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• Threading 101: What is a Dispatcher?

  - by Water Cooler v2

  Once upon a time, I remembered this stuff by heart. Over time, my understanding has diluted and I mean to refresh it. As I recall, any so called single threaded application has two threads: a) the primary thread that has a pointer to the main or DllMain entry points; and b) For applications that have some UI, a UI thread, a.k.a the secondary thread, on which the WndProc runs, i.e. the thread that executes the WndProc that recieves messages that Windows posts to it. In short, the thread that executes the Windows message loop. For UI apps, the primary thread is in a blocking state waiting for messages from Windows. When it recieves them, it queues them up and dispatches them to the message loop (WndProc) and the UI thread gets kick started. As per my understanding, the primary thread, which is in a blocking state, is this: C++ while(getmessage(/* args &msg, etc. */)) { translatemessage(&msg, 0, 0); dispatchmessage(&msg, 0, 0); } C# or VB.NET WinForms apps: Application.Run( new System.Windows.Forms() ); Is this what they call the Dispatcher? My questions are: a) Is my above understanding correct? b) What in the name of hell is the Dispatcher? c) Point me to a resource where I can get a better understanding of threads from a Windows/Win32 perspective and then tie it up with high level languages like C#. Petzold is sparing in his discussion on the subject in his epic work. Although I believe I have it somewhat right, a confirmation will be relieving.

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• What components and IDE add-ins do you install with Delphi?

  - by Mick

  After a clean install of Delphi, what components and IDE add-ins do you make certain that you install? What's your Delphi "rig"? Here's what I install after a clean installation: Delphi 2007 JCL / JVCL - JEDI Code Library and JEDI Visual Code Library (600+ components) JWA / JWSCL - JEDI API Library & Security Code Library GExperts - GExperts is a free set of tools built to increase the productivity of Delphi and C++Builder programmers by adding several features to the IDE. TWM's experimental GExperts code formatter - adds code formatting capabilities to Delphi Virtual TreeView - Virtual Treeview is a treeview control built from ground up. More than 5 years of development made it one of the most flexible and advanced tree controls available today. MustangPeak Components (EasyList View, Virtual ShellTools, etc) - EasyListview is a control that has no dependance on the Microsoft Listview control but has all the features of the latest version from Microsoft. Also includes 'Explorer.exe' like shell components. Synapse lightweight networking components - contains simple low level non-visual objects for easy programming without problems. (no required multi-threaded synchronization, no need for windows message processing,…) Great for command line utilities, visual projects, NT services EurekaLog - EurekaLog is a complete bug resolution tool for Delphi and C++Builder developers that gives your application the power to catch every exception and memory leak, directly on the end user PC, generating a detailed log of the call stack (with file, class, method and line number), optionally sending you a copy of each log entry via email or to a web bug-tracker. DelphiSpeedUp - DelphiSpeedUp is an IDE plugin for Delphi and C++Builder. It improves the IDE’s startup speed and increases the general speed of the whole IDE. DDevExtensions - DDevExtensions extends the Delphi/C++Builder IDE by adding some new productivity features. IDE Fix Pack - The IDE Fix Pack installs is a DLL-Expert that fixes the following RAD Studio 2007 bugs at runtime. All changes are done in memory. No file on disk is modified. TPerlRegex - Regular Expression library for Delphi How about other Delphi developers?

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• How does firefox chose which plugin to use?

  - by Brian Postow

  I have written a plugin which allows the user to view multi-page TIFF images within firefox. The problem is that Quicktime also thinks it can view TIFF images. How does Firefox chose which one gets used? through trial and error I've determined that: Sometimes, my plugin (Accel VIewTIFF) just runs, and everyone is happy. Sometimes I need to disable Quicktime in the Add-ons window. Sometimes I need to remove the QuickTime plugin files from the / Library/Internet Plug-ins folder (I'm on a mac) Sometimes I can put QuickTime BACK after having successfully run Accel ViewTIFF. I've yet to figure out when (if ever) each step is necessary. Please help me escape the cargo cult! (or at least point me to the right place in a manual.) thanks.

