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• Getting Dell E6320 with I7 to work with 3 monitors at 1920x1080p x 3

  - by MadBoy

  I want to buy Dell E6320 which comes with Intel Core I7-2620M (2.70GHz, 4MB cache, Dual Core) with Intel HD Graphics 3000. Laptop will come with docking station. I want to connect 3 monitors to that docking station so that working at home would give me some additional boost. Docking station will allow me to connect only 2 monitors so I'm looking at following other options: Matrox TRIPLEHEAD2GO DIGITAL Edition or TRIPLEHEAD2GO DP Edition. But reading Matrox Support Page intel GPU can't run the highest resolution with 3 monitors connected, it even gets worse since it seems monitors would have to be able to work at 50hz. Also I'm not sure but it seems that Matrox doesn't split the monitors as 3 separate monitors but simply as one big space (which is a bit opposite to what I need) Buy 2 or maybe just 1 USB based monitor but it would also mean having 1 or 2 different monitors then the main one, unless I buy 3 USB based monitors which would mean more money to spend. Also I found only couple of models and most of them require USB 3.0 and no other cables to plug in (nice but costly - couldn't find decent monitor with only USB for sending signal and having power connected normally) . But docking station has only one USB 3.0 port. Can I use hub and still get it to work? Find some converters from Digital to USB (I think DisplayLink does some?) Buy different laptop but what kind? I need it to be I7, small (13"), fast and lightweight. At same time it requires docking station that I can use at home to connect 3 external monitors. Some other suggested solution... Edit: I need 3 monitors for work in terms of coding in Visual Studio or having word/excel/outlook open. Nothing fancy. Maybe some movie once in a while.

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• Inserting newlines into a GtkTextView widget (GTK+ programming)

  - by Mark Roberts

  I've got a button which when clicked copies and appends the text from a GtkEntry widget into a GtkTextView widget. (This code is a modified version of an example found in the "The Text View Widget" chapter of Foundations of GTK+ Development.) I'm looking to insert a newline character before the text which gets copied and appended, such that each line of text will be on its own line in the GtkTextView widget. How would I do this? I'm brand new to GTK+. Here's the code sample: #include <gtk/gtk.h> typedef struct { GtkWidget *entry, *textview; } Widgets; static void insert_text (GtkButton*, Widgets*); int main (int argc, char *argv[]) { GtkWidget *window, *scrolled_win, *hbox, *vbox, *insert; Widgets *w = g_slice_new (Widgets); gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_window_set_title (GTK_WINDOW (window), "Text Iterators"); gtk_container_set_border_width (GTK_CONTAINER (window), 10); gtk_widget_set_size_request (window, -1, 200); w->textview = gtk_text_view_new (); w->entry = gtk_entry_new (); insert = gtk_button_new_with_label ("Insert Text"); g_signal_connect (G_OBJECT (insert), "clicked", G_CALLBACK (insert_text), (gpointer) w); scrolled_win = gtk_scrolled_window_new (NULL, NULL); gtk_container_add (GTK_CONTAINER (scrolled_win), w->textview); hbox = gtk_hbox_new (FALSE, 5); gtk_box_pack_start_defaults (GTK_BOX (hbox), w->entry); gtk_box_pack_start_defaults (GTK_BOX (hbox), insert); vbox = gtk_vbox_new (FALSE, 5); gtk_box_pack_start (GTK_BOX (vbox), scrolled_win, TRUE, TRUE, 0); gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, TRUE, 0); gtk_container_add (GTK_CONTAINER (window), vbox); gtk_widget_show_all (window); gtk_main(); return 0; } /* Insert the text from the GtkEntry into the GtkTextView. */ static void insert_text (GtkButton *button, Widgets *w) { GtkTextBuffer *buffer; GtkTextMark *mark; GtkTextIter iter; const gchar *text; buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (w->textview)); text = gtk_entry_get_text (GTK_ENTRY (w->entry)); mark = gtk_text_buffer_get_insert (buffer); gtk_text_buffer_get_iter_at_mark (buffer, &iter, mark); gtk_text_buffer_insert (buffer, &iter, text, -1); } You can compile this command (assuming the file is named file.c): gcc file.c -o file `pkg-config --cflags --libs gtk+-2.0` Thanks everybody!

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• Windows 7 Won't Boot

  - by Vie

  I recently built a new computer, my fifth one. ASUS Maximus III Formula LGA 1156 Intel P55 ATX Motherboard EVGA 01G-P3-1452-TR GeForce GTS 450 Superclocked 1GB 128-bit GDDR5 PCI Express 2.0 x16 HDCP Video Card COOLMAX RM-1000B 1000W ATX psu Intel Core i7-875K lynnfield 2.93GHz LGA 1156 95w Quad-Core unlocked processor G.SKILL Ripjaws Series 16 (4x4GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) memory WD VelociRaptor WD3000GLFS 300gb 10000 RPM SATA 3.0Gb/s Hard Drive Sony Optiarc CD/DVD Burner model AD-7261S-0B LightScribe Windows 7 Home Premium 64-bit It gets hung up on the starting windows screen. When I went to install the OS it did the same thing wouldn't go past the windows logo, so I put the new HDD into my old computer and installed windows 7 thinking it was just an installer error. Put the fully installed HDD back into my new machine and it still gets stuck on the starting windows screen. I've tried most everything I've looked up. Disabled USB, Disabled Turbo Boost, Disabled everything that wasn't essential(just about every configuration I can think of), took it apart and put it back together, took all the ram out save one 4g stick(wouldn't even boot when I did this), did a memory scan which came back successful, I don't know what could be wrong. Only thing I can think of is a compatibility issue somewhere, but I've ran over it again and again and I don't know where there would be an issue like that. Need Backup! .<

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• GlusterFS as elastic file storage?

  - by Christopher Vanderlinden

  Is there any way to run GlusterFS in a replicated mode, but with the ability to dynamically scale the volume up and down? Say you have 3 servers all running glusterd. your Gluster volume would have to be setup with replica 3 gluster volume create test-volume replica 3 192.168.0.150:/test-volume 192.168.0.151:/test-volume 192.168.0.152:/test-volume You would then mount it as say \mnt\gfs_test What happens when I want to add 2 more servers to the storage pool and then also use them in this volume? Is there any easy way to expand the volume AND increase that replica count to 5? My end goal is to run this on EC2 instances, say 3 Apache front ends, with the webroot setup on the gluster volume mount. My concern is that if I ever need to spin up a server, I would want the server to not only be an additional Apache front end, but also another server in the gluster file system, adding to fault tolerance as well as possibly giving a slight boost in read speed. Maybe there are better options that would fit the bill here? Thanks.

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• Server freezes while installing Redhat Enterprise Linux Server 6

  - by eisaacson

  We've tried both the first options Install or upgrade an existing system Install system with basic video driver When trying option #1, it gets to a screen that has a solid cursor about halfway down, then freezes. When trying option #2, it freezes at the point where it says: Waiting for hardware to initialize... Of course, we bought the unsupported version and haven't found anything to help us so far. Here are the specs to the server in the original post: ASUS P8Z68-M Pro LGA 1155 Intel Z68 HDMI SATA 6Gb/s USB 3.0 Micro ATX Intel Motherboard with UEFI BIOS RAIDMAX Reiter ATX-305WBP Black Steel / Plastic ATX Mid Tower Computer Case 450W Power Supply Intel Core i7-2600 Sandy Bridge 3.4GHz (3.8GHz Turbo Boost) LGA 1155 95W Quad-Core Desktop Processor Intel HD Graphics 2000 BX80623I72600 16GB Ram OCZ Agility 3 SSD 120GB From some of the posts out there could the UEFI Bios or the Sandy Bridge processor be a culprit here? We just tried the DVD on a different computer and it got past that point with ease. It's a standard Dell build compared to our custom machine. Could it be having difficulty recognizing drivers? How do we get past that?

