04 Community Edition. We are building our new Intranet using it, but performance is terrible. We have five people adding pages and content to it and every 15-30 seconds they experience a pause of 10 seconds or longer before the system continues and the next screens loads. The server is Windows 2003, 3.8GHz with 1GB of RAM. I'm told by our server admin that the CPU and memory performance don't appear to be the bottleneck. We currently have 350 pages in the system, we a plan to add 1000. So we need to resolve this performance problem so that we can enter content and so we can go live. I just can't see where the bottleneck is. Is there a good why to determine the bottleneck when using DotNetNuke? Modules installed Publish:Engage (Not currently in use) Page Blaster (Doesn't appear to providing caching when users logged in using Integrated Authentication) SimpleGallery XMod Content Manager IIS Setup Application recycling completely disabled (Apart from a 2am recycle) New findings: 18th March 2010 The main bottleneck was due to version 5.1.4 having a bug which caused 1300 database roundtrips on an average page, due to broken database in-memory caching. We've upgraded to 5.2.4 which has resolved this bottleneck. Now the next biggest bottleneck is the navigation. We've used both DDR:Menu and DDN:Nav, but both have a major impact on performance. Is there a navigation interface out there that doesn't drain performance so badly?

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• Can i use a different parser for Axis 1.4?

  - by NishM

  The current SAX parser takes a lot of time (20 minutes) and heap memory(around 400mb) to deserialize the response coming from the soap server as per the logs. Our response XMLs are of average size 4 mb. A part of the log when it runs the applicaiton out of heap is below DEBUG (org.apache.axis.encoding.DeserializationContext) Pushing handler org.apache.axis.message.SOAPHandler@16d22f1 DEBUG (org.apache.axis.i18n.ProjectResourceBundle) org.apache.axis.i18n.resource::handleGetObject(newElem00) DEBUG (org.apache.axis.message.MessageElement) New MessageElement (org.apache.axis.message.MessageElement@112c22) named {}name DEBUG (org.apache.axis.encoding.DeserializationContext) Pushing element name DEBUG (org.apache.axis.utils.NSStack) NSPush (32) DEBUG (org.apache.axis.encoding.DeserializationContext) Exit: DeserializationContext::startElement() DEBUG (org.apache.axis.encoding.DeserializationContext) Enter: DeserializationContext::endElement(, name) DEBUG (org.apache.axis.i18n.ProjectResourceBundle) org.apache.axis.i18n.resource::handleGetObject(popHandler00) DEBUG (org.apache.axis.encoding.DeserializationContext) Popping handler org.apache.axis.message.SOAPHandler@16d22f1 DEBUG (org.apache.axis.utils.NSStack) NSPop (32) DEBUG (org.apache.axis.encoding.DeserializationContext) Popped element stack to org.apache.axis.message.MessageElement:property DEBUG (org.apache.axis.encoding.DeserializationContext) Exit: DeserializationContext::endElement() DEBUG (org.apache.axis.encoding.DeserializationContext) Enter: DeserializationContext::startElement(, value) DEBUG (org.apache.axis.i18n.ProjectResourceBundle) org.apache.axis.i18n.resource::handleGetObject(pushHandler00) DEBUG (org.apache.axis.encoding.DeserializationContext) Pushing handler org.apache.axis.message.SOAPHandler@16880ba DEBUG (org.apache.axis.i18n.ProjectResourceBundle) org.apache.axis.i18n.resource::handleGetObject(newElem00) DEBUG (org.apache.axis.message.MessageElement) New MessageElement (org.apache.axis.message.MessageElement@1db74af) named {}value DEBUG (org.apache.axis.encoding.DeserializationContext) Pushing element value DEBUG (org.apache.axis.utils.NSStack) NSPush (32) DEBUG (org.apache.axis.encoding.DeserializationContext) Exit: DeserializationContext::startElement() DEBUG (org.apache.axis.encoding.DeserializationContext) Enter: DeserializationContext::endElement(, value) DEBUG (org.apache.axis.i18n.ProjectResourceBundle) org.apache.axis.i18n.resource::handleGetObject(popHandler00) DEBUG (org.apache.axis.encoding.DeserializationContext) Popping handler org.apache.axis.message.SOAPHandler@16880ba DEBUG (org.apache.axis.utils.NSStack) NSPop (32) I cannot use Axis2 because of technical reasons. I have tried using HTTP Commons client instead of HTTP client but the response time remains the same. How can i link a different parser(example xerces 2.10.0 or xstream 1.3.1?) to Axis 1.4 framework in this context so that memory management and response time is favorable?.

