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• Cannot change default application association of certain file types

  - by H.B.

  After associating my MP3 files with MPlayer i can no longer change that association using the Choose default program... dialogue, the Always use this [...] Checkbox is always greyed out (Control Panel > Default Programs > Associate a file type or protocol with a program does not let me change it either). That also happened for MP4s but not for MKVs for example, and if i associate my MP3s with other applications like VLC it does not get blocked. I would really like to know why that is and if i can avoid this beforehand (thankfully i know ways to fix it afterwards already). Edit: Another obervation: The blocking programs (i managed to block it with an association to Visual Studio as well) do not appear in the Recommended Programs of the open-with-dialogue (And the explorer said: "The current program is not recommended, but i won't let you change it, ha!"). Edit: A screenshot as requested: As you can see on the top left (if you know the icon of MPlayer), the file is currently associated with MPlayer. Edit: Ways to fix it (Note: This question is not about fixing it) Using the Default Programs Control Panel > Default Programs > Set Default Programs, select WMP, Choose defaults for this program, check .mp3 This should reassociate the files with WMP and you can create a new association in the explorer. Using the registry (As always, keep your hands off it unless you know what you are doing or if you are fine with accidentally breaking your system) HKEY_CURRENT_USER > Software > Microsoft > Windows > CurrentVersion > Explorer > FileExts > .mp3 Here you could for example clean up the open-with-list, and the current default program seems to be saved here as well in the key UserChoice, there you can change the ProgId string to another application, you can associate it with WMP by entering WMP11.AssocFile.MP3 or just pick another application right away. You may need to mess with permissions on the key though, if you cannot change the ProgId value.

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• Cannot Send Item error in Outlook - permissions to registry?

  - by Tim Alexander

  The issue I am trying to solve is to do with users getting a Cannot Send Item error in Outlook 2007 connecting to Exchange 2007. Basically if there is an image in the email (either one they have pasted in or one from another email in the chain) they get a "Cannot Send Item" error. Initially thought it was a citrix issue but users get it when they RDP to a server as well. Changing the message to Rich Text works 80% of the time but I do not think this is a solution but more of a temporary workaround. After some troubleshooting we found that the error can be fixed by adding the user as a member of the local power users group. of course this is not really a fix. My thoughts were that the ability of a power user to add/remove software may give them more access to the registry which might allow them to get round a restriction that is in place for a normal user. I have tried going through a procmon but the wealth of information is confusing. It initially looked like it may be an Outlook 2007 email security setting but this does not change between power user and normal user (set to 1 in the registry, "Use the security setting from Outlook Security Settings Public Folders"). I am struggling to fine tune my troubleshooting to work out exactly what is blocking it. Has anyone had an experience with an error similar to this? Or are there any tips for trying to track down issues via procmon as I must admit my approach seems somewhat lacking :) EDIT: So I have trawled through the two logs we have from process monitor (one as a power user and one a normal user). annoyingly I can find no obvious difference where something is denied access. There are more access denied events in the normal user log but these are quickly followed by sucessful entries to the same path fractions of a second later. The only thing that does stand out is an access denied to HKCR.html. This does not even appear in the power user version of the log. From what I understand this helps determine the default browser which ties in nicely with the fact that 9 out of 10 times you can send the message as Rich Text. EDIT: Looks like KB2509470 was causing the issue. Not really sure why but when I can work out what it does and why it causes the problem will post here unless anyone beats me to it!

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• Excessive Outbound DNS Traffic

  - by user1318414

  I have a VPS system which I have had for 3 years on one host without issue. Recently, the host started sending an extreme amount of outbound DNS traffic to 31.193.132.138. Due to the way that Linode responded to this, I have recently left Linode and moved to 6sync. The server was completely rebuilt on 6sync with the exception of postfix mail configurations. Currently, the daemons run are as follows: sshd nginx postfix dovecot php5-fpm (localhost only) spampd (localhost only) clamsmtpd (localhost only) Given that the server was 100% rebuilt, I can't find any serious exploits against the above stated daemons, passwords have changed, ssh keys don't even exist on the rebuild yet, etc... it seems extremely unlikely that this is a compromise which is being used to DoS the address. The provided IP is noted online as a known SPAM source. My initial assumption was that it was attempting to use my postfix server as a relay, and the bogus addresses it was providing were domains with that IP registered as their nameservers. I would imagine given my postfix configuration that DNS queries for things such as SPF information would come in with equal or greater amount than the number of attempted spam e-mails sent. Both Linode and 6Sync have said that the outbound traffic is extremely disproportionate. The following is all the information I received from Linode regarding the outbound traffic: 21:28:28.647263 IP 97.107.134.33.32775 > 31.193.132.138.53: 28720 op8+% [b2&3=0x4134] [17267a] [30550q] [28773n] [14673au][|domain] 21:28:28.647264 IP 97.107.134.33 > 31.193.132.138: udp 21:28:28.647264 IP 97.107.134.33.32775 > 31.193.132.138.53: 28720 op8+% [b2&3=0x4134] [17267a] [30550q] [28773n] [14673au][|domain] 21:28:28.647265 IP 97.107.134.33 > 31.193.132.138: udp 21:28:28.647265 IP 97.107.134.33.32775 > 31.193.132.138.53: 28720 op8+% [b2&3=0x4134] [17267a] [30550q] [28773n] [14673au][|domain] 21:28:28.647266 IP 97.107.134.33 > 31.193.132.138: udp 6sync cannot confirm whether or not the recent spike in outbound traffic was to the same IP or over DNS, but I have presumed as such. For now my server is blocking the entire 31.0.0.0/8 subnet to help deter this while I figure it out. Anyone have any idea what is going on?

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• OpenVPN multiple servers on the same subnet, high availability

  - by andre

  Hey everyone. Let me start by saying that my Linux experience isn't super awesome but I can usually find my way around things easily. Over at work we have an OpenVPN setup that's been due for some improvement for a while now. The main server (tap mode) runs in our office, behind a rather slow DSL connection. The main problem is that, since I'm usually out of the office, every time I want to access something on the virtual network I have to go through that server to get anywhere else. We have two servers up on 100 Mbit connections that we use for development and production purposes, about 3 more servers in the office (one of them behind a different T1 line for VOIP) and about two dozen clients who use the network on a daily basis from various locations. We've had situations where network routing (outside of our control) would not allow people to reach our main OpenVPN server whilst the other locations were connectable. Also any time someone outside the office wants to fetch something from any of the servers (say, a 500 MB code repository), a whopping 20 KB/s download speed is just unacceptable these days (did I mention slow DSL? ok). We had to implement traffic shaping on this server since maxing out this connection was fairly trivial. I had the thought of running two (or more) OpenVPN servers in the network. These would have to have the same subnet though, as our application relies on virtual network's IP addresses for some of its core functionality. The clients would also preferably retain the same IP addresses but that's not vital. For simplicity, lets call the current server office and the second server I'm setting up, cloud. Call the server on the T1 phone. This proved to be rather complex because as soon as I connect to cloud, I cannot see office. Any routes to a server that would go through office also do not work while I'm connected to cloud (no ping, nothing) and vice-versa. There's no rules for iptables that would be blocking the traffic either. Recently I came across this article on linuxjournal but the solution they provide seems to only cover the use of two servers and somewhat outdated (can't even find much documentation, their wiki is offline). They also state that adding more servers would be a complex task. Ideally I would like to keep the existing server office running the virtual network and also run the OpenVPN daemon on the cloud and phone servers (100 Mbit and very reliable connection, respectively) so that we're on safe ground in case of a hardware failure, DSL failure, etc. So, in essence, I'm looking for a highly available OpenVPN solution (fix, patch, hack, tweak, whatever you want to call it) that will accept connections on multiple hosts (2 or more) whilst keeping the same IP address subnet regardless of the server to which you connect to. Thanks for reading and sorry for the long post, I hope it gets the point across :P

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• Init script & the green [ OK ]

  - by Lord Loh.

  I am trying to install fast-cgi for nginx on an EC2 instance. I followed the steps explained here, but that is meant for Debian and does not work out of the box for a red-hat based system. I modified the script a bit to look like - #!/bin/bash ### BEGIN INIT INFO # Provides: php-fcgi # Required-Start: $nginx # Required-Stop: $nginx # Default-Start: 2 3 4 5 # Default-Stop: 0 1 6 # Short-Description: starts php over fcgi # Description: starts php over fcgi ### END INIT INFO . /etc/rc.d/init.d/functions (( EUID )) && echo .You need to have root priviliges.. && exit 1 BIND=/tmp/php.socket USER=nginx PHP_FCGI_CHILDREN=15 PHP_FCGI_MAX_REQUESTS=1000 PHP_CGI=/usr/bin/php-cgi PHP_CGI_NAME=`basename $PHP_CGI` PHP_CGI_ARGS="- USER=$USER PATH=/usr/bin PHP_FCGI_CHILDREN=$PHP_FCGI_CHILDREN PHP_FCGI_MAX_REQUESTS=$PHP_FCGI_MAX_REQUESTS $PHP_CGI -b $BIND" RETVAL=0 start() { echo -n "Starting PHP FastCGI: " #ORIGINAL LINE #daemon $PHP_CGI --quiet --start --background --chuid "$USER" --exec /usr/bin/env -- $PHP_CGI_ARGS #MODIFIED LINE daemon --user=$USER $PHP_CGI -b $BIND& RETVAL=$? echo [ $RETVAL -eq 0 ] && touch /var/lock/subsys/php-fcgi #echo "$PHP_CGI_NAME." } stop() { echo -n "Stopping PHP FastCGI: " killall -q -w -u $USER $PHP_CGI RETVAL=$? echo "$PHP_CGI_NAME." rm /var/lock/subsys/php-fcgi } case "$1" in start) start ;; stop) stop ;; restart) stop start ;; *) echo "Usage: php-fastcgi {start|stop|restart}" exit 1 ;; esac exit $RETVAL The problem I have now is - service php-fcgi start keeps the shell blocked. If I run service php-fcgi start & and then ps aux, I see the php-cgi process running bound to the socket. I see the start command stop only when I execute service php-fcgi stop. How do I solve this blocking issue? I have tried adding an & at the end of the line spawning the daemon. But other scripts do not seem to be doing this. This is the most complicated script I am attempting to modify yet :-( How do I get the script to display the green [ OK ]? I checked scripts like httpd and saw that all they were doing was something as shown below. But I never see a green [ OK ] when I execute php-fcgi. I also discovered that putting echo_success with functions sourced displays the green [ OK ] but I do not see any other scripts in the /etc/rc.d/init.d/ executing echo_success or echo_failure. What have I got wrong? Also, How do i specify PHP_FCGI_CHILDREN with daemon? echo [ $RETVAL -eq 0 ] && touch /var/lock/subsys/