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• Coroutines in Java

  - by JUST MY correct OPINION

  I would like to do some stuff in Java that would be clearer if written using concurrent routines, but for which full-on threads are serious overkill. The answer, of course, is the use of coroutines, but there doesn't appear to be any coroutine support in the standard Java libraries and a quick Google on it brings up tantalising hints here or there, but nothing substantial. Here's what I've found so far: JSIM has a coroutine class, but it looks pretty heavyweight and conflates, seemingly, with threads at points. The point of this is to reduce the complexity of full-on threading, not to add to it. Further I'm not sure that the class can be extracted from the library and used independently. Xalan has a coroutine set class that does coroutine-like stuff, but again it's dubious if this can be meaningfully extracted from the overall library. It also looks like it's implemented as a tightly-controlled form of thread pool, not as actual coroutines. There's a Google Code project which looks like what I'm after, but if anything it looks more heavyweight than using threads would be. I'm basically nervous of something that requires software to dynamically change the JVM bytecode at runtime to do its work. This looks like overkill and like something that will cause more problems than coroutines would solve. Further it looks like it doesn't implement the whole coroutine concept. By my glance-over it gives a yield feature that just returns to the invoker. Proper coroutines allow yields to transfer control to any known coroutine directly. Basically this library, heavyweight and scary as it is, only gives you support for iterators, not fully-general coroutines. The promisingly-named Coroutine for Java fails because it's a platform-specific (obviously using JNI) solution. And that's about all I've found. I know about the native JVM support for coroutines in the Da Vinci Machine and I also know about the JNI continuations trick for doing this. These are not really good solutions for me, however, as I would not necessarily have control over which VM or platform my code would run on. (Indeed any bytecode manipulation system would suffer similar problems -- it would be best were this pure Java if possible. Runtime bytecode manipulation would restrict me from using this on Android, for example.) So does anybody have any pointers? Is this even possible? If not, will it be possible in Java 7?

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• Performance tweaks and upgrades for VMWare Server 2

  - by sjohnston

  Our software department has a server running VMWare Server 2. We typically have 8-10 VMs running as test environments (Win XP and Server 08) for various versions of our software, and one VM that is used as a build server (Win XP). The host is running Server 2003 R2. It has 32GB RAM, 8 core Xeon 3.16GHz CPU, one disk for host OS and two raid disks for VMs. The majority of the time, this setup behaves very well and there are no complaints. Other times, the VMs can be very laggy. This is sometimes, but not always, correlated to heavy load on the build server. I'm a software developer, not an IT pro, but it seems to me that this machine should be beefy enough to handle this many VMs. Is this occasional performance hit likely just because we're hitting the limits of the hardware, or should I be looking for another culprit? From what I've read, I'm guessing if there's a bottleneck, it's probably disk I/O with all these VMs running off two disks (especially the build server). Would spreading the VMs over more disks, and/or switching to SSDs give us a significant performance boost? Other things I've read may increase performance: single virtual processor per VM removing/disabling unused virtual hardware preallocated disk space not using snapshots setting a reserved memory limit on the host and disabling VM memory swapping Can anyone confirm or deny if any of these improve performance? What other good tweaks have I missed?

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• Move OS from RAID5 array to RAID 1 arrays

  - by Antoine

  I want to give a last boost to my old ProLiant ML350 G5 server which just needs to be reliable for a few more year only ! With a defined budget of about 1500$ (I do not have more), i plan to replace the CPU (+ adding a second one), the battery cache of my raid controller (E200i), double the RAM, and change all hard drives. I have 7 HDD (SAS 10krpm, 72Gb) + 1 spare in RAID5, and my system is all FULL (no empty tray, full disks). in my current RAID5 array, I have 2 partitions: - 1 OS partition, 20Gb - 1 data partition, 350 Gb I plan to replace these 8 disks with : - 2 x 300Gb SAS 15krpm in RAID 1 (= 1 partition for OS) - 2 x 2Tb SATA 7.2krpm in RAID 1 (= 1 partition for DATA) My biggest constraint is that I have only 01 day to upgrade my server. Therefore, I'm looking for cloning all my files (OS + data partition) to my new arrays, i.e : - the OS partition shall be cloned to the RAID1 "2x300Gb array" - the data partition shall be cloned to the RAID1 "2x2Tb array" My second problem is that I need to physically remove all the old hard drives before inserting the new ones. I'm running Windows Server 2003 R2, and even if MS support will expire soon, I cannot buy a new licence and spent time in configuration. Obviously, with 1500$, I cannot also buy a new server that I could start configuring from now ! Thought about ASR (NTBackup), but I have no floppy drive (and do not really want to invest in one !) Thought about a clonezilla clone, and read this interesting link : Windows Server 2003 - move C: partition to a new SAS disk , but i'm not so confident in using Clonezilla with RAID5. What should be the best option to quickly and easily (if possible!) "copy/paste" my OS (so no need to reinstall and reconfigure all) and DATA / programs / services, etc... ? Thanks for your comments

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• Subdomain is preventing my search results from rising as expected in page rank

  - by culov

  My problem is that I have a site which has requires a dedicated page for every city I choose to support. Early on, I decided to use subdomains rather than a directly after my domain (ie i used la.truxmap.com rather than truxmap.com/la). I realize now that this was a major mistake because Google seems to treat la.truxmap.com as a completely different site as ny.truxmap.com. So for instance, if i search "la food truck map" my site will be near the top, however, if i search "nyc food truck map" im no where in sight because ny.truxmap.com wouldnt be very high in the page rank by itself, and it doesnt have the boost that it ought to be getting from the better known la.truxmap.com So a mistake I made a year ago is now haunting my page rank. I'd like to know what the most painless way of resolving my dilemma might be. I have received so much press at la.truxmap.com that I can't just kill the site, but could I re-direct all requests at la.truxmap.com to truxmap.com/la and do the same for all cities supported without trashing my current, satisfactory page rank results I'm getting from la.truxmap.com ?? EDIT I left out some critical information. I am using Google Apps to manage my domain (that is, to add the subdomains) and Google App Engine to host my site. Thus, Google Apps provides a simple mechanism to mask truxmap.appspot.com (the app engine domain) as la.truxmap.com, but I don't see how I can mask it as truxmap.com/la. If I can get this done, then I can just 301 redirect la.truxmap.com to truxmap.com/la as suggested below. Thanks so much!

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• Upgrade to Q9550 or i7 920 on a budget?

  - by evan

  I'm planning to upgrade my computer and torn between maxing out the system I have or investing in the X58 architecture. I'm currently using a E6600 Core 2 Duo with 4GB of RAM (800mhz) on an Asus PK5-E motherboard which I built two years ago. My original plan was that one day I'd upgrade machine to 8GB (1066mhz, the max the PK5-E allows) and to the Core 2 QuadQ9550 to give the machine a good four years of life. However, that was before the i7 came out. I use my computer mainly for software development , which I do inside Virtual Machines, and the i7 seems ideal for that because it no longer is limited by the speed of the FSB? And when I looked into it, getting 8GB DDR3 RAM isn't much more expensive than the 8GB of DDR2 and the i7 920 is comparable in price to the Q9550, which doesn't make much sense to me? So the question is it worth swapping the motherboard out for around $250 and upgrading all three components or using that money on SSD or 10rpm drive for the existing system's OS/Apps/Virtual Machine drive? Or just put the $250 towards a completely new machine in a year or two? Would the i7 really give that much of boost compared to the Q9550 for what I'd be using it for? Thanks in advance for your input!!!

