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• What are the responsibilities of the data layer?

  - by alimac83

  I'm working on a project where I had to add a data layer to my application. I've always thought that the data layer is purely responsible for CRUD functions ie. shouldn't really contain any logic but should simply retrieve data for the business layer to manipulate. However I'm a little confused with my project because I'm not sure whether I've structured my app correctly for this scenario. Basically I'm trying to retrieve a list of products from the database that fall within a certain pricing threshold. At the moment I have a function in my data layer that basically returns all products where price min threshold and price < max threshold. But it got me thinking that maybe this is incorrect. Should the data layer simply return a list of ALL products and then the business logic do the filtering? I'm pretty confused over whether the data layer should simply provide methods that allow the business layer to get raw data or whether it should be responsible for getting filtered data too? If anyone has an article or something explaining this in detail it'd be very helpful. Thanks

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• how to get access to private members of nested class?

  - by macias

  Background: I have enclosed (parent) class E with nested class N with several instances of N in E. In the enclosed (parent) class I am doing some calculations and I am setting the values for each instance of nested class. Something like this: n1.field1 = ...; n1.field2 = ...; n1.field3 = ...; n2.field1 = ...; ... It is one big eval method (in parent class). My intention is -- since all calculations are in parent class (they cannot be done per nested instance because it would make code more complicated) -- make the setters only available to parent class and getters public. And now there is a problem: when I make the setters private, parent class cannot acces them when I make them public, everybody can change the values and C# does not have friend concept I cannot pass values in constructor because lazy evaluation mechanism is used (so the instances have to be created when referencing them -- I create all objects and the calculation is triggered on demand) I am stuck -- how to do this (limit access up to parent class, no more, no less)? I suspect I'll get answer-question first -- "but why you don't split the evaluation per each field" -- so I answer this by example: how do you calculate min and max value of a collection? In a fast way? The answer is -- in one pass. This is why I have one eval function which does calculations and sets all fields at once.

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• [MySQL/PHP] Avoid using RAND()

  - by Andrew Ellis

  So... I have never had a need to do a random SELECT on a MySQL DB until this project I'm working on. After researching it seems the general populous says that using RAND() is a bad idea. I found an article that explains how to do another type of random select. Basically, if I want to select 5 random elements, I should do the following (I'm using the Kohana framework here)? If not, what is a better solution? Thanks, Andrew <?php final class Offers extends Model { /** * Loads a random set of offers. * * @param integer $limit * @return array */ public function random_offers($limit = 5) { // Find the highest offer_id $sql = ' SELECT MAX(offer_id) AS max_offer_id FROM offers '; $max_offer_id = DB::query(Database::SELECT, $sql) ->execute($this->_db) ->get('max_offer_id'); // Check to make sure we're not trying to load more offers // than there really is... if ($max_offer_id < $limit) { $limit = $max_offer_id; } $used = array(); $ids = ''; for ($i = 0; $i < $limit; ) { $rand = mt_rand(1, $max_offer_id); if (!isset($used[$rand])) { // Flag the ID as used $used[$rand] = TRUE; // Set the ID if ($i > 0) $ids .= ','; $ids .= $rand; ++$i; } } $sql = ' SELECT offer_id, offer_name FROM offers WHERE offer_id IN(:ids) '; $offers = DB::query(Database::SELECT, $sql) ->param(':ids', $ids) ->as_object(); ->execute($this->_db); return $offers; } }

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• Python's asyncore to periodically send data using a variable timeout. Is there a better way?

