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• Apache URL rewriting in reverse proxy

  - by Jeremy Gooch

  I'm deploying Apache in front of a Karaf-hosted application (Apache and Karaf are on separate servers). I want Apache to operate as a reverse proxy and also to hide part of the URL. The URL to get the log-in page of the application directly from the app server is http://app-server:8181/jellyfish. Pages are served by the Jetty instance running within Karaf. Of course, this behaviour would usually be blocked by the firewall for everything except the reverse proxy server. With the firewall off, if you hit this URL then Jetty loads the log-in page. The browser's address bar correctly changes to http://app-server:8181/jellyfish/login?0 and everything works. What I want is for http://web-server (i.e. from the root) to map to Jetty on the app server with the name of the app (jellyfish) suppressed. e.g. The browser would change to show http://web-server/login?0 in the address bar and all subsequent URLs and content would be served with the web-server's domain and without the jellyfish clutter. I can get Apache to operate as a simple reverse proxy, using the following config (snippet):- ProxyPass /jellyfish http://app-server:8181/jellyfish ProxyPassReverse / http://app-server:8181/ ...but this requires the browser's URL to contain jellyfish and going to the root URL (http://web-server) gives a 404 Not Found. I've spent a lot of time trying to use mod_rewrite with and without its [P] flag to get around this, but without success. I then tried the ProxyPassMatch directive, but I can't seem to get that quite correct either. Here's the current config, as is loaded into /etc/apache2/sites-available/ on the web server. Note that there is a locally-hosted images directory. I've also kept the mod_rewrite proxy exploit protection and am suppressing a couple of mod_security rules that were giving false positives. <VirtualHost *:80> ServerAdmin admin@drummer-server ServerName drummer-server ErrorLog ${APACHE_LOG_DIR}/error.log LogLevel warn CustomLog ${APACHE_LOG_DIR}/access.log combined Alias /images/ "/var/www/images/" RewriteEngine On RewriteCond %{REQUEST_URI} !^$ RewriteCond %{REQUEST_URI} !^/ RewriteRule .* - [R=400,L] ProxyPass /images ! ProxyPassMatch ^/(.*) http://granny-server:8181/jellyfish/$1 ProxyPassReverse / http://granny-server:8181/jellyfish ProxyPreserveHost On SecRuleRemoveById 981059 981060 <Directory "/var/www/images"> Options Indexes MultiViews FollowSymLinks AllowOverride None Order allow,deny Allow from all </Directory> </VirtualHost> If I go to http://web-server, I get redirected to http://web-server/jellyfish/home but this gives a 404, with a complaint about trying to access /jellyfish/jellyfish/home - NB the browser's address bar does not contain the double /jellyfish. HTTP ERROR 404 Problem accessing /jellyfish/jellyfish/home. Reason: Not Found And, if I go to http://web-server/login, I get redirected to http://web-server/jellyfish/login?0 but this gives a 404, with a complaint about trying to access /jellyfish/jellyfish/login. HTTP ERROR 404 Problem accessing /jellyfish/jellyfish/login. Reason: Not Found So, I'm guessing I'm somehow passing through the rules twice. I am also slightly bemused as to where the home bit of the URL comes from in the first example. Can someone point me in the right direction, please? Thanks, J.

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• At times, you need to hire a professional.

  - by Phil Factor

  After months of increasingly demanding toil, the development team I belonged to was told that the project was to be canned and the whole team would be fired.  I’d been brought into the team as an expert in the data implications of a business re-engineering of a major financial institution. Nowadays, you’d call me a data architect, I suppose.  I’d spent a happy year being paid consultancy fees solving a succession of interesting problems until the point when the company lost is nerve, and closed the entire initiative. The IT industry was in one of its characteristic mood-swings downwards.  After the announcement, we met in the canteen. A few developers had scented the smell of death around the project already hand had been applying unsuccessfully for jobs. There was a sense of doom in the mass of dishevelled and bleary-eyed developers. After giving vent to anger and despair, talk turned to getting new employment. It was then that I perked up. I’m not an obvious choice to give advice on getting, or passing,  IT interviews. I reckon I’ve failed most of the job interviews I’ve ever attended. I once even failed an interview for a job I’d already been doing perfectly well for a year. The jobs I’ve got have mostly been from personal recommendation. Paradoxically though, from years as a manager trying to recruit good staff, I know a lot about what IT managers are looking for.  I gave an impassioned speech outlining the important factors in getting to an interview.  The most important thing, certainly in my time at work is the quality of the résumé or CV. I can’t even guess the huge number of CVs (résumés) I’ve read through, scanning for candidates worth interviewing.  Many IT Developers find it impossible to describe their  career succinctly on two sides of paper.  They leave chunks of their life out (were they in prison?), get immersed in detail, put in irrelevancies, describe what was going on at work rather than what they themselves did, exaggerate their importance, criticize their previous employers, aren’t  aware of the important aspects of a role to a potential employer, suffer from shyness and modesty,  and lack any sort of organized perspective of their work. There are many ways of failing to write a decent CV. Many developers suffer from the delusion that their worth can be recognized purely from the code that they write, and shy away from anything that seems like self-aggrandizement. No.  A resume must make a good impression, which means presenting the facts about yourself in a clear and positive way. You can’t do it yourself. Why not have your resume professionally written? A good professional CV Writer will know the qualities being looked for in a CV and interrogate you to winkle them out. Their job is to make order and sense out of a confused career, to summarize in one page a mass of detail that presents to any recruiter the information that’s wanted. To stand back and describe an accurate summary of your skills, and work-experiences dispassionately, without rancor, pity or modesty. You are no more capable of producing an objective documentation of your career than you are of taking your own appendix out.  My next recommendation was more controversial. This is to have a professional image overhaul, or makeover, followed by a professionally-taken photo portrait. I discovered this by accident. It is normal for IT professionals to face impossible deadlines and long working hours by looking more and more like something that had recently blocked a sink. Whilst working in IT, and in a state of personal dishevelment, I’d been offered the role in a high-powered amateur production of an old ex- Broadway show, purely for my singing voice. I was supposed to be the presentable star. When the production team saw me, the air was thick with tension and despair. I was dragged kicking and protesting through a succession of desperate grooming, scrubbing, dressing, dieting. I emerged feeling like “That jewelled mass of millinery, That oiled and curled Assyrian bull, Smelling of musk and of insolence.” (Tennyson Maud; A Monodrama (1855) Section v1 stanza 6) I was then photographed by a professional stage photographer.  When the photographs were delivered, I was amazed. It wasn’t me, but it looked somehow respectable, confident, trustworthy.   A while later, when the show had ended, I took the photos, and used them for work. They went with the CV to job applications. It did the trick better than I could ever imagine.  My views went down big with the developers. Old rivalries were put immediately to one side. We voted, with a show of hands, to devote our energies for the entire notice period to getting employable. We had a team sourcing the CV Writer,  a team organising the make-overs and photographer, and a third team arranging  mock interviews. A fourth team determined the best websites and agencies for recruitment, with the help of friends in the trade.  Because there were around thirty developers, we were in a good negotiating position.  Of the three CV Writers we found who lived locally, one proved exceptional. She was an ex-journalist with an eye to detail, and years of experience in manipulating language. We tried her skills out on a developer who seemed a hopeless case, and he was called to interview within a week.  I was surprised, too, how many companies were experts at image makeovers. Within the month, we all looked like those weird slick  people in the ‘Office-tagged’ stock photographs who stare keenly and interestedly at PowerPoint slides in sleek chromium-plated high-rise offices. The portraits we used still adorn the entries of many of my ex-colleagues in LinkedIn. After a months’ worth of mock interviews, and technical Q&A, our stutters, hesitations, evasions and periphrastic circumlocutions were all gone.  There is little more to relate. With the résumés or CVs, mugshots, and schooling in how to pass interviews, we’d all got new and better-paid jobs well  before our month’s notice was ended. Whilst normally, an IT team under the axe is a sad and depressed place to belong to, this wonderful group of people had proved the power of organized group action in turning the experience to advantage. It left us feeling slightly guilty that we were somehow cheating, but I guess we were merely leveling the playing-field.