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• [C++] A minimalistic smart array (container) class template

  - by legends2k

  I've written a (array) container class template (lets call it smart array) for using it in the BREW platform (which doesn't allow many C++ constructs like STD library, exceptions, etc. It has a very minimal C++ runtime support); while writing this my friend said that something like this already exists in Boost called MultiArray, I tried it but the ARM compiler (RVCT) cries with 100s of errors. I've not seen Boost.MultiArray's source, I've just started learning template only lately; template meta programming interests me a lot, although am not sure if this is strictly one, which can be categorised thus. So I want all my fellow C++ aficionados to review it ~ point out flaws, potential bugs, suggestions, optimisations, etc.; somthing like "you've not written your own Big Three which might lead to...". Possibly any criticism that'll help me improve this class and thereby my C++ skills. smart_array.h #include <vector> using std::vector; template <typename T, size_t N> class smart_array { vector < smart_array<T, N - 1> > vec; public: explicit smart_array(vector <size_t> &dimensions) { assert(N == dimensions.size()); vector <size_t>::iterator it = ++dimensions.begin(); vector <size_t> dimensions_remaining(it, dimensions.end()); smart_array <T, N - 1> temp_smart_array(dimensions_remaining); vec.assign(dimensions[0], temp_smart_array); } explicit smart_array(size_t dimension_1 = 1, ...) { static_assert(N > 0, "Error: smart_array expects 1 or more dimension(s)"); assert(dimension_1 > 1); va_list dim_list; vector <size_t> dimensions_remaining(N - 1); va_start(dim_list, dimension_1); for(size_t i = 0; i < N - 1; ++i) { size_t dimension_n = va_arg(dim_list, size_t); assert(dimension_n > 0); dimensions_remaining[i] = dimension_n; } va_end(dim_list); smart_array <T, N - 1> temp_smart_array(dimensions_remaining); vec.assign(dimension_1, temp_smart_array); } smart_array<T, N - 1>& operator[](size_t index) { assert(index < vec.size() && index >= 0); return vec[index]; } size_t length() const { return vec.size(); } }; template<typename T> class smart_array<T, 1> { vector <T> vec; public: explicit smart_array(vector <size_t> &dimension) : vec(dimension[0]) { assert(dimension[0] > 0); } explicit smart_array(size_t dimension_1 = 1) : vec(dimension_1) { assert(dimension_1 > 0); } T& operator[](size_t index) { assert(index < vec.size() && index >= 0); return vec[index]; } size_t length() { return vec.size(); } }; Sample Usage: #include <iostream> using std::cout; using std::endl; int main() { // testing 1 dimension smart_array <int, 1> x(3); x[0] = 0, x[1] = 1, x[2] = 2; cout << "x.length(): " << x.length() << endl; // testing 2 dimensions smart_array <float, 2> y(2, 3); y[0][0] = y[0][1] = y[0][2] = 0; y[1][0] = y[1][1] = y[1][2] = 1; cout << "y.length(): " << y.length() << endl; cout << "y[0].length(): " << y[0].length() << endl; // testing 3 dimensions smart_array <char, 3> z(2, 4, 5); cout << "z.length(): " << z.length() << endl; cout << "z[0].length(): " << z[0].length() << endl; cout << "z[0][0].length(): " << z[0][0].length() << endl; z[0][0][4] = 'c'; cout << z[0][0][4] << endl; // testing 4 dimensions smart_array <bool, 4> r(2, 3, 4, 5); cout << "z.length(): " << r.length() << endl; cout << "z[0].length(): " << r[0].length() << endl; cout << "z[0][0].length(): " << r[0][0].length() << endl; cout << "z[0][0][0].length(): " << r[0][0][0].length() << endl; // testing copy constructor smart_array <float, 2> copy_y(y); cout << "copy_y.length(): " << copy_y.length() << endl; cout << "copy_x[0].length(): " << copy_y[0].length() << endl; cout << copy_y[0][0] << "\t" << copy_y[1][0] << "\t" << copy_y[0][1] << "\t" << copy_y[1][1] << "\t" << copy_y[0][2] << "\t" << copy_y[1][2] << endl; return 0; }

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• Ubuntu inside VirtualBox is slow

  - by Kapsh

  I am running an Ubuntu instance on VirtualBox inside XP. Here are the details: Host: Windows XP Pro Guest: Ubuntu 8.10 Total RAM: 3GB RAM For VM: 1GB Total Video Memory: 128MB Video Memory for VM: 40MB Hard Drive: 200GB Hard Drive for VM: 30GB Processor: 2.80GHz Core Duo The problem is that whenever I am inside the virtual machine, things seem so much slower in general. For example Firefox, Eclipse take longer to load, dragging windows show a lag etc. I have tried running Ubuntu before (not inside a VM) and it seemed fantastically fast. So I am disappointed to have to deal with this situation. But I need access to the XP partition without having to reboot and hence the attempt. I am surprised with the perceived slowness since the whole world seems to be doing virtualization and I cannot imagine everyone works on slow systems knowingly. My question is - is there something I should be doing to boost performance? Am I doing something wrong? This is my home machine and I am not sure if this is the right forum to ask. Thanks.

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• Network switches for LAN party

  - by guywhoneedsahand

  I am working on setting up the network for a small LAN party (less than 16 people). Most of them do not have wireless cards in their rigs, so I need to set up some way for everyone to a) play LAN games and b) access the internet. The LAN party will probably take place in my basement, where I have enough space. However, the basement is not wired up with the router which is actually on the floor above. I make a cantenna a while back that can boost the wireless performance of my computer significantly. How can I use this to provide internet and LAN to guests? My hope was that I could use a switch like this http://www.newegg.com/Product/Product.aspx?Item=N82E16833181166 for the LAN - but how can I give people access to the internet? Is there such thing as a network extender / 16-port switch? Obviously, the internet performance doesn't need to be super stellar, because the games will be using LAN - so I am looking to provide some usable internet for web browsing, and very high speed LAN for games. Thanks!

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• C++ linked list based tree structure. Sanely move nodes between lists.