  - by Nick Sonneveld

  I wanted to write a server that a client could connect to and receive periodic updates without having to poll. The problem I have experienced with asyncore is that if you do not return true when dispatcher.writable() is called, you have to wait until after the asyncore.loop has timed out (default is 30s). The two ways I have tried to work around this is 1) reduce timeout to a low value or 2) query connections for when they will next update and generate an adequate timeout value. However if you refer to 'Select Law' in 'man 2 select_tut', it states, "You should always try to use select() without a timeout." Is there a better way to do this? Twisted maybe? I wanted to try and avoid extra threads. I'll include the variable timeout example here: #!/usr/bin/python import time import socket import asyncore # in seconds UPDATE_PERIOD = 4.0 class Channel(asyncore.dispatcher): def __init__(self, sock, sck_map): asyncore.dispatcher.__init__(self, sock=sock, map=sck_map) self.last_update = 0.0 # should update immediately self.send_buf = '' self.recv_buf = '' def writable(self): return len(self.send_buf) > 0 def handle_write(self): nbytes = self.send(self.send_buf) self.send_buf = self.send_buf[nbytes:] def handle_read(self): print 'read' print 'recv:', self.recv(4096) def handle_close(self): print 'close' self.close() # added for variable timeout def update(self): if time.time() >= self.next_update(): self.send_buf += 'hello %f\n'%(time.time()) self.last_update = time.time() def next_update(self): return self.last_update + UPDATE_PERIOD class Server(asyncore.dispatcher): def __init__(self, port, sck_map): asyncore.dispatcher.__init__(self, map=sck_map) self.port = port self.sck_map = sck_map self.create_socket(socket.AF_INET, socket.SOCK_STREAM) self.bind( ("", port)) self.listen(16) print "listening on port", self.port def handle_accept(self): (conn, addr) = self.accept() Channel(sock=conn, sck_map=self.sck_map) # added for variable timeout def update(self): pass def next_update(self): return None sck_map = {} server = Server(9090, sck_map) while True: next_update = time.time() + 30.0 for c in sck_map.values(): c.update() # <-- fill write buffers n = c.next_update() #print 'n:',n if n is not None: next_update = min(next_update, n) _timeout = max(0.1, next_update - time.time()) asyncore.loop(timeout=_timeout, count=1, map=sck_map)

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• I am looking for an actual functional web browser control for .NET, maybe a C++ library

  - by Joshua

  I am trying to emulate a web browser in order to execute JavaScript code and then parse the DOM. The System.Windows.Forms.WebBrowser object does not give me the functionality I need. It let's me set the headers, but you cannot set the proxy or clear cookies. Well you can, but it is not ideal and messes with IE's settings. I've been extending the WebBrowser control pinvoking native windows functions so far, but it is really one hack on top of another. I can mess with the proxy and also clear cookies and such, but this control has its issues as I mentioned. I found something called WebKit .NET (http://webkitdotnet.sourceforge.net/), but I don't see support for setting proxies or cookie manipulation. Can someone recommend a c++/.NET/whatever library to do this: Basically tell me what I need to do to get an interface to similar this in .NET: // this should probably pause the current thread for the max timeout, // throw an exception on failure or return null w/e, VAGUELY similar to this string WebBrowserEmu::FetchBrowserParsedHtml(Uri url, WebProxy p, int timeoutSeconds, byte[] headers, byte[] postdata); void WebBrowserEmu::ClearCookies(); I am not responsible for my actions.

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• Piping EOF problems with stdio and C++/Python

  - by yeus

  I got some problems with EOF and stdio. I have no idea what I am doing wrong. When I see an EOF in my program I clear the stdin and next round I try to read in a new line. The problem is: for some reason the getline function immediatly (from the second run always, the first works just as intended) returns an EOF instead of waiting for a new input from py python process... Any idea? alright Here is the code: #include <string> #include <iostream> #include <iomanip> #include <limits> using namespace std; int main(int argc, char **argv) { for (;;) { string buf; if (getline(cin,buf)) { if (buf=="q") break; /*****///do some stuff with input //my actual filter program cout<<buf; /*****/ } else { if ((cin.rdstate() & istream::eofbit)!=0)cout<<"eofbit"<<endl; if ((cin.rdstate() & istream::failbit)!=0)cout<<"failbit"<<endl; if ((cin.rdstate() & istream::badbit)!=0)cout<<"badbit"<<endl; if ((cin.rdstate() & istream::goodbit)!=0)cout<<"goodbit"<<endl; cin.clear(); cin.ignore(numeric_limits<streamsize>::max()); //break;//I am not using break, because I //want more input when the parent //process puts data into stdin; } } return 0; } and in python: from subprocess import Popen, PIPE import os from time import sleep proc=Popen(os.getcwd()+"/Pipingtest",stdout=PIPE,stdin=PIPE,stderr=PIPE); while(1): sleep(0.5) print proc.communicate("1 1 1") print "running"

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• Technology and language for a stable Digital Audio Workstation development