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• Multithreading 2D gravity calculations

  - by Postman

  I'm building a space exploration game and I've currently started working on gravity ( In C# with XNA). The gravity still needs tweaking, but before I can do that, I need to address some performance issues with my physics calculations. This is using 100 objects, normally rendering 1000 of them with no physics calculations gets well over 300 FPS (which is my FPS cap), but any more than 10 or so objects brings the game (and the single thread it runs on) to its knees when doing physics calculations. I checked my thread usage and the first thread was killing itself from all the work, so I figured I just needed to do the physics calculation on another thread. However when I try to run the Gravity.cs class's Update method on another thread, even if Gravity's Update method has nothing in it, the game is still down to 2 FPS. Gravity.cs public void Update() { foreach (KeyValuePair<string, Entity> e in entityEngine.Entities) { Vector2 Force = new Vector2(); foreach (KeyValuePair<string, Entity> e2 in entityEngine.Entities) { if (e2.Key != e.Key) { float distance = Vector2.Distance(entityEngine.Entities[e.Key].Position, entityEngine.Entities[e2.Key].Position); if (distance > (entityEngine.Entities[e.Key].Texture.Width / 2 + entityEngine.Entities[e2.Key].Texture.Width / 2)) { double angle = Math.Atan2(entityEngine.Entities[e2.Key].Position.Y - entityEngine.Entities[e.Key].Position.Y, entityEngine.Entities[e2.Key].Position.X - entityEngine.Entities[e.Key].Position.X); float mult = 0.1f * (entityEngine.Entities[e.Key].Mass * entityEngine.Entities[e2.Key].Mass) / distance * distance; Vector2 VecForce = new Vector2((float)Math.Cos(angle), (float)Math.Sin(angle)); VecForce.Normalize(); Force = Vector2.Add(Force, VecForce * mult); } } } entityEngine.Entities[e.Key].Position += Force; } } Yeah, I know. It's a nested foreach loop, but I don't know how else to do the gravity calculation, and this seems to work, it's just so intensive that it needs its own thread. (Even if someone knows a super efficient way to do these calculations, I'd still like to know how I COULD do it on multiple threads instead) EntityEngine.cs (manages an instance of Gravity.cs) public class EntityEngine { public Dictionary<string, Entity> Entities = new Dictionary<string, Entity>(); public Gravity gravity; private Thread T; public EntityEngine() { gravity = new Gravity(this); } public void Update() { foreach (KeyValuePair<string, Entity> e in Entities) { Entities[e.Key].Update(); } T = new Thread(new ThreadStart(gravity.Update)); T.IsBackground = true; T.Start(); } } EntityEngine is created in Game1.cs, and its Update() method is called within Game1.cs. I need my physics calculation in Gravity.cs to run every time the game updates, in a separate thread so that the calculation doesn't slow the game down to horribly low (0-2) FPS. How would I go about making this threading work? (any suggestions for an improved Planetary Gravity system are welcome if anyone has them) I'm also not looking for a lesson in why I shouldn't use threading or the dangers of using it incorrectly, I'm looking for a straight answer on how to do it. I've already spent an hour googling this very question with little results that I understood or were helpful. I don't mean to come off rude, but it always seems hard as a programming noob to get a straight meaningful answer, I usually rather get an answer so complex I'd easily be able to solve my issue if I understood it, or someone saying why I shouldn't do what I want to do and offering no alternatives (that are helpful). Thank you for the help!

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• About the K computer

  - by nospam(at)example.com (Joerg Moellenkamp)

  Okay ? after getting yet another mail because of the new #1 on the Top500 list, I want to add some comments from my side: Yes, the system is using SPARC processor. And that is great news for a SPARC fan like me. It is using the SPARC VIIIfx processor from Fujitsu clocked at 2 GHz. No, it isn't the only one. Most people are saying there are two in the Top500 list using SPARC (#77 JAXA and #1 K) but in fact there are three. The Tianhe-1 (#2 on the Top500 list) super computer contains 2048 Galaxy "FT-1000" 1 GHz 8-core processors. Don't know it? The FeiTeng-1000 ? this proc is a 8 core, 8 threads per core, 1 ghz processor made in China. And it's SPARC based. By the way ? this sounds really familiar to me ? perhaps the people just took the opensourced UltraSPARC-T2 design, because some of the parameters sound just to similar. However it looks like that Tianhe-1 is using the SPARCs as input nodes and not as compute notes. No, I don't see it as the next M-series processor. Simple reason: You can't create SMP systems out of them ? it simply hasn't the functionality to do so. Even when there are multiple CPUs on a single board, they are not connected like an SMP/NUMA machine to a shared memory machine ? they are connected with the cluster interconnect (in this case the Tofu interconnect) and work like a large cluster. Yes, it has a lot of oomph in Linpack ? however I assume a lot came from the extensions to the SPARCv9 standard. No, Linpack has no relevance for any commercial workload ? Linpack is such a special load, that even some HPC people are arguing that it isn't really a good benchmark for HPC. It's embarrassingly parallel, it can work with relatively small interconnects compared to the interconnects in SMP systems (however we get in spheres SMP interconnects where a few years ago). Amdahl isn't hitting that hard when running Linpack. Yes, it's a good move to use SPARC. At some time in the last 10 years, there was an interesting twist in perception: SPARC was considered as proprietary architecture and x86 was the open architecture. However it's vice versa ? try to create a x86 clone and you have a lot of intellectual property problems, create a SPARC clone and you have to spend 100 bucks or so to get the specification from the SPARC Foundation and develop your own SPARC processor. Fujitsu is doing this for a long time now. So they had their own processor, their own know-how. So why was SPARC a good choice? Well ? essentially Fujitsu can do what they want with their core as it is their core, for example adding the extensions to the SPARCv9 chipset ? getting Intel to create extensions to x86 to help you with your product is a little bit harder. So Fujitsu could do they needed to do with their processor in order to create such a supercomputer. No, the K is really using no FPGA or GPU as accelerators. The K is really using the CPU at doing this job. Yes, it has a significantly enhanced FPU capable to execute 8 instructions in parallel. No, it doesn't run Solaris. Yes, it uses Linux. No, it doesn't hurt me ... as my colleague Roland Rambau (he knows a lot about HPC) said once to me ... it doesn't matter which OS is staying out of the way of the workload in HPC.