  - by krunk

  The requirements: Each Node in the list must contain a reference to its previous sibling Each Node in the list must contain a reference to its next sibling Each Node may have a list of child nodes Each child Node must have a reference to its parent node Basically what we have is a tree structure of arbitrary depth and length. Something like: -root(NULL) --Node1 ----ChildNode1 ------ChildOfChild --------AnotherChild ----ChildNode2 --Node2 ----ChildNode1 ------ChildOfChild ----ChildNode2 ------ChildOfChild --Node3 ----ChildNode1 ----ChildNode2 Given any individual node, you need to be able to either traverse its siblings. the children, or up the tree to the root node. A Node ends up looking something like this: class Node { Node* previoius; Node* next; Node* child; Node* parent; } I have a container class that stores these and provides STL iterators. It performs your typical linked list accessors. So insertAfter looks like: void insertAfter(Node* after, Node* newNode) { Node* next = after->next; after->next = newNode; newNode->previous = after; next->previous = newNode; newNode->next = next; newNode->parent = after->parent; } That's the setup, now for the question. How would one move a node (and its children etc) to another list without leaving the previous list dangling? For example, if Node* myNode exists in ListOne and I want to append it to listTwo. Using pointers, listOne is left with a hole in its list since the next and previous pointers are changed. One solution is pass by value of the appended Node. So our insertAfter method would become: void insertAfter(Node* after, Node newNode); This seems like an awkward syntax. Another option is doing the copying internally, so you'd have: void insertAfter(Node* after, const Node* newNode) { Node *new_node = new Node(*newNode); Node* next = after->next; after->next = new_node; new_node->previous = after; next->previous = new_node; new_node->next = next; new_node->parent = after->parent; } Finally, you might create a moveNode method for moving and prevent raw insertion or appending of a node that already has been assigned siblings and parents. // default pointer value is 0 in constructor and a operator bool(..) // is defined for the Node bool isInList(const Node* node) const { return (node->previous || node->next || node->parent); } // then in insertAfter and friends if(isInList(newNode) // throw some error and bail I thought I'd toss this out there and see what folks came up with.

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• string s; &s+1; Legal? UB?

  - by John Dibling

  Consider the following code: #include <cstdlib> #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main() { string myAry[] = { "Mary", "had", "a", "Little", "Lamb" }; const size_t numStrs = sizeof(myStr)/sizeof(myAry[0]); vector<string> myVec(&myAry[0], &myAry[numStrs]); copy( myVec.begin(), myVec.end(), ostream_iterator<string>(cout, " ")); return 0; } Of interest here is &myAry[numStrs]: numStrs is equal to 5, so &myAry[numStrs] points to something that doesn't exist; the sixth element in the array. There is another example of this in the above code: myVec.end(), which points to one-past-the-end of the vector myVec. It's perfecly legal to take the address of this element that doesn't exist. We know the size of string, so we know where the address of the 6th element of a C-style array of strings must point to. So long as we only evaluate this pointer and never dereference it, we're fine. We can even compare it to other pointers for equality. The STL does this all the time in algorithms that act on a range of iterators. The end() iterator points past the end, and the loops keep looping while a counter != end(). So now consider this: #include <cstdlib> #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main() { string myStr = "Mary"; string* myPtr = &myStr; vector<string> myVec2(myPtr, &myPtr[1]); copy( myVec2.begin(), myVec2.end(), ostream_iterator<string>(cout, " ")); return 0; } Is this code legal and well-defined? It is legal and well-defined to take the address of an array element past the end, as in &myAry[numStrs], so should it be legal and well-defined to pretend that myPtr is also an array?

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• A minimalistic smart array (container) class template

  - by legends2k

  I've written a (array) container class template (lets call it smart array) for using it in the BREW platform (which doesn't allow many C++ constructs like STD library, exceptions, etc. It has a very minimal C++ runtime support); while writing this my friend said that something like this already exists in Boost called MultiArray, I tried it but the ARM compiler (RVCT) cries with 100s of errors. I've not seen Boost.MultiArray's source, I've started learning templates only lately; template meta programming interests me a lot, although am not sure if this is strictly one that can be categorized thus. So I want all my fellow C++ aficionados to review it ~ point out flaws, potential bugs, suggestions, optimizations, etc.; something like "you've not written your own Big Three which might lead to...". Possibly any criticism that will help me improve this class and thereby my C++ skills. Edit: I've used std::vector since it's easily understood, later it will be replaced by a custom written vector class template made to work in the BREW platform. Also C++0x related syntax like static_assert will also be removed in the final code. smart_array.h #include <vector> #include <cassert> #include <cstdarg> using std::vector; template <typename T, size_t N> class smart_array { vector < smart_array<T, N - 1> > vec; public: explicit smart_array(vector <size_t> &dimensions) { assert(N == dimensions.size()); vector <size_t>::iterator it = ++dimensions.begin(); vector <size_t> dimensions_remaining(it, dimensions.end()); smart_array <T, N - 1> temp_smart_array(dimensions_remaining); vec.assign(dimensions[0], temp_smart_array); } explicit smart_array(size_t dimension_1 = 1, ...) { static_assert(N > 0, "Error: smart_array expects 1 or more dimension(s)"); assert(dimension_1 > 1); va_list dim_list; vector <size_t> dimensions_remaining(N - 1); va_start(dim_list, dimension_1); for(size_t i = 0; i < N - 1; ++i) { size_t dimension_n = va_arg(dim_list, size_t); assert(dimension_n > 0); dimensions_remaining[i] = dimension_n; } va_end(dim_list); smart_array <T, N - 1> temp_smart_array(dimensions_remaining); vec.assign(dimension_1, temp_smart_array); } smart_array<T, N - 1>& operator[](size_t index) { assert(index < vec.size() && index >= 0); return vec[index]; } size_t length() const { return vec.size(); } }; template<typename T> class smart_array<T, 1> { vector <T> vec; public: explicit smart_array(vector <size_t> &dimension) : vec(dimension[0]) { assert(dimension[0] > 0); } explicit smart_array(size_t dimension_1 = 1) : vec(dimension_1) { assert(dimension_1 > 0); } T& operator[](size_t index) { assert(index < vec.size() && index >= 0); return vec[index]; } size_t length() { return vec.size(); } }; Sample Usage: #include "smart_array.h" #include <iostream> using std::cout; using std::endl; int main() { // testing 1 dimension smart_array <int, 1> x(3); x[0] = 0, x[1] = 1, x[2] = 2; cout << "x.length(): " << x.length() << endl; // testing 2 dimensions smart_array <float, 2> y(2, 3); y[0][0] = y[0][1] = y[0][2] = 0; y[1][0] = y[1][1] = y[1][2] = 1; cout << "y.length(): " << y.length() << endl; cout << "y[0].length(): " << y[0].length() << endl; // testing 3 dimensions smart_array <char, 3> z(2, 4, 5); cout << "z.length(): " << z.length() << endl; cout << "z[0].length(): " << z[0].length() << endl; cout << "z[0][0].length(): " << z[0][0].length() << endl; z[0][0][4] = 'c'; cout << z[0][0][4] << endl; // testing 4 dimensions smart_array <bool, 4> r(2, 3, 4, 5); cout << "z.length(): " << r.length() << endl; cout << "z[0].length(): " << r[0].length() << endl; cout << "z[0][0].length(): " << r[0][0].length() << endl; cout << "z[0][0][0].length(): " << r[0][0][0].length() << endl; // testing copy constructor smart_array <float, 2> copy_y(y); cout << "copy_y.length(): " << copy_y.length() << endl; cout << "copy_x[0].length(): " << copy_y[0].length() << endl; cout << copy_y[0][0] << "\t" << copy_y[1][0] << "\t" << copy_y[0][1] << "\t" << copy_y[1][1] << "\t" << copy_y[0][2] << "\t" << copy_y[1][2] << endl; return 0; }

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• Are these hardwares compatible?