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• 3D Web Sites and Applications

  - by Scott Evernden

  I have for the last several years been struggling to understand why the Internet has so few actually useful 3D web applications. It's 2009 and still everything looks like pages from a Sears catalog. You can turn on your TV and find flying logos every night. After that you can get nostalgic and flip on ol' N-64 and play some Zelda or Mario Kart. On the PC, Sims 2 is approaching 6 years old already.. And then there's WoW. Current generation of users - the Facebook crowd, let's say - has ~no~ problem dealing with multi-dimensional environments.. And yet, nothing really immersive seems to happen on the web. I've been hearing about VRML and X3D for at least 10 years and ... pffft .. - nothing earth shaking going on there. Java 3D ? .. cool ! .. but ...... Still .... waiting and waiting. Do you think it will take a killer-web app before people become accustomed-to or will seek to use what could more more engaging web experiences? I am not talking about Second Life and other dedicated downloaded applications. I probably am more focused on apps like Lively or SceneCaster or Hangout or a half dozen others that are delivered 'painlessly' directly into web pages. My own particular interest is in the domain of virtual stores and immersive shopping. Its been a challenge trying to understand why an average user would not want to browse and wander a changing mall-space - like in the real world -- entertained by unexpected discovery. Is the 3D web always going to be 5 years in the future ?

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• Boost Mersenne Twister: how to seed with more than one value?

  - by Eamon Nerbonne

  I'm using the boost mt19937 implementation for a simulation. The simulation needs to be reproducible, and that means storing and potentially reusing the RNG seeds later. I'm using the windows crypto api to generate the seed values because I need an external source for the seeds and not because of any particular guarantees of randomness. The output of any simulation run will have a note including the RNG seed - so the seed needs to be reasonably short. On the other hand, as part of the analysis of the simulation, I'll be comparing several runs - but to be sure that these runs are actually different, I'll need to use different seeds - so the seed needs to be long enough to avoid accidental collisions. I've determined that 64-bits of seeding should suffice; the chance of a collision will reach 50% after about 2^32 runs - that probability is low enough that the average error caused by it is negligible to me. Using just 32-bits of seed is tricky; the chance of a collision reaches 50% already after 2^16 runs; and that's a little too likely for my tastes. Unfortunately, the boost implementation either seeds with a full state vector - which is far, far too long - or a single 32-bit unsigned long - which isn't ideal. How can I seed the generator with more than 32-bits but less than a full state vector? I tried just padding the vector or repeating the seeds to fill the state vector, but even a cursory glance at the results shows that that generates poor results.

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• SQLiteDataAdapter Fill exception C# ADO.NET

  - by Lirik

  I'm trying to use the OleDb CSV parser to load some data from a CSV file and insert it into a SQLite database, but I get an exception with the OleDbAdapter.Fill method and it's frustrating: An unhandled exception of type 'System.Data.ConstraintException' occurred in System.Data.dll Additional information: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. Here is the source code: public void InsertData(String csvFileName, String tableName) { String dir = Path.GetDirectoryName(csvFileName); String name = Path.GetFileName(csvFileName); using (OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + dir + @";Extended Properties=""Text;HDR=No;FMT=Delimited""")) { conn.Open(); using (OleDbDataAdapter adapter = new OleDbDataAdapter("SELECT * FROM " + name, conn)) { QuoteDataSet ds = new QuoteDataSet(); adapter.Fill(ds, tableName); // <-- Exception here InsertData(ds, tableName); // <-- Inserts the data into the my SQLite db } } } class Program { static void Main(string[] args) { SQLiteDatabase target = new SQLiteDatabase(); string csvFileName = "D:\\Innovations\\Finch\\dev\\DataFeed\\YahooTagsInfo.csv"; string tableName = "Tags"; target.InsertData(csvFileName, tableName); Console.ReadKey(); } } The "YahooTagsInfo.csv" file looks like this: tagId,tagName,description,colName,dataType,realTime 1,s,Symbol,symbol,VARCHAR,FALSE 2,c8,After Hours Change,afterhours,DOUBLE,TRUE 3,g3,Annualized Gain,annualizedGain,DOUBLE,FALSE 4,a,Ask,ask,DOUBLE,FALSE 5,a5,Ask Size,askSize,DOUBLE,FALSE 6,a2,Average Daily Volume,avgDailyVolume,DOUBLE,FALSE 7,b,Bid,bid,DOUBLE,FALSE 8,b6,Bid Size,bidSize,DOUBLE,FALSE 9,b4,Book Value,bookValue,DOUBLE,FALSE I've tried the following: Removing the first line in the CSV file so it doesn't confuse it for real data. Changing the TRUE/FALSE realTime flag to 1/0. I've tried 1 and 2 together (i.e. removed the first line and changed the flag). None of these things helped... One constraint is that the tagId is supposed to be unique. Here is what the table look like in design view: Can anybody help me figure out what is the problem here?