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• Suggestions for a nice&small - high battery life programmer notebook

  - by Emir

  Hi guys, I'm planning to buy a new notebook since the Toshiba I have now sucks in battery life. I'm a web designer & programmer, and the main features of the notebook should be: High battery life Small, 13.3" or 14" screen A fast processor and RAM that won't let me down while multi-tasking Anything other than these is secondary, I wouldn't like it to be very pricey though :) I'm now leaning towards Macbook Pro 13.3", 2.66 Ghz; it has 10 hours of battery life. However, I mostly develop on Windows, so I don't know how many hours of battery will I get if I run Windows 7 on Bootcamp. Your ideas and suggestions will be much appreciated.

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• Can I tell Castle Windsor to create a component in a separate AppDomain?

  - by Michael L Perry

  I've created a multi-threaded service that uses Castle Windsor to create components to run on separate threads. I Resolve an component by name with parameters for each thread. I'm running into concurrency problems with a 3rd party library used by the components. I suspect that isolating those components in separate AppDomains will resolve the problem. Is there a way to have Resolve create the component using a different AppDomain? private ActivityThread NewActivityThread(ActivityInstance activityInstance) { // Set up the creation arguments. System.Collections.IDictionary arguments = new Dictionary<string, string>(); activityInstance.Parameters.ForEach(p => arguments.Add(p.Name, p.Value)); // Get the activity handler from the container. IActivity activity = Program.Container.Resolve<IActivity>(activityInstance.Name, arguments); // Create a thread for the activity. ActivityThread thread = new ActivityThread(activity, activityInstance, _nextActivityID++); return thread; } public ActivityThread(IActivity activity, ActivityInstance instance, int id) { _activity = activity; _instance = instance; _id = id; } public void Start() { if (_thread == null) { // Create a new thread to run this activity. _thread = new Thread(delegate() { _activity.Run(); }); _thread.Name = _activity.ToString(); _thread.SetApartmentState(ApartmentState.STA); _thread.Start(); } }

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• ECC RAM in GA-G33M-DS2R? Or any Gigabyte/G33M motherboard?

  - by Gregory Hoerner

  I'm looking to retire a server which has 12GB of ECC DDR2 RAM. I'd like to upgrade my multi-purpose machine (firewall, file server, VM host for Windows Home Server, etc.) using the RAM from the server. I was just wondering: Has anyone had experience using ECC RAM in a GA-G33M-DS2R motherboard (or any Gigabyte GA-G33M-XXXX motherboard for that matter)? Has anyone had experience using ECC RAM in a motherboard with a G33M chipset. I've searched everywhere and found the attitude positive of ECC memory working in a Non-ECC board, but I would like some specific positive feedback before proceeding tonight. I have to kick the entire house offline, which I don't like to do without good reason :)

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• ADSIEdit freezes gettings properties of a group with hundred of thousands members

  - by ixe013

  Doing performance testing on an AD-LDS (Server 2008 R2 64 bits), we created a milion user in a single OU. We also created a single group object and made those milion users member of that group. When we try to list the milion of users ADSIEdit times out with an error message saying it cannot display that many users. Fine. But if we open the properties for the group, ADSIEdit freezes, eating up all available memory and CPU trashing (nearly 60M page faults in under an hour). AD-LDS (running on another computer) is barely hitting the 1% CPU mark, servicing other ldap requests as if nothing were. We can throw more memory at the problem, but more users will have to be managed one day and we will be back at square one. Is there a way to set a limit in ADSIEdit so that it will not hang the computer when retreving a very large multi-value object ?

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• Why would cat6 connectors not work with cat5e patch cable?

  - by Lee Tickett

  I had a naff batch of cat5 connectors (the latching mechanism didn't work) so decided to order in some cat6 connectors in preparation for the inevitable upgrade. My existing reel of for making patch cables is cat5e utp stranded. I made up a few cables and tested them- none of them worked. I recrimped and still nothing. When i check them with a multi-meter not all pins are connected. This reel has always worked with the previous cat5 connectors so I tested the cat6 connectors on a reel of solid cat5e cable and they work fine. Any ideas what I might be doing wrong? Or what might be at fault? (cable/connectors) and how I can diagnose? Thanks Lee

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• httpd not starting with systemd on F17