  - by Tom Kaufmann

  I am trying to upgrade my new machine but I want to do it myself. This is my 1st attempt at building system. After carefully reading reviewing feedback and my budget I have decided to select the below listed components. Can anybody let me know are they compatible or not? Transcend 64 GB 2.5" SATA Solid State Drive Asus GeForce GTX550 1GB DDR5 ENGTX550 TI DI/1GD5 Graphics Card Seagate Barracuda 1 TB HDD Internal Hard Drive Cooler Master eXtreme Power Pro 600 Power Supply Intel Core i5 2500K Sandy Bridge 3.30 GHz 95 W 4 Core Desktop Processor Intel DX79TO Motherboard Corsair CMZ8GX3M2A1600C9 8 GB DDR3 SDRAM 1600 MHz Dual Channel Kit Desktop Memory Sony AD-7260S-ZS Internal DVD Writer - Black Cooler Master Hyper TX3 EVO Intel CPU Cooler Cooler Master Elite 335U Cabinet LG E2051T 20.1 Inch SuperSlim Monitor Is any of these hardware components incompatible with I5 2500K? If you have any other suggestions for selecting any other harwdware that can boost up my performance or lower my cost while having the same performance, please suggest. But my primary questions is whether they are compatible or not! Any help is appreciated. Thank you.

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• Is there a way to efficiently yield every file in a directory containing millions of files?

  - by Josh Smeaton

  I'm aware of os.listdir, but as far as I can gather, that gets all the filenames in a directory into memory, and then returns the list. What I want, is a way to yield a filename, work on it, and then yield the next one, without reading them all into memory. Is there any way to do this? I worry about the case where filenames change, new files are added, and files are deleted using such a method. Some iterators prevent you from modifying the collection during iteration, essentially by taking a snapshot of the state of the collection at the beginning, and comparing that state on each move operation. If there is an iterator capable of yielding filenames from a path, does it raise an error if there are filesystem changes (add, remove, rename files within the iterated directory) which modify the collection? There could potentially be a few cases that could cause the iterator to fail, and it all depends on how the iterator maintains state. Using S.Lotts example: filea.txt fileb.txt filec.txt Iterator yields filea.txt. During processing, filea.txt is renamed to filey.txt and fileb.txt is renamed to filez.txt. When the iterator attempts to get the next file, if it were to use the filename filea.txt to find it's current position in order to find the next file and filea.txt is not there, what would happen? It may not be able to recover it's position in the collection. Similarly, if the iterator were to fetch fileb.txt when yielding filea.txt, it could look up the position of fileb.txt, fail, and produce an error. If the iterator instead was able to somehow maintain an index dir.get_file(0), then maintaining positional state would not be affected, but some files could be missed, as their indexes could be moved to an index 'behind' the iterator. This is all theoretical of course, since there appears to be no built-in (python) way of iterating over the files in a directory. There are some great answers below, however, that solve the problem by using queues and notifications. Edit: The OS of concern is Redhat. My use case is this: Process A is continuously writing files to a storage location. Process B (the one I'm writing), will be iterating over these files, doing some processing based on the filename, and moving the files to another location. Edit: Definition of valid: Adjective 1. Well grounded or justifiable, pertinent. (Sorry S.Lott, I couldn't resist). I've edited the paragraph in question above.

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• How can I change the default program installation directory in Windows 7?

  - by Max

  Windows 7 is installed on my C drive, which is quite small. I am very tired of instructing new programs to put their files on my larger D drive during installation; I would like to change the default drive. This article says that you can use a registry hack, but I am giving Microsoft the benefit of the doubt and naively assuming that a configuration option exists somewhere. It's 2010... do I really have to hack my registry to make a simple tweak like this? Also, there's a ServerFault question that explains how to move the "Users" directory and create a symlink, which could also work. However, at the moment I have some apps in C:\Program Files, some apps in C:\Program Files (x86), and some apps in the corresponding folders on D:\, so it would be a hassle. Also, my small OS boot drive is a 10k RPM WD Raptor, and I feel like that probably gives a speed boost to apps installed on it that need to read & write to their directories a bunch. I wonder if it actually matters.

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• Pass variables between separate instances of ruby (without writing to a text file or database)

  - by boulder_ruby

  Lets say I'm running a long worker-script in one of several open interactive rails consoles. The script is updating columns in a very, very, very large table of records. I've muted the ActiveRecord logger to speed up the process, and instruct the script to output some record of progress so I know how roughly how long the process is going to take. That is what I am currently doing and it would look something like this: ModelName.all.each_with_index do |r, i| puts i if i % 250 ...runs some process... r.save end Sometimes its two nested arrays running, such that there would be multiple iterators and other things running all at once. Is there a way that I could do something like this and access that variable from a separate rails console? (such that the variable would be overwritten every time the process is run without much slowdown) records = ModelName.all $total = records.count records.each_with_index do |r, i| $i = i ...runs some process... r.save end meanwhile mid-process in other console puts "#{($i/$total * 100).round(2)}% complete" #=> 67.43% complete I know passing global variables from one separate instance of ruby to the next doesn't work. I also just tried this to no effect as well unix console 1 $X=5 echo {$X} #=> 5 unix console 2 echo {$X} #=> "" Lastly, I also know using global variables like this is a major software design pattern no-no. I think that's reasonable, but I'd still like to know how to break that rule if I'd like. Writing to a text file obviously would work. So would writing to a separate database table or something. That's not a bad idea. But the really cool trick would be sharing a variable between two instances without writing to a text file or database column. What would this be called anyway? Tunneling? I don't quite know how to tag this question. Maybe bad-idea is one of them. But honestly design-patterns isn't what this question is about.

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• Build-Essentials installation failing