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• A* PathFinding Poor Performance

  - by RedShft

  After debugging for a few hours, the algorithm seems to be working. Right now to check if it works i'm checking the end node position to the currentNode position when the while loop quits. So far the values look correct. The problem is, the farther I get from the NPC, who is current stationary, the worse the performance gets. It gets to a point where the game is unplayable less than 10 fps. My current PathGraph is 2500 nodes, which I believe is pretty small, right? Any ideas on how to improve performance? struct Node { bool walkable; //Whether this node is blocked or open vect2 position; //The tile's position on the map in pixels int xIndex, yIndex; //The index values of the tile in the array Node*[4] connections; //An array of pointers to nodes this current node connects to Node* parent; int gScore; int hScore; int fScore; } class AStar { private: SList!Node openList; SList!Node closedList; //Node*[4] connections; //The connections of the current node; Node currentNode; //The current node being processed Node[] Path; //The path found; const int connectionCost = 10; Node start, end; ////////////////////////////////////////////////////////// void AddToList(ref SList!Node list, ref Node node ) { list.insert( node ); } void RemoveFrom(ref SList!Node list, ref Node node ) { foreach( elem; list ) { if( node.xIndex == elem.xIndex && node.yIndex == elem.yIndex ) { auto a = find( list[] , elem ); list.linearRemove( take(a, 1 ) ); } } } bool IsInList( SList!Node list, ref Node node ) { foreach( elem; list ) { if( node.xIndex == elem.xIndex && node.yIndex == elem.yIndex ) return true; } return false; } void ClearList( SList!Node list ) { list.clear; } void SetParentNode( ref Node parent, ref Node child ) { child.parent = &parent; } void SetStartAndEndNode( vect2 vStart, vect2 vEnd, Node[] PathGraph ) { int startXIndex, startYIndex; int endXIndex, endYIndex; startXIndex = cast(int)( vStart.x / 32 ); startYIndex = cast(int)( vStart.y / 32 ); endXIndex = cast(int)( vEnd.x / 32 ); endYIndex = cast(int)( vEnd.y / 32 ); foreach( node; PathGraph ) { if( node.xIndex == startXIndex && node.yIndex == startYIndex ) { start = node; } if( node.xIndex == endXIndex && node.yIndex == endYIndex ) { end = node; } } } void SetStartScores( ref Node start ) { start.gScore = 0; start.hScore = CalculateHScore( start, end ); start.fScore = CalculateFScore( start ); } Node GetLowestFScore() { Node lowest; lowest.fScore = 10000; foreach( elem; openList ) { if( elem.fScore < lowest.fScore ) lowest = elem; } return lowest; } //This function current sets the program into an infinite loop //I still need to debug to figure out why the parent nodes aren't correct void GeneratePath() { while( currentNode.position != start.position ) { Path ~= currentNode; currentNode = *currentNode.parent; } } void ReversePath() { Node[] temp; for(int i = Path.length - 1; i >= 0; i-- ) { temp ~= Path[i]; } Path = temp.dup; } public: //@FIXME It seems to find the path, but now performance is terrible void FindPath( vect2 vStart, vect2 vEnd, Node[] PathGraph ) { openList.clear; closedList.clear; SetStartAndEndNode( vStart, vEnd, PathGraph ); SetStartScores( start ); AddToList( openList, start ); while( currentNode.position != end.position ) { currentNode = GetLowestFScore(); if( currentNode.position == end.position ) break; else { RemoveFrom( openList, currentNode ); AddToList( closedList, currentNode ); for( int i = 0; i < currentNode.connections.length; i++ ) { if( currentNode.connections[i] is null ) continue; else { if( IsInList( closedList, *currentNode.connections[i] ) && currentNode.gScore < currentNode.connections[i].gScore ) { currentNode.connections[i].gScore = currentNode.gScore + connectionCost; currentNode.connections[i].hScore = abs( currentNode.connections[i].xIndex - end.xIndex ) + abs( currentNode.connections[i].yIndex - end.yIndex ); currentNode.connections[i].fScore = currentNode.connections[i].gScore + currentNode.connections[i].hScore; currentNode.connections[i].parent = &currentNode; } else if( IsInList( openList, *currentNode.connections[i] ) && currentNode.gScore < currentNode.connections[i].gScore ) { currentNode.connections[i].gScore = currentNode.gScore + connectionCost; currentNode.connections[i].hScore = abs( currentNode.connections[i].xIndex - end.xIndex ) + abs( currentNode.connections[i].yIndex - end.yIndex ); currentNode.connections[i].fScore = currentNode.connections[i].gScore + currentNode.connections[i].hScore; currentNode.connections[i].parent = &currentNode; } else { currentNode.connections[i].gScore = currentNode.gScore + connectionCost; currentNode.connections[i].hScore = abs( currentNode.connections[i].xIndex - end.xIndex ) + abs( currentNode.connections[i].yIndex - end.yIndex ); currentNode.connections[i].fScore = currentNode.connections[i].gScore + currentNode.connections[i].hScore; currentNode.connections[i].parent = &currentNode; AddToList( openList, *currentNode.connections[i] ); } } } } } writeln( "Current Node Position: ", currentNode.position ); writeln( "End Node Position: ", end.position ); if( currentNode.position == end.position ) { writeln( "Current Node Parent: ", currentNode.parent ); //GeneratePath(); //ReversePath(); } } Node[] GetPath() { return Path; } } This is my first attempt at A* so any help would be greatly appreciated.

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• Cablemodem (SBG6580) firewall denying some outbound traffic? Why? Not configured [migrated]