  - by malfy

  Title says it all. This is a fresh Fedora 17 system running on a Xen hypervisor. No idea why it won't start [root@box~]  uname -a Linux box.localhost 3.5.4-2.fc17.i686.PAE #1 SMP Wed Sep 26 22:10:23 UTC 2012 i686 i686 i386 GNU/Linux [root@box~]  cat /etc/redhat-release Fedora release 17 (Beefy Miracle) [root@box~]  systemctl enable httpd.service ln -s '/usr/lib/systemd/system/httpd.service' '/etc/systemd/system/multi-user.target.wants/httpd.service' [root@box~]  systemctl start httpd.service Job failed. See system journal and 'systemctl status' for details. [root@box~]  systemctl status httpd.service httpd.service - The Apache HTTP Server (prefork MPM) Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled) Active: failed (Result: exit-code) since Fri, 19 Oct 2012 22:43:37 -0500; 3s ago Process: 18225 ExecStart=/usr/sbin/httpd $OPTIONS -k start (code=exited, status=226/NAMESPACE) CGroup: name=systemd:/system/httpd.service Oct 19 22:43:37 box.localhost systemd[18225]: Failed at step NAMESPACE spawning /usr/sbin/httpd: No such file or directory [root@box~]  ls -al /usr/sbin/httpd -rwxr-xr-x 1 root root 343496 Apr 30 04:56 /usr/sbin/httpd

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• Flex textarea control not updating properly.

  - by ielashi

  I am writing a flex application that involves modifying a textarea very frequently. I have encountered issues with the textarea sometimes not displaying my modifications. The following actionscript code illustrates my problem: <?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" minWidth="955" minHeight="600"> <mx:TextArea x="82" y="36" width="354" height="291" id="textArea" creationComplete="initApp()"/> <mx:Script> <![CDATA[ private var testSentence:String = "The big brown fox jumps over the lazy dog."; private var testCounter:int = 0; private function initApp():void { var timer:Timer = new Timer(10); timer.addEventListener(TimerEvent.TIMER, playSentence); timer.start(); } private function playSentence(event:TimerEvent):void { textArea.editable = false; if (testCounter == testSentence.length) { testCounter = 0; textArea.text += "\n"; } else { textArea.text += testSentence.charAt(testCounter++); } textArea.editable = true; } ]]> </mx:Script> </mx:Application> When you run the above code in a flex project, it should repeatedly print, character by character, the sentence "The big brown fox jumps over the lazy dog.". But, if you are typing into the textarea at the same time, you will notice the text the timer prints is distorted. I am really curious as to why this happens. The single-threaded nature of flex and disabling user input for the textarea when I make modifications should prevent this from happening, but for some reason this doesn't seem to be working. I must note too that, when running the timer at larger intervals (around 100ms) it seems to work perfectly, so I am tempted to think it's some kind of synchronization issue in the internals of the flex framework. Any ideas on what could be causing the problem?

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• Thread resource sharing

  - by David

  I'm struggling with multi-threaded programming... I have an application that talks to an external device via a CAN to USB module. I've got the application talking on the CAN bus just fine, but there is a requirement for the application to transmit a "heartbeat" message every second. This sounds like a perfect time to use threads, so I created a thread that wakes up every second and sends the heartbeat. The problem I'm having is sharing the CAN bus interface. The heartbeat must only be sent when the bus is idle. How do I share the resource? Here is pseudo code showing what I have so far: TMainThread { Init: CanBusApi =new TCanBusApi; MutexMain =CreateMutex( "CanBusApiMutexName" ); HeartbeatThread =new THeartbeatThread( CanBusApi ); Execution: WaitForSingleObject( MutexMain ); CanBusApi->DoSomething(); ReleaseMutex( MutexMain ); } THeartbeatThread( CanBusApi ) { Init: MutexHeart =CreateMutex( "CanBusApiMutexName" ); Execution: Sleep( 1000 ); WaitForSingleObject( MutexHeart ); CanBusApi->DoHeartBeat(); ReleaseMutex( MutexHeart ); } The problem I'm seeing is that when DoHeartBeat is called, it causes the main thread to block while waiting for MutexMain as expected, but DoHeartBeat also stops. DoHeartBeat doesn't complete until after WaitForSingleObject(MutexMain) times out in failure. Does DoHeartBeat execute in the context of the MainThread or HeartBeatThread? It seems to be executing in MainThread. What am I doing wrong? Is there a better way? Thanks, David

