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  • How are you taking advantage of Multicore?

    - by tgamblin
    As someone in the world of HPC who came from the world of enterprise web development, I'm always curious to see how developers back in the "real world" are taking advantage of parallel computing. This is much more relevant now that all chips are going multicore, and it'll be even more relevant when there are thousands of cores on a chip instead of just a few. My questions are: How does this affect your software roadmap? I'm particularly interested in real stories about how multicore is affecting different software domains, so specify what kind of development you do in your answer (e.g. server side, client-side apps, scientific computing, etc). What are you doing with your existing code to take advantage of multicore machines, and what challenges have you faced? Are you using OpenMP, Erlang, Haskell, CUDA, TBB, UPC or something else? What do you plan to do as concurrency levels continue to increase, and how will you deal with hundreds or thousands of cores? If your domain doesn't easily benefit from parallel computation, then explaining why is interesting, too. Finally, I've framed this as a multicore question, but feel free to talk about other types of parallel computing. If you're porting part of your app to use MapReduce, or if MPI on large clusters is the paradigm for you, then definitely mention that, too. Update: If you do answer #5, mention whether you think things will change if there get to be more cores (100, 1000, etc) than you can feed with available memory bandwidth (seeing as how bandwidth is getting smaller and smaller per core). Can you still use the remaining cores for your application?

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  • Passive and active sockets

    - by davsan
    Quoting from this socket tutorial: Sockets come in two primary flavors. An active socket is con­nect­ed to a remote active socket via an open data con­nec­tion... A passive socket is not con­nect­ed, but rather awaits an in­com­ing con­nec­tion, which will spawn a new active socket once a con­nec­tion is es­tab­lished ... Each port can have a single passive socket binded to it, await­ing in­com­ing con­nec­tions, and mul­ti­ple active sockets, each cor­re­spond­ing to an open con­nec­tion on the port. It's as if the factory worker is waiting for new mes­sages to arrive (he rep­re­sents the passive socket), and when one message arrives from a new sender, he ini­ti­ates a cor­re­spon­dence (a con­nec­tion) with them by del­e­gat­ing someone else (an active socket) to ac­tu­al­ly read the packet and respond back to the sender if nec­es­sary. This permits the factory worker to be free to receive new packets. ... Then the tutorial explains that, after a connection is established, the active socket continues receiving data until there are no remaining bytes, and then closes the connection. What I didn't understand is this: Suppose there's an incoming connection to the port, and the sender wants to send some little data every 20 minutes. If the active socket closes the connection when there are no remaining bytes, does the sender have to reconnect to the port every time it wants to send data? How do we persist a once established connection for a longer time? Can you tell me what I'm missing here? My second question is, who determines the limit of the concurrently working active sockets?

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  • How to decide between using PLINQ and LINQ at runtime?

    - by Hamish Grubijan
    Or decide between a parallel and a sequential operation in general. It is hard to know without testing whether parallel or sequential implementation is best due to overhead. Obviously it will take some time to train "the decider" which method to use. I would say that this method cannot be perfect, so it is probabilistic in nature. The x,y,z do influence "the decider". I think a very naive implementation would be to give both 1/2 chance at the beginning and then start favoring them according to past performance. This disregards x,y,z, however. I suspect that this question would be better answered by academics than practitioners. Anyhow, please share your heuristic, your experience if any, your tips on this. Sample code: public interface IComputer { decimal Compute(decimal x, decimal y, decimal z); } public class SequentialComputer : IComputer { public decimal Compute( ... // sequential implementation } public class ParallelComputer : IComputer { public decimal Compute( ... // parallel implementation } public class HybridComputer : IComputer { private SequentialComputer sc; private ParallelComputer pc; private TheDecider td; // Helps to decide between the two. public HybridComputer() { sc = new SequentialComputer(); pc = new ParallelComputer(); td = TheDecider(); } public decimal Compute(decimal x, decimal y, decimal z) { decimal result; decimal time; if (td.PickOneOfTwo() == 0) { // Time this and save result into time. result = sc.Compute(...); } else { // Time this and save result into time. result = pc.Compute(); } td.Train(time); return result; } }

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  • Can't open COM1 from application launched at startup