  - by Kill KRT

  Hi, I'm designing a cross platform (Windows/Linux/OS X) application, something like a digital audio workstation. I'd like to create a software where users have a fully featured sequencer (multiple tracks with automation) and where it is possible to create instruments using a visual language (as Pure Data/Max MSP). Ehm... I know that I've already posted a question about a related issue... But in order to decide which technology I should use, I think I'd better to make more investigation. I'm a quite experted user of audio trackers (Renoise, Protracker,...) and sequencers (FL Studio, Cubase 5), but I didn't ever try to develop even a basic audio tracker. I know just the basic theory of mixing sound and know how basically a DSP works. My questions are: Where I can find a good tutorial/guide/book about this issue? Do you think using C# (with NAudio) could dramatically reduce performance? I know C++ would be the best choice, but I find C# so elegant and easy to build and port, while C++ is so powerful and fast, but there are too #define and bad things for my taste! ;-) Thank you.

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• No Buffer Space available(maximum connection reached?) Form Postgres EDB Driver

  - by Listening.Platform

  We are facing an exception while connecting to database through our java application. The stack trace is as follows com.edb.util.PSQLException: The connection attempt failed. at com.edb.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:189) at com.edb.core.ConnectionFactory.openConnection(ConnectionFactory.java:64) at com.edb.jdbc2.AbstractJdbc2Connection.<init>(AbstractJdbc2Connection.java:161) at com.edb.jdbc3.AbstractJdbc3Connection.<init>(AbstractJdbc3Connection.java:30) at com.edb.jdbc3.Jdbc3Connection.<init>(Jdbc3Connection.java:24) at com.edb.Driver.makeConnection(Driver.java:391) at com.edb.Driver.connect(Driver.java:266) at java.sql.DriverManager.getConnection(Unknown Source) at java.sql.DriverManager.getConnection(Unknown Source) ... 12 more Caused by: java.net.SocketException: No buffer space available (maximum connections reached?): connect at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(Unknown Source) at java.net.PlainSocketImpl.connectToAddress(Unknown Source) at java.net.PlainSocketImpl.connect(Unknown Source) at java.net.SocksSocketImpl.connect(Unknown Source) at java.net.Socket.connect(Unknown Source) at java.net.Socket.connect(Unknown Source) at java.net.Socket.<init>(Unknown Source) at java.net.Socket.<init>(Unknown Source) at com.edb.core.PGStream.<init>(PGStream.java:70) at com.edb.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:115) ... 20 more When the error occured we were not able to connect to internet and DB and had to reboot the system. But the error occured again after 3 days at same code i.e while connecting to DB. We checked TCP connections using netstat. But there were not many TCP connections i.e it has not reached the max limit. Our application has multiple long running Java processes that pools the DB connections (not more than 60) and keeps it alive for firing the next query (as it has to poll the DB every 2 seconds). Some of the queries in our application are joining large tables (10 million records) to get the related data. We are using following System and applications Windows 2003 server SP2 Java 1.6 Postgres Plus Advanced server 8.4 Database edb-jdbc14.jar driver for connection DB from Java We have used the default configuration of Postgres DB except increasing the connection to 120 from 100. Has anybody encountred the same error with postgres edb driver? Can anybody help us finding the solution?