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• OpenVPN on ec2 bridged mode connects but no Ping, DNS or forwarding

  - by michael

  I am trying to use OpenVPN to access the internet over a secure connection. I have openVPN configured and running on Amazon EC2 in bridge mode with client certs. I can successfully connect from the client, but I cannot get access to the internet or ping anything from the client I checked the following and everything seems to shows a successful connection between the vpn client/server and UDP traffic on 1194 [server] sudo tcpdump -i eth0 udp port 1194 (shows UDP traffic after establishing connection) [server] sudo iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere Chain FORWARD (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination [server] sudo iptables -L -t nat Chain PREROUTING (policy ACCEPT) target prot opt source destination Chain POSTROUTING (policy ACCEPT) target prot opt source destination MASQUERADE all -- ip-W-X-Y-0.us-west-1.compute.internal/24 anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination [server] openvpn.log Wed Oct 19 03:11:26 2011 localhost/a.b.c.d:61905 [localhost] Inactivity timeout (--ping-restart), restarting Wed Oct 19 03:11:26 2011 localhost/a.b.c.d:61905 SIGUSR1[soft,ping-restart] received, client-instance restarting Wed Oct 19 03:41:31 2011 MULTI: multi_create_instance called Wed Oct 19 03:41:31 2011 a.b.c.d:57889 Re-using SSL/TLS context Wed Oct 19 03:41:31 2011 a.b.c.d:57889 LZO compression initialized Wed Oct 19 03:41:31 2011 a.b.c.d:57889 Control Channel MTU parms [ L:1574 D:166 EF:66 EB:0 ET:0 EL:0 ] Wed Oct 19 03:41:31 2011 a.b.c.d:57889 Data Channel MTU parms [ L:1574 D:1450 EF:42 EB:135 ET:32 EL:0 AF:3/1 ] Wed Oct 19 03:41:31 2011 a.b.c.d:57889 Local Options hash (VER=V4): '360696c5' Wed Oct 19 03:41:31 2011 a.b.c.d:57889 Expected Remote Options hash (VER=V4): '13a273ba' Wed Oct 19 03:41:31 2011 a.b.c.d:57889 TLS: Initial packet from [AF_INET]a.b.c.d:57889, sid=dd886604 ab6ebb38 Wed Oct 19 03:41:35 2011 a.b.c.d:57889 VERIFY OK: depth=1, /C=US/ST=CA/L=SanFrancisco/O=EXAMPLE/CN=EXAMPLE_CA/[email protected] Wed Oct 19 03:41:35 2011 a.b.c.d:57889 VERIFY OK: depth=0, /C=US/ST=CA/L=SanFrancisco/O=EXAMPLE/CN=localhost/[email protected] Wed Oct 19 03:41:37 2011 a.b.c.d:57889 Data Channel Encrypt: Cipher 'BF-CBC' initialized with 128 bit key Wed Oct 19 03:41:37 2011 a.b.c.d:57889 Data Channel Encrypt: Using 160 bit message hash 'SHA1' for HMAC authentication Wed Oct 19 03:41:37 2011 a.b.c.d:57889 Data Channel Decrypt: Cipher 'BF-CBC' initialized with 128 bit key Wed Oct 19 03:41:37 2011 a.b.c.d:57889 Data Channel Decrypt: Using 160 bit message hash 'SHA1' for HMAC authentication Wed Oct 19 03:41:37 2011 a.b.c.d:57889 Control Channel: TLSv1, cipher TLSv1/SSLv3 DHE-RSA-AES256-SHA, 1024 bit RSA Wed Oct 19 03:41:37 2011 a.b.c.d:57889 [localhost] Peer Connection Initiated with [AF_INET]a.b.c.d:57889 Wed Oct 19 03:41:39 2011 localhost/a.b.c.d:57889 PUSH: Received control message: 'PUSH_REQUEST' Wed Oct 19 03:41:39 2011 localhost/a.b.c.d:57889 SENT CONTROL [localhost]: 'PUSH_REPLY,redirect-gateway def1 bypass-dhcp,route-gateway W.X.Y.Z,ping 10,ping-restart 120,ifconfig W.X.Y.Z 255.255.255.0' (status=1) Wed Oct 19 03:41:40 2011 localhost/a.b.c.d:57889 MULTI: Learn: (IPV6) -> localhost/a.b.c.d:57889 [client] tracert google.com Tracing route to google.com [74.125.71.104] over a maximum of 30 hops: 1 347 ms 349 ms 348 ms PC [w.X.Y.Z] 2 * * * Request timed out. I can also successfully ping the server IP address from the client, and ping google.com from an SSH shell on the server. What am I doing wrong? Here is my config (Note: W.X.Y.Z == amazon EC2 private ipaddress) bridge config on br0 ifconfig eth0 0.0.0.0 promisc up brctl addbr br0 brctl addif br0 eth0 ifconfig br0 W.X.Y.X netmask 255.255.255.0 broadcast W.X.Y.255 up route add default gw W.X.Y.1 br0 /etc/openvpn/server.conf (from https://help.ubuntu.com/10.04/serverguide/C/openvpn.html) local W.X.Y.Z dev tap0 up "/etc/openvpn/up.sh br0" down "/etc/openvpn/down.sh br0" ;server W.X.Y.0 255.255.255.0 server-bridge W.X.Y.Z 255.255.255.0 W.X.Y.105 W.X.Y.200 ;push "route W.X.Y.0 255.255.255.0" push "redirect-gateway def1 bypass-dhcp" push "dhcp-option DNS 208.67.222.222" push "dhcp-option DNS 208.67.220.220" tls-auth ta.key 0 # This file is secret user nobody group nogroup log-append openvpn.log iptables config sudo iptables -A INPUT -i tap0 -j ACCEPT sudo iptables -A INPUT -i br0 -j ACCEPT sudo iptables -A FORWARD -i br0 -j ACCEPT sudo iptables -t nat -A POSTROUTING -s W.X.Y.0/24 -o eth0 -j MASQUERADE echo 1 > /proc/sys/net/ipv4/ip_forward Routing Tables added route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface W.X.Y.0 0.0.0.0 255.255.255.0 U 0 0 0 br0 0.0.0.0 W.X.Y.1 0.0.0.0 UG 0 0 0 br0 C:>route print =========================================================================== Interface List 32...00 ff ac d6 f7 04 ......TAP-Win32 Adapter V9 15...00 14 d1 e9 57 49 ......Microsoft Virtual WiFi Miniport Adapter #2 14...00 14 d1 e9 57 49 ......Realtek RTL8191SU Wireless LAN 802.11n USB 2.0 Net work Adapter 10...00 1f d0 50 1b ca ......Realtek PCIe GBE Family Controller 1...........................Software Loopback Interface 1 11...00 00 00 00 00 00 00 e0 Teredo Tunneling Pseudo-Interface 16...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter 17...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #2 18...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #3 36...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter #5 =========================================================================== IPv4 Route Table =========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric 0.0.0.0 0.0.0.0 10.1.2.1 10.1.2.201 25 10.1.2.0 255.255.255.0 On-link 10.1.2.201 281 10.1.2.201 255.255.255.255 On-link 10.1.2.201 281 10.1.2.255 255.255.255.255 On-link 10.1.2.201 281 127.0.0.0 255.0.0.0 On-link 127.0.0.1 306 127.0.0.1 255.255.255.255 On-link 127.0.0.1 306 127.255.255.255 255.255.255.255 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 127.0.0.1 306 224.0.0.0 240.0.0.0 On-link 10.1.2.201 281 255.255.255.255 255.255.255.255 On-link 127.0.0.1 306 255.255.255.255 255.255.255.255 On-link 10.1.2.201 281 =========================================================================== Persistent Routes: Network Address Netmask Gateway Address Metric 0.0.0.0 0.0.0.0 10.1.2.1 Default =========================================================================== C:>tracert google.com Tracing route to google.com [74.125.71.147] over a maximum of 30 hops: 1 344 ms 345 ms 343 ms PC [W.X.Y.221] 2 * * * Request timed out.