    - by n0rd
    I'm using WinLIRC with IR receiver connected to serial port COM1 on Windows 7 x64. WinLIRC is added to Startup folder (Start-All applications-Startup) so it starts every time I log in. Very often (but not all the time) I see initialization error messages from WinLIRC, which continue for some time (couple of minutes) if I retry initialization, and after some retries it initializes correctly and works fine. If I remove it from Startup and start manually at any other moment it starts without errors. I've downloaded WinLIRC sources and added MessageBox calls here and there so I can see what happens during initialization and found out that CreateFile call fails: if((hPort=CreateFile( settings.port,GENERIC_READ | GENERIC_WRITE, 0,0,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,0))==INVALID_HANDLE_VALUE) { char buffer[256]; sprintf_s(buffer, "CreateFile(%s) failed with %d", settings.port, GetLastError()); MessageBox(NULL, buffer, "debug", MB_OK); hPort=NULL; return false; } I see message box saying "CreateFile(COM1) failed with 5", and 5 is an error code for "Access denied" error according to this link. So the question is why opening COM-port can fail with such error right after booting Windows and proceed normally few seconds or minutes later?

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  • pfSense: How to route traffic out the WAN port?

    - by Ian Boyd
    Expert version i want to create a route in pfSense that will send traffic out the physical WAN port, not the PPPoE WAN port. i want to talk to talk to the web-server on my DSL modem, but it doesn't see packets wrapped in a PPPoE header. Long version My pfSense router is responsible for setting up the PPPoE connection over DSL to my ISP. When a machine on the LAN wants to sent packets to the internet, the default route sends packets out over the PPPoE connection. Those packets, wrapped in a PPPoE header, are sent on the ethernet cable to my DSL modem. From there they are sent the ISP, and the internet at large. i want a way to send a packet out the WAN port itself - not the PPPoE WAN port. My modem is sitting out there, with a http interface where i can monitor connection speed signal-to-noise ratio bandwidth connection time Whenever i try to set a route for destination of 192.168.2.1 (the IP that the modem will listen to for HTTP requests) to go out the WAN port, they instead end up going out the PPPoE port. The difference being that they're wrapped in a PPPoE protocol packet, and the modem isn't being sent the packet, it's being delivered to the ISP. Given that pfSense has no ability to direct traffic out the physical WAN port: how can i direct traffic out the physical WAN port on pfSense?

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  • better tool than netstat

    - by Stan
    OS: Windows server/ Windows XP Is there any port scan tool that can do what netstat does and also has a filter feature? So unnecessary connections can be hide. Thanks.

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  • Can't access Postfix TLS/SSL

    - by skerit
    I have set up my Postfix, with TLS/SSL, correctly. Every test on the machine itself (with telnet) runs fine. However, when I want to access the server from somewhere else, it fails. So port 587 and the rest is blocked for some reason, but I don't really know where.

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  • rsync to multiple destinations using same filelist?

    - by Dylan B.
    I'm wondering if it's possible for rsync to copy one directory to multiple remote destinations all in one go, or even in parallel. (not necessary, but would be useful.) Normally, something like the following would work just fine: $ rsync -Pav /junk user@host1:/backup $ rsync -Pav /junk user@host2:/backup $ rsync -Pav /junk user@host3:/backup And if that's the only option, I'll use that. However, /junk is located on a slow drive with quite a few files, and rebuilding the filelist of some ~12,000 files each time is agonizingly slow (~5 minutes) compared to the actual transfer/updating. Is it possible to do something like this, to accomplish the same thing: $ rsync -Pav /junk user@host1:/backup user@host2:/backup user@host3:/backup Thanks for looking!

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  • Can I have a virtual firewall forward packets to another virtual machine on the same server?

    - by cowgod
    I currently have a web server running Apache using iptables for a firewall. What I would like to do is setup a new machine with XenServer and install two virtual machines--one running IPCop and one running Linux with Apache. Then I would configure IPCop to have the external IP address and forward port 80 to an internal IP on the second virtual machine. Is this even possible?