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• Ubuntu hardware wireless switch has no effect after suspend and 13.10 upgrade

  - by blaineh

  I'm posting this on SU after it stalled on askubuntu. I hope someone here can help! If you'd prefer to answer on AU itself, here's the link: http://askubuntu.com/questions/365177/hardware-wireless-switch-has-no-effect-after-suspend-and-13-10-upgrade Wireless works fine after a reboot, but after a suspend the hardware switch (for my laptop this is f12) has no effect on the wireless, it is just permanently off, and shows that it is with a red LED. My rfkill list all reads: 0: phy0: Wireless LAN Soft blocked: no Hard blocked: yes 1: hp-wifi: Wireless LAN Soft blocked: no Hard blocked: yes Any combination with rfkill <un>block wifi doesn't work, although one time first blocking then unblocking actually turned it on again. sudo lshw -C network reads: *-network DISABLED description: Wireless interface product: AR9285 Wireless Network Adapter (PCI-Express) vendor: Qualcomm Atheros physical id: 0 bus info: pci@0000:02:00.0 logical name: wlan0 version: 01 serial: 78:e4:00:65:2e:3f width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless configuration: broadcast=yes driver=ath9k driverversion=3.11.0-12-generic firmware=N/A latency=0 link=no multicast=yes wireless=IEEE 802.11bgn resources: irq:17 memory:90100000-9010ffff *-network DISABLED description: Ethernet interface product: RTL8101E/RTL8102E PCI Express Fast Ethernet controller vendor: Realtek Semiconductor Co., Ltd. physical id: 0 bus info: pci@0000:03:00.0 logical name: eth0 version: 02 serial: c8:0a:a9:89:b4:30 size: 10Mbit/s capacity: 100Mbit/s width: 64 bits clock: 33MHz capabilities: pm msi pciexpress msix vpd bus_master cap_list rom ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=half latency=0 link=no multicast=yes port=MII speed=10Mbit/s resources: irq:42 ioport:2000(size=256) memory:90010000-90010fff memory:90000000-9000ffff memory:90020000-9002ffff Also, adding a /etc/pm/sleep.d/brcm.sh file as recommended here simply prevents the laptop from suspending at all, which of course is no good. This question has an answer urging to install the original driver, but it wasn't an "accepted answer" so I'd rather not take a chance on it. Also I'll admit I'm a bit lost on that and would like help doing so with the specific information I've given. I would be happy to provide more information, so long as you're willing to help me find it for you! This is a very annoying bug. I have a Compaq Presario CQ62. Edit. Output of lspci | grep Network: 02:00.0 Network controller: Qualcomm Atheros AR9285 Wireless Network Adapter (PCI-Express) (rev 01) Edit. This morning, I had had the laptop suspended all night, and then when I tried to awake it, it simply wouldn't. It would try, and then it would sleep again (I guess it felt a little bit like me! </badjoke>). Is it possible these problems are related? Edit. I don't have enough reputation on SU proper to post links to pastebins and other questions I've tried, so I'm putting them in comments, and of course they're available in the original question.

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• weird SSH connection timed out

  - by bran

  This problem started when I tried to login to my brand spaning new VPS server. I remember that in my first SSH try on the server I actually got prompt for password several times which would mean that there is no port blocking problem from my isp. Since the password did'nt work for me (for some reason). I had a lot of authentication failure. After that attempting to log in to the server just timed out. I did the same at mediatemple (which used to work before with sftp) and put in wrong password and now trying to ssh (or even SFTP) gives me timeout error. So some kind of security feature is preventing me from trying too many times to log in, either from my side or from the server side. Any idea what it could be? TRaceroute and ping works on the ips. I am using a zyxel wimax modem (max-206m1r - if that's relevent) c:\Program Files (x86)\OpenSSH\bin>ssh.exe [email protected] ssh: connect to host 109.169.7.136 port 22: Connection timed out c:\Program Files (x86)\OpenSSH\bin>ssh.exe [email protected] ssh: connect to host 109.169.7.131 port 22: Connection timed out c:\Program Files (x86)\OpenSSH\bin>ssh.exe [email protected] ssh: connect to host 87.117.249.227 port 22: Connection timed out c:\Program Files (x86)\OpenSSH\bin>ssh.exe [email protected] -vv OpenSSH_5.6p1, OpenSSL 0.9.8r 8 Feb 2011 debug1: Reading configuration data /etc/ssh_config debug2: ssh_connect: needpriv 0 debug1: Connecting to 87.117.249.227 [87.117.249.227] port 22. debug1: connect to address 87.117.249.227 port 22: Connection timed out ssh: connect to host 87.117.249.227 port 22: Connection timed out c:\Program Files (x86)\OpenSSH\bin>ssh.exe s122797.gridserver.com Could not create directory '/home/pavs/.ssh'. The authenticity of host 's122797.gridserver.com (205.186.175.110)' can't be est ablished. RSA key fingerprint is 33:24:1e:38:bc:fd:75:02:81:d8:39:42:16:f6:f6:ff. Are you sure you want to continue connecting (yes/no)? yes Failed to add the host to the list of known hosts (/home/pavs/.ssh/known_hosts). Password: Password: Password: [email protected]'s password: Permission denied, please try again. [email protected]'s password: Permission denied, please try again. [email protected]'s password: Received disconnect from 205.186.175.110: 2: Too many authentication failures fo r pavs c:\Program Files (x86)\OpenSSH\bin>ssh.exe s122797.gridserver.com ssh: connect to host s122797.gridserver.com port 22: Connection timed out c:\Program Files (x86)\OpenSSH\bin>ssh.exe s122797.gridserver.com ssh: connect to host s122797.gridserver.com port 22: Connection timed out

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• tc rules block traffic from some hosts at network

  - by user139430

  I have a problem I can not solve. The script, which sets the rules for traffic shaping is blocking the traffic from some hosts.If I remove all the rules, then it works. I can not understand why? Here is my script... #!/bin/sh cmdTC=/sbin/tc rateLANDl="60mbit" ceilLANDl="60mbit" rateLANUl="40mbit" ceilLANUl="40mbit" quantLAN="1514" # Nowaday bandwidth limit set to 100mbit. # We devide it with 60mbit download and 40mbit upload bandthes. rateHiDl="30mbit" ceilHiDl="60mbit" rateHiUl="20mbit" ceilHiUl="40mbit" quantHi="1514" rateLoDl="30mbit" ceilLoDl="60mbit" rateLoUl="20mbit" ceilLoUl="40mbit" quantLo="1514" devNIF=eth0 devFIF=ifb0 modprobe ifb ip link set $devFIF up 2>/dev/null #exit 0 ################################################################################################ # Remove discuiplines from network and fake interfaces ################################################################################################ $cmdTC qdisc del dev $devNIF root 2>/dev/null $cmdTC qdisc del dev $devFIF root 2>/dev/null $cmdTC qdisc del dev $devNIF ingress 2>/dev/null if [ "$1" = "down" ]; then exit 0 fi ################################################################################################ # Create discuiplines for network interface ################################################################################################ $cmdTC qdisc add dev $devNIF root handle 1:0 htb default 12 # Create classes for network interface $cmdTC class add dev $devNIF parent 1:0 classid 1:1 htb rate ${rateLANDl} ceil ${ceilLANDl} quantum ${quantLAN} $cmdTC class add dev $devNIF parent 1:1 classid 1:11 htb rate ${rateHiDl} ceil ${ceilHiDl} quantum ${quantHi} $cmdTC class add dev $devNIF parent 1:1 classid 1:12 htb rate ${rateLoDl} ceil ${ceilLoDl} quantum ${quantLo} $cmdTC qdisc add dev $devNIF parent 1:11 handle 111: sfq perturb 10 $cmdTC qdisc add dev $devNIF parent 1:12 handle 112: sfq perturb 10 # Create filters for network interface $cmdTC filter add dev $devNIF protocol all parent 1:0 u32 match ip dst 10.252.2.0/24 flowid 1:11 $cmdTC filter add dev $devNIF protocol all parent 111: handle 111 flow hash keys dst divisor 1024 baseclass 1:11 $cmdTC filter add dev $devNIF protocol all parent 112: handle 112 flow hash keys dst divisor 1024 baseclass 1:12 ################################################################################################ # Create discuiplines for fake interface ################################################################################################ $cmdTC qdisc add dev $devFIF root handle 1:0 htb default 12 # Create classes for network interface $cmdTC class add dev $devFIF parent 1:0 classid 1:1 htb rate ${rateLANUl} ceil ${ceilLANUl} quantum ${quantLAN} $cmdTC class add dev $devFIF parent 1:1 classid 1:11 htb rate ${rateHiUl} ceil ${ceilHiUl} quantum ${quantHi} $cmdTC class add dev $devFIF parent 1:1 classid 1:12 htb rate ${rateLoUl} ceil ${ceilLoUl} quantum ${quantLo} $cmdTC qdisc add dev $devFIF parent 1:11 handle 111: sfq perturb 10 $cmdTC qdisc add dev $devFIF parent 1:12 handle 112: sfq perturb 10 # Create filters for network interface $cmdTC filter add dev $devFIF protocol all parent 1:0 u32 match ip src 10.252.2.0/24 flowid 1:11 $cmdTC filter add dev $devFIF protocol all parent 111: handle 111 flow hash keys src divisor 1024 baseclass 1:11 $cmdTC filter add dev $devFIF protocol all parent 112: handle 112 flow hash keys src divisor 1024 baseclass 1:12 ################################################################################################ # Create redirect discuiplines from network to fake interface ################################################################################################ $cmdTC qdisc add dev $devNIF handle ffff:0 ingress $cmdTC filter add dev $devNIF parent ffff:0 protocol all u32 match u32 0 0 action mirred egress redirect dev $devFIF Here is my /etc/modules: loop ifb ppp_mppe nf_conntrack_pptp nt_conntrack_proto_gre nf_nat_pptp nf_nat_proto_gre The system is Linux wall 2.6.32-5-amd64 #1 SMP Sun Sep 23 10:07:46 UTC 2012 x86_64 GNU/Linux