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• MySQL performance

  - by kapil.israni

  Hi, I have this LAMP application with about 900k rows in MySQL and I am having some performance issues. Background - Apart from the LAMP stack , there's also a Java process (multi-threaded) that runs in its own JVM. So together with LAMP & java, they form the complete solution. The java process is responsible for inserts/updates and few selects as well. These inserts/updates are usually in bulk/batch, anywhere between 5-150 rows. The PHP front-end code only does SELECT's. Issue - the PHP/SELECT queries become very slow when the java process is running. When the java process is stopped, SELECT's perform alright. I mean the performance difference is huge. When the java process is running, any action performed on the php front-end results in 80% and more CPU usage for mysqld process. Any help would be appreciated. MySQL is running with default parameters & settings. Software stack - Apache - 2.2.x MySQL -5.1.37-1ubuntu5 PHP - 5.2.10 Java - 1.6.0_15 OS - Ubuntu 9.10 (karmic)

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• Delay between printing via lp in opensuse

  - by adamweeks

  I am experiencing a 10-15 second delay when printing multiple documents to a barcode printer in opensuse. I have had the same setup on other systems with older versions of opensuse without any issue. The setup is as follows: The print queue is setup as a "generic with driver Raw Queue". The files being sent down to the printers are simple text files with the lp command: lp -dprinter1 /path/file The printer is a JetDirect compatible device (Intermec brand) with a standard 9100 port socket setup. If I send a multi-page document to the printer, it will print nonstop the multiple pages. If I send 2 or more text files down via separate "lp" commands, the delay will be there between each printout. I've tried multiple different printers and they all experience the same issue.

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• systemd initiated uwsgi process shuts down after a while

  - by Calvin Cheng

  So I wrote this simple systemd service script:- [Unit] Description=uwsgi server script [Service] User=web Group=web WorkingDirectory=/var/www/prod/myproject/releases/current ExecStart=/bin/bash -c 'source ~/.bash_profile; workon myproject; uwsgi --ini /var/www/prod/myproject/releases/current/myproject/uwsgi_prod.ini' [Install] WantedBy=multi-user.target which works fine - it starts up and I can see my uwsgi processes in htop. However, it inexplicably shuts down after being idle for 5 minutes. If I start this process manually in bash console by executing, as web user:- source ~/.bash_profile workon myproject uwsgi --ini /var/www/prod/myproject/releases/current/myproject/uwsgi_prod.ini my process does not die after being idle. What could the problem be?

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• POSIX AIO Library and Callback Handlers

  - by Charles Salvia

  According to the documentation on aio_read/write, there are basically 2 ways that the AIO library can inform your application that an async file I/O operation has completed. Either 1) you can use a signal, 2) you can use a callback function I think that callback functions are vastly preferable to signals, and would probably be much easier to integrate into higher-level multi-threaded libraries. Unfortunately, the documentation for this functionality is a mess to say the least. Some sources, such as the man page for the sigevent struct, indicate that you need to set the sigev_notify data member in the sigevent struct to SIGEV_CALLBACK and then provide a function handler. Presumably, the handler is invoked in the same thread. Other documentation indicates you need to set sigev_notify to SIGEV_THREAD, which will invoke the callback handler in a newly created thread. In any case, on my Linux system (Ubuntu with a 2.6.28 kernel) SIGEV_CALLBACK doesn't seem to be defined anywhere, but SIGEV_THREAD works as advertised. Unfortunately, creating a new thread to invoke the callback handler seems really inefficient, especially if you need to invoke many handlers. It would be better to use an existing pool of threads, similar to the way most network I/O event demultiplexers work. Some versions of UNIX, such as QNX, include a SIGEV_SIGNAL_THREAD flag, which allows you to invoke handlers using a specified existing thread, but this doesn't seem to be available on Linux, nor does it seem to even be a part of the POSIX standard. So, is it possible to use the POSIX AIO library in a way that invokes user handlers in a pre-allocated background thread/threadpool, rather than creating/destroying a new thread everytime a handler is invoked?

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• Dealing with asynchronous control structures (Fluent Interface?)