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• SIP UAS asks for OPTIONS

  - by TacB0sS

  Hey, I have UAC that registers to a UAS, after registration the UAS sends me an OPTIONS request, what should I answer it? only the audio media streams? Update I: Allow me to explain myself better... if I want to invite someone to a session I USE the INVITE method and negotiate the media then, for that specific session. But once I register to the server, and it asks me for OPTIONS, then what should I supply, everything my client supports? once I answer it would it deduce that every INVITE I would request from now on would use these medias? or would I need to supply new media with every request? Update II: Hi Wiz, I was in the process of building a negotiation system, so i tried it out and replied the UAS here is the sort dialog we had: OPTIONS sip:[email protected] SIP/2.0 Via: SIP/2.0/UDP xx.xx.xx.xx:5060;branch=z9hG4bK45b197cb;rport=5060;received=xx.xx.xx.xx From: "Unknown" <sip:[email protected]>;tag=as66cf26df To: <sip:[email protected]> Contact: <sip:[email protected]> Call-ID: [email protected] CSeq: 102 OPTIONS User-Agent: Freeswitch 1.2.3 Max-Forwards: 70 Date: Sat, 05 Jun 2010 12:06:43 GMT Allow: INVITE,ACK,CANCEL,OPTIONS,BYE,REFER,SUBSCRIBE,NOTIFY,INFO Supported: replaces Content-Length: 0 OPTIONS In Response To 102: SIP/2.0 200 OK Via: SIP/2.0/UDP xx.xx.xx.xx:5060;branch=z9hG4bK45b197cb;rport=5060;received=xx.xx.xx.xx From: "Unknown" <sip:[email protected]>;tag=as66cf26df To: <sip:[email protected]> CSeq: 102 OPTIONS Call-ID: [email protected] Allow: INVITE,CANCEL,ACK,BYE,OPTIONS Content-Type: application/sdp Content-Length: 248 v=0 o=310 4515233118481497946 4515233118481497946 IN IP4 10.0.0.1 s=- i=Nu-Art Software - TacB0sS VoIP information c=IN IP4 10.0.0.1 m=audio 40000 RTP/AVP 0 8 101 a=rtpmap:0 PCMU/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:101 telephone-event/8000 This response caused the server to stop sending me the options request, does this means I can only use these parameters with the server now? or as you said, it does not matter? Thanks, Adam.

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• Newsletter send using AJAX to avoid PHP timeout

  - by simPod

  I need to send newsletters. I have already a PHP script that sends mass emails but it won't work for long as email database is growing because of PHP max script run time. So, to avoid it I came up with a solution: I would call my PHP script using AJAX in javascript and I will give it $_GET parameter with a count 20 so the script would sent only 20 emails. Than AJAX would receive success response, and call my script again and again till all emails are send. Is it possible? I'm asking because I have never seen such a solution so I'm wondering if it is real (It's kinda hard to implement this into my PHP framework so I'm asking experts here first) To sum it up here's a code skeleton: <script> var emailCount = 1000; //would get this from DB var runCount = 20; //number of emails sent in one cycle var from = 0; //start number function sendMail(){ if(from<emailCount){ jQuery.ajaxfunction({ path: 'script.php?from='+from+'&count='+runCount successFc: function(){ from+=runCount; sendMail(); } }) } } sendMail(); </script> So, are there any obstacles? Thanks a lot.

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• X-Forwarded-For causing Undefined index in PHP

  - by bateman_ap

  Hi, I am trying to integrate some third party tracking code into one of my sites, however it is throwing up some errors, and their support isn't being much use, so i want to try and fix their code myself. Most I have fixed, however this function is giving me problems: private function getXForwardedFor() { $s =& $this; $xff_ips = array(); $headers = $s->getHTTPHeaders(); if ($headers['X-Forwarded-For']) { $xff_ips[] = $headers['X-Forwarded-For']; } if ($_SERVER['REMOTE_ADDR']) { $xff_ips[] = $_SERVER['REMOTE_ADDR']; } return implode(', ', $xff_ips); // will return blank if not on a web server } In my dev enviroment where I am showing all errors I am getting: Notice: Undefined index: X-Forwarded-For in /sites/webs/includes/OmnitureMeasurement.class.php on line 1129 Line 1129 is: if ($headers['X-Forwarded-For']) { If I print out $headers I get: Array ( [Host] => www.domain.com [User-Agent] => Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3 [Accept] => text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 [Accept-Language] => en-gb,en;q=0.5 [Accept-Encoding] => gzip,deflate [Accept-Charset] => ISO-8859-1,utf-8;q=0.7,*;q=0.7 [Keep-Alive] => 115 [Connection] => keep-alive [Referer] => http://www10.toptable.com/ [Cookie] => PHPSESSID=nh9jd1ianmr4jon2rr7lo0g553; __utmb=134653559.30.10.1275901644; __utmc=134653559 [Cache-Control] => max-age=0 ) I can't see X-Forwarded-For in there which I think is causing the problem. Is there something I should add to the function to take this into account? I am using PHP 5.3 and Apache 2 on Fedora

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• What is happening in this T-SQL code? (Concatenting the results of a SELECT statement)