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• Echo 404 directly from nginx to improve performance

  - by user64204

  I am in charge of production servers serving static content for a website. Those servers are constantly being crawled by bots looking for potential exploits (which isn't that much of a problem security-wise because no application can be reached behind the web server) but generates thousands of 404 per day, sometimes per hour. I am looking into ways of blocking those requests but it's tricky (you want to make sure you don't block legitimate traffic and these bots are becoming more and more clever at looking like they're legit) and is going to take me a while to find an acceptable solution. In the meantime I would like to reduce the performance impact of serving those 404 pages. Indeed we're using nginx which by default is configured to serve it's 404 page from the disk (This can be changed using the error_page directive but in the end the 404 will either have to be served from disk or from another external source (e.g. upstream application which would be worst)) which isn't ideal. I ran a test with ab on my local machine with a basic configuration: in one case I echo a message directly from nginx so the disk isn't touched at all, in the other case I hit a missing page and nginx serves its 404 from disk. server { # [...] the default nginx stuff location / { } location /this_page_exists { echo "this page was found"; } } Here are the test results (my laptop has Intel(R) Core(TM) i7-2670QM + SSD in case you're wondering why they are so high): $ ab -n 500000 -c 1000 http://localhost/this_page_exists Requests per second: 25609.16 [#/sec] (mean) $ ab -n 500000 -c 1000 http://localhost/this_page_doesnt_exists Requests per second: 22905.72 [#/sec] (mean) As you can see, returning a value with echo is 11% ((25609-22905)÷22905×100) faster than serving the 404 page from disk. Accordingly I would like to echo a simple 404 Page not Found string from nginx. I tried many things so far but they all failed, essentially the idea was this: location / { try_files $uri @not_found; } location @not_found { echo "404 - Page not found"; } The problem is that as soon as the echo directive is used, the http response code is set to 200. I tried changing that by doing error_page 200 = 400 but that breaks the configuration. How can I serve a 404 page directly from nginx? (without hacking the source which may be might next step)

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• ntpdate works, but ntpd can't synchronize

  - by dafydd

  This is in RHEL 5.5. First, ntpdate to the remote host works: $ ntpdate XXX.YYY.4.21 24 Oct 16:01:17 ntpdate[5276]: adjust time server XXX.YYY.4.21 offset 0.027291 sec Second, here are the server lines in my /etc/ntp.conf. All restrict lines have been commented out for troubleshooting. server 127.127.1.0 server XXX.YYY.4.21 I execute service ntpd start and check with ntpq: $ ntpq ntpq> peer remote refid st t when poll reach delay offset jitter ============================================================================== *LOCAL(0) .LOCL. 5 l 36 64 377 0.000 0.000 0.001 timeserver.doma .LOCL. 1 u 39 128 377 0.489 51.261 58.975 ntpq> opeer remote local st t when poll reach delay offset disp ============================================================================== *LOCAL(0) 127.0.0.1 5 l 40 64 377 0.000 0.000 0.001 timeserver.doma XXX.YYY.22.169 1 u 43 128 377 0.489 51.261 58.975 XXX.YYY.22.169 is the address of the host I'm working on. A reverse lookup on the IP address in my ntp.conf file validates that the ntpq output is correctly naming the remote server. However, as you can see, it appears to just roll over to my .LOCL. time server. Also, ntptrace just returns the local time server, and ntptrace XXX.YYY.4.21 times out. $ ntptrace localhost.localdomain: stratum 6, offset 0.000000, synch distance 0.948181 $ ntptrace XXX.YYY.4.21 XXX.YYY.4.21: timed out, nothing received ***Request timed out This looks like my ntp daemon is just querying itself. I am thinking about the possibility that the router-I-don't-control between my test network timeserver and the corporate network timeserver is blocking on source port. (I think ntpdate sends on port 123, which gets it around that filter and is why I can't use it while ntpd is running.) I have email in to the network folks to check that. Finally, telnet XXX.YYY.4.21 123 never times out or completes a connection. The questions: What am I missing, here? What else can I check to try to figure out where this connection is failing? Would strace ntptrace XXX.YYY.4.21 show me the source port ntptrace is sending from? I can deconstruct most strace calls, but I can't figure out the location of that datum. If I can't directly examine the gateway router between my test network and the timeserver, how might I build evidence that it's responsible for these disconnections? Alternately, how might I rule it out?

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• Windows Update and IE fail to connect, but Chrome fine?

  - by I Gottlieb

  Out of ideas on this one. (Running Windows Vista.) I have a program that accesses the internet to retrieve financial market data. One day it tells me that it can't log in -- timeout error. I check the documentation and it says must have a working copy of IE browser installed. I check IE (have IE9) and sure enough -- it just spins. No error message, not timeout, no 'try later' -- just spins -- as far as I can tell, indefinitely. Any page, any address. Even access to a localhost site just spins. Chrome works fine. So does another program I have that fetches market data. Windows 'diagnose and repair' says my internet connection is working fine. I tried uninstall/re-install of IE. Same spinning. I tried to install Windows Updates, and guess what? I can't. I comes up with error 80072efd; checked documentation for the error and it says I should check firewall blockage. Thing is, the only firewall I have is Windows Firewall, and obviously it wouldn't be blocking Windows Update. In contrast, Windows 'Help' in all programs has no problem accessing the Internet. I had a filter on the internet connection, and this was updated just prior to first appearance of the problem. But I uninstalled the filter entirely (official, with passwd from the company's service rep) -- and no difference. I'm guessing that a high level Windows network service file is corrupted -- used only by MS programs and their ilk, but how do I find it? I'd like to avoid having to do a clean install of Windows. Much obliged for any insight. IG Ramhound -- Thanks for reply. I'm familiar with virtual machines as in e.g. JVM or an emulator for an alternative architecture or (theoretical) Turing Machine equivalence. But I'm not familiar with the way you're using the term. Please clarify -- what one needs for this VM 'test' and why you expect it will provide an advantage of insight into the problem. And what sort of 'configuration issue' are you referring to? IG

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• SQL SERVER – Beginning of SQL Server Architecture – Terminology – Guest Post

  - by pinaldave

  SQL Server Architecture is a very deep subject. Covering it in a single post is an almost impossible task. However, this subject is very popular topic among beginners and advanced users.  I have requested my friend Anil Kumar who is expert in SQL Domain to help me write  a simple post about Beginning SQL Server Architecture. As stated earlier this subject is very deep subject and in this first article series he has covered basic terminologies. In future article he will explore the subject further down. Anil Kumar Yadav is Trainer, SQL Domain, Koenig Solutions. Koenig is a premier IT training firm that provides several IT certifications, such as Oracle 11g, Server+, RHCA, SQL Server Training, Prince2 Foundation etc. In this Article we will discuss about MS SQL Server architecture. The major components of SQL Server are: Relational Engine Storage Engine SQL OS Now we will discuss and understand each one of them. 1) Relational Engine: Also called as the query processor, Relational Engine includes the components of SQL Server that determine what your query exactly needs to do and the best way to do it. It manages the execution of queries as it requests data from the storage engine and processes the results returned. Different Tasks of Relational Engine: Query Processing Memory Management Thread and Task Management Buffer Management Distributed Query Processing 2) Storage Engine: Storage Engine is responsible for storage and retrieval of the data on to the storage system (Disk, SAN etc.). to understand more, let’s focus on the following diagram. When we talk about any database in SQL server, there are 2 types of files that are created at the disk level – Data file and Log file. Data file physically stores the data in data pages. Log files that are also known as write ahead logs, are used for storing transactions performed on the database. Let’s understand data file and log file in more details: Data File: Data File stores data in the form of Data Page (8KB) and these data pages are logically organized in extents. Extents: Extents are logical units in the database. They are a combination of 8 data pages i.e. 64 KB forms an extent. Extents can be of two types, Mixed and Uniform. Mixed extents hold different types of pages like index, System, Object data etc. On the other hand, Uniform extents are dedicated to only one type. Pages: As we should know what type of data pages can be stored in SQL Server, below mentioned are some of them: Data Page: It holds the data entered by the user but not the data which is of type text, ntext, nvarchar(max), varchar(max), varbinary(max), image and xml data. Index: It stores the index entries. Text/Image: It stores LOB ( Large Object data) like text, ntext, varchar(max), nvarchar(max),  varbinary(max), image and xml data. GAM & SGAM (Global Allocation Map & Shared Global Allocation Map): They are used for saving information related to the allocation of extents. PFS (Page Free Space): Information related to page allocation and unused space available on pages. IAM (Index Allocation Map): Information pertaining to extents that are used by a table or index per allocation unit. BCM (Bulk Changed Map): Keeps information about the extents changed in a Bulk Operation. DCM (Differential Change Map): This is the information of extents that have modified since the last BACKUP DATABASE statement as per allocation unit. Log File: It also known as write ahead log. It stores modification to the database (DML and DDL). Sufficient information is logged to be able to: Roll back transactions if requested Recover the database in case of failure Write Ahead Logging is used to create log entries Transaction logs are written in chronological order in a circular way Truncation policy for logs is based on the recovery model SQL OS: This lies between the host machine (Windows OS) and SQL Server. All the activities performed on database engine are taken care of by SQL OS. It is a highly configurable operating system with powerful API (application programming interface), enabling automatic locality and advanced parallelism. SQL OS provides various operating system services, such as memory management deals with buffer pool, log buffer and deadlock detection using the blocking and locking structure. Other services include exception handling, hosting for external components like Common Language Runtime, CLR etc. I guess this brief article gives you an idea about the various terminologies used related to SQL Server Architecture. In future articles we will explore them further. Guest Author  The author of the article is Anil Kumar Yadav is Trainer, SQL Domain, Koenig Solutions. Koenig is a premier IT training firm that provides several IT certifications, such as Oracle 11g, Server+, RHCA, SQL Server Training, Prince2 Foundation etc. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Security, SQL Server, SQL Tips and Tricks, SQL Training, T SQL, Technology