  - by Christophe Herreman

  The initialization code of our Flex application is doing a series of asynchronous calls to check user credentials, load external data, connecting to a JMS topic, etc. Depending on the context the application runs in, some of these calls are not executed or executed with different parameters. Since all of these calls happen asynchronously, the code controlling them is hard to read, understand, maintain and test. For each call, we need to have some callback mechanism in which we decide what call to execute next. I was wondering if anyone had experimented with wrapping these calls in executable units and having a Fluent Interface (FI) that would connect and control them. From the top of my head, the code might look something like: var asyncChain:AsyncChain = execute(LoadSystemSettings) .execute(LoadAppContext) .if(IsAutologin) .execute(AutoLogin) .else() .execute(ShowLoginScreen) .etc; asyncChain.execute(); The AsyncChain would be an execution tree, build with the FI (and we could of course also build one without a FI). This might be an interesting idea for environments that run in a single threaded model like the Flash Player, Silverlight, JavaFX?, ... Before I dive into the code to try things out, I was hoping to get some feedback.

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• best practice for directory polling

  - by Hieu Lam

  Hi all, I have to do batch processing to automate business process. I have to poll directory at regular interval to detect new files and do processing. While old files is being processed, new files can come in. For now, I use quartz scheduler and thread synchronization to ensure that only one thread can process files. Part of the code are: application-context.xml <bean id="methodInvokingJob" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean" <property name="targetObject" ref="documentProcessor" / <property name="targetMethod" value="processDocuments" / </bean DocumentProcessor ..... public void processDocuments() { LOG.info(Thread.currentThread().getName() + " attempt to run."); if (!processing) { synchronized (this) { try { processing = true; LOG.info(Thread.currentThread().getName() + " is processing"); List xmlDocuments = documentManager.getFileNamesFromFolder(incomingFolderPath); // loop over the files and processed unlock files. for (String xmlDocument : xmlDocuments) { processDocument(xmlDocument); } } finally { processing = false; } } } } For the current code, I have to prevent other thread to process files when one thread is processing. Is that a good idea ? or we support multi-threaded processing. In that case how can I know which files is being process and which files has just arrived ? Any idea is really appreciated.

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• How to create systemd.service in Fedora 16 (x86_64)?

  - by marverix

  I have big problem with creating service in new way - by systemctl (systemd.service) in Fedora 16. I wonna to create very simple service for minidlna server. I have created new file called minidlna.service in /lib/systemd/system/ and here is how it's looks like: [Unit] Description=Mini DLNA [Service] Type=oneshot ExecStart=/usr/sbin/minidlna [Install] WantedBy=multi-user.target Unfortunately systemctl status minidlna.service prints: Loaded: loaded (/lib/systemd/system/minidlna.service; enabled) Active: inactive (dead) since Sat, 03 Dec 2011 20:49:23 +0100; 9s ago Main PID: 1580 (code=exited, status=0/SUCCESS) CGroup: name=systemd:/system/minidlna.service Any ideas how to fix it? Cheers!

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• Scalable / Parallel Large Graph Analysis Library?

  - by Joel Hoff

  I am looking for good recommendations for scalable and/or parallel large graph analysis libraries in various languages. The problems I am working on involve significant computational analysis of graphs/networks with 1-100 million nodes and 10 million to 1+ billion edges. The largest SMP computer I am using has 256 GB memory, but I also have access to an HPC cluster with 1000 cores, 2 TB aggregate memory, and MPI for communication. I am primarily looking for scalable, high-performance graph libraries that could be used in either single or multi-threaded scenarios, but parallel analysis libraries based on MPI or a similar protocol for communication and/or distributed memory are also of interest for high-end problems. Target programming languages include C++, C, Java, and Python. My research to-date has come up with the following possible solutions for these languages: C++ -- The most viable solutions appear to be the Boost Graph Library and Parallel Boost Graph Library. I have looked briefly at MTGL, but it is currently slanted more toward massively multithreaded hardware architectures like the Cray XMT. C - igraph and SNAP (Small-world Network Analysis and Partitioning); latter uses OpenMP for parallelism on SMP systems. Java - I have found no parallel libraries here yet, but JGraphT and perhaps JUNG are leading contenders in the non-parallel space. Python - igraph and NetworkX look like the most solid options, though neither is parallel. There used to be Python bindings for BGL, but these are now unsupported; last release in 2005 looks stale now. Other topics here on SO that I've looked at have discussed graph libraries in C++, Java, Python, and other languages. However, none of these topics focused significantly on scalability. Does anyone have recommendations they can offer based on experience with any of the above or other library packages when applied to large graph analysis problems? Performance, scalability, and code stability/maturity are my primary concerns. Most of the specialized algorithms will be developed by my team with the exception of any graph-oriented parallel communication or distributed memory frameworks (where the graph state is distributed across a cluster).