  - by lairdb

  I finally got around to turning the syslog on for my cablemodem (Motorola Surfboard SBG6580) and I'm seeing about the expected amount of inbound attackage being blocked... 2014-05-30 21:59:02 Local0.Alert 192.168.111.1 May 31 04:58:56 2014 SYSLOG[0]: [Host 192.168.111.1] UDP 12.230.209.198,4500 --> 66.27.xx.xx,61459 DENY:Firewall interface [IP Fragmented Packet] attack 2014-05-30 21:59:02 Local0.Alert 192.168.111.1 May 31 04:58:56 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 17.172.232.109,5223 --> 66.27.xx.xx,53814 DENY:Firewall interface access request 2014-05-30 21:59:02 Local0.Alert 192.168.111.1 May 31 04:58:57 2014 SYSLOG[0]: [Host 192.168.111.1] UDP 12.230.209.198,443 --> 66.27.xx.xx,53385 DENY: Firewall interface [IP Fragmented Packet] attack 2014-05-30 21:59:02 Local0.Alert 192.168.111.1 May 31 04:58:57 2014 SYSLOG[0]: [Host 192.168.111.1] UDP 12.230.209.198,4500 --> 66.27.xx.xx,61459 DENY:Firewall interface [IP Fragmented Packet] attack 2014-05-30 21:59:10 Local0.Alert 192.168.111.1 May 31 04:59:04 2014 SYSLOG[0]: [Host 192.168.111.1] UDP 12.230.209.198,443 --> 66.27.xx.xx,59960 DENY: Firewall interface [IP Fragmented Packet] attack 2014-05-30 21:59:10 Local0.Alert 192.168.111.1 May 31 04:59:04 2014 SYSLOG[0]: [Host 192.168.111.1] UDP 12.230.209.198,4500 --> 66.27.xx.xx,61459 DENY:Firewall interface [IP Fragmented Packet] attack ...and that's great. (Sad, but great.) But I'm also seeing a HUGE amount of what appears to be denied outbound connectivity: 2014-05-30 16:30:10 Local0.Alert 192.168.111.1 May 30 23:30:04 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 192.168.111.100,58969 --> 38.81.66.127,443 DENY: Inbound or outbound access request 2014-05-30 16:30:10 Local0.Alert 192.168.111.1 May 30 23:30:04 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 192.168.111.100,58969 --> 38.81.66.127,443 DENY: Inbound or outbound access request 2014-05-30 16:30:10 Local0.Alert 192.168.111.1 May 30 23:30:04 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 192.168.111.100,58965 --> 162.222.41.13,443 DENY: Inbound or outbound access request 2014-05-30 16:30:10 Local0.Alert 192.168.111.1 May 30 23:30:04 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 192.168.111.100,58965 --> 162.222.41.13,443 DENY: Inbound or outbound access request 2014-05-30 16:30:10 Local0.Alert 192.168.111.1 May 30 23:30:04 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 192.168.111.100,58964 --> 38.81.66.179,443 DENY: Inbound or outbound access request 2014-05-30 16:30:10 Local0.Alert 192.168.111.1 May 30 23:30:04 2014 SYSLOG[0]: [Host 192.168.111.1] TCP 192.168.111.100,58964 --> 38.81.66.179,443 DENY: Inbound or outbound access request ...and Spot checking suggests that it's all legitimate traffic (Opening connections to CrashPlan, etc.), I have no restrictions configured in the modem; I don't see why it should be blocking anything. Am I misreading the log entry, and it's not actually being denied? (Seems unlikely.) Is the ISP (TWC) pushing deny tables that are not exposed in the UI? (Tinfoil hat too tight.) I'm confused. (The good news, such as it is, is that AFAIK I'm not experiencing any actual issues... but maybe I am; tough to tell.) Thanks.

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• Why am I unable to telnet to a local port that has a listening service?

  - by Skip Huffman

  I suspect this is either a very simple question, or a very complex one. I have a headless server running ubuntu 10.04 that I can ssh into. I have full root access to the system. I am trying to set up an ssh tunnel to allow me to vnc to the system (but that isn't my question. I have vnc running on port 5903, here is the netstat output for that: Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 0.0.0.0:5903 0.0.0.0:* LISTEN 7173/Xtightvnc tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 465/sshd But when I try to telnet to that port, from within the same system and login, I get unable to connect errors # telnet localhost 5903 Trying ::1... Trying 127.0.0.1... telnet: Unable to connect to remote host: Connection timed out I am able to telnet to port 22 (as a verification) ~# telnet localhost 22 Trying ::1... Connected to localhost. Escape character is '^]'. SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu7 I have tried to open up any possible ports using ufw (probably clumsy fashion) # ufw status numbered Status: active To Action From -- ------ ---- [ 1] 5903 ALLOW IN Anywhere [ 2] 22 ALLOW IN Anywhere What else might be blocking this connection locally? Thank you, Edit: The only reference to port 5903 in iptable -L -n is this: Chain ufw-user-input (1 references) target prot opt source destination ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:5903 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:5903 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:22 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:8080 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:8080 I can post the whole output if that will be useful. hosts.allow and hosts.deny both contain only comments. Re-Edit: Some other questions pointed me to nmap, so I ran a portscan through that utility: # nmap -v -sT localhost -p1-65535 Starting Nmap 5.00 ( http://nmap.org ) at 2011-11-09 09:58 PST NSE: Loaded 0 scripts for scanning. Warning: Hostname localhost resolves to 2 IPs. Using 127.0.0.1. Initiating Connect Scan at 09:58 Scanning localhost (127.0.0.1) [65535 ports] Discovered open port 22/tcp on 127.0.0.1 Connect Scan Timing: About 18.56% done; ETC: 10:01 (0:02:16 remaining) Connect Scan Timing: About 44.35% done; ETC: 10:00 (0:01:17 remaining) Completed Connect Scan at 10:00, 112.36s elapsed (65535 total ports) Host localhost (127.0.0.1) is up (0.00s latency). Interesting ports on localhost (127.0.0.1): Not shown: 65533 filtered ports PORT STATE SERVICE 22/tcp open ssh 80/tcp closed http Read data files from: /usr/share/nmap Nmap done: 1 IP address (1 host up) scanned in 112.43 seconds Raw packets sent: 0 (0B) | Rcvd: 0 (0B) I think this shows that 5903 is blocked somehow. Which I pretty much knew. The question remains what is blocking it and how to modify. Re-re-edit: To check Paul Lathrop's suggested answer, I first verified my ip address with ifconfig: eth0 Link encap:Ethernet HWaddr 02:16:3e:42:28:8f inet addr:10.0.10.3 Bcast:10.0.10.255 Mask:255.255.255.0 Then tried to telnet to 5903 from that address: # telnet 10.0.10.3 5903 Trying 10.0.10.3... telnet: Unable to connect to remote host: Connection timed out No luck. Re-re-re-re-edit: Ok, I think I have isolated it a bit to vncserver, not the firewall, darn it. I shut off vncserver and had netcat listen on port 5903. My vnc client then was able to establish a connnection and sit and wait for a response. Looks like I should be chasing a vnc problem. At least that is progress Thanks for the help