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• Parallelism in .NET – Part 8, PLINQ’s ForAll Method

  - by Reed

  Parallel LINQ extends LINQ to Objects, and is typically very similar.  However, as I previously discussed, there are some differences.  Although the standard way to handle simple Data Parellelism is via Parallel.ForEach, it’s possible to do the same thing via PLINQ. PLINQ adds a new method unavailable in standard LINQ which provides new functionality… LINQ is designed to provide a much simpler way of handling querying, including filtering, ordering, grouping, and many other benefits.  Reading the description in LINQ to Objects on MSDN, it becomes clear that the thinking behind LINQ deals with retrieval of data.  LINQ works by adding a functional programming style on top of .NET, allowing us to express filters in terms of predicate functions, for example. PLINQ is, generally, very similar.  Typically, when using PLINQ, we write declarative statements to filter a dataset or perform an aggregation.  However, PLINQ adds one new method, which provides a very different purpose: ForAll. The ForAll method is defined on ParallelEnumerable, and will work upon any ParallelQuery<T>.  Unlike the sequence operators in LINQ and PLINQ, ForAll is intended to cause side effects.  It does not filter a collection, but rather invokes an action on each element of the collection. At first glance, this seems like a bad idea.  For example, Eric Lippert clearly explained two philosophical objections to providing an IEnumerable<T>.ForEach extension method, one of which still applies when parallelized.  The sole purpose of this method is to cause side effects, and as such, I agree that the ForAll method “violates the functional programming principles that all the other sequence operators are based upon”, in exactly the same manner an IEnumerable<T>.ForEach extension method would violate these principles.  Eric Lippert’s second reason for disliking a ForEach extension method does not necessarily apply to ForAll – replacing ForAll with a call to Parallel.ForEach has the same closure semantics, so there is no loss there. Although ForAll may have philosophical issues, there is a pragmatic reason to include this method.  Without ForAll, we would take a fairly serious performance hit in many situations.  Often, we need to perform some filtering or grouping, then perform an action using the results of our filter.  Using a standard foreach statement to perform our action would avoid this philosophical issue: // Filter our collection var filteredItems = collection.AsParallel().Where( i => i.SomePredicate() ); // Now perform an action foreach (var item in filteredItems) { // These will now run serially item.DoSomething(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } This would cause a loss in performance, since we lose any parallelism in place, and cause all of our actions to be run serially. We could easily use a Parallel.ForEach instead, which adds parallelism to the actions: // Filter our collection var filteredItems = collection.AsParallel().Where( i => i.SomePredicate() ); // Now perform an action once the filter completes Parallel.ForEach(filteredItems, item => { // These will now run in parallel item.DoSomething(); }); This is a noticeable improvement, since both our filtering and our actions run parallelized.  However, there is still a large bottleneck in place here.  The problem lies with my comment “perform an action once the filter completes”.  Here, we’re parallelizing the filter, then collecting all of the results, blocking until the filter completes.  Once the filtering of every element is completed, we then repartition the results of the filter, reschedule into multiple threads, and perform the action on each element.  By moving this into two separate statements, we potentially double our parallelization overhead, since we’re forcing the work to be partitioned and scheduled twice as many times. This is where the pragmatism comes into play.  By violating our functional principles, we gain the ability to avoid the overhead and cost of rescheduling the work: // Perform an action on the results of our filter collection .AsParallel() .Where( i => i.SomePredicate() ) .ForAll( i => i.DoSomething() ); The ability to avoid the scheduling overhead is a compelling reason to use ForAll.  This really goes back to one of the key points I discussed in data parallelism: Partition your problem in a way to place the most work possible into each task.  Here, this means leaving the statement attached to the expression, even though it causes side effects and is not standard usage for LINQ. This leads to my one guideline for using ForAll: The ForAll extension method should only be used to process the results of a parallel query, as returned by a PLINQ expression. Any other usage scenario should use Parallel.ForEach, instead.

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• New Replication, Optimizer and High Availability features in MySQL 5.6.5!

  - by Rob Young

  As the Product Manager for the MySQL database it is always great to announce when the MySQL Engineering team delivers another great product release.  As a field DBA and developer it is even better when that release contains improvements and innovation that I know will help those currently using MySQL for apps that range from modest intranet sites to the most highly trafficked web sites on the web.  That said, it is my pleasure to take my hat off to MySQL Engineering for today's release of the MySQL 5.6.5 Development Milestone Release ("DMR"). The new highlighted features in MySQL 5.6.5 are discussed here: New Self-Healing Replication ClustersThe 5.6.5 DMR improves MySQL Replication by adding Global Transaction Ids and automated utilities for self-healing Replication clusters.  Prior to 5.6.5 this has been somewhat of a pain point for MySQL users with most developing custom solutions or looking to costly, complex third-party solutions for these capabilities.  With 5.6.5 these shackles are all but removed by a solution that is included with the GPL version of the database and supporting GPL tools.  You can learn all about the details of the great, problem solving Replication features in MySQL 5.6 in Mat Keep's Developer Zone article.  New Replication Administration and Failover UtilitiesAs mentioned above, the new Replication features, Global Transaction Ids specifically, are now supported by a set of automated GPL utilities that leverage the new GTIDs to provide administration and manual or auto failover to the most up to date slave (that is the default, but user configurable if needed) in the event of a master failure. The new utilities, along with links to Engineering related blogs, are discussed in detail in the DevZone Article noted above. Better Query Optimization and ThroughputThe MySQL Optimizer team continues to amaze with the latest round of improvements in 5.6.5. Along with much refactoring of the legacy code base, the Optimizer team has improved complex query optimization and throughput by adding these functional improvements: Subquery Optimizations - Subqueries are now included in the Optimizer path for runtime optimization.  Better throughput of nested queries enables application developers to simplify and consolidate multiple queries and result sets into a single unit or work. Optimizer now uses CURRENT_TIMESTAMP as default for DATETIME columns - For simplification, this eliminates the need for application developers to assign this value when a column of this type is blank by default. Optimizations for Range based queries - Optimizer now uses ready statistics vs Index based scans for queries with multiple range values. Optimizations for queries using filesort and ORDER BY.  Optimization criteria/decision on execution method is done now at optimization vs parsing stage. Print EXPLAIN in JSON format for hierarchical readability and Enterprise tool consumption. You can learn the details about these new features as well all of the Optimizer based improvements in MySQL 5.6 by following the Optimizer team blog. You can download and try the MySQL 5.6.5 DMR here. (look under "Development Releases")  Please let us know what you think!  The new HA utilities for Replication Administration and Failover are available as part of the MySQL Workbench Community Edition, which you can download here .Also New in MySQL LabsAs has become our tradition when announcing DMRs we also like to provide "Early Access" development features to the MySQL Community via the MySQL Labs.  Today is no exception as we are also releasing the following to Labs for you to download, try and let us know your thoughts on where we need to improve:InnoDB Online OperationsMySQL 5.6 now provides Online ADD Index, FK Drop and Online Column RENAME.  These operations are non-blocking and will continue to evolve in future DMRs.  You can learn the grainy details by following John Russell's blog.InnoDB data access via Memcached API ("NotOnlySQL") - Improved refresh of an earlier feature releaseSimilar to Cluster 7.2, MySQL 5.6 provides direct NotOnlySQL access to InnoDB data via the familiar Memcached API. This provides the ultimate in flexibility for developers who need fast, simple key/value access and complex query support commingled within their applications.Improved Transactional Performance, ScaleThe InnoDB Engineering team has once again under promised and over delivered in the area of improved performance and scale.  These improvements are also included in the aggregated Spring 2012 labs release:InnoDB CPU cache performance improvements for modern, multi-core/CPU systems show great promise with internal tests showing:    2x throughput improvement for read only activity 6x throughput improvement for SELECT range Read/Write benchmarks are in progress More details on the above are available here. You can download all of the above in an aggregated "InnoDB 2012 Spring Labs Release" binary from the MySQL Labs. You can also learn more about these improvements and about related fixes to mysys mutex and hash sort by checking out the InnoDB team blog.MySQL 5.6.5 is another installment in what we believe will be the best release of the MySQL database ever.  It also serves as a shining example of how the MySQL Engineering team at Oracle leads in MySQL innovation.You can get the overall Oracle message on the MySQL 5.6.5 DMR and Early Access labs features here. As always, thanks for your continued support of MySQL, the #1 open source database on the planet!