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• The cost of passing by shared_ptr

  - by Artem

  I use std::tr1::shared_ptr extensively throughout my application. This includes passing objects in as function arguments. Consider the following: class Dataset {...} void f( shared_ptr< Dataset const > pds ) {...} void g( shared_ptr< Dataset const > pds ) {...} ... While passing a dataset object around via shared_ptr guarantees its existence inside f and g, the functions may be called millions of times, which causes a lot of shared_ptr objects being created and destroyed. Here's a snippet of the flat gprof profile from a recent run: Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls s/call s/call name 9.74 295.39 35.12 2451177304 0.00 0.00 std::tr1::__shared_count::__shared_count(std::tr1::__shared_count const&) 8.03 324.34 28.95 2451252116 0.00 0.00 std::tr1::__shared_count::~__shared_count() So, ~17% of the runtime was spent on reference counting with shared_ptr objects. Is this normal? A large portion of my application is single-threaded and I was thinking about re-writing some of the functions as void f( const Dataset& ds ) {...} and replacing the calls shared_ptr< Dataset > pds( new Dataset(...) ); f( pds ); with f( *pds ); in places where I know for sure the object will not get destroyed while the flow of the program is inside f(). But before I run off to change a bunch of function signatures / calls, I wanted to know what the typical performance hit of passing by shared_ptr was. Seems like shared_ptr should not be used for functions that get called very often. Any input would be appreciated. Thanks for reading. -Artem

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• Keep only "lock" a single app open in iOS?

  - by CT.

  Is there anyway to "lock" open a single app in iOS? My use case for this is simple. There are many apps and games designed for children. While these applications are appropriate for children, many other applications installed on an iPad are not. But even more so than protecting them from inappropriate content, I would just like to prevent them from leaving the application. They accidentally hit the home button or multi-touch gesture out of the application. I know you can turn gestures off. Developers also have links to their website or other related applications. Kids are constantly exiting the application and then bringing the device to me asking "Can you get me back into the game?" every couple minutes. How can I hand a child an iPad with "Angry Birds" running and make sure only "Angry Birds" runs? Cydia or jailbreak tweaks welcome. Thanks.

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• Online OCR website for processing an entire pdf file at one time?

  - by Tim

  I am looking for an online OCR website for processing a multi-page pdf file at one time. Free preferably. I know http://www.newocr.com/. If I am correct, it can only OCR one page at a time, by manually clicking "Preview" and then clicking "OCR" for each page. After each page is OCRed, I have to copy out the text result manually too. If my pdf file has 30~ pages, it will be tedious to repeat the above process for each page. I wonder if there is some other online websites that OCR a whole pdf file, without asking me for manual operation? Thanks!

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• apply seach criteria to whole cells

  - by Tom

  I am trying to use MATCH() and/or LOOKUP() in LibreOffice Calc. I have the "Search criteria = and < must apply to whole cells" and the "Enable regular expressions in formulas" options selected. The item I am looking for is a multi word string. How do I provide a search criteria as a cell reference (E3) in to LOOKUP(E3, B1:B20, C1:C20) and have it match the value in B1:B20 EXACTLY? Right now it is matching partial strings rather than matching the cell values exactly.

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• best ftp program (paid - not free)

  - by Victor Kimura

  Just would like some feedback on the best ftp program (not free). The requirements I'm looking for is: - secure ftp - for use on mac, linux, windows - backup utility with scheduler - for use on more than one computer (multi-license) I'm using wsftp from 2007 right now but it's only good for windows. It's license is only good for one computer. And after some vista updates it's making some strange noises. I tried to turn off the noise (via control panel) and it's still making that noise and I turned off the sound within wsftp too. I like the program but I think it's time to look for a new one. Thank you, Victor

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