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  • Zyxel P-320W: How to connect to my web server using public IP

    - by hvtuananh
    My company's router is Zyxel P-320W and I have a public static IP. I registered a few domains name and point to this IP address. I already setup Virtual Hosts and configured port-forwarding to my internal server and it works well. I can connect to all domains from outside The problem is I cannot connect to my domains from inside One workaround way is modify hosts file to add internal IP for those domains, but my company have many computers and I don't want to setup all PC manually

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  • Zyxel P-320W: How to connect to my web server using public IP

    - by hvtuananh
    My company's router is Zyxel P-320W and I have a public static IP. I registered a few domains name and point to this IP address. I already setup Virtual Hosts and configured port-forwarding to my internal server and it works well. I can connect to all domains from outside The problem is I cannot connect to my domains from inside One workaround way is modify hosts file to add internal IP for those domains, but my company have many computers and I don't want to setup all PC manually

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  • How to access an IP address as if on a different network using SSH

    - by NT3RP
    In preparation for a lengthy business trip, I set up my router such that I can access my home computer over the internet via port forwarding over SSH. One thing I neglected to do was setup access to my router remotely. Normally, I can just access the router configuration page via 192.168.1.1. I know that it's possible to tunnel traffic through SSH, but how do I access an IP address as if I were on my home network using SSH?

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  • Building a new cluster for mathematical calculations (Win/Lin)

    - by Muhammad Farhan
    I would like to build a new cluster to perform heavy mathematical calculations in Matlab and Abaqus. One of my friend told me that distributed computing is way faster than parallel computing, which is very true after reading a bit on the internet. However, I have never clustered before. Current workstation I own: Dell Precision T5400 2 x Intel Xeon 2.5 GHz 16 GB RAM (2GB x 8) 1 x Western Digital 1TB HDD 7200 rpm 1 x nVidia Quadro FX4600 768MB GPU 1 x 870W PSU OS: Windows 7 Ultimate 64-bit 2nd WS: I can buy another WS similar configuration to the one I own I am not bothered about OS, I am willing to cluster with either Windows or Linux. However, my software are compatible with windows 64-bit only. Please help me setup a cluster. Thank you.

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  • OpenVPN/Tunnelblick through wireless router, no connection.

    - by Oscar
    I'm using OpenVPN with Tunneblick on my Macbook Pro to access a server on my job. I't works fine, but i can't get it working with my Netgear WGT624v3 wireless router. I get this warning: WARNING: potential route subnet conflict between local LAN [192.168.1.0/255.255.255.0] and remote VPN [192.168.1.0/255.255.255.0] Someone told me that i should "port forward" on my router, but i can't figure out the right settings. Also not shure i'm doing it right.

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  • Any tool to check which ports/protocols firewalls prevent?

    - by Jus12
    Suppose I have a setup as: host_1 --- Firewall_1 --- Internet --- Firewall_2 --- host_2 I need to check which ports are open on host_2 from host_1 (which may be blocked by either firewalls) If there a tool that comes in two parts (one running on host_1 and other on host_2) that does this for me? It should be something like: 1 Listen to all ports on host_2 2 Try to connect to every port on host_2 from host_1 3 Give a report what ports are allowed.

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  • Dynamic DNS on D-Link DWR-112 3G router uses a private IP address

    - by user270151
    I'm using a D-Link DWR-112 3G router to connect to the internet by using Celcom broadband plug-in. How can I do the port forwarding to my server? I already have correctly configured my DynDNS, but every time the DynDNS will not set to public address but local private address with in the range 10.xxx.xxx.xxx. My router address is 192.168.1.1 and server address is 192.168.1.5. Can someone give me some guideline about this issue?

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  • Zyxel P-320W: How to connect to my web server using public IP

    - by hvtuananh
    My company's router is Zyxel P-320W and I have a public static IP. I registered a few domains name and point to this IP address. I already setup Virtual Hosts and configured port-forwarding to my internal server and it works well. I can connect to all domains from outside The problem is I cannot connect to my domains from inside One workaround way is modify hosts file to add internal IP for those domains, but my company have many computers and I don't want to setup all PC manually

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  • How to execute a command on multiple hosts using IPv6 only?