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• Better documentation for tasks waiting on resources

  - by SQLOS Team

  The sys.dm_os_waiting_tasks DMV contains a wealth of useful information about tasks waiting on a resource, but until now detailed information about the resource being consumed - sys.dm_os_waiting_tasks.resource_description - hasn't been documented, apart from a rather self-evident "Description of the resource that is being consumed."   Thanks to a recent Connect suggestion this column will get more information added. Here is a summary of the possible values that can appear in this column - Note this information is current for SQL Server 2008 R2 and Denali:   Thread-pool resource owner:•       threadpool id=scheduler<hex-address> Parallel query resource owner:•       exchangeEvent id={Port|Pipe}<hex-address> WaitType=<exchange-wait-type> nodeId=<exchange-node-id> Exchange-wait-type can be one of the following.•       e_waitNone•       e_waitPipeNewRow•       e_waitPipeGetRow•       e_waitSynchronizeConsumerOpen•       e_waitPortOpen•       e_waitPortClose•       e_waitRange Lock resource owner:<type-specific-description> id=lock<lock-hex-address> mode=<mode> associatedObjectId=<associated-obj-id>               <type-specific-description> can be:• For DATABASE: databaselock subresource=<databaselock-subresource> dbid=<db-id>• For FILE: filelock fileid=<file-id> subresource=<filelock-subresource> dbid=<db-id>• For OBJECT: objectlock lockPartition=<lock-partition-id> objid=<obj-id> subresource=<objectlock-subresource> dbid=<db-id>• For PAGE: pagelock fileid=<file-id> pageid=<page-id> dbid=<db-id> subresource=<pagelock-subresource>• For Key: keylock  hobtid=<hobt-id> dbid=<db-id>• For EXTENT: extentlock fileid=<file-id> pageid=<page-id> dbid=<db-id>• For RID: ridlock fileid=<file-id> pageid=<page-id> dbid=<db-id>• For APPLICATION: applicationlock hash=<hash> databasePrincipalId=<role-id> dbid=<db-id>• For METADATA: metadatalock subresource=<metadata-subresource> classid=<metadatalock-description> dbid=<db-id>• For HOBT: hobtlock hobtid=<hobt-id> subresource=<hobt-subresource> dbid=<db-id>• For ALLOCATION_UNIT: allocunitlock hobtid=<hobt-id> subresource=<alloc-unit-subresource> dbid=<db-id> <mode> can be:• Sch-S• Sch-M• S• U• X• IS• IU• IX• SIU• SIX• UIX• BU• RangeS-S• RangeS-U• RangeI-N• RangeI-S• RangeI-U• RangeI-X• RangeX-S• RangeX-U• RangeX-X External resource owner:•       External ExternalResource=<wait-type> Generic resource owner:•       TransactionMutex TransactionInfo Workspace=<workspace-id>•       Mutex•       CLRTaskJoin•       CLRMonitorEvent•       CLRRWLockEvent•       resourceWait Latch resource owner:•       <db-id>:<file-id>:<page-in-file>•       <GUID>•       <latch-class> (<latch-address>)   Further Information Slava Oks's weblog: sys.dm_os_waiting_tasks.Informit.com: Identifying Blocking Using sys.dm_os_waiting_tasks - Ken Henderson   - Guy

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• C# async and actors

  - by Alex.Davies

  If you read my last post about async, you might be wondering what drove me to write such odd code in the first place. The short answer is that .NET Demon is written using NAct Actors. Actors are an old idea, which I believe deserve a renaissance under C# 5. The idea is to isolate each stateful object so that only one thread has access to its state at any point in time. That much should be familiar, it's equivalent to traditional lock-based synchronization. The different part is that actors pass "messages" to each other rather than calling a method and waiting for it to return. By doing that, each thread can only ever be holding one lock. This completely eliminates deadlocks, my least favourite concurrency problem. Most people who use actors take this quite literally, and there are plenty of frameworks which help you to create message classes and loops which can receive the messages, inspect what type of message they are, and process them accordingly. But I write C# for a reason. Do I really have to choose between using actors and everything I love about object orientation in C#? Type safety Interfaces Inheritance Generics As it turns out, no. You don't need to choose between messages and method calls. A method call makes a perfectly good message, as long as you don't wait for it to return. This is where asynchonous methods come in. I have used NAct for a while to wrap my objects in a proxy layer. As long as I followed the rule that methods must always return void, NAct queued up the call for later, and immediately released my thread. When I needed to get information out of other actors, I could use EventHandlers and callbacks (continuation passing style, for any CS geeks reading), and NAct would call me back in my isolated thread without blocking the actor that raised the event. Using callbacks looks horrible though. To remind you: m_BuildControl.FilterEnabledForBuilding(    projects,    enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(        enabledProjects,             newDirtyProjects =             {                 ....... Which is why I'm really happy that NAct now supports async methods. Now, methods are allowed to return Task rather than just void. I can await those methods, and C# 5 will turn the rest of my method into a continuation for me. NAct will run the other method in the other actor's context, but will make sure that when my method resumes, we're back in my context. Neither actor was ever blocked waiting for the other one. Apart from when they were actually busy doing something, they were responsive to concurrent messages from other sources. To be fair, you could use async methods with lock statements to achieve exactly the same thing, but it's ugly. Here's a realistic example of an object that has a queue of data that gets passed to another object to be processed: class QueueProcessor {    private readonly ItemProcessor m_ItemProcessor = ...     private readonly object m_Sync = new object();    private Queue<object> m_DataQueue = ...    private List<object> m_Results = ...     public async Task ProcessOne() {         object data = null;         lock (m_Sync)         {             data = m_DataQueue.Dequeue();         }         var processedData = await m_ItemProcessor.ProcessData(data); lock (m_Sync)         {             m_Results.Add(processedData);         }     } } We needed to write two lock blocks, one to get the data to process, one to store the result. The worrying part is how easily we could have forgotten one of the locks. Compare that to the version using NAct: class QueueProcessorActor : IActor { private readonly ItemProcessor m_ItemProcessor = ... private Queue<object> m_DataQueue = ... private List<object> m_Results = ... public async Task ProcessOne()     {         // We are an actor, it's always thread-safe to access our private fields         var data = m_DataQueue.Dequeue();         var processedData = await m_ItemProcessor.ProcessData(data);         m_Results.Add(processedData);     } } You don't have to explicitly lock anywhere, NAct ensures that your code will only ever run on one thread, because it's an actor. Either way, async is definitely better than traditional synchronous code. Here's a diagram of what a typical synchronous implementation might do: The left side shows what is running on the thread that has the lock required to access the QueueProcessor's data. The red section is where that lock is held, but doesn't need to be. Contrast that with the async version we wrote above: Here, the lock is released in the middle. The QueueProcessor is free to do something else. Most importantly, even if the ItemProcessor sometimes calls the QueueProcessor, they can never deadlock waiting for each other. So I thoroughly recommend you use async for all code that has to wait a while for things. And if you find yourself writing lots of lock statements, think about using actors as well. Using actors and async together really takes the misery out of concurrent programming.

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• Azure Mobile Services: available modules

  - by svdoever

  Azure Mobile Services has documented a set of objects available in your Azure Mobile Services server side scripts at their documentation page Mobile Services server script reference. Although the documented list is a nice list of objects for the common things you want to do, it will be sooner than later that you will look for more functionality to be included in your script, especially with the new provided feature that you can now create your custom API’s. If you use GIT it is now possible to add any NPM module (node package manager module, say the NuGet of the node world), but why include a module if it is already available out of the box. And you can only use GIT with Azure Mobile Services if you are an administrator on your Azure Mobile Service, not if you are a co-administrator (will be solved in the future). Until now I did some trial and error experimentation to test if a certain module was available. This is easiest to do as follows:   Create a custom API, for example named experiment. In this API use the following code: exports.get = function (request, response) { var module = "nonexistingmodule"; var m = require(module); response.send(200, "Module '%s' found.", module); }; You can now test your service with the following request in your browser: https://yourservice.azure-mobile.net/api/experiment If you get the result: {"code":500,"error":"Error: Internal Server Error"} you know that the module does not exist. In your logs you will find the following error: Error in script '/api/experiment.json'. Error: Cannot find module 'nonexistingmodule' [external code] atC:\DWASFiles\Sites\yourservice\VirtualDirectory0\site\wwwroot\App_Data\config\scripts\api\experiment.js:3:13[external code] If you require an existing (undocumented) module like the OAuth module in the following code, you will get success as a result: exports.get = function (request, response) { var module = "oauth"; var m = require(module); response.send(200, "Module '" + module + "' found."); }; If we look at the standard node.js documentation we see an extensive list of modules that can be used from your code. If we look at the list of files available in the Azure Mobile Services platform as documented in the blog post Azure Mobile Services: what files does it consist of? we see a folder node_modules with many more modules are used to build the Azure Mobile Services functionality on, but that can also be utilized from your server side node script code: apn - An interface to the Apple Push Notification service for Node.js. dpush - Send push notifications to Android devices using GCM. mpns - A Node.js interface to the Microsoft Push Notification Service (MPNS) for Windows Phone. wns - Send push notifications to Windows 8 devices using WNS. pusher - Node library for the Pusher server API (see also: http://pusher.com/) azure - Windows Azure Client Library for node. express - Sinatra inspired web development framework. oauth - Library for interacting with OAuth 1.0, 1.0A, 2 and Echo. Provides simplified client access and allows for construction of more complex apis and OAuth providers. request - Simplified HTTP request client. sax - An evented streaming XML parser in JavaScript sendgrid - A NodeJS implementation of the SendGrid Api. sqlserver – In node repository known as msnodesql - Microsoft Driver for Node.js for SQL Server. tripwire - Break out from scripts blocking node.js event loop. underscore - JavaScript's functional programming helper library. underscore.string - String manipulation extensions for Underscore.js javascript library. xml2js - Simple XML to JavaScript object converter. xmlbuilder - An XML builder for node.js. As stated before, many of these modules are used to provide the functionality of Azure Mobile Services platform, and in general should not be used directly. On the other hand, I needed OAuth badly to authenticate to the new v1.1 services of Twitter, and was very happy that a require('oauth') and a few lines of code did the job. Based on the above modules and a lot of code in the other javascript files in the Azure Mobile Services platform a set of global objects is provided that can be used from your server side node.js script code. In future blog posts I will go into more details with respect to how this code is built-up, all starting at the node.js express entry point app.js.