  - by Ben McCormack

  I'm just starting to learn T-SQL and could use some help in understanding what's going on in a particular block of code. I modified some code in an answer I received in a previous question, and here is the code in question: DECLARE @column_list AS varchar(max) SELECT @column_list = COALESCE(@column_list, ',') + 'SUM(Case When Sku2=' + CONVERT(varchar, Sku2) + ' Then Quantity Else 0 End) As [' + CONVERT(varchar, Sku2) + ' - ' + Convert(varchar,Description) +'],' FROM OrderDetailDeliveryReview Inner Join InvMast on SKU2 = SKU and LocationTypeID=4 GROUP BY Sku2 , Description ORDER BY Sku2 Set @column_list = Left(@column_list,Len(@column_list)-1) Select @column_list ---------------------------------------- 1 row is returned: ,SUM(Case When Sku2=157 Then Quantity Else 0 End) As [157 -..., SUM(Case ... The T-SQL code does exactly what I want, which is to make a single result based on the results of a query, which will then be used in another query. However, I can't figure out how the SELECT @column_list =... statement is putting multiple values into a single string of characters by being inside a SELECT statement. Without the assignment to @column_list, the SELECT statement would simply return multiple rows. How is it that by having the variable within the SELECT statement that the results get "flattened" down into one value? How should I read this T-SQL to properly understand what's going on?

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• C++: select argmax over vector of classes w.r.t. arbitrary expression

  - by karpathy

  Hello, I have trouble describing my problem so I'll give an example: I have a class description that has a couple of variables in it, for example: class A{ float a, b, c, d; } Now, I maintain a vector<A> that contains many of these classes. What I need to do very very often is to find the object inside this vector that satisfies that one of it's parameters is maximal w.r.t to the others. i.e code looks something like: int maxi=-1; float maxa=-1000; for(int i=0;i<vec.size();i++){ res= vec[i].a; if(res > maxa) { maxa= res; maxi=i; } } return vec[maxi]; However, sometimes I need to find class with maximal a, sometimes with maximal b, sometimes the class with maximal 0.8*a + 0.2*b, sometimes I want a maximal a*VAR + b, where VAR is some variable that is assigned in front, etc. In other words, I need to evaluate an expression for every class, and take the max. I find myself copy-pasting this everywhere, and only changing the single line that defines res. What makes it even more complicated is that even the name of the vector changes. Sometimes it's vec, sometimes it can be something else. I have many vectors that contain A's. This could be changed if this makes the problem too hard. Is there some nice way to avoid this insanity in C++? What's the neatest way to handle this? Thank you!

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• capturing CMD batch file parameter list; write to file for later processing

  - by BobB

  I have written a batch file that is launched as a post processing utility by a program. The batch file reads ~24 parameters supplied by the calling program, stores them into variables, and then writes them to various text files. Since the max input variable in CMD is %9, it's necessary to use the 'shift' command to repeatedly read and store these individually to named variables. Because the program outputs several similar batch files, the result is opening several CMD windows sequentially, assigning variables and writing data files. This ties up the calling program for too long. It occurs to me that I could free up the calling program much faster if maybe there's a way to write a very simple batch file that can write all the command parameters to a text file, where I can process them later. Basically, just grab the parameter list, write it and done. Q: Is there some way to treat an entire series of parameter data as one big text string and write it to one big variable... and then echo the whole big thing to one text file? Then later read the string into %n variables when there's no program waiting to resume? Parameter list is something like 25 - 30 words, less than 200 characters. Sample parameter list: "First Name" "Lastname" "123 Steet Name Way" "Cityname" ST 12345 1004968 06/01/2010 "Firstname+Lastname" 101738 "On Account" 20.67 xy-1z 1 8.95 3.00 1.39 0 0 239 8.95 Items in quotes are processed as string variables. List is space delimited. Any suggestions?

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• Why Illegal cookies are send by Browser and received by web servers (rfc2109)?

  - by Artyom

  Hello, According to RFC 2109 cookie's value can be either HTTP token or quoted string, and token can't include non-ASCII characters. Cookie's RFC 2109: http://tools.ietf.org/html/rfc2109#page-3 HTTP's RFC 2068 token definition: http://tools.ietf.org/html/rfc2068#page-16 However I had found that Firefox browser (3.0.6) sends cookies with utf-8 string as-is and three web servers I tested (apache2, lighttpd, nginx) pass this string as-is to the application. For example, raw request from browser: $ nc -l -p 8080 GET /hello HTTP/1.1 Host: localhost:8080 User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.0.9) Gecko/2009050519 Firefox/2.0.0.13 (Debian-3.0.6-1) Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: windows-1255,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Cookie: wikipp=1234; wikipp_username=?????? Cache-Control: max-age=0 And raw response of apache, nginx and lighttpd HTTP_COOKIE CGI variable: wikipp=1234; wikipp_username=?????? What do I miss? Can somebody explain me?