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• High Resolution Timeouts

  - by user12607257

  The default resolution of application timers and timeouts is now 1 msec in Solaris 11.1, down from 10 msec in previous releases. This improves out-of-the-box performance of polling and event based applications, such as ticker applications, and even the Oracle rdbms log writer. More on that in a moment. As a simple example, the poll() system call takes a timeout argument in units of msec: System Calls poll(2) NAME poll - input/output multiplexing SYNOPSIS int poll(struct pollfd fds[], nfds_t nfds, int timeout); In Solaris 11, a call to poll(NULL,0,1) returns in 10 msec, because even though a 1 msec interval is requested, the implementation rounds to the system clock resolution of 10 msec. In Solaris 11.1, this call returns in 1 msec. In specification lawyer terms, the resolution of CLOCK_REALTIME, introduced by POSIX.1b real time extensions, is now 1 msec. The function clock_getres(CLOCK_REALTIME,&res) returns 1 msec, and any library calls whose man page explicitly mention CLOCK_REALTIME, such as nanosleep(), are subject to the new resolution. Additionally, many legacy functions that pre-date POSIX.1b and do not explicitly mention a clock domain, such as poll(), are subject to the new resolution. Here is a fairly comprehensive list: nanosleep pthread_mutex_timedlock pthread_mutex_reltimedlock_np pthread_rwlock_timedrdlock pthread_rwlock_reltimedrdlock_np pthread_rwlock_timedwrlock pthread_rwlock_reltimedwrlock_np mq_timedreceive mq_reltimedreceive_np mq_timedsend mq_reltimedsend_np sem_timedwait sem_reltimedwait_np poll select pselect _lwp_cond_timedwait _lwp_cond_reltimedwait semtimedop sigtimedwait aiowait aio_waitn aio_suspend port_get port_getn cond_timedwait cond_reltimedwait setitimer (ITIMER_REAL) misc rpc calls, misc ldap calls This change in resolution was made feasible because we made the implementation of timeouts more efficient a few years back when we re-architected the callout subsystem of Solaris. Previously, timeouts were tested and expired by the kernel's clock thread which ran 100 times per second, yielding a resolution of 10 msec. This did not scale, as timeouts could be posted by every CPU, but were expired by only a single thread. The resolution could be changed by setting hires_tick=1 in /etc/system, but this caused the clock thread to run at 1000 Hz, which made the potential scalability problem worse. Given enough CPUs posting enough timeouts, the clock thread could be a performance bottleneck. We fixed that by re-implementing the timeout as a per-CPU timer interrupt (using the cyclic subsystem, for those familiar with Solaris internals). This decoupled the clock thread frequency from timeout resolution, and allowed us to improve default timeout resolution without adding CPU overhead in the clock thread. Here are some exceptions for which the default resolution is still 10 msec. The thread scheduler's time quantum is 10 msec by default, because preemption is driven by the clock thread (plus helper threads for scalability). See for example dispadmin, priocntl, fx_dptbl, rt_dptbl, and ts_dptbl. This may be changed using hires_tick. The resolution of the clock_t data type, primarily used in DDI functions, is 10 msec. It may be changed using hires_tick. These functions are only used by developers writing kernel modules. A few functions that pre-date POSIX CLOCK_REALTIME mention _SC_CLK_TCK, CLK_TCK, "system clock", or no clock domain. These functions are still driven by the clock thread, and their resolution is 10 msec. They include alarm, pcsample, times, clock, and setitimer for ITIMER_VIRTUAL and ITIMER_PROF. Their resolution may be changed using hires_tick. Now back to the database. How does this help the Oracle log writer? Foreground processes post a redo record to the log writer, which releases them after the redo has committed. When a large number of foregrounds are waiting, the release step can slow down the log writer, so under heavy load, the foregrounds switch to a mode where they poll for completion. This scales better because every foreground can poll independently, but at the cost of waiting the minimum polling interval. That was 10 msec, but is now 1 msec in Solaris 11.1, so the foregrounds process transactions faster under load. Pretty cool.

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• Core Data managed object context thread synchronisation

  - by Ben Reeves

  I'm have an issue where i'm updating a many-to-many relationship in a background thread, which works fine in that threa, but when I send the object back to the main thread the changes do not show. If I close the app and reopen the data is saved fine and the changes show on the main thread. Also using [context lock] instead of a different managed object context works fine. I have tried NSManagedObjectContext: - (BOOL)save:(NSError **)error; - (void)refreshObject:(NSManagedObject *)object mergeChanges:(BOOL)flag; at different stages throughout the process but it doesn't seem to help. My core data code uses the following getter to ensure any operations are thread safe: - (NSManagedObjectContext *) managedObjectContext { NSThread * thisThread = [NSThread currentThread]; if (thisThread == [NSThread mainThread]) { //Main thread just return default context return managedObjectContext; } else { //Thread safe trickery NSManagedObjectContext * threadManagedObjectContext = [[thisThread threadDictionary] objectForKey:CONTEXT_KEY]; if (threadManagedObjectContext == nil) { threadManagedObjectContext = [[[NSManagedObjectContext alloc] init] autorelease]; [threadManagedObjectContext setPersistentStoreCoordinator: [self persistentStoreCoordinator]]; [[thisThread threadDictionary] setObject:threadManagedObjectContext forKey:CONTEXT_KEY]; } return threadManagedObjectContext; } } and when I pass object between threads i'm using -(NSManagedObject*)makeSafe:(NSManagedObject*)object { if ([object managedObjectContext] != [self managedObjectContext]) { NSError * error = nil; object = [[self managedObjectContext] existingObjectWithID:[object objectID] error:&error]; if (error) { NSLog(@"Error makeSafe: %@", error); } } return object; } Any help appreciated

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• System.Runtime.InteropServices.COMException (0x80070008): Not enough storage is available to process

  - by Darryl Braaten

  I am trying to diagnose this exception. "System.Runtime.InteropServices.COMException (0x80070008): Not enough storage is available to process this command. (Exception from HRESULT: 0x80070008) at System.Runtime.Remoting.RemotingServices.AllocateUninitializedObject(RuntimeType objectType) at System.Runtime.Remoting.RemotingServices.AllocateUninitializedObject(Type objectType) at System.Runtime.Remoting.Activation.ActivationServices.CreateInstance(Type serverType) at System.Runtime.Remoting.Activation.ActivationServices.IsCurrentContextOK(Type serverType, Object[] props, Boolean bNewObj) at Oracle.DataAccess.Client.CThreadPool..ctor() at Oracle.DataAccess.Client.OracleCommand.set_CommandTimeout(Int32 value) ... It does not look like any of the normal types of "storage" have hit any limits. The application is using about 400MB of memory, 70 threads, 2000 handles and the hard drive has many GB free. The machine is running Windows 2003 Enterprise server with 16GB of RAM so memory shouldn't be an issue. The application is running as a windows service so there are no GDI objects being used. Running out of GDI handles is a common cause of this exception. Database connections, commands & readers are all all wrapped with using blocks so they should be getting cleaned up correctly.