    - by math
    First of all there is pdsh which is essentially a parallel distributed shell which may execute commands on a list of given hosts. However, I find myself in an IPv6 only problem setting. It seems that pdsh is not able to use IPv6, as I am getting error messages: pdsh -w ^hostnames my_command pdsh@myhost: gethostbyname("foobar") failed I also tried to use IPv6 addresses only, which also didn't work. So how do you run a single shell script for administrative purpose (no SGE stuff, or similar) on a bunch of hosts that is IPv6 reachable only?

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  • How can I login (send text) with minicom?

    - by Travis
    I am attempting to login from a Linux client to a set top box running Linux via a USB to serial cable. When I power on the device, I can see the init messages scroll past, and I get to the login prompt, like this: (none) login: but I cannot login. The cursor stops flashing as if it is receiving input, but there is no response. My serial port setup is: Device: /dev/ttyUSB0 Bps: 115200 8N1 Hardware Flow Control: Yes Software Flow Control: No Any help would be greatly appreciated!

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  • Getting Serial Port Information and Sorting the Results in C#

    - by Jim Fell
    I have some code that loads the serial ports into a combo-box: comboBoxComPort.Items.Add("Select COM port..."); foreach (string s in SerialPort.GetPortNames()) { comboBoxComPort.Items.Add(s); } comboBoxComPort.SelectedIndex = 0; Ideally, I would like to add the port descriptions to the list and sort the items in the list that are after index 0. Does anyone have any suggestions for doing this? Any thoughts you may have would be appreciated. Thanks.

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  • java serial I/O: handling USB serial connection/disconnection in a robust manner

    - by Jason S
    I'm using rxtx for serial I/O handling in Java with an FTDI2232H that provides a USB comm port. It works great, with one exception: if I unplug the USB cable, so that the COM port disappears at runtime, it spews exceptions left and right: java.io.IOException: No error in nativeavailable at gnu.io.RXTXPort.nativeavailable(Native Method) at gnu.io.RXTXPort$SerialInputStream.read(RXTXPort.java:1427) at gnu.io.RXTXPort$SerialInputStream.read(RXTXPort.java:1339) and when I re-plug the cable in again, it does not recover. Is there any way to get rxtx to work properly with USB comm port connection/disconnection? (I've tried to post to the rxtx mailing list but for some strange reason I cannot send messages even though I am subscribed to the list. I've emailed the list admin and have gotten no response.) If not, is there another serial I/O framework that does?

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  • Configure a Port with an SSL Certificate w\o using Httpcfg

    - by dudia
    Hi, When one develops a self-hosted WCF http server, one of the steps needed is to bind an SSL certificate to a port number: httpcfg set ssl -i 0.0.0.0:8012 -h 0000000000003ed9cd0c315bbb6dc1c08da5e6 as stated in: http://msdn.microsoft.com/en-us/library/ms733791.aspx However, It is hardly expected that in my deployment environment one would be able to do it. (I don't even know if the httpcfg.exe is redistributable) Moreover, if the user changed the port after he installed the product then he will need to run the command again.... how can this step be automated pro grammatically? preferably in C# but if it can only be done in C++ (direct access to the Http Server API) then I will manage :)

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  • sudo port install cmake trouble (for MGTwitterEngine)

    - by RexOnRoids
    I am following This Tutorial on installing MGTwitterEngine on my MAC osx 10.6.2. I am stuck on this step: sudo port install cmake it gives me the following error: dlopen(/opt/local/share/macports/Tcl/pextlib1.0/Pextlib.dylib, 10): no suitable image found. Did find: /opt/local/share/macports/Tcl/pextlib1.0/Pextlib.dylib: no matching architecture in universal wrapper while executing "load /opt/local/share/macports/Tcl/pextlib1.0/Pextlib.dylib" ("package ifneeded Pextlib 1.0" script) invoked from within "package require Pextlib 1.0" (file "/opt/local/bin/port" line 40) Rex-MacBook-Pro:~ Rex$ Thus, I cannot use TERMINAL to install YAJL to get my app to build. Help needed. P.S. In terminal preferences, Shells Open With is either /usr/bin/login or /bin/bash YAJL is supposedly installed at /Users/Rex I am using OSX 10.6.2

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