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• python tkinter gui

  - by Lewis Townsend

  I'm wanting to make a small python program for yearly temperatures. I can get nearly everything working in the standard console but I'm wanting to implement it into a GUI. The program opens a csv file reads it into lists, works out the average, and min & max temps. Then on closing the application will save a summary to a new text file. I am wanting the default start up screen to show All Years. When a button is clicked it just shows that year's data. Here is a what I want it to look like. Pretty simple layout with just the 5 buttons and the out puts for each. I can make up the buttons for the top fine with: Code: class App: def __init__(self, master): frame = Frame(master) frame.pack() self.hi_there = Button(frame, text="All Years", command=self.All) self.hi_there.pack(side=LEFT) self.hi_there = Button(frame, text="2011", command=self.Y1) self.hi_there.pack(side=LEFT) self.hi_there = Button(frame, text="2012", command=self.Y2) self.hi_there.pack(side=LEFT) self.hi_there = Button(frame, text="2013", command=self.Y3) self.hi_there.pack(side=LEFT) self.hi_there = Button(frame, text="Save & Exit", command=self.Exit) self.hi_there.pack(side=LEFT) I'm not sure as to how to make the other elements, such as the title & table. I was going to post the code of the small program but decided not to. Once I have the structure/framework I think I can populate the fields & I might learn better this way. Using Python 2.7.3

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• How to save timers with connection to OrderId?

  - by Adrian Serafin

  Hi! I have a system where clients can make orders. After making order they have 60 minutes to pay fot it before it will be deleted. On the server side when order is made i create timer and set elapsed time to 60 minutes System.Timer.Timers timer = new System.Timers.Timer(1000*60*60); timer.AutoReset = false; timer.Elapsed += HandleElapsed; timer.Start(); Because I want to be able to dispose timer if client decides to pay and I want to be able to cancel order if he doesn't I keep two Dictionaries: Dictionary<int, Timer> _orderTimer; Dictionary<Timer, int> _timerOrder; Then when client pay's I can access Timer by orderId with O(1) thanks to _orderTimer dictionary and when time elapsed I can access order with O(1) thanks to _timerOrder dictionary. My question is: Is it good aproach? Assuming that max number of rows I have to keep in dictionary in one moment will be 50000? Maybe it would be better to derive from Timer class, add property called OrderId, keep it all in List and search for order/timer using linq? Or maybe you I should do this in different way?

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• How frequently IP packets are fragmented at the source host?

  - by Methos

  I know that if IP payload MTU then routers usually fragment the IP packet. Finally all the fragmented packets are assembled at the destination using the fields IP-ID, IP fragment offsets and fragmentation flags. Max length of IP payload is 64K. Thus its very plausible for L4 to hand over payload which is 64K. If the L2 protocol is Ethernet, which often is the case, then the MTU will be about 1600 bytes. Hence IP packet will be fragmented at the source host itself. However, a quick search about IP implementation in Linux tells me that in recent kernels, L4 protocols are fragment friendly i.e. they try to save the fragmentation work for IP by handing over buffers of size which is close to MTU. Considering these two facts, I am wondering about how frequently does the IP packet gets fragmented at the source host itself. Does it occur sometimes/rarely/never? Does anyone know if there are exceptions to the rule of fragmentation in linux kernel (i.e. are there situations where L4 protocols are not fragment friendly)? How is this handled in other common OSes like windows? In general how frequently IP packets are fragmented?

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• Compute weighted averages for large numbers

  - by Travis

  I'm trying to get the weighted average of a few numbers. Basically I have: Price - 134.42 Quantity - 15236545 There can be as few as one or two or as many as fifty or sixty pairs of prices and quantities. I need to figure out the weighted average of the price. Basically, the weighted average should give very little weight to pairs like Price - 100000000.00 Quantity - 3 and more to the pair above. The formula I currently have is: ((price)(quantity) + (price)(quantity) + ...)/totalQuantity So far I have this done: double optimalPrice = 0; int totalQuantity = 0; double rolling = 0; System.out.println(rolling); Iterator it = orders.entrySet().iterator(); while(it.hasNext()) { System.out.println("inside"); Map.Entry order = (Map.Entry)it.next(); double price = (Double)order.getKey(); int quantity = (Integer)order.getValue(); System.out.println(price + " " + quantity); rolling += price * quantity; totalQuantity += quantity; System.out.println(rolling); } System.out.println(rolling); return totalQuantity / rolling; The problem is I very quickly max out the "rolling" variable. How can I actually get my weighted average? Thanks!