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• Select videos using UIImagePickerController in 2G/3G

  - by Raj

  Hi, I am facing a problem where-in I cannot select videos from the photo album in iPhone 2G/3G device. The default photos application does show videos and is capable of playing them, which in turn means that UIImagePickerController should clearly be capable of showing videos in photo album and selecting them. I have coded this to determine whether the device is capable of snapping a photo, recording video, selecting photos and selecting videos: // Check if camera and video recording are available: [self setCameraAvailable:NO]; [self setVideoRecordingAvailable:NO]; [self setPhotoSelectionAvailable:NO]; [self setVideoSelectionAvailable:NO]; // For live mode: NSArray *availableTypes = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypeCamera]; NSLog(@"Available types for source as camera = %@", availableTypes); if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) { if ([availableTypes containsObject:(NSString*)kUTTypeMovie]) [self setVideoRecordingAvailable:YES]; if ([availableTypes containsObject:(NSString*)kUTTypeImage]) [self setCameraAvailable:YES]; } // For photo library mode: availableTypes = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypePhotoLibrary]; NSLog(@"Available types for source as photo library = %@", availableTypes); if ([availableTypes containsObject:(NSString*)kUTTypeImage]) [self setPhotoSelectionAvailable:YES]; if ([availableTypes containsObject:(NSString*)kUTTypeMovie]) [self setVideoSelectionAvailable:YES]; The resulting logs for 3G device is as follows: 2010-05-03 19:09:09.623 xyz [348:207] Available types for source as camera = ( "public.image" ) 2010-05-03 19:09:09.643 xyz [348:207] Available types for source as photo library = ( "public.image" ) As the logs state, for photo library the string equivalent of kUTTypeMovie is not available and hence the UIImagePickerController does not show up (or rather throws exception if we set the source types array which includes kUTTypeMovie) the movie files in photo library. I havent tested for 3GS, but I am sure that this problem does not exist in it with reference to other threads. I have built the app for both 3.0 (base SDK) and 3.1 but with the same results. This issue is already discussed in the thread: http://www.iphonedevsdk.com/forum/iphone-sdk-development/36197-uiimagepickercontroller-does-not-show-movies-albums.html But it does not seem to host a solution. Any solutions to this problem? Thanks and Regards, Raj Pawan

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• How to extract $lastexitcode from c# powershell script execution.

  - by scope-creep

  Hi, I've got a scipt executing in C# using the powershell async execution code on code project here: http://www.codeproject.com/KB/threads/AsyncPowerShell.aspx?display=PrintAll&fid=407636&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=2130851#xx2130851xx I need to return the $lastexitcode and Jean-Paul describes how you can use a custom pshost class to return it. I can't find any method or property in pshost that returns the exit code. This engine I have needs to ensure that script executes correctly. Any help would be appreciated. regards Bob. Its the $lastexitcode and the $? variables I need to bring back. Hi, Finally answered. I found out about the $host variable. It implements a callback into the host, specifically a custom PSHost object, enabling you to return the $lastexitcode. Here is a link to an explanation of $host. http://mshforfun.blogspot.com/2006/08/do-you-know-there-is-host-variable.html It seems to be obscure, badly documented, as usual with powershell docs. Using point 4, calling $host.SetShouldExit(1) returns 1 to the SetShouldExit method of pshost, as described here. http://msdn.microsoft.com/en-us/library/system.management.automation.host.pshost.setshouldexit(VS.85).aspx Its really depends on defining your own exit code defintion. 0 and 1 suffixes I guess. regards Bob.

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• Why isn't uploadify and asp.net mvc 2 playing nice for me?

  - by Paperino

  First of all, I've checked out all the SO threads, and googled my brains out. I must be missing something obvious. I'd really appreciate some help! This is what I've got. UploadController.cs using System.Web; using System.Web.Mvc; namespace NIMDocs.Controllers { public class UploadController : Controller { public ActionResult Index() { return View(); } public string Procssed(HttpPostedFileBase FileData) { // DO STUFF return "DUHR I AM SMART"; } } } Index for Upload <%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head> <title>ITS A TITLE </title> <script src="../../Content/jqueryPlugins/uploadify/jquery-1.3.2.min.js" type="text/javascript"></script> <script src="../../Content/jqueryPlugins/uploadify/swfobject.js" type="text/javascript"></script> <script src="../../Content/jqueryPlugins/uploadify/jquery.uploadify.v2.1.0.min.js" type="text/javascript"></script> <script type="text/javascript"> $(document).ready(function () { $('#uploadify').fileUpload({ 'uploader': '../../Content/jqueryPlugins/uploadify/uploadify.swf', 'script': '/Upload/Processed', 'folder': '/uploads', 'multi': 'true', 'buttonText': 'Browse', 'displayData': 'speed', 'simUploadLimit': 2, 'cancelImg': '/Content/Images/cancel.png' }); }); </script> </head> <body> <input type="file" name="uploadify" id="uploadify" /> <p><a href="javascript:jQuery('#uploadify').uploadifyClearQueue()">Cancel All Uploads</a></p> </body> </html> What am I missing here? I've tried just about every path permutation for uploadify's "uploader" option. Absolute path, '/' prefixed, etc.

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• Self hosted WCF ServiceHost/WebServiceHost Concurrency/Peformance Design Options (.NET 3.5)

  - by Kyle

  So I'll be providing a few functions via a self hosted (in a WindowsService) WebServiceHost (not sure how to process HTTP GET/POST with ServiceHost), one of which may be called a large amount of the time. This function will also rely on a connection in the appdomain (hosted by the WindowsService so it can stay alive over multiple requests). I have the following concerns and would be oh so thankful for any input/thoughts/comments: Concurrent access - how does the WebServiceHost handle a bunch of concurrent requests. Are they queued and processes sequentially or are new instances of the contracts automagically created? WebServiceHost - WindowsService communication - I need some form of communication from the WebServiceHost to the hosting WindowsService for things like requesting a new session if one does not exist. Perhaps implementing a class which extends the WebServiceHost with events which the WindowsService subscribes to... (unless there is another way I can set off an event in the WindowsService when a request is made...) Multiple WebServiceHosts or Contracts - Would it give any real performance gain to be running multiple WebServiceHost instances in different threads (one per endpoint perhaps?) - A better understanding of the first point would probably help here. WSDL - I'm not sure why (probably just need to do more reading), but I'm not sure how to get the WebServiceHost base endpoint to respond with a WDSL document describing the available contract. Not required as all the operations will be done via GET requests which will not likely change, but it would be nice to have... That's about it for the moment ;) I've been reading a lot on WCF and wish I'd gotten into it long ago, but definitely still learning.

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• Build 32-bit with 64-bit llvm-gcc

  - by Jay Conrod

  I have a 64-bit version of llvm-gcc, but I want to be able to build both 32-bit and 64-bit binaries. Is there a flag for this? I tried passing -m32 (which works on the regular gcc), but I get an error message like this: [jay@andesite]$ llvm-gcc -m32 test.c -o test Warning: Generation of 64-bit code for a 32-bit processor requested. Warning: 64-bit processors all have at least SSE2. /tmp/cchzYo9t.s: Assembler messages: /tmp/cchzYo9t.s:8: Error: bad register name `%rbp' /tmp/cchzYo9t.s:9: Error: bad register name `%rsp' ... This is backwards; I want to generate 32-bit code for a 64-bit processor! I'm running llvm-gcc 4.2, the one that comes with Ubuntu 9.04 x86-64. EDIT: Here is the relevant part of the output when I run llvm-gcc with the -v flag: [jay@andesite]$ llvm-gcc -v -m32 test.c -o test.bc Using built-in specs. Target: x86_64-linux-gnu Configured with: ../llvm-gcc4.2-2.2.source/configure --host=x86_64-linux-gnu --build=x86_64-linux-gnu --prefix=/usr/lib/llvm/gcc-4.2 --enable-languages=c,c++ --program-prefix=llvm- --enable-llvm=/usr/lib/llvm --enable-threads --disable-nls --disable-shared --disable-multilib --disable-bootstrap Thread model: posix gcc version 4.2.1 (Based on Apple Inc. build 5546) (LLVM build) /usr/lib/llvm/gcc-4.2/libexec/gcc/x86_64-linux-gnu/4.2.1/cc1 -quiet -v -imultilib . test.c -quiet -dumpbase test.c -m32 -mtune=generic -auxbase test -version -o /tmp/ccw6TZY6.s I looked in /usr/lib/llvm/gcc-4.2/libexec/gcc hoping to find another binary, but the only directory there is x86_64-linux-gnu. I will probably look at compiling llvm-gcc from source with appropriate options next.