  - by Brickman

  I am having trouble accessing the several critical header files that show to be a part of the build process. The "Ubuntu Software Center" shows "Build Essentials" as installed: Next I did the following two commands, which did not improve the problem: ~$ sudo apt-get install build-essential [sudo] password for: Reading package lists... Done Building dependency tree Reading state information... Done build-essential is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. :~$ sudo apt-get install -f Reading package lists... Done Building dependency tree Reading state information... Done 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. :~$ Dump of headers after installation attempts. > /usr/include/boost/interprocess/detail/atomic.hpp > /usr/include/boost/interprocess/smart_ptr/detail/sp_counted_base_atomic.hpp > /usr/include/qt4/Qt/qatomic.h /usr/include/qt4/Qt/qbasicatomic.h > /usr/include/qt4/QtCore/qatomic.h > /usr/include/qt4/QtCore/qbasicatomic.h > /usr/share/doc/git-annex/html/bugs/git_annex_unlock_is_not_atomic.html > /usr/src/linux-headers-3.11.0-15/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/h8300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-15/include/asm-generic/atomic.h > /usr/src/linux-headers-3.11.0-15/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.11.0-15/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.11.0-15/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.11.0-15/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-15-generic/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/h8300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-17/include/asm-generic/atomic.h > /usr/src/linux-headers-3.11.0-17/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.11.0-17/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.11.0-17/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.11.0-17/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-17-generic/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/h8300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-18/include/asm-generic/atomic.h > /usr/src/linux-headers-3.11.0-18/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.11.0-18/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.11.0-18/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.11.0-18/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-18-generic/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/h8300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-19/include/asm-generic/atomic.h > /usr/src/linux-headers-3.11.0-19/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.11.0-19/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.11.0-19/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.11.0-19/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-19-generic/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/h8300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-20/include/asm-generic/atomic.h > /usr/src/linux-headers-3.11.0-20/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.11.0-20/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.11.0-20/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.11.0-20/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-20-generic/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/h8300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.11.0-22/include/asm-generic/atomic.h > /usr/src/linux-headers-3.11.0-22/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.11.0-22/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.11.0-22/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.11.0-22/include/linux/atomic.h > /usr/src/linux-headers-3.11.0-22-generic/include/linux/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/alpha/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/arc/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/arm/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/arm64/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/avr32/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/blackfin/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/cris/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/frv/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/hexagon/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/ia64/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/m32r/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/m68k/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/metag/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/microblaze/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/mips/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/mn10300/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/parisc/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/powerpc/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/s390/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/score/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/sh/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/sparc/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/tile/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/x86/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/arch/xtensa/include/asm/atomic.h > /usr/src/linux-headers-3.14.4-031404/include/asm-generic/atomic.h > /usr/src/linux-headers-3.14.4-031404/include/asm-generic/bitops/atomic.h > /usr/src/linux-headers-3.14.4-031404/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-headers-3.14.4-031404/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-headers-3.14.4-031404/include/linux/atomic.h > /usr/src/linux-headers-3.14.4-031404-generic/include/linux/atomic.h > /usr/src/linux-headers-3.14.4-031404-lowlatency/include/linux/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/alpha/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/arc/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/arm/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/arm64/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/avr32/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/blackfin/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/cris/include/arch-v10/arch/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/cris/include/arch-v32/arch/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/cris/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/frv/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/h8300/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/hexagon/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/ia64/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/m32r/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/m68k/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/metag/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/microblaze/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/mips/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/mn10300/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/parisc/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/powerpc/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/s390/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/score/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/sh/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/sparc/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/tile/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/x86/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/arch/xtensa/include/asm/atomic.h > /usr/src/linux-lts-saucy-3.11.0/include/asm-generic/atomic.h > /usr/src/linux-lts-saucy-3.11.0/include/asm-generic/bitops/atomic.h > /usr/src/linux-lts-saucy-3.11.0/include/asm-generic/bitops/ext2-atomic.h > /usr/src/linux-lts-saucy-3.11.0/include/asm-generic/bitops/non-atomic.h > /usr/src/linux-lts-saucy-3.11.0/include/linux/atomic.h > /usr/src/linux-lts-saucy-3.11.0/ubuntu/lttng/lib/ringbuffer/vatomic.h > /usr/src/linux-lts-saucy-3.11.0/ubuntu/lttng/wrapper/ringbuffer/vatomic.h > /usr/src/linux-lts-saucy-3.11.0/ubuntu/lttng-modules/lib/ringbuffer/vatomic.h > /usr/src/linux-lts-saucy-3.11.0/ubuntu/lttng-modules/wrapper/ringbuffer/vatomic.h Yes, I know there are multiple headers of the same type here, but they are different versions. Version "linux-headers-3.14.4-031404" shows to be the latest. Ubuntu shows "Nothing needed to be installed." However, the following C/C++ headers files show to be missing for Eclipse and QT4. #include <linux/version.h> #include <linux/module.h> #include <linux/socket.h> #include <linux/miscdevice.h> #include <linux/list.h> #include <linux/vmalloc.h> #include <linux/slab.h> #include <linux/init.h> #include <asm/uaccess.h> #include <asm/atomic.h> #include <linux/delay.h> #include <linux/usb.h> This problem appears on my 32-bit version of Ubuntu and on both of my 64-bit versions. What I am doing wrong?

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• C#: Does an IDisposable in a Halted Iterator Dispose?

  - by James Michael Hare

  If that sounds confusing, let me give you an example. Let's say you expose a method to read a database of products, and instead of returning a List<Product> you return an IEnumerable<Product> in iterator form (yield return). This accomplishes several good things: The IDataReader is not passed out of the Data Access Layer which prevents abstraction leak and resource leak potentials. You don't need to construct a full List<Product> in memory (which could be very big) if you just want to forward iterate once. If you only want to consume up to a certain point in the list, you won't incur the database cost of looking up the other items. This could give us an example like: 1: // a sample data access object class to do standard CRUD operations. 2: public class ProductDao 3: { 4: private DbProviderFactory _factory = SqlClientFactory.Instance 5:  6: // a method that would retrieve all available products 7: public IEnumerable<Product> GetAvailableProducts() 8: { 9: // must create the connection 10: using (var con = _factory.CreateConnection()) 11: { 12: con.ConnectionString = _productsConnectionString; 13: con.Open(); 14:  15: // create the command 16: using (var cmd = _factory.CreateCommand()) 17: { 18: cmd.Connection = con; 19: cmd.CommandText = _getAllProductsStoredProc; 20: cmd.CommandType = CommandType.StoredProcedure; 21:  22: // get a reader and pass back all results 23: using (var reader = cmd.ExecuteReader()) 24: { 25: while(reader.Read()) 26: { 27: yield return new Product 28: { 29: Name = reader["product_name"].ToString(), 30: ... 31: }; 32: } 33: } 34: } 35: } 36: } 37: } The database details themselves are irrelevant. I will say, though, that I'm a big fan of using the System.Data.Common classes instead of your provider specific counterparts directly (SqlCommand, OracleCommand, etc). This lets you mock your data sources easily in unit testing and also allows you to swap out your provider in one line of code. In fact, one of the shared components I'm most proud of implementing was our group's DatabaseUtility library that simplifies all the database access above into one line of code in a thread-safe and provider-neutral way. I went with my own flavor instead of the EL due to the fact I didn't want to force internal company consumers to use the EL if they didn't want to, and it made it easy to allow them to mock their database for unit testing by providing a MockCommand, MockConnection, etc that followed the System.Data.Common model. One of these days I'll blog on that if anyone's interested. Regardless, you often have situations like the above where you are consuming and iterating through a resource that must be closed once you are finished iterating. For the reasons stated above, I didn't want to return IDataReader (that would force them to remember to Dispose it), and I didn't want to return List<Product> (that would force them to hold all products in memory) -- but the first time I wrote this, I was worried. What if you never consume the last item and exit the loop? Are the reader, command, and connection all disposed correctly? Of course, I was 99.999999% sure the creators of C# had already thought of this and taken care of it, but inspection in Reflector was difficult due to the nature of the state machines yield return generates, so I decided to try a quick example program to verify whether or not Dispose() will be called when an iterator is broken from outside the iterator itself -- i.e. before the iterator reports there are no more items. So I wrote a quick Sequencer class with a Dispose() method and an iterator for it. Yes, it is COMPLETELY contrived: 1: // A disposable sequence of int -- yes this is completely contrived... 2: internal class Sequencer : IDisposable 3: { 4: private int _i = 0; 5: private readonly object _mutex = new object(); 6:  7: // Constructs an int sequence. 8: public Sequencer(int start) 9: { 10: _i = start; 11: } 12:  13: // Gets the next integer 14: public int GetNext() 15: { 16: lock (_mutex) 17: { 18: return _i++; 19: } 20: } 21:  22: // Dispose the sequence of integers. 23: public void Dispose() 24: { 25: // force output immediately (flush the buffer) 26: Console.WriteLine("Disposed with last sequence number of {0}!", _i); 27: Console.Out.Flush(); 28: } 29: } And then I created a generator (infinite-loop iterator) that did the using block for auto-Disposal: 1: // simply defines an extension method off of an int to start a sequence 2: public static class SequencerExtensions 3: { 4: // generates an infinite sequence starting at the specified number 5: public static IEnumerable<int> GetSequence(this int starter) 6: { 7: // note the using here, will call Dispose() when block terminated. 8: using (var seq = new Sequencer(starter)) 9: { 10: // infinite loop on this generator, means must be bounded by caller! 11: while(true) 12: { 13: yield return seq.GetNext(); 14: } 15: } 16: } 17: } This is really the same conundrum as the database problem originally posed. Here we are using iteration (yield return) over a large collection (infinite sequence of integers). If we cut the sequence short by breaking iteration, will that using block exit and hence, Dispose be called? Well, let's see: 1: // The test program class 2: public class IteratorTest 3: { 4: // The main test method. 5: public static void Main() 6: { 7: Console.WriteLine("Going to consume 10 of infinite items"); 8: Console.Out.Flush(); 9:  10: foreach(var i in 0.GetSequence()) 11: { 12: // could use TakeWhile, but wanted to output right at break... 13: if(i >= 10) 14: { 15: Console.WriteLine("Breaking now!"); 16: Console.Out.Flush(); 17: break; 18: } 19:  20: Console.WriteLine(i); 21: Console.Out.Flush(); 22: } 23:  24: Console.WriteLine("Done with loop."); 25: Console.Out.Flush(); 26: } 27: } So, what do we see? Do we see the "Disposed" message from our dispose, or did the Dispose get skipped because from an "eyeball" perspective we should be locked in that infinite generator loop? Here's the results: 1: Going to consume 10 of infinite items 2: 0 3: 1 4: 2 5: 3 6: 4 7: 5 8: 6 9: 7 10: 8 11: 9 12: Breaking now! 13: Disposed with last sequence number of 11! 14: Done with loop. Yes indeed, when we break the loop, the state machine that C# generates for yield iterate exits the iteration through the using blocks and auto-disposes the IDisposable correctly. I must admit, though, the first time I wrote one, I began to wonder and that led to this test. If you've never seen iterators before (I wrote a previous entry here) the infinite loop may throw you, but you have to keep in mind it is not a linear piece of code, that every time you hit a "yield return" it cedes control back to the state machine generated for the iterator. And this state machine, I'm happy to say, is smart enough to clean up the using blocks correctly. I suspected those wily guys and gals at Microsoft engineered it well, and I wasn't disappointed. But, I've been bitten by assumptions before, so it's good to test and see. Yes, maybe you knew it would or figured it would, but isn't it nice to know? And as those campy 80s G.I. Joe cartoon public service reminders always taught us, "Knowing is half the battle...". Technorati Tags: C#,.NET