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• Polite busy-waiting with WRPAUSE on SPARC

  - by Dave

  Unbounded busy-waiting is an poor idea for user-space code, so we typically use spin-then-block strategies when, say, waiting for a lock to be released or some other event. If we're going to spin, even briefly, then we'd prefer to do so in a manner that minimizes performance degradation for other sibling logical processors ("strands") that share compute resources. We want to spin politely and refrain from impeding the progress and performance of other threads — ostensibly doing useful work and making progress — that run on the same core. On a SPARC T4, for instance, 8 strands will share a core, and that core has its own L1 cache and 2 pipelines. On x86 we have the PAUSE instruction, which, naively, can be thought of as a hardware "yield" operator which temporarily surrenders compute resources to threads on sibling strands. Of course this helps avoid intra-core performance interference. On the SPARC T2 our preferred busy-waiting idiom was "RD %CCR,%G0" which is a high-latency no-nop. The T4 provides a dedicated and extremely useful WRPAUSE instruction. The processor architecture manuals are the authoritative source, but briefly, WRPAUSE writes a cycle count into the the PAUSE register, which is ASR27. Barring interrupts, the processor then delays for the requested period. There's no need for the operating system to save the PAUSE register over context switches as it always resets to 0 on traps. Digressing briefly, if you use unbounded spinning then ultimately the kernel will preempt and deschedule your thread if there are other ready threads than are starving. But by using a spin-then-block strategy we can allow other ready threads to run without resorting to involuntary time-slicing, which operates on a long-ish time scale. Generally, that makes your application more responsive. In addition, by blocking voluntarily we give the operating system far more latitude regarding power management. Finally, I should note that while we have OS-level facilities like sched_yield() at our disposal, yielding almost never does what you'd want or naively expect. Returning to WRPAUSE, it's natural to ask how well it works. To help answer that question I wrote a very simple C/pthreads benchmark that launches 8 concurrent threads and binds those threads to processors 0..7. The processors are numbered geographically on the T4, so those threads will all be running on just one core. Unlike the SPARC T2, where logical CPUs 0,1,2 and 3 were assigned to the first pipeline, and CPUs 4,5,6 and 7 were assigned to the 2nd, there's no fixed mapping between CPUs and pipelines in the T4. And in some circumstances when the other 7 logical processors are idling quietly, it's possible for the remaining logical processor to leverage both pipelines. Some number T of the threads will iterate in a tight loop advancing a simple Marsaglia xor-shift pseudo-random number generator. T is a command-line argument. The main thread loops, reporting the aggregate number of PRNG steps performed collectively by those T threads in the last 10 second measurement interval. The other threads (there are 8-T of these) run in a loop busy-waiting concurrently with the T threads. We vary T between 1 and 8 threads, and report on various busy-waiting idioms. The values in the table are the aggregate number of PRNG steps completed by the set of T threads. The unit is millions of iterations per 10 seconds. For the "PRNG step" busy-waiting mode, the busy-waiting threads execute exactly the same code as the T worker threads. We can easily compute the average rate of progress for individual worker threads by dividing the aggregate score by the number of worker threads T. I should note that the PRNG steps are extremely cycle-heavy and access almost no memory, so arguably this microbenchmark is not as representative of "normal" code as it could be. And for the purposes of comparison I included a row in the table that reflects a waiting policy where the waiting threads call poll(NULL,0,1000) and block in the kernel. Obviously this isn't busy-waiting, but the data is interesting for reference. _table { border:2px black dotted; margin: auto; width: auto; } _tr { border: 2px red dashed; } _td { border: 1px green solid; } _table { border:2px black dotted; margin: auto; width: auto; } _tr { border: 2px red dashed; } td { background-color : #E0E0E0 ; text-align : right ; } th { text-align : left ; } td { background-color : #E0E0E0 ; text-align : right ; } th { text-align : left ; } Aggregate progress T = #worker threads Wait Mechanism for 8-T threadsT=1T=2T=3T=4T=5T=6T=7T=8 Park thread in poll() 32653347334833483348334833483348 no-op 415 831 124316482060249729303349 RD %ccr,%g0 "pause" 14262429269228623013316232553349 PRNG step 412 829 124616702092251029303348 WRPause(8000) 32443361333133483349334833483348 WRPause(4000) 32153308331533223347334833473348 WRPause(1000) 30853199322432513310334833483348 WRPause(500) 29173070315032223270330933483348 WRPause(250) 26942864294930773205338833483348 WRPause(100) 21552469262227902911321433303348

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• How is the gimbal locked problem solved using accumulative matrix transformations

  - by Luke San Antonio

  I am reading the online "Learning Modern 3D Graphics Programming" book by Jason L. McKesson As of now, I am up to the gimbal lock problem and how to solve it using quaternions. However right here, at the Quaternions page. Part of the problem is that we are trying to store an orientation as a series of 3 accumulated axial rotations. Orientations are orientations, not rotations. And orientations are certainly not a series of rotations. So we need to treat the orientation of the ship as an orientation, as a specific quantity. I guess this is the first spot I start to get confused, the reason is because I don't see the dramatic difference between orientations and rotations. I also don't understand why an orientation cannot be represented by a series of rotations... Also: The first thought towards this end would be to keep the orientation as a matrix. When the time comes to modify the orientation, we simply apply a transformation to this matrix, storing the result as the new current orientation. This means that every yaw, pitch, and roll applied to the current orientation will be relative to that current orientation. Which is precisely what we need. If the user applies a positive yaw, you want that yaw to rotate them relative to where they are current pointing, not relative to some fixed coordinate system. The concept, I understand, however I don't understand how if accumulating matrix transformations is a solution to this problem, how the code given in the previous page isn't just that. Here's the code: void display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClearDepth(1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glutil::MatrixStack currMatrix; currMatrix.Translate(glm::vec3(0.0f, 0.0f, -200.0f)); currMatrix.RotateX(g_angles.fAngleX); DrawGimbal(currMatrix, GIMBAL_X_AXIS, glm::vec4(0.4f, 0.4f, 1.0f, 1.0f)); currMatrix.RotateY(g_angles.fAngleY); DrawGimbal(currMatrix, GIMBAL_Y_AXIS, glm::vec4(0.0f, 1.0f, 0.0f, 1.0f)); currMatrix.RotateZ(g_angles.fAngleZ); DrawGimbal(currMatrix, GIMBAL_Z_AXIS, glm::vec4(1.0f, 0.3f, 0.3f, 1.0f)); glUseProgram(theProgram); currMatrix.Scale(3.0, 3.0, 3.0); currMatrix.RotateX(-90); //Set the base color for this object. glUniform4f(baseColorUnif, 1.0, 1.0, 1.0, 1.0); glUniformMatrix4fv(modelToCameraMatrixUnif, 1, GL_FALSE, glm::value_ptr(currMatrix.Top())); g_pObject->Render("tint"); glUseProgram(0); glutSwapBuffers(); } To my understanding, isn't what he is doing (modifying a matrix on a stack) considered accumulating matrices, since the author combined all the individual rotation transformations into one matrix which is being stored on the top of the stack. My understanding of a matrix is that they are used to take a point which is relative to an origin (let's say... the model), and make it relative to another origin (the camera). I'm pretty sure this is a safe definition, however I feel like there is something missing which is blocking me from understanding this gimbal lock problem. One thing that doesn't make sense to me is: If a matrix determines the difference relative between two "spaces," how come a rotation around the Y axis for, let's say, roll, doesn't put the point in "roll space" which can then be transformed once again in relation to this roll... In other words shouldn't any further transformations to this point be in relation to this new "roll space" and therefore not have the rotation be relative to the previous "model space" which is causing the gimbal lock. That's why gimbal lock occurs right? It's because we are rotating the object around set X, Y, and Z axes rather than rotating the object around it's own, relative axes. Or am I wrong? Since apparently this code I linked in isn't an accumulation of matrix transformations can you please give an example of a solution using this method. So in summary: What is the difference between a rotation and an orientation? Why is the code linked in not an example of accumulation of matrix transformations? What is the real, specific purpose of a matrix, if I had it wrong? How could a solution to the gimbal lock problem be implemented using accumulation of matrix transformations? Also, as a bonus: Why are the transformations after the rotation still relative to "model space?" Another bonus: Am I wrong in the assumption that after a transformation, further transformations will occur relative to the current? Also, if it wasn't implied, I am using OpenGL, GLSL, C++, and GLM, so examples and explanations in terms of these are greatly appreciated, if not necessary. The more the detail the better! Thanks in advance...