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• How spoof referrer using curl

  - by golu molu

  I am using curl code below to spoof referrer , it works fine but there is error on every page - Curl error: $url = somesite.com function doMagic($url) { $curl = curl_init(); $header[0] = "Accept: text/xml,application/xml,application/xhtml+xml,"; $header[0] .= "text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5"; $header[] = "Cache-Control: max-age=0"; $header[] = "Connection: keep-alive"; $header[] = "Keep-Alive: 300"; $header[] = "Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7"; $header[] = "Accept-Language: en-us,en;q=0.5"; $header[] = "Pragma: "; curl_setopt($curl, CURLOPT_URL, $url); curl_setopt($curl, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:7.0.1) Gecko/20100101 Firefox/7.0.12011-10-16 20:23:00"); curl_setopt($curl, CURLOPT_HTTPHEADER, $header); curl_setopt($curl, CURLOPT_REFERER, "http://www.facebook.com"); curl_setopt($curl, CURLOPT_ENCODING, "gzip,deflate"); curl_setopt($curl, CURLOPT_AUTOREFERER, true); curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1); curl_setopt($curl, CURLOPT_TIMEOUT, 30); curl_setopt($curl, CURLOPT_FOLLOWLOCATION,true); $html = curl_exec($curl); echo 'Curl error: '. curl_error($curl); curl_close($curl); return $html; } $text = doMagic($url); print("$text"); what i'm doing wrong?

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• How can I differentiate a manual scroll (via mousewheel/scrollbar) from a Javascript/jQuery scroll?

  - by David Murdoch

  UPDATE: Here is a jsbin example demonstrating the problem. Basically, I have the following javascript which scrolls the window to an anchor on the page: // get anchors with href's that start with "#" $("a[href^=#]").live("click", function(){ var target = $($(this).attr("href")); // if the target exists: scroll to it... if(target[0]){ // If the page isn't long enough to scroll to the target's position // we want to scroll as much as we can. This part prevents a sudden // stop when window.scrollTop reaches its maximum. var y = Math.min(target.offset().top, $(document).height() - $(window).height()); // also, don't try to scroll to a negative value... y=Math.max(y,0); // OK, you can scroll now... $("html,body").stop().animate({ "scrollTop": y }, 1000); } return false; }); It works perfectly......until I manually try to scroll the window. When the scrollbar or mousewheel is scrolled I need to stop the current scroll animation...but I'm not sure how to do this. This is probably my starting point... $(window).scroll(e){ if(IsManuallyScrolled(e)){ $("html,body").stop(); } } ...but I'm not sure how to code the IsManuallyScrolled function. I've checked out e (the event object) in Google Chrome's console and AFAIK there is not way to differentiate between a manual scroll and jQuery's animate() scroll. How can I differentiate between a manual scroll and one called via jQuery's $.fn.animate function?

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• Want to display a 3D model on the iPhone: how to get started?

  - by JeremyReimer

  I want to display and rotate a single 3D model, preferably textured, on the iPhone. Doesn't have to zoom in and out, or have a background, or anything. I have the following: an iPhone a MacBook the iPhone SDK Blender My knowledge base: I can make 3D models in various 3D programs (I'm most comfortable with 3D Studio Max, which I once took a course on, but I've used others) General knowledge of procedural programming from years ago (QuickBasic - I'm old!) Beginner's knowledge of object-oriented programming from going through simple Java and C# tutorials (Head Start C# book and my wife's intro to OOP course that used Java) I have managed to display a 3D textured model and spin it using a tutorial in C# I got off the net (I didn't just copy and paste, I understand basically how it works) and the XNA game development library, using Visual Studio on Windows. What I do not know: Much about Objective C Anything about OpenGL or OpenGL ES, which the iPhone apparently uses Anything about XCode My main problem is that I don't know where to start! All the iPhone books I found seem to be about creating GUI applications, not OpenGL apps. I found an OpenGL book but I don't know how much, if any, applies to iPhone development. And I find the Objective C syntax somewhat confusing, with the weird nested method naming, things like "id" that don't make sense, and the scary thought that I have to do manual memory management. Where is the best place to start? I couldn't find any tutorials for this sort of thing, but maybe my Google-Fu is weak. Or maybe I should start with learning Objective C? I know of books like Aaron Hillgrass', but I've also read that they are outdated and much of the sample code doesn't work on the iPhone SDK, plus it seems geared towards the Model-View-Controller paradigm which doesn't seem that suited for 3D apps. Basically I'm confused about what my first steps should be.