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• Premature-Optimization and Performance Anxiety

  - by James Michael Hare

  While writing my post analyzing the new .NET 4 ConcurrentDictionary class (here), I fell into one of the classic blunders that I myself always love to warn about.  After analyzing the differences of time between a Dictionary with locking versus the new ConcurrentDictionary class, I noted that the ConcurrentDictionary was faster with read-heavy multi-threaded operations.  Then, I made the classic blunder of thinking that because the original Dictionary with locking was faster for those write-heavy uses, it was the best choice for those types of tasks.  In short, I fell into the premature-optimization anti-pattern. Basically, the premature-optimization anti-pattern is when a developer is coding very early for a perceived (whether rightly-or-wrongly) performance gain and sacrificing good design and maintainability in the process.  At best, the performance gains are usually negligible and at worst, can either negatively impact performance, or can degrade maintainability so much that time to market suffers or the code becomes very fragile due to the complexity. Keep in mind the distinction above.  I'm not talking about valid performance decisions.  There are decisions one should make when designing and writing an application that are valid performance decisions.  Examples of this are knowing the best data structures for a given situation (Dictionary versus List, for example) and choosing performance algorithms (linear search vs. binary search).  But these in my mind are macro optimizations.  The error is not in deciding to use a better data structure or algorithm, the anti-pattern as stated above is when you attempt to over-optimize early on in such a way that it sacrifices maintainability. In my case, I was actually considering trading the safety and maintainability gains of the ConcurrentDictionary (no locking required) for a slight performance gain by using the Dictionary with locking.  This would have been a mistake as I would be trading maintainability (ConcurrentDictionary requires no locking which helps readability) and safety (ConcurrentDictionary is safe for iteration even while being modified and you don't risk the developer locking incorrectly) -- and I fell for it even when I knew to watch out for it.  I think in my case, and it may be true for others as well, a large part of it was due to the time I was trained as a developer.  I began college in in the 90s when C and C++ was king and hardware speed and memory were still relatively priceless commodities and not to be squandered.  In those days, using a long instead of a short could waste precious resources, and as such, we were taught to try to minimize space and favor performance.  This is why in many cases such early code-bases were very hard to maintain.  I don't know how many times I heard back then to avoid too many function calls because of the overhead -- and in fact just last year I heard a new hire in the company where I work declare that she didn't want to refactor a long method because of function call overhead.  Now back then, that may have been a valid concern, but with today's modern hardware even if you're calling a trivial method in an extremely tight loop (which chances are the JIT compiler would optimize anyway) the results of removing method calls to speed up performance are negligible for the great majority of applications.  Now, obviously, there are those coding applications where speed is absolutely king (for example drivers, computer games, operating systems) where such sacrifices may be made.  But I would strongly advice against such optimization because of it's cost.  Many folks that are performing an optimization think it's always a win-win.  That they're simply adding speed to the application, what could possibly be wrong with that?  What they don't realize is the cost of their choice.  For every piece of straight-forward code that you obfuscate with performance enhancements, you risk the introduction of bugs in the long term technical debt of the application.  It will become so fragile over time that maintenance will become a nightmare.  I've seen such applications in places I have worked.  There are times I've seen applications where the designer was so obsessed with performance that they even designed their own memory management system for their application to try to squeeze out every ounce of performance.  Unfortunately, the application stability often suffers as a result and it is very difficult for anyone other than the original designer to maintain. I've even seen this recently where I heard a C++ developer bemoaning that in VS2010 the iterators are about twice as slow as they used to be because Microsoft added range checking (probably as part of the 0x standard implementation).  To me this was almost a joke.  Twice as slow sounds bad, but it almost never as bad as you think -- especially if you're gaining safety.  The only time twice is really that much slower is when once was too slow to begin with.  Think about it.  2 minutes is slow as a response time because 1 minute is slow.  But if an iterator takes 1 microsecond to move one position and a new, safer iterator takes 2 microseconds, this is trivial!  The only way you'd ever really notice this would be in iterating a collection just for the sake of iterating (i.e. no other operations).  To my mind, the added safety makes the extra time worth it. Always favor safety and maintainability when you can.  I know it can be a hard habit to break, especially if you started out your career early or in a language such as C where they are very performance conscious.  But in reality, these type of micro-optimizations only end up hurting you in the long run. Remember the two laws of optimization.  I'm not sure where I first heard these, but they are so true: For beginners: Do not optimize. For experts: Do not optimize yet. This is so true.  If you're a beginner, resist the urge to optimize at all costs.  And if you are an expert, delay that decision.  As long as you have chosen the right data structures and algorithms for your task, your performance will probably be more than sufficient.  Chances are it will be network, database, or disk hits that will be your slow-down, not your code.  As they say, 98% of your code's bottleneck is in 2% of your code so premature-optimization may add maintenance and safety debt that won't have any measurable impact.  Instead, code for maintainability and safety, and then, and only then, when you find a true bottleneck, then you should go back and optimize further.