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• Thread.Interrupt Is Evil

  - by Alois Kraus

  Recently I have found an interesting issue with Thread.Interrupt during application shutdown. Some application was crashing once a week and we had not really a clue what was the issue. Since it happened not very often it was left as is until we have got some memory dumps during the crash. A memory dump usually means WindDbg which I really like to use (I know I am one of the very few fans of it).  After a quick analysis I did find that the main thread already had exited and the thread with the crash was stuck in a Monitor.Wait. Strange Indeed. Running the application a few thousand times under the debugger would potentially not have shown me what the reason was so I decided to what I call constructive debugging. I did create a simple Console application project and try to simulate the exact circumstances when the crash did happen from the information I have via memory dump and source code reading. The thread that was  crashing was actually MS code from an old version of the Microsoft Caching Application Block. From reading the code I could conclude that the main thread did call the Dispose method on the CacheManger class which did call Thread.Interrupt on the cache scavenger thread which was just waiting for work to do. My first version of the repro looked like this   static void Main(string[] args) { Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); } static void ThreadFunc() { while (true) { object value = Dequeue(); // block until unblocked or awaken via ThreadInterruptedException } } static object WaitObject = new object(); static object Dequeue() { object lret = "got value"; try { lock (WaitObject) { } } catch (ThreadInterruptedException) { Console.WriteLine("Got ThreadInterruptException"); lret = null; } return lret; } I do start a background thread and call Thread.Interrupt on it and then directly let the application terminate. The thread in the meantime does plenty of Monitor.Enter/Leave calls to simulate work on it. This first version did not crash. So I need to dig deeper. From the memory dump I did know that the finalizer thread was doing just some critical finalizers which were closing file handles. Ok lets add some long running finalizers to the sample. class FinalizableObject : CriticalFinalizerObject { ~FinalizableObject() { Console.WriteLine("Hi we are waiting to finalize now and block the finalizer thread for 5s."); Thread.Sleep(5000); } } class Program { static void Main(string[] args) { FinalizableObject fin = new FinalizableObject(); Thread t = new Thread(ThreadFunc) { IsBackground = true, Name = "Test Thread" }; t.Start(); Console.WriteLine("Interrupt Thread"); t.Interrupt(); GC.KeepAlive(fin); // prevent finalizing it too early // After leaving main the other thread is woken up via Thread.Abort // while we are finalizing. This causes a stackoverflow in the CLR ThreadAbortException handling at this time. } With this changed Main method and a blocking critical finalizer I did get my crash just like the real application. The funny thing is that this is actually a CLR bug. When the main method is left the CLR does suspend all threads except the finalizer thread and declares all objects as garbage. After the normal finalizers were called the critical finalizers are executed to e.g. free OS handles (usually). Remember that I did call Thread.Interrupt as one of the last methods in the Main method. The Interrupt method is actually asynchronous and does wake a thread up and throws a ThreadInterruptedException only once unlike Thread.Abort which does rethrow the exception when an exception handling clause is left. It seems that the CLR does not expect that a frozen thread does wake up again while the critical finalizers are executed. While trying to raise a ThreadInterrupedException the CLR goes down with an stack overflow. Ups not so nice. Why has this nobody noticed for years is my next question. As it turned out this error does only happen on the CLR for .NET 4.0 (x86 and x64). It does not show up in earlier or later versions of the CLR. I have reported this issue on connect here but so far it was not confirmed as a CLR bug. But I would be surprised if my console application was to blame for a stack overflow in my test thread in a Monitor.Wait call. What is the moral of this story? Thread.Abort is evil but Thread.Interrupt is too. It is so evil that even the CLR of .NET 4.0 contains a race condition during the CLR shutdown. When the CLR gurus can get it wrong the chances are high that you get it wrong too when you use this constructs. If you do not believe me see what Patrick Smacchia does blog about Thread.Abort and List.Sort. Not only the CLR creators can get it wrong. The BCL writers do sometimes have a hard time with correct exception handling as well. If you do tell me that you use Thread.Abort frequently and never had problems with it I do suspect that you do not have looked deep enough into your application to find such sporadic errors.

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• Profiling Startup Of VS2012 &ndash; YourKit Profiler

  - by Alois Kraus

  The YourKit (v7.0.5) profiler is interesting in terms of price (79€ single place license, 409€ + 1 year support and upgrades) and feature set. You do get a performance and memory profiler in one package for which you normally need also to pay extra from the other vendors. As an interesting side note the profiler UI is written in Java because they do also sell Java profilers with the same feature set. To get all methods of a VS startup you need first to configure it to include System* in the profiled methods and you need to configure * to measure wall clock time. By default it does record only CPU times which allows you to optimize CPU hungry operations. But you will never see a Thread.Sleep(10000) in the profiler blocking the UI in this mode. It can profile as all others processes started from within the profiler but it can also profile the next or all started processes. As usual it can profile in sampling and tracing mode. But since it is a memory profiler as well it does by default also record all object allocations > 1MB. With allocation recording enabled VS2012 did crash but without allocation recording there were no problems. The CPU tab contains the time line of the application and when you click in the graph you the call stacks of all threads at this time. This is really a nice feature. When you select a time region you the CPU Usage estimation for this time window. I have seen many applications consuming 100% CPU only because they did create garbage like crazy. For this is the Garbage Collection tab interesting in conjunction with a time range. This view is like the CPU table only that the CPU graph (green) is missing. All relevant information except for GCs/s is already visible in the CPU tab. Very handy to pinpoint excessive GC or CPU bound issues. The Threads tab does show the thread names and their lifetime. This is useful to see thread interactions or which thread is hottest in terms of CPU consumption. On the CPU tab the call tree does exist in a merged and thread specific view. When you click on a method you get below a list of all called methods. There you can sort for methods with a high own time which are worth optimizing. In the Method List you can select which scope you want to see. Back Traces are the methods which did call you. Callees ist the list of methods called directly or indirectly by your method as a flat list. This is not a call stack but still very useful to see which methods were slow so you can see the “root” cause quite quickly without the need to click trough long call stacks. The last view Merged Calles is a call stacked view of the previous view. This does help a lot to understand did call each method at run time. You would get the same view with a debugger for one call invocation but here you get the full statistics (invocation count) as well. Since YourKit is also a memory profiler you can directly see which objects you have on your managed heap and which objects do hold most of your precious memory. You can in in the Object Explorer view also examine the contents of your objects (strings or whatsoever) to get a better understanding which objects where potentially allocating this stuff.   YourKit is a very easy to use combined memory and performance profiler in one product. The unbeatable single license price makes it very attractive to straightly buy it. Although it is a Java UI it is very responsive and the memory consumption is considerably lower compared to dotTrace and ANTS profiler. What I do really like is to start the YourKit ui and then start the processes I want to profile as usual. There is no need to alter your own application code to be able to inject a profiler into your new started processes. For performance and memory profiling you can simply select the process you want to investigate from the list of started processes. That's the way I like to use profilers. Just get out of the way and let the application run without any special preparations.   Next: Telerik JustTrace

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• Application Composer: Exposing Your Customizations in BI Analytics and Reporting

  - by Richard Bingham

  Introduction This article explains in simple terms how to ensure the customizations and extensions you have made to your Fusion Applications are available for use in reporting and analytics. It also includes four embedded demo videos from our YouTube channel (if they don't appear check the browser address bar for a blocking shield icon). If you are new to Business Intelligence consider first reviewing our getting started article, and you can read more about the topic of custom subject areas in the documentation book Extending Sales. There are essentially four sections to this post. First we look at how custom fields added to standard objects are made available for reporting. Secondly we look at creating custom subject areas on the standard objects. Next we consider reporting on custom objects, starting with simple standalone objects, then child custom objects, and finally custom objects with relationships. Finally this article reviews how flexfields are exposed for reporting. Whilst this article applies to both Cloud/SaaS and on-premises deployments, if you are an on-premises developer then you can also use the BI Administration Tool to customize your BI metadata repository (the RPD) and create new subject areas. Whilst this is not covered here you can read more in Chapter 8 of the Extensibility Guide for Developers. Custom Fields on Standard Objects If you add a custom field to your standard object then it's likely you'll want to include it in your reports. This is very simple, since all new fields are instantly available in the "[objectName] Extension" folder in existing subject areas. The following two minute video demonstrates this. Custom Subject Areas for Standard Objects You can create your own subject areas for use in analytics and reporting via Application Composer. An example use-case could be to simplify the seeded subject areas, since they sometimes contain complex data fields and internal values that could confuse business users. One thing to note is that you cannot create subject areas in a sandbox, as it is not supported by BI, so once your custom object is tested and complete you'll need to publish the sandbox before moving forwards. The subject area creation processes is essentially two-fold. Once the request is submitted the ADF artifacts are generated, then secondly the related metadata is sent to the BI presentation server API's to make the updates there. One thing to note is that this second step may take up to ten minutes to complete. Once finished the status of the custom subject area request should show as 'OK' and it is then ready for use. Within the creation processes wizard-like steps there are three concepts worth highlighting: Date Flattening - this feature permits the roll up of reports at various date levels, such as data by week, month, quarter, or year. You simply check the box to enable it for that date field. Measures - these are your own functions that you can build into the custom subject area. They are related to the field data type and include min-max for dates, and sum(), avg(), and count() for  numeric fields. Implicit Facts - used to make the BI metadata join between your object fields and the calculated measure fields. The advice is to choose the most frequently used measure to ensure consistency. This video shows a simple example, where a simplified subject area is created for the customer 'Contact' standard object, picking just a few fields upon which users can then create reports. Custom Objects Custom subject areas support three types of custom objects. First is a simple standalone custom object and for which the same process mentioned above applies. The next is a custom child object created on a standard object parent, and finally a custom object that is related to a parent object - usually through a dynamic choice list. Whilst the steps in each of these last two are mostly the same, there are differences in the way you choose the objects and their fields. This is illustrated in the videos below.The first video shows the process for creating a custom subject area for a simple standalone custom object. This second video demonstrates how to create custom subject areas for custom objects that are of parent:child type, as well as those those with dynamic-choice-list relationships. &lt;span id=&quot;XinhaEditingPostion&quot;&gt;&lt;/span&gt; Flexfields Dynamic and Extensible Flexfields satisfy a similar requirement as custom fields (for Application Composer), with flexfields common across the Fusion Financials, Supply Chain and Procurement, and HCM applications. The basic principle is when you enable and configure your flexfields, in the edit page under each segment region (for both global and context segments) there is a BI Enabled check box. Once this is checked and you've completed your configuration, you run the Scheduled Process job named 'Import Oracle Fusion Data Extensions for Transactional Business Intelligence' to generate and migrate the related BI artifacts and data. This applies for dynamic, key, and extensible flexfields. Of course there is more to consider in terms of how you wish your flexfields to be implemented and exposed in your reports, and details are given in Chapter 4 of the Extending Applications guide.

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• IE9, LightSwitch Beta 2 and Zune HD: A Study in Risk Management?