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• Benchmarking a UDP server

  - by Nicolas

  I am refactoring a UDP listener from Java to C. It needs to handle between 1000 and 10000 UDP messages per second, with an average data length of around 60 bytes. There is no reply necessary. Data cannot be lost (Don't ask why UDP was decided). I fork off a process to deal with the incoming data so that I can recvfrom as quickly as possible - without filling up my kernel buffers. The child then handles the data received. In short, my algo is: Listen for data. When data is received, check for errors. Fork off a child. If I'm a child, do what I with the data and exit. If I'm a parent, reap any zombie children waitpid(-1, NULL, WNOHANG). Repeat. Firstly, any comments about the above? I'm creating the socket with socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP), binding with AF_INET and INADDR_ANY and recvfrom with no flags. Secondly, can anyone suggest something that I can use to test that this application (or at least the listener) can handle more messages than what I am expecting? Or, would I need to hack something together to do this. I'd guess the latter would be better, so that I can compare data that is generated versus data that is received. But, comments would be appreciated.

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• Difference in performance between Stax and DOM parsing

  - by Fazal

  I have been using DOM for a long time and as such DOM parsing performance wise has been pretty good. Even when dealing with XML of about 4-7 MB the parsing has been fast. The issue we face with DOM is the memory footprint which become huge as soon as we start dealing with large XMLs. Lately I tried moving to Stax (Streaming parsers for XML) which are supposed top be second generation parsers (reading about Stax it said its the fastest parser now). When I tried stax parser for large XML for about 4MB memory footprint definitely reduced drastically but time take to parse entire XML and create java object out of it increased almost by 5 times over DOM. I used sjsxp.jar implementation of Stax. I can deuce to some extent logically that performance may not be extremely good due to streaming nature of the parser but a reduction of 5 time (e.g. DOM takes about 8 seconds to build object for this XML, whereas Stax parsing took about 40 seconds on average) is definitely not going to be acceptable. Am I missing some point here completely as I am not able to come to terms with these performance numbers

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• Best fit curve for trend line

  - by Dave Jarvis

  Problem Constraints Size of the data set, but not the data itself, is known. Data set grows by one data point at a time. Trend line is graphed one data point at a time (using a spline/Bezier curve). Graphs The collage below shows data sets with reasonably accurate trend lines: The graphs are: Upper-left. By hour, with ~24 data points. Upper-right. By day for one year, with ~365 data points. Lower-left. By week for one year, with ~52 data points. Lower-right. By month for one year, with ~12 data points. User Inputs The user can select: the type of time series (hourly, daily, monthly, quarterly, annual); and the start and end dates for the time series. For example, the user could select a daily report for 30 days in June. Trend Weight To calculate the window size (i.e., the number of data points to average when calculating the trend line), the following expression is used: data points / trend weight Where data points is derived from user inputs and trend weight is 6.4. Even though a trend weight of 6.4 produces good fits, it is rather arbitrary, and might not be appropriate for different user inputs. Question How should trend weight be calculated given the constraints of this problem?

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• Can a single developer still make money with shareware?

  - by Wouter van Nifterick

  I'm wondering if the shareware concept is dead nowadays. Like most developers, I've built up quite a collection of self-made tools and code libraries that help me to be productive. Some examples to give you an idea of the type of thing I'm talking about: A self-learning program that renames and orders all my mp3 files and adds information to the id3 tags; A Delphi component that wraps the Google Maps API; A text-to-singing-voice converter for musical purposes; A program to control a music synthesizer; A Gps-log <- KML <- ESRI-shapefile converter; I've got one of these already freely downloadable on my website, and on average it gets downloaded about a 150 times per month. Let's say I'd start charging 15 euro's for it; would there actually be people who buy it? How many? What would it depend on? If I could get some money for some of these, I'd finish them up a bit and put them online, but without that, I probably won't bother. Maintaining a SourceForge project is not very rewarding by itself. Is there anyone who is making money with shareware? How much? Any tips?