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• Refactoring an ERB Template to Haml

  - by Liam McLennan

  ERB is the default view templating system used by Ruby on Rails. Haml is an alternative templating system that uses whitespace to represent document structure. The example from the haml website shows the following equivalent markup: Haml ERB #profile .left.column #date= print_date #address= current_user.address .right.column #email= current_user.email #bio= current_user.bio <div id="profile"> <div class="left column"> <div id="date"><%= print_date %></div> <div id="address"><%= current_user.address %></div> </div> <div class="right column"> <div id="email"><%= current_user.email %></div> <div id="bio"><%= current_user.bio %></div> </div> </div> I like haml because it is concise and the significant whitespace makes it easy to see the structure at a glance. This post is about a ruby project but nhaml makes haml available for asp.net MVC also. The ERB Template Today I spent some time refactoring an ERB template to Haml. The template is called list.html.erb and its purpose is to render a list of tweets (twitter messages). <style> form { float: left; } </style> <h1>Tweets</h1> <table> <thead><tr><th></th><th>System</th><th>Human</th><th></th></tr></thead> <% @tweets.each do |tweet| %> <tr> <td><%= h(tweet['text']) %></td> <td><%= h(tweet['system_classification']) %></td> <td><%= h(tweet['human_classification']) %></td> <td><form action="/tweet/rate" method="post"> <%= token_tag %> <input type="submit" value="Positive"/> <input type="hidden" value="<%= tweet['id']%>" name="id" /> <input type="hidden" value="positive" name="rating" /> </form> <form action="/tweet/rate" method="post"> <%= token_tag %> <input type="submit" value="Neutral"/> <input type="hidden" value="<%= tweet['id']%>" name="id" /> <input type="hidden" value="neutral" name="rating" /> </form> <form action="/tweet/rate" method="post"> <%= token_tag %> <input type="submit" value="Negative"/> <input type="hidden" value="<%= tweet['id']%>" name="id" /> <input type="hidden" value="negative" name="rating" /> </form> </td> </tr> <% end %> </table> Haml Template: Take 1 My first step was to convert this page to a Haml template in place. Directly translating the ERB template to Haml resulted in: list.haml %style form {float: left;} %h1 Tweets %table %thead %tr %th %th System %th Human %th %tbody - @tweets.each do |tweet| %tr %td= tweet['text'] %td= tweet['system_classification'] %td= tweet['human_classification'] %td %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag <input type="submit" value="Positive"/> <input type="hidden" value="positive" name="rating" /> %input{ :type=>"hidden", :value => tweet['id']} %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag <input type="submit" value="Neutral"/> <input type="hidden" value="neutral" name="rating" /> %input{ :type=>"hidden", :value => tweet['id']} %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag <input type="submit" value="Negative"/> <input type="hidden" value="negative" name="rating" /> %input{ :type=>"hidden", :value => tweet['id']} end I like this better already but I can go further. Haml Template: Take 2 The haml documentation says to avoid using iterators so I introduced a partial template (_tweet.haml) as the template to render a single tweet. _tweet.haml %tr %td= tweet['text'] %td= tweet['system_classification'] %td= tweet['human_classification'] %td %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag <input type="submit" value="Positive"/> <input type="hidden" value="positive" name="rating" /> %input{ :type=>"hidden", :value => tweet['id']} %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag <input type="submit" value="Neutral"/> <input type="hidden" value="neutral" name="rating" /> %input{ :type=>"hidden", :value => tweet['id']} %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag <input type="submit" value="Negative"/> <input type="hidden" value="negative" name="rating" /> %input{ :type=>"hidden", :value => tweet['id']} and the list template is simplified to: list.haml %style form {float: left;} %h1 Tweets %table     %thead         %tr             %th             %th System             %th Human             %th     %tbody         = render(:partial => "tweet", :collection => @tweets) That is definitely an improvement, but then I noticed that _tweet.haml contains three form tags that are nearly identical.   Haml Template: Take 3 My first attempt, later aborted, was to use a helper to remove the duplication. A much better solution is to use another partial.  _rate_button.haml %form{ :action=>"/tweet/rate", :method=>"post"} = token_tag %input{ :type => "submit", :value => rate_button[:rating].capitalize } %input{ :type => "hidden", :value => rate_button[:rating], :name => 'rating' } %input{ :type => "hidden", :value => rate_button[:id], :name => 'id' } and the tweet template is now simpler: _tweet.haml %tr %td= tweet['text'] %td= tweet['system_classification'] %td= tweet['human_classification'] %td = render( :partial => 'rate_button', :object => {:rating=>'positive', :id=> tweet['id']}) = render( :partial => 'rate_button', :object => {:rating=>'neutral', :id=> tweet['id']}) = render( :partial => 'rate_button', :object => {:rating=>'negative', :id=> tweet['id']}) list.haml remains unchanged. Summary I am extremely happy with the switch. No doubt there are further improvements that I can make, but I feel like what I have now is clean and well factored.

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• 5 reason why you should upgrade to new iPad (3rd generation)

  - by Gopinath

  Apple released the new iPad, 3rd generation, couple of days ago and they will be available in stores from March 16 onwards.  It’s the best tablet available in the market and for first time buyers it’s a no brainer to choose it. What about the iPad owners? Should they upgrade their iPad 2 to the new iPad? This is the question on the lips of most of the iPad owners. In this post we will provide you 5 reasons why you should upgrade your iPad, if more than two reasons are convincing then you should upgrade to the new iPad. Retina display – The best display ever made for mobile device, a game changer The new iPad comes with Retina display with screen resolution of 2048 x 1536, which is twice the resolution of iPad 2. Undoubtedly the iPad 3’s display is the best display ever made for a mobile device and it’s a game changer. With better resolution on iPad 3 eBook reading is going to be a pleasure with clear and crisp text Watching HD movies on iPad is going to be unbelievably good The new Games targeted for Retina display are going to be more realistic and needless to explain the pleasure of playing such games Graphic artists and photo editors get a professional on screen rendering support to create beautiful graphics 2x Faster & 2x Memory – Better Games and powerful Apps The new iPad is more powerful with 2x faster graphics and 2x more memory. Apple claims that the A5x processor of new iPad is 2x faster than iPad 2 and 4x faster than the best graphic chips available from other vendors. The RAM of  new iPad  is upgraded to 1 GB compared from 512 MB of iPad 2. With the fast processor and more memory, Apps and games are going to be blazing fast. 4G Internet – Browse the web at the speeds of 42 MB/sec Half of the iPad owners are frequent commuters who access internet over cellular networks, the new iPad’s 4G LTE is going to be a big boom for their  high data access needs. With the new iPad’s 4G LTE connectivity you can browse the web at 42 MB/sec and it mean you can watch a HD video without buffering issues. iPad 2 comes with 3G network support and it’s browsing speeds are way less than the new iPad. 5MP Camera – HD Movie Recording & gorgeous Photography iPad 2 has a 0.7 mega pixel camera and the new iPad comes with 5 megapixels camera. That is a huge boost for hobbyist  photographers and videographers. With the new iPad you can shoot gorgeous photos and 1080p HD video. The iSight camera of new iPad uses advanced optics with features like auto exposure, auto focus and face detection up to 10 faces. Amazon Pays up to $300 for old iPad 2 16 GB Wifi and more for other models Do you know that you can trade in your iPad 2 16 GB Wifi for upto $300? Amazon has an excellent trade in program for selling your used iPad 2s. Depending on the condition of the iPad 2  Amazon offers $234, $270, $300.00 for 16 GB Wifi versions that in Acceptable, Good and Like New conditions respectively.  The higher models of iPad 2s fetch you more money. With this great deal from Amazon the amount of extra money you need to spend for new iPad is almost half of their price. Visit Amazon Trade In’s website or read Amazon’s brilliant plan to pay you crazy money for your iPad 2 for more details. Related: New IPad Vs. IPad 2–Side By Side Comparison Of Hardware Specification [Infographic]

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