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• iPhone locationManager:didFailWithError problem when GPS disabled

  - by BenG

  So, I've followed other related threads, but for some reason I'm still having this error and I'm about ready to tear my hair out. I have implemented locationManager:didFailWithError to check and see if a user selects 'Don't Allow' to use the current location. -(void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error { NSLog(@"IN ERROR"); if ([error code] == kCLErrorDenied){ [manager stopUpdatingLocation]; } } However, the following error always appears when the user selects 'Don't Allow'...it's strange, especially the order that the text 'IN ERROR' appears. ERROR,Time,293420691.000,Function,"void CLClientHandleDaemonDataRegistration(__CLClient*, const CLDaemonCommToClientRegistration*, const __CFDictionary*)",server did not accept client registration 1 2010-04-19 21:44:51.000 testApp[1414:207] IN ERROR So, it's outputting this error even before it has a chance to get into the didFailWithError function. Does anyone have any ideas of what might be happening? The rest of the locationManager code is as follows: self.locationManager = [[[CLLocationManager alloc] init] autorelease]; locationManager.delegate = self; locationManager.desiredAccuracy = kCLLocationAccuracyKilometer; locationManager.distanceFilter = 2; [locationManager startUpdatingLocation];

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• Stresstesting ASP.NET/IIS with WCAT

  - by MartinHN

  I'm trying to setup a stress/load test using the WCAT toolkit included in the IIS Resources. Using LogParser, I've processed a UBR file with configuration. It looks something like this: [Configuration] NumClientMachines: 1 # number of distinct client machines to use NumClientThreads: 100 # number of threads per machine AsynchronousWait: TRUE # asynchronous wait for think and delay Duration: 5m # length of experiment (m = minutes, s = seconds) MaxRecvBuffer: 8192K # suggested maximum received buffer ThinkTime: 0s # maximum think-time before next request WarmupTime: 5s # time to warm up before taking statistics CooldownTime: 6s # time to cool down at the end of the experiment [Performance] [Script] SET RequestHeader = "Accept: */*\r\n" APP RequestHeader = "Accept-Language: en-us\r\n" APP RequestHeader = "User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705)\r\n" APP RequestHeader = "Host: %HOST%\r\n" NEW TRANSACTION classId = 1 NEW REQUEST HTTP ResponseStatusCode = 200 Weight = 45117 verb = "GET" URL = "http://Url1.com" NEW TRANSACTION classId = 3 NEW REQUEST HTTP ResponseStatusCode = 200 Weight = 13662 verb = "GET" URL = "http://Url1.com/test.aspx" Does it look OK? I execute the controller with this command: wcctl -z StressTest.ubr -a localhost The Client(s) is executed like this: wcclient localhost When the client is executed, I get this error: main client thread Connect Attempt 0 Failed. Error = 10061 Has anyone in this world ever used WCAT?

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• Android threading and database locking

  - by Sena Gbeckor-Kove

  Hi, We are using AsyncTasks to access database tables and cursors. Unfortunately we are seeing occasional exceptions regarding the database being locked. E/SQLiteOpenHelper(15963): Couldn't open iviewnews.db for writing (will try read-only): E/SQLiteOpenHelper(15963): android.database.sqlite.SQLiteException: database is locked E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.native_setLocale(Native Method) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.setLocale(SQLiteDatabase.java:1637) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1587) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:638) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:659) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:652) E/SQLiteOpenHelper(15963): at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:482) E/SQLiteOpenHelper(15963): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98) E/SQLiteOpenHelper(15963): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158) E/SQLiteOpenHelper(15963): at com.iview.android.widget.IViewNewsTopStoryWidget.initData(IViewNewsTopStoryWidget.java:73) E/SQLiteOpenHelper(15963): at com.iview.android.widget.IViewNewsTopStoryWidget.updateNewsWidgets(IViewNewsTopStoryWidget.java:121) E/SQLiteOpenHelper(15963): at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:338) E/SQLiteOpenHelper(15963): at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:1) E/SQLiteOpenHelper(15963): at android.os.AsyncTask$2.call(AsyncTask.java:185) E/SQLiteOpenHelper(15963): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:256) E/SQLiteOpenHelper(15963): at java.util.concurrent.FutureTask.run(FutureTask.java:122) E/SQLiteOpenHelper(15963): at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:648) E/SQLiteOpenHelper(15963): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:673) E/SQLiteOpenHelper(15963): at java.lang.Thread.run(Thread.java:1060) Does anybody have a general example for code which writes to a database from a different thread than the one reading and how can we ensure thread safety. One suggestion I've had is to use a ContentProvider, as this would handle the access of the database from multiple threads. I am going to look at this, but is this the recommended method of handling such a problem? It seems rather heavyweight considering we're talking about in front or behind Thanks in advance.

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• Why might changes be populated from one NSManagedObjectContext to another without an explicit merge?

  - by Mike Laurence

  I'm working on an object import feature that utilizes multiple threads/NSManagedObjectContexts, using http://www.mac-developer-network.com/columns/coredata/may2009/ as my guide (note that I am developing for iPhone). For some reason, when I save one of my contexts the other is immediately updated with the changes, even though I have commented out my calls to mergeChangesFromContextDidSaveNotification. Are there any reasons the contexts might be merging into one another without an explicit call? Here a log of what's going on: // 1.) Main context is saved with "Peter Gabriel" // 2.) Test context is created, begins with same contents as main context // 3.) Main context is inserted with "Spoon" // 4.) Test context is inserted with "Phoenix" // Contents at this point: CoreTest[4341:903] Artists in main context: ( "Peter Gabriel", "Spoon" ) CoreTest[4341:903] Artists in test context: ( "Peter Gabriel", "Phoenix" ) // 5.) testContext is saved // New contents of contexts: CoreTest[4341:903] Artists in main context: ( "Peter Gabriel", "Phoenix", "Spoon" ) CoreTest[4341:903] Artists in test context: ( "Peter Gabriel", "Phoenix" ) As you can see, the test context is saved midway through, and the main context suddenly has the new objects from the test context, even though I haven't performed the whole NSManagedObjectContextDidSaveNotification/mergeChangesFromContext combo. My understanding is that no changes will ever be merged unless done so explicitly... does anyone know what's going on here?

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• What do these MS DTC Exceptions mean?