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• detecting pauses in a spoken word audio file using pymad, pcm, vad, etc

  - by james

  First I am going to broadly state what I'm trying to do and ask for advice. Then I will explain my current approach and ask for answers to my current problems. Problem I have an MP3 file of a person speaking. I'd like to split it up into segments roughly corresponding to a sentence or phrase. (I'd do it manually, but we are talking hours of data.) If you have advice on how to do this programatically or for some existing utilities, I'd love to hear it. (I'm aware of voice activity detection and I've looked into it a bit, but I didn't see any freely available utilities.) Current Approach I thought the simplest thing would be to scan the MP3 at certain intervals and identify places where the average volume was below some threshold. Then I would use some existing utility to cut up the mp3 at those locations. I've been playing around with pymad and I believe that I've successfully extracted the PCM (pulse code modulation) data for each frame of the mp3. Now I am stuck because I can't really seem to wrap my head around how the PCM data translates to relative volume. I'm also aware of other complicating factors like multiple channels, big endian vs little, etc. Advice on how to map a group of pcm samples to relative volume would be key. Thanks!

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• What programming languages do the top tier Universities teach?

  - by Simucal

  I'm constantly being inundated with articles and people talking about how most of today's Universities are nothing more than Java vocational schools churning out mediocre programmer after mediocre programmer. Our very own Joel Spolsky has his famous article, "The Perils of Java Schools." Similarly, Alan Kay, a famous Computer Scientist (and SO member) has said this in the past: "I fear — as far as I can tell — that most undergraduate degrees in computer science these days are basically Java vocational training." - Alan Kay (link) If the languages being taught by the schools are considered such a contributing factor to the quality of the school's program then I'm curious what languages do the "top-tier" computer science schools teach (MIT, Carnegie Mellon, Stanford, etc)? If the average school is performing so poorly due in large part the languages (or lack of) that they teach then what languages do the supposed "good" cs programs teach that differentiate them? If you can, provide the name of the school you attended, followed by a list of the languages they use throughout their coursework. Edit: Shog-9 asks why I don't get this information directly from the schools websites themselves. I would, but many schools websites don't discuss the languages they use in their class descriptions. Quite a few will say, "using high-level languages we will...", without elaborating on which languages they use. So, we should be able to get a pretty accurate list of languages taught at various well known institutions from the various SO members who have attended at them.

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• Cross-platform game development: ease of development vs security

  - by alcuadrado

  Hi, I'm a member and contributor of the Argentum Online (AO) community, the first MMORPG from Argentina, which is Free Software; which, although it's not 3D, it's really addictive and has some dozens of thousands of users. Really unluckily AO was developed in Visual Basic (yes, you can laugh) but the former community, so imagine, the code not only sucks, it has zero portability. I'm planning, with some friends to rewrite the client, and as a GNU/Linux frantic, want to do it cross-platform. Some other people is doing the same with the server in Java. So my biggest problem is that we would like to use a rapid development language (like Java, Ruby or Python) but the client would be pretty insecure. Ruby/Python version would have all it's code available, and the Java one would be easily decompilable (yes, we have some crackers in the community) We have consider the option to implement the security module in C/C++ as a dynamic library, but it can be replaced with a custom one, so it's not really secure. We are also considering the option of doing the core application in C++ and the GUI in Ruby/Python. But haven't analysed all it's implications yet. But we really don't want to code the entire game in C/C++ as it doesn't need that much performance (the game is played at 18fps on average) and we want to develop it as fast as possible. So what would you choose in my case? Thank you!

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• Surprising results with .NET multi-theading algorithm

  - by Myles J

  Hi, I've recently wrote a C# console time tabling algorithm that is based on a combination of a genetic algorithm with a few brute force routines thrown in. The initial results were promising but I figured I could improve the performance by splitting the brute force routines up to run in parallel on multi processor architectures. To do this I used the well documented Producer/Consumer model (as documented in this fantastic article http://www.albahari.com/threading/part2.aspx#_ProducerConsumerQWaitHandle). I changed my code to create one thread per logical processor during the brute force routines. The performance gains on my work station were very pleasing. I am running Windows XP on the following hardware: Intel Core 2 Quad CPU 2.33 GHz 3.49 GB RAM Initial tests indicated average performance gains of approx 40% when using 4 threads. The next step was to deploy the new multi-threading version of the algorithm to our higher spec UAT server. Here is the spec of our UAT server: Windows 2003 Server R2 Enterprise x64 8 cpu (Quad-Core) AMD Opteron 2.70 GHz 255 GB RAM After running the first round of tests we were all extremely surprised to find that the algorithm actually runs slower on the high spec W2003 server than on my local XP work station! In fact the tests seem to indicate that it doesn't matter how many threads are generated (tests were ran with the app spawning between 2 to 32 threads). The algorithm always runs significantly slower on the UAT W2003 server? How could this be? Surely the app should run faster on a 8 cpu (Quad-Core) than my 2 Quad work station? Why are we seeing no performance gains with the multi-threading on the W2003 server whilst the XP workstation tests show gains of up to 40%? Any help or pointers would be appreciated. Regards Myles

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