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  • Why is execution-time method resolution faster than compile-time resolution?

    - by Felix
    At school, we about virtual functions in C++, and how they are resolved (or found, or matched, I don't know what the terminology is -- we're not studying in English) at execution time instead of compile time. The teacher also told us that compile-time resolution is much faster than execution-time (and it would make sense for it to be so). However, a quick experiment would suggest otherwise. I've built this small program: #include <iostream> #include <limits.h> using namespace std; class A { public: void f() { // do nothing } }; class B: public A { public: void f() { // do nothing } }; int main() { unsigned int i; A *a = new B; for (i=0; i < UINT_MAX; i++) a->f(); return 0; } Where I made A::f() once normal, once virtual. Here are my results: [felix@the-machine C]$ time ./normal real 0m25.834s user 0m25.742s sys 0m0.000s [felix@the-machine C]$ time ./virtual real 0m24.630s user 0m24.472s sys 0m0.003s [felix@the-machine C]$ time ./normal real 0m25.860s user 0m25.735s sys 0m0.007s [felix@the-machine C]$ time ./virtual real 0m24.514s user 0m24.475s sys 0m0.000s [felix@the-machine C]$ time ./normal real 0m26.022s user 0m25.795s sys 0m0.013s [felix@the-machine C]$ time ./virtual real 0m24.503s user 0m24.468s sys 0m0.000s There seems to be a steady ~1 second difference in favor of the virtual version. Why is this? Relevant or not: dual-core pentium @ 2.80Ghz, no extra applications running between two tests. Archlinux with gcc 4.5.0. Compiling normally, like: $ g++ test.cpp -o normal Also, -Wall doesn't spit out any warnings, either.

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  • Weighted round robins via TTL - possible?

    - by Joe Hopfgartner
    I currently use DNS round robin for load balancing, which works great. The records look like this (I have a ttl of 120 seconds) ;; ANSWER SECTION: orion.2x.to. 116 IN A 80.237.201.41 orion.2x.to. 116 IN A 87.230.54.12 orion.2x.to. 116 IN A 87.230.100.10 orion.2x.to. 116 IN A 87.230.51.65 I learned that not every ISP / device treats such a response the same way. For example some DNS servers rotate the addresses randomly or always cycle them through. Some just propagate the first entry, others try to determine which is best (regionally near) by looking at the ip address. However if the userbase is big enough (spreads over multiple ISPs etc) it balances pretty well. The discrepancies from highest to lowest loaded server hardly every exceeds 15%. However now I have the problem that I am introducing more servers into the systems, that not all have the same capacities. I currently only have 1gbps servers, but I want to work with 100mbit and also 10gbps servers too. So what I want is I want to introduce a server with 10 GBps with a weight of 100, a 1 gbps server with a weight of 10 and a 100 mbit server with a weight of 1. I used to add servers twice to bring more traffic to them (which worked nice. the bandwidth doubled almost.) But adding a 10gbit server 100 times to DNS is a bit rediculous. So I thought about using the TTL. If I give server A 240 seconds ttl and server B only 120 seconds (which is about about the minimum to use for round robin, as a lot of dns servers set to 120 if a lower ttl is specified.. so i have heard) I think something like this should occour in an ideal scenario: first 120 seconds 50% of requests get server A -> keep it for 240 seconds. 50% of requests get server B -> keep it for 120 seconds second 120 seconds 50% of requests still have server A cached -> keep it for another 120 seconds. 25% of requests get server A -> keep it for 240 seconds 25% of requests get server B -> keep it for 120 seconds third 120 seconds 25% will get server A (from the 50% of Server A that now expired) -> cache 240 sec 25% will get server B (from the 50% of Server A that now expired) -> cache 120 sec 25% will have server A cached for another 120 seconds 12.5% will get server B (from the 25% of server B that now expired) -> cache 120sec 12.5% will get server A (from the 25% of server B that now expired) -> cache 240 sec fourth 120 seconds 25% will have server A cached -> cache for another 120 secs 12.5% will get server A (from the 25% of b that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of b that now expired) -> cache 120 secs 12.5% will get server A (from the 25% of a that now expired) -> cache 240 secs 12.5% will get server B (from the 25% of a that now expired) -> cache 120 secs 6.25% will get server A (from the 12.5% of b that now expired) -> cache 240 secs 6.25% will get server B (from the 12.5% of b that now expired) -> cache 120 secs 12.5% will have server A cached -> cache another 120 secs ... i think i lost something at this point but i think you get the idea.... As you can see this gets pretty complicated to predict and it will for sure not work out like this in practice. But it should definitely have an effect on the distribution! I know that weighted round robin exists and is just controlled by the root server. It just cycles through dns records when responding and returns dns records with a set propability that corresponds to the weighting. My DNS server does not support this, and my requirements are not that precise. If it doesnt weight perfectly its okay, but it should go into the right direction. I think using the TTL field could be a more elegant and easier solution - and it deosnt require a dns server that controls this dynamically, which saves resources - which is in my opinion the whole point of dns load balancing vs hardware load balancers. My question now is... are there any best prectices / methos / rules of thumb to weight round robin distribution using the TTL attribute of DNS records? Edit: The system is a forward proxy server system. The amount of Bandwidth (not requests) exceeds what one single server with ethernet can handle. So I need a balancing solution that distributes the bandwidth to several servers. Are there any alternative methods than using DNS? Of course I can use a load balancer with fibre channel etc, but the costs are rediciulous and it also increases only the width of the bottleneck and does not eliminate it. The only thing i can think of are anycast (is it anycast or multicast?) ip addresses, but I don't have the means to set up such a system.