  - by andrewbrust

  Photo by parl, 'Risk.’ Under Creative Commons Attribution-NonCommercial-NoDerivs License This has been a busy week for Microsoft, and for me as well.  On Monday, Microsoft launched Internet Explorer 9 at South by Southwest (SXSW) in Austin, TX.  That evening I flew from New York to Seattle.  On Tuesday morning, Microsoft launched Visual Studio LightSwitch, Beta 2 with a Go-Live license, in Redmond, and I had the privilege of speaking at the keynote presentation where the announcement was made.  Readers of this blog know I‘m a fan of LightSwitch, so I was happy to tell the app dev tools partners in the audience that I thought the LightSwitch extensions ecosystem represented a big opportunity – comparable to the opportunity when Visual Basic 1.0 was entering its final beta roughly 20 years ago.  On Tuesday evening, I flew back to New York (and wrote most of this post in-flight). Two busy, productive days.  But there was a caveat that impacts the accomplishments, because Monday was also the day reports surfaced from credible news agencies that Microsoft was discontinuing its dedicated Zune hardware efforts.  While the Zune brand, technology and service will continue to be a component of Windows Phone and a piece of the Xbox puzzle as well, speculation is that Microsoft will no longer be going toe-to-toe with iPod touch in the portable music player market. If we take all three of these developments together (even if one of them is based on speculation), two interesting conclusions can reasonably be drawn, one good and one less so. Microsoft is doubling down on technologies it finds strategic and de-emphasizing those that it does not.  HTML 5 and the Web are strategic, so here comes IE9, and it’s a very good browser.  Try it and see.  Silverlight is strategic too, as is SQL Server, Windows Azure and SQL Azure, so here comes Visual Studio LightSwitch Beta 2 and a license to deploy its apps to production.  Downloads of that product have exceeded Microsoft’s projections by more than 50%, and the company is even citing analyst firms’ figures covering the number of power-user developers that might use it. (I happen to think the product will be used by full-fledged developers as well, but that’s a separate discussion.) Windows Phone is strategic too…I wasn’t 100% positive of that before, but the Nokia agreement has made me confident.  Xbox as an entertainment appliance is also strategic.  Standalone music players are not strategic – and even if they were, selling them has been a losing battle for Microsoft.  So if Microsoft has consolidated the Zune content story and the ZunePass subscription into Xbox and Windows Phone, it would make sense, and would be a smart allocation of resources.  Essentially, it would be for the greater good. But it’s not all good.  In this scenario, Zune player customers would lose out.  Unless they wanted to switch to Windows Phone, and then use their phone’s battery for the portable media needs, they’re going to need a new platform.  They’re going to feel abandoned.  Even if Zune lives, there have been other such cul de sacs for customers.  Remember SPOT watches?  Live Spaces?  The original Live Mesh?  Microsoft discontinued each of these products.  The company is to be commended for cutting its losses, as admitting a loss isn’t easy.  But Redmond won’t be well-regarded by the victims of those decisions.  Instead, it gets black marks. What’s the answer?  I think it’s a bit like the 1980’s New York City “don’t block the box” gridlock rules: don’t enter an intersection unless you see a clear path through it.  If the light turns red and you’re blocking the perpendicular traffic, that’s your fault in judgment.  You get fined and get points on your license and you don’t get to shrug it off as beyond your control.  Accountability is key.  The same goes for Microsoft.  If it decides to enter a market, it should see a reasonable path through success in that market. Switching analogies, Microsoft shouldn’t make investments haphazardly, and it certainly shouldn’t ask investors to buy into a high-risk fund that is sold as safe and which offers only moderate returns.  People won’t continue to invest with a fund manager with a track record of over-zealous, imprudent, sub-prime investments.  The same is true on the product side for Microsoft, and not just with music players and geeky wrist watches.  It’s true of Web browsers, and line-of-business app dev tools, and smartphones, and cloud platforms and operating systems too.  When Microsoft is casual about its own risk, it raises risk for its customers, and weakens its reputation, market share and credibility.  That doesn’t mean all risk is bad, but it does mean no product team’s risk should be taken lightly. For mutual fund companies, it’s the CEO’s job to give his fund managers autonomy, but to make sure they’re conforming to a standard of rational risk management.  Because all those funds carry the same brand, and many of them serve the same investors. The same goes for Microsoft, its product portfolio, its executive ranks and its product managers.

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• Plagued by multithreaded bugs

  - by koncurrency

  On my new team that I manage, the majority of our code is platform, TCP socket, and http networking code. All C++. Most of it originated from other developers that have left the team. The current developers on the team are very smart, but mostly junior in terms of experience. Our biggest problem: multi-threaded concurrency bugs. Most of our class libraries are written to be asynchronous by use of some thread pool classes. Methods on the class libraries often enqueue long running taks onto the thread pool from one thread and then the callback methods of that class get invoked on a different thread. As a result, we have a lot of edge case bugs involving incorrect threading assumptions. This results in subtle bugs that go beyond just having critical sections and locks to guard against concurrency issues. What makes these problems even harder is that the attempts to fix are often incorrect. Some mistakes I've observed the team attempting (or within the legacy code itself) includes something like the following: Common mistake #1 - Fixing concurrency issue by just put a lock around the shared data, but forgetting about what happens when methods don't get called in an expected order. Here's a very simple example: void Foo::OnHttpRequestComplete(statuscode status) { m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } So now we have a bug in which Shutdown could get called while OnHttpNetworkRequestComplete is occuring on. A tester finds the bug, captures the crash dump, and assigns the bug to a developer. He in turn fixes the bug like this. void Foo::OnHttpRequestComplete(statuscode status) { AutoLock lock(m_cs); m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { AutoLock lock(m_cs); m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } The above fix looks good until you realize there's an even more subtle edge case. What happens if Shutdown gets called before OnHttpRequestComplete gets called back? The real world examples my team has are even more complex, and the edge cases are even harder to spot during the code review process. Common Mistake #2 - fixing deadlock issues by blindly exiting the lock, wait for the other thread to finish, then re-enter the lock - but without handling the case that the object just got updated by the other thread! Common Mistake #3 - Even though the objects are reference counted, the shutdown sequence "releases" it's pointer. But forgets to wait for the thread that is still running to release it's instance. As such, components are shutdown cleanly, then spurious or late callbacks are invoked on an object in an state not expecting any more calls. There are other edge cases, but the bottom line is this: Multithreaded programming is just plain hard, even for smart people. As I catch these mistakes, I spend time discussing the errors with each developer on developing a more appropriate fix. But I suspect they are often confused on how to solve each issue because of the enormous amount of legacy code that the "right" fix will involve touching. We're going to be shipping soon, and I'm sure the patches we're applying will hold for the upcoming release. Afterwards, we're going to have some time to improve the code base and refactor where needed. We won't have time to just re-write everything. And the majority of the code isn't all that bad. But I'm looking to refactor code such that threading issues can be avoided altogether. One approach I am considering is this. For each significant platform feature, have a dedicated single thread where all events and network callbacks get marshalled onto. Similar to COM apartment threading in Windows with use of a message loop. Long blocking operations could still get dispatched to a work pool thread, but the completion callback is invoked on on the component's thread. Components could possibly even share the same thread. Then all the class libraries running inside the thread can be written under the assumption of a single threaded world. Before I go down that path, I am also very interested if there are other standard techniques or design patterns for dealing with multithreaded issues. And I have to emphasize - something beyond a book that describes the basics of mutexes and semaphores. What do you think? I am also interested in any other approaches to take towards a refactoring process. Including any of the following: Literature or papers on design patterns around threads. Something beyond an introduction to mutexes and semaphores. We don't need massive parallelism either, just ways to design an object model so as to handle asynchronous events from other threads correctly. Ways to diagram the threading of various components, so that it will be easy to study and evolve solutions for. (That is, a UML equivalent for discussing threads across objects and classes) Educating your development team on the issues with multithreaded code. What would you do?

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• GROUP_CONCAT in CodeIgniter

  - by mickaelb91

  I'm just blocking to how create my group_concat with my sql request in CodeIgniter. All my queries are listed in a table, using Jtable library. All work fine, except when I try to insert GROUP_CONCAT. Here's my model page : function list_all() { $login_id = $this->session->userdata('User_id'); $this->db->select('p.project_id, p.Project, p.Description, p.Status, p.Thumbnail, t.Template'); $this->db->from('assigned_projects_ppeople a'); $this->db->where('people_id', $login_id); $this->db->join('projects p', 'p.project_id = a.project_id'); $this->db->join('project_templates t', 't.template_id = p.template_id'); $this->db->select('GROUP_CONCAT(u.Asset SEPARATOR ",") as assetslist', FALSE); $this->db->from('assigned_assets_pproject b'); $this->db->join('assets u', 'u.asset_id = b.asset_id'); $query = $this->db->get(); $rows = $query->result_array(); //Return result to jTable $jTableResult = array(); $jTableResult['Result'] = "OK"; $jTableResult['Records'] = $rows; return $jTableResult; } My controller page : function listRecord(){ $this->load->model('project_model'); $result = $this->project_model->list_all(); print json_encode($result); } And to finish my view page : <table id="listtable"></table> <script type="text/javascript"> $(document).ready(function () { $('#listtable').jtable({ title: 'Table test', actions: { listAction: '<?php echo base_url().'project/listRecord';?>', createAction: '/GettingStarted/CreatePerson', updateAction: '/GettingStarted/UpdatePerson', deleteAction: '/GettingStarted/DeletePerson' }, fields: { project_id: { key: true, list: false }, Project: { title: 'Project Name' }, Description: { title: 'Description' }, Status: { title: 'Status', width: '20px' }, Thumbnail: { title: 'Thumbnail', display: function (data) { return '<a href="<?php echo base_url('project');?>/' + data.record.project_id + '"><img class="thumbnail" width="50px" height="50px" src="' + data.record.Thumbnail + '" alt="' + data.record.Thumbnail + '" ></a>'; } }, Template: { title: 'Template' }, Asset: { title: 'Assets' }, RecordDate: { title: 'Record date', type: 'date', create: false, edit: false } } }); //Load person list from server $('#listtable').jtable('load'); }); </script> I read lot of posts talking about that, like replace ',' separator by ",", or use OUTER to the join, or group_by('p.project_id') before using get method, don't work. Here is a the output of the query in json : {"Result":"OK","Records":[{"project_id":"1","Project":"Adam & Eve : A Famous Story","Description":"The story about Adam & Eve reviewed in 3D Animation movie !","Status":"wip","Thumbnail":"http:\/\/localhost\/assets\/images\/thumb\/projectAdamAndEve.png","Template":"Animation Movie","assetslist":"Apple, Adam, Eve, Garden of Eden"}]} We can see the GROUP_CONCAT is here (after "assetslist"), but the column stills empty. If asked, I can post the database SQL file. Thank you.

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