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• Altering an embedded truetype font so it will be useable by Windows GDI

  - by Ritsaert Hornstra

  I am trying to render PDF content to a GDI device context (a 24bit bitmap to be exact). Parsing the PDF stream into PDF objects and rendering the PDF commands from the content dictionary works well, inclduing font rendering. Embedded fonts are decompressed from their FontFile streams and "loaded" using AddFontMemResourceEx. Now some embedded fonts remove some TrueType tables that are needed by GDI, like the NAME table. Because of this, I tried to modify the font by parsing the TrueType subset font into it's tables and modify those tables that have data missing / missing tables are regenerated with as correct information as possible. I use the Microsoft Font Validator tool to see how "correct" the generated font is. I still get a few errors, like for the maxp table the max values are usually too large (it is a subset) or The xAvgCharWidth field does not equal the calculated value of the OS/2 table is not correct but this does not stop other embedded fonts to be useable.The fonts embedded using PDFCreator are the ones that are problematic. Question: - How can I determine what I need to change to the font file in order for GDI to be able to use it? - Are there any other font validation tools that might give me insight into what is still wrong with the fontfile? If needed: I can make an original fontfile and an altered fontfile available for download somewhere.

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• Performance impact when using XML columns in a table with MS SQL 2008

  - by Sam Dahan

  I am using a simple table with 6 columns, 3 of which are of XML type, not schema-constrained. When the table reaches a size around 120,000 or 150,000 rows, I see a dramatic performance cost in doing any query in the table. For comparison, I have another table, which grows in size at about the same rate, but only contain scalar types (int, datetime, a few float columns). That table performs perfectly fine even after 200,000 rows. And by the way, I am not using XQuery on the xml columns, i am only using regular SQL query statements. Some specifics: both tables contain a DateTime field called SampleTime. a statement like (it's in a stored procedure but I show you the actual statement) SELECT MAX(sampleTime) SampleTime FROM dbo.MyRecords WHERE PlacementID=@somenumber takes 0 seconds on the table without xml columns, and anything from 13 to 20 seconds on the table with XML columns. That depends on which drive I set my database on. At the moment it sits on a different spindle (not C:) and it takes 13 seconds. Has anyone seen this behavior before, or have any hint at what I am doing wrong? I tried this with SQL 2008 EXPRESS and the full-blown SQL Server 2008, that made no difference. Oh, one last detail: I am doing this from a C# application, .NET 3.5, using SqlConnection, SqlReader, etc.. I'd appreciate some insight into that, thanks! Sam

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• nginx multiple domain virtual host configuration

  - by Poe

  I'm setting up nginx with multiple domain or wildcard support for convenience sake, rather than setting up 50+ different sites-available/* files. Hopefully this is enough to show you what I'm trying to do. Some are static sites, some are dynamic with usually wordpress installed. If an index.php exists, everything works as expected. If a file is requested that does not exist (missing.html), a 500 error is given due to the rewrite. The logged error is: *112 rewrite or internal redirection cycle while processing "/index.php/index.php/index.php/index.php/index.php/index.php/index.php/index.php/index.php/index.php/index.php/missing.html" The basic nginx configuration I'm currently using is: ` listen 80 default; server _; ... location / { root /var/www/$host; if (-f $request_filename) { expires max; break; } # problem, what if index.php does not exist? if (!-e $request_filename) { rewrite ^/(.*)$ /index.php/$1 last; } } ... ` If an index.php does not exist, and the file also does not exist, I would like it to error 404. Currently, nginx does not support multiple condition if's or nested if so I need a workaround.

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