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  • What do you use to loadbalance IPv6 services?

    - by Michael Renner
    Hi, the current Linux software environment for IPv6 load balancing looks a bit grim. IPVS has rudimentary support for IPv6 but it's far from complete. NAT for IPv6 seems to be a no-go. Are there any other projects which aim for this goal? Does the IPv6 support in other OS look better? Are there any commercial products which have been successfully used in production environments with non-trivial load patterns? Or is it just that the time for IPv6 hasn't come... yet? ;) best regards, Michael

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  • Bullet Time in Real Life: Impacts Slowed Down with High Speed Cameras

    - by Jason Fitzpatrick
    Combine a little shooting range fun with a camera capable of shooting a million frames per second and you’ve got yourself the basis of pretty hypnotizing video. In the video above various rifle and handgun rounds are fired at a variety of materials–sheet metal, plate metal, gelatin–and captured in a halo of fragments and splatters. Have an equally enthralling high speed video to share? Throw a link in the comments! [via Mashable] How To Be Your Own Personal Clone Army (With a Little Photoshop) How To Properly Scan a Photograph (And Get An Even Better Image) The HTG Guide to Hiding Your Data in a TrueCrypt Hidden Volume

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  • google maps api v2 - dynamic load (tens of thousands of) markers

    - by Adam
    Hello, how made with JavaScript+PHP+MYSQL and Google Maps API v2 dynamic load of markers? atm I have map follow example http://googlemapsapi.martinpearman.co.uk/infusions/google_maps_api/basic_page.php?map_id=8 but my marker_data_01.php (where are all markers listed - look code of example) have atm 4MB and will only have more, and more. So the question is: how load only this markers to marker_data_01.php (of some other modification of it, can be on same file as map, meaningless, I load it all from MySQL atm) what I look now: so for example (I dont know what number will good but I write this only for show what I wanna made OR JUST something like it), so top left corner for example have position: 10, top right corner for example have position: 30, bottom left corner for example have position: 5, bottom right corner for example have position: 15. -- so load only this markers what are in this box 10-30-5-15 with for example GET, and when I move map for example to 17-12-48-20 box then made next GET request and with this mysql quote and download next markers that what I see now, with this I can have map with unlimited markers, and when will be a lot of markers then clustering can link them, so with this ppl dont will need do "preload" of all markers DB (what have 4mb now and will have more), but only download that what they see at the moment, I know that is possible because a lot sites have it but I am not master of code langs, I know only a bit php and mysql (and html) :) // sorry for my english

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  • login takes long time

    - by Arkaprovo Bhattacharjee
    I am using Ubuntu 12.04 from past 12 days. In the beginning login was fast enough after I put the password it hardly takes 3 to 4 sec to enter in desktop, but now its taking like more that 40 sec to show desktop after entering password. whats the problem, is there any solution? P.S there is only two programs (psensor and jupiter) that starts automatically after login. boot.log fsck from util-linux 2.20.1 /dev/sda6: clean, 254544/3325952 files, 2133831/13285632 blocks * Stopping Userspace bootsplash[164G[ OK ] * Stopping Flush boot log to disk[164G[ OK ] * Starting mDNS/DNS-SD daemon[164G[ OK ] Skipping profile in /etc/apparmor.d/disable: usr.sbin.rsyslogd Skipping profile in /etc/apparmor.d/disable: usr.bin.firefox * Starting bluetooth daemon[164G[ OK ] * Starting network connection manager[164G[ OK ] * Starting AppArmor profiles [170G [164G[ OK ] * Stopping System V initialisation compatibility[164G[ OK ] * Starting CUPS printing spooler/server[164G[ OK ] * Starting System V runlevel compatibility[164G[ OK ] * Starting Bumblebee supporting nVidia Optimus cards[164G[ OK ] * Starting LightDM Display Manager[164G[ OK ] * Starting save kernel messages[164G[ OK ] * Starting anac(h)ronistic cron[164G[ OK ] * Starting ACPI daemon[164G[ OK ] * Starting regular background program processing daemon[164G[ OK ] * Starting deferred execution scheduler[164G[ OK ] speech-dispatcher disabled; edit /etc/default/speech-dispatcher * Starting CPU interrupts balancing daemon[164G[ OK ]

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  • Which is the best way to deploy a JBoss application?

    - by andreash
    Hi there, we are currently developing a JBoss application. To deploy it, we have a total of four servers (three years old). I am wondering which might be the best to do? There could be a load balancer (even a load-balancer cluster, for failover) in front of two servers, each holding one JBoss and one PostgreSQl host inside XEN environments. Does this make sense? Are there other, better options? Thanks a lot for your advice!

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  • Dynamic User Specific CSS Selection at Run Time

    I had a cool question while I was at MIX. A developer needed the ability to have his site render pages using a CSS file selected based on some user specific criteria. ASP.NET 4 controls generate CSS friendly output and more and more we web developers are using CSS for layout etc. Using multiple CSS files in our site wide templates we can not only provide different aesthetic experiences but we can chage the style based on the device type (Printer ot Phone) or the special needs of the end user...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • No date/time shown before my page in Google search results

    - by Ruut
    I know that by changing the meta description of my webpage, I can control the texts shown by Google in the search results. However I do not know how I can control the text shown just before the search results, for example the date when the page was last updated. Which meta tag to use to accomplish this? UPDATE: My webpage is automatically updated on a weekly basis on irregular intervals by a cronjob which makes changes to the MySQL database which holds the content of my webpages. So the question is what (meta) info to add to my page.

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  • High Availability Configuration using Heartbeat and Pacemaker

    - by pradeepchhetri
    I have the following setup: I have configured high availability between two load balancers (HAProxy) so that if HAProxy1 get down, the floating IP gets transferred to the other load balancer HAProxy2, hence all the clients will get the response from HAProxy2, which at the back-end is doing LB among the sme two webserver. This is for removing the single point of failure in case of only one HAProxy. Whenever I stops the hearbeat in HAProxy1, the floating IP goes to HAProxy2. But I want to configure such that whenever the process haproxy goes down, the floating IP should get assigned to HAProxy2. Can someone tell me how to implement it ?

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  • Lending epub files for limited time to users

    - by JP Hellemons
    I am looking for components to build a digital library who lends people epub (ebooks) for about a week. It's like a digital version of the offline old public library. Now I have found several flash (pdf) file streaming solutions. But that would require an active internet link. And like the public library, you are able to take your books to the beach or pool on holiday abroad where you have no connection. So streaming is no option. The other file restriction method I have found was DRM, but that would require a really expensive license of Adobe Content Server 4 which is not suitable for my little hobby project. But it seems that adobe content server and Adobe Digital Editions is the only option at the moment. Or are there open source alternatives?

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  • Wikipedia A* pathfinding algorithm takes a lot of time

    - by Vee
    I've successfully implemented A* pathfinding in C# but it is very slow, and I don't understand why. I even tried not sorting the openNodes list but it's still the same. The map is 80x80, and there are 10-11 nodes. I took the pseudocode from here Wikipedia And this is my implementation: public static List<PGNode> Pathfind(PGMap mMap, PGNode mStart, PGNode mEnd) { mMap.ClearNodes(); mMap.GetTile(mStart.X, mStart.Y).Value = 0; mMap.GetTile(mEnd.X, mEnd.Y).Value = 0; List<PGNode> openNodes = new List<PGNode>(); List<PGNode> closedNodes = new List<PGNode>(); List<PGNode> solutionNodes = new List<PGNode>(); mStart.G = 0; mStart.H = GetManhattanHeuristic(mStart, mEnd); solutionNodes.Add(mStart); solutionNodes.Add(mEnd); openNodes.Add(mStart); // 1) Add the starting square (or node) to the open list. while (openNodes.Count > 0) // 2) Repeat the following: { openNodes.Sort((p1, p2) => p1.F.CompareTo(p2.F)); PGNode current = openNodes[0]; // a) We refer to this as the current square.) if (current == mEnd) { while (current != null) { solutionNodes.Add(current); current = current.Parent; } return solutionNodes; } openNodes.Remove(current); closedNodes.Add(current); // b) Switch it to the closed list. List<PGNode> neighborNodes = current.GetNeighborNodes(); double cost = 0; bool isCostBetter = false; for (int i = 0; i < neighborNodes.Count; i++) { PGNode neighbor = neighborNodes[i]; cost = current.G + 10; isCostBetter = false; if (neighbor.Passable == false || closedNodes.Contains(neighbor)) continue; // If it is not walkable or if it is on the closed list, ignore it. if (openNodes.Contains(neighbor) == false) { openNodes.Add(neighbor); // If it isn’t on the open list, add it to the open list. isCostBetter = true; } else if (cost < neighbor.G) { isCostBetter = true; } if (isCostBetter) { neighbor.Parent = current; // Make the current square the parent of this square. neighbor.G = cost; neighbor.H = GetManhattanHeuristic(current, neighbor); } } } return null; } Here's the heuristic I'm using: private static double GetManhattanHeuristic(PGNode mStart, PGNode mEnd) { return Math.Abs(mStart.X - mEnd.X) + Math.Abs(mStart.Y - mEnd.Y); } What am I doing wrong? It's an entire day I keep looking at the same code.

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  • Brasero Burns Data, Not Time - or Piles of Discs

    <b>Linux Insider:</b> "There are a lot of CD/DVD burners for Linux out there, but Brasero stands out as a straightforward, easy-to-use, burner that has some nice extra features but won't make you relearn a lot of complex commands if you only use it occasionally. One nicety is the option to start a burn project and finish it much later, even if you're not using a rewritable disc."

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  • creating the nodes for path finding during run time - more like path making and more

    - by bigbadbabybear
    i'm making my 1st game. i'm using javascript as i currently want to learn to make games without needing to learn another language but this is more of a general game dev question its a 2d turn-based tile/grid game. you can check it here http://www.patinterotest.tk/ it creates a movable area when you hover a player and it implements the A* algo for moving the player. The Problem: i want to make the 'dynamic movable area creation' already implement a limited number of steps for a player. The Questions: what is a good way to do this? is there another algorithm to use for this? the A* algorithm needs a start and destination, with what i want to do i don't have a destination or should i just limit the iteration of the A* algo to the steps variable? hopefully you understand the problem & questions easily

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  • Is event sourcing ready for prime time?

    - by Dakotah North
    Event Sourcing was popularized by LMAX as a means to provide speed, performance scalability, transparent persistence and transparent live mirroring. Before being rebranded as Event Sourcing, this type of architectural pattern was known as System Prevalence but yet I was never familiar with this pattern before the LMAX team went public. Has this pattern proved itself in numerous production systems and therefore even conservative individuals should feel empowered to embrace this pattern or is event sourcing / system prevalence an exotic pattern that is best left for the fearless?

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  • How to change harddrive spindown time?

    - by norpol
    if I run my notebook on battery mode, ubuntu spindown my hardrive every few seconds. How can I fix that? I have tried it with sudo hdparm -S 127 /dev/sda* but I am not able to disable the spindown and can´t find the reason for this "bug". Running Ubuntu 12.04 - Bug is since 12.04 Recent updates are installed, the problem is still recent. I can change the settings via. sudo hdparm -B 127 but if I change hdparm.conf, Ubuntu does not recognize it. /dev/sda { apm_battery=127 }

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  • How-to create a select one choice listing common time zones

    - by frank.nimphius
    Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} ADF Faces provides an option to query a list of common timezones for display in a Select One Choice component. The EL expression for this is #{af:getCommonTimeZoneSelectItems()}. To use this expression in a Single Select One Choice component, drag and drop the component from the Oracle JDeveloper Component Palette into a JSF page.  In the opened dialog, copy the expression into the Value property below the Bind to list (select items) header. <af:selectOneChoice label="TimeZones" id="soc1">  <f:selectItems value="#{af:getCommonTimeZoneSelectItems()}"                          id="si1"/></af:selectOneChoice>

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  • At the time of installing ubuntu, i am getting dark black screen only

    - by faruque
    I am trying to install Ubuntu 12.04 LTS dual boot with Windows 7, but when i click on Try or even Install ubuntu, i am getting black screen only. I can't see any text or anything else. When i see my Laptop's screen from close look, ubuntu in the middle of screen shown but screen is dark black. So because of this i am unable to install Ubuntu on my laptop. Please help in this regard. Following deatails of my laptop. Details of my Laptop: Manufacturer- Acer Aspire 4736 Processor- Intel core 2 duo CPU T660 Graphics driver- Mobile Intel(R) 4 series express chipset family (Microsoft corporation - WDDM 1.1), Current version installed- 8.15.10.2302 In ubuntu 11.04 i know how to boot into nomodeset, but i don't know how to boot through nomodeset in ubuntu 12.04 LTS. Because there is no option shown for F6 key. My laptop is Acer aspire 4736, and my Video/Graphics card shows unknown by ubuntu. Please someone help me. Can changing or upgrading my laptop's graphic card solve this problem..?? If yes then, which graphic card should i go for which is supported by Ubuntu and other Linux distros? Please someone help.

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  • Down Time

    - by andyleonard
    Introduction Every now and then, everyone needs a break. How do we respond when community leaders need a break? How should we respond? It's Normal People are cyclic animals - humans are diurnal by nature. We eat at regular intervals and are most comfortable when things go according to schedule. This is the lizard brain in action. So it's perfectly normal for community volunteers and leaders to engage in cycles of activity and inactivity in the community. It is, after all, another cycle. We rely on...(read more)

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