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  • ID generator with local static variable - thread-safe?

    - by Poseidon
    Will the following piece of code work as expected in a multi-threaded scenario? int getUniqueID() { static int ID=0; return ++ID; } It's not necessary that the IDs to be contiguous - even if it skips a value, it's fine. Can it be said that when this function returns, the value returned will be unique across all threads?

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  • C++ STL: Trouble with iterators

    - by Rosarch
    I'm having a beginner problem: bool _isPalindrome(const string& str) { return _isPalindrome(str.begin(), str.end()); // won't compile } bool _isPalindrome(string::iterator begin, string::iterator end) { return begin == end || *begin == *end && _isPalindrome(++begin, --end); } What am I doing wrong here? Why doesn't str.begin() get type checked to be a string::iterator?

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  • Java synchronizing static list ?

    - by JavaUser
    Hi, In a Java class , i am having a static list so this list is shared across all the objects of this class.The business logic in this class will run periodically which is invoked by some method with out passing instance parameters.Now I want to invoke this run method based on the list(I will add some vales into this list based on JMS) ,this list may empty sometimes and after finishing the run , i am emptying this list.Now my question is , whether I need to synchronize this list or not? Also let me know is there any other way to pass value in one object instance(Thread1) to other object instance (Thread2) other than having Static variable(static list)? Thx

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  • Threading in java vs C#

    - by ffayyaz
    I need a little confirmation over something i am confused at . I know how threads work in java. new DialList(string a , string b).start(); // where DialList is a class public class DialList extends Thread { public DialList(String a, string b) { FilePath = a; ThreadLogFile = b"; } public void run() { // some code to run in different thread } } Now i want to run same code in C# , Shall i put the code which is in run() into a method and do something like Thread t = new Thread (runcsharp); // Kick off a new thread t.Start(); static void runcsharp() { // code } or is there some other way to do it ?

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  • OpenGL multiple threads, variable handling [closed]

    - by toeplitz
    I have written an OpenGL program which runs in the following way: Main: - Initialize SDL - Create thread which has the OpenGL context: - Renderloop - Set camera (view) matrix with glUniform. - glDrawElements() .... etc. - Swapbuffers(); - Main SDL loop handling input events and such. - Update camera matrix of type glm::mat4. This is how I pass my camera object to the class that handles opengl. Camera *cam = new Camera(); gl.setCam(cam); where void setCam(Camera *camera) { this->camera = camera; } For rendering in the opengl context thread, this happens: glm::mat4 modelView = camera->view * model; glUniformMatrix4fv(shader->bindUniform("modelView"), 1, GL_FALSE, glm::value_ptr(modelView)); In the main program where my SDL and other things are handles I then recompute the view matrix. This his working fine without me using any mutex locks. Is this correct? On the other hand, I add objects to my scene by an "upload queue" and in this case I have to mutex lock my upload queue vector (vector class type) when adding items to it or else the program crashes. In summary: I recompute my matrix in a different thread and then use it in the opengl thread without any mutex lock. Why is this working? Edit: I think my question is similar to what was asked here: Should I lock a variable in one thread if I only need it's value in other threads, and why does it work if I don't?, only in my case it is even more simple with only one matrix being changed.

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  • Iterators over a LInked List in a Game in Java

    - by Matthew
    I am using OpenGl in android and they have a callback method called draw that gets called with out my control. (As fast as the device can handle if I am not mistaken) I have a list of "GameObjects" that have a .draw method and a .update method. I have two different threads that handle each of those. So, the question is, can I declare two different iterators in two different methods in two different threads that iterate over the same Linked List? If so, do I simply declare ListIterator<GameObject> l = objets.listIterator() each time I want a new iterator and it won't interfere with other iterators?

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  • Optimal strategy to make a C++ hash table, thread safe

    - by Ajeet
    (I am interested in design of implementation NOT a readymade construct that will do it all.) Suppose we have a class HashTable (not hash-map implemented as a tree but hash-table) and say there are eight threads. Suppose read to write ratio is about 100:1 or even better 1000:1. Case A) Only one thread is a writer and others including writer can read from HashTable(they may simply iterate over entire hash table) Case B) All threads are identical and all could read/write. Can someone suggest best strategy to make the class thread safe with following consideration 1. Top priority to least lock contention 2. Second priority to least number of locks My understanding so far is thus : One BIG reader-writer lock(semaphore). Specialize the semaphore so that there could be eight instances writer-resource for case B, where each each writer resource locks one row(or range for that matter). (so i guess 1+8 mutexes) Please let me know if I am thinking on the correct line, and how could we improve on this solution.

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  • How important do you find exception safety to be in your C++ code?

    - by Kai
    Every time I consider making my code strongly exception safe, I justify not doing it because it would be so time consuming. Consider this relatively simple snippet: Level::Entity* entity = new Level::Entity(); entity->id = GetNextId(); entity->AddComponent(new Component::Position(x, y)); entity->AddComponent(new Component::Movement()); entity->AddComponent(new Component::Render()); allEntities.push_back(entity); // std::vector entityById[entity->id] = entity; // std::map return entity; To implement a basic exception guarantee, I could use a scoped pointer on the new calls. This would prevent memory leaks if any of the calls were to throw an exception. However, let's say I want to implement a strong exception guarantee. At the least, I would need to implement a shared pointer for my containers (I'm not using Boost), a nothrow Entity::Swap for adding the components atomically, and some sort of idiom for atomically adding to both the Vector and Map. Not only would these be time consuming to implement, but they would be expensive since it involves a lot more copying than the exception unsafe solution. Ultimately, it feels to me like that time spent doing all of that wouldn't be justified just so that the a simple CreateEntity function is strongly exception safe. I probably just want the game to display an error and close at that point anyway. How far do you take this in your own game projects? Is it generally acceptable to write exception unsafe code for a program that can just crash when there is an exception?

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  • "Unable to initialize module" fileinfo php-pecl-Fileinfo.x86_64

    - by Myers Network
    I have a brand new server server that I am trying to get setup up. This is a 64 bit machine that I can not install "fileinfo" or "memcache". I have uninstalled these and reinstalled them using yum and pecl with no luck. Yum install fine "no error" but then get error when running php. pecl from what I can tell is only installing 32bit. Does not put anything in the lib64 directory. Here is my output from php -v: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP 5.2.14 (cli) (built: Aug 12 2010 16:03:48) Copyright (c) 1997-2010 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies Here is some other system info incase you need it uname: Linux server.actham.us 2.6.18-194.26.1.el5 #1 SMP Tue Nov 9 12:54:20 EST 2010 x86_64 x86_64 x86_64 GNU/Linux php -m: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 [PHP Modules] bz2 calendar ctype curl date dbase dom exif filter ftp gd gettext gmp hash iconv imap json ldap libxml mbstring mcrypt mysql mysqli openssl pcntl pcre PDO pdo_mysql pdo_sqlite readline Reflection session shmop SimpleXML sockets SPL standard tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl zip zlib [Zend Modules] Any help would be greatly appreciated, thanks....

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  • "Unable to initialize module" fileinfo php-pecl-Fileinfo.x86_64

    - by Myers Network
    I have a brand new server server that I am trying to get setup up. This is a 64 bit machine that I can not install "fileinfo" or "memcache". I have uninstalled these and reinstalled them using yum and pecl with no luck. Yum install fine "no error" but then get error when running php. pecl from what I can tell is only installing 32bit. Does not put anything in the lib64 directory. Here is my output from php -v: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP 5.2.14 (cli) (built: Aug 12 2010 16:03:48) Copyright (c) 1997-2010 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies Here is some other system info incase you need it uname: Linux server.actham.us 2.6.18-194.26.1.el5 #1 SMP Tue Nov 9 12:54:20 EST 2010 x86_64 x86_64 x86_64 GNU/Linux php -m: PHP Warning: PHP Startup: fileinfo: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 PHP Warning: PHP Startup: memcache: Unable to initialize module Module compiled with module API=20050922, debug=0, thread-safety=0 PHP compiled with module API=20060613, debug=0, thread-safety=0 These options need to match in Unknown on line 0 [PHP Modules] bz2 calendar ctype curl date dbase dom exif filter ftp gd gettext gmp hash iconv imap json ldap libxml mbstring mcrypt mysql mysqli openssl pcntl pcre PDO pdo_mysql pdo_sqlite readline Reflection session shmop SimpleXML sockets SPL standard tokenizer wddx xml xmlreader xmlrpc xmlwriter xsl zip zlib [Zend Modules] Any help would be greatly appreciated, thanks....

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  • How to solve this Java type safety warning? (Struts2)

    - by Nicolas Raoul