  - by David B

  I wrote a program to demonstrate the behavior of DTC timeouts with multiple threads. I'm getting several exceptions, seemingly at random. Are all of these simple Timeouts, or are some of them indicative of deeper problems (connection pool interactions, etc)? The Microsoft Distributed Transaction Coordinator (MS DTC) has cancelled the distributed transaction. Distributed transaction completed. Either enlist this session in a new transaction or the NULL transaction. The transaction associated with the current connection has completed but has not been disposed. The transaction must be disposed before the connection can be used to execute SQL statements. The operation is not valid for the state of the transaction. ExecuteReader requires an open and available Connection. The connection's current state is closed. Here's the data part of the code: using (DemoDataDataContext dc1 = new DemoDataDataContext(Conn1)) using (DemoDataDataContext dc2 = new DemoDataDataContext(Conn2)) { WriteMany(dc1, 100); //generate 100 records for insert WriteMany(dc2, 100000); //generate 100,000 records for insert Console.WriteLine("{0} : {1}", Name, " generated records for insert."); using (TransactionScope ts = new TransactionScope()) { dc1.SubmitChanges(); dc2.SubmitChanges(); ts.Complete(); } }

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• Any task-control algorithms programming practices?

  - by NumberFour

  Hi, I was just wondering if there's any field which concerns the task-control programming (or at least that's the way I call it). For a better explanation of task-control consider the following scenario: An application (master-thread) waits for a command - which might be a particular action or a set of actions the application should perform. When a command is received the master-thread creates a task (= spawns an independent thread which actually does the action) and adds a record in it's task-list - thus keeping track of the time of execution, thread handle, task priority...etc. The master-thread awaits for any other incoming commands while taking care of all the tasks - e.g: kills tasks running too long, prioritizes tasks with higher priorities, kills a task on a request of another task, limits the number of currently running tasks, allows task scheduling, cleans finished tasks (threads) and so on. The model is pretty similar to what we can see in OS dealing with running processes. Are there any good practices programming such task-models or is there some theoretical work done in this field? Maybe my question is too generalized, but at least I wanted to know whether there are any experiences working on such models or if there's a better approach. Thanks for any answers.

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• How do I install LFE on Ubuntu Karmic?

  - by karlthorwald

  Erlang was already installed: $dpkg -l|grep erlang ii erlang 1:13.b.3-dfsg-2ubuntu2 Concurrent, real-time, distributed function ii erlang-appmon 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP application monitor ii erlang-asn1 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP modules for ASN.1 support ii erlang-base 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP virtual machine and base applica ii erlang-common-test 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP application for automated testin ii erlang-debugger 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP application for debugging and te ii erlang-dev 1:13.b.3-dfsg-2ubuntu2 Erlang/OTP development libraries and header [... many more] Erlang seems to work: $ erl Erlang R13B03 (erts-5.7.4) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false] Eshell V5.7.4 (abort with ^G) 1> I downloaded lfe from github and checked out 0.5.2: git clone http://github.com/rvirding/lfe.git cd lfe git checkout -b local0.5.2 e207eb2cad $ configure configure: command not found $ make mkdir -p ebin erlc -I include -o ebin -W0 -Ddebug +debug_info src/*.erl #erl -I -pa ebin -noshell -eval -noshell -run edoc file src/leex.erl -run init stop #erl -I -pa ebin -noshell -eval -noshell -run edoc_run application "'Leex'" '"."' '[no_packages]' #mv src/*.html doc/ Must be something stupid i missed :o $ sudo make install make: *** No rule to make target `install'. Stop. $ erl -noshell -noinput -s lfe_boot start {"init terminating in do_boot",{undef,[{lfe_boot,start,[]},{init,start_it,1},{init,start_em,1}]}} Crash dump was written to: erl_crash.dump init terminating in do_boot () Is there an example how I would create a hello world source file and compile and run it?

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• [C#] Lock a file and avoid readings while it's writing

  - by vtortola

  Hi, My web application returns a file from the filesystem. These files are dynamic, so I have no way to know the names o how many of them will there be. When this file doesn't exist, the application creates it from the database. I want to avoid that two different threads recreate the same file at the same time, or that a thread try to return the file while other thread is creating it. So I want to lock a file till its recreation is complete, if other thread try to access it ... it will have to wait the file be unlocked. I've been reading about FileStream.Lock, but I have to know the file length and it won't prevent that other thread try to read the file, so it doesn't work for my particular case. I've been reading also about FileAccess.None, but it will throw an exception (which exception type?) if other thread/process try to access the file... so I should develop a "try again while is faulting" ... and I don't like too much that approach, although maybe there is not a better way. How could I archieve this? Kind regards.

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• git push merge error, but git pull is already up-to-date. Tried reclone, same problem.

  - by Jasie

  I do: git commit . git push error: Entry 'file.php' not uptodate. Cannot merge. Then I do git pull Already up-to-date. What do I do? I just want to get the latest version from the remote copy, and overwrite anything on my local copy. Edit: I tried everything. I deleted my local repo, and git clone ssh://[email protected]/directory ... Checking out files: 100%, done. git status On branch master nothing to commit (working directory clean) All looks good, right? Pull just in case. git pull Already up-to-date. I make a one line change in a file to see if I can push it. git commit . [master 1e18af1] Rando change 1 files changed, 2 insertions(+), 0 deletions(-) git push Counting objects: 13, done. Delta compression using up to 2 threads. Compressing objects: 100% (6/6), done. Writing objects: 100% (7/7), 646 bytes, done. Total 7 (delta 3), reused 0 (delta 0) From /directory d6d61aa..1e18af1 master -> origin/master error: Entry 'someotherfile.php' not uptodate. Cannot merge. Updating b8f9a54..1e18af1 To ssh://[email protected]/directory d6d61aa..1e18af1 master - master I have no idea what's going on! How can I commit/pull again normally? Thanks very much!

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• Asynchronous HTTP Client for Java

  - by helifreak

  As a relative newbie in the Java world, I am finding many things frustratingly obtuse to accomplish that are relatively trivial in many other frameworks. A primary example is a simple solution for asynchronous http requests. Seeing as one doesn't seem to already exist, what is the best approach? Creating my own threads using a blocking type lib like httpclient or the built-in java http stuff, or should I use the newer non-blocking io java stuff - it seems particularly complex for something which should be simple. What I am looking for is something easy to use from a developer point of view - something similar to URLLoader in AS3 - where you simply create a URLRequest - attach a bunch of event handlers to handle the completion, errors, progress, etc, and call a method to fire it off. If you are not familiar with URLLoader in AS3, its so super easy and looks something like this: private void getURL(String url) { URLLoader loader = new URLLoader(); loader.addEventListener(Event.Complete, completeHandler); loader.addEventListener(HTTPStatusEvent.HTTP_STATUS, httpStatusHandler); loader.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler); URLRequest request = new URLRequest(url); // fire it off - this is asynchronous so we handle // completion with event handlers loader.load(request); } private void completeHandler(Event event) { URLLoader loader = (URLLoader)event.target; Object results = loader.data; // process results } private void httpStatusHandler(Event event) { // check status code } private void ioErrorHandler(Event event) { // handle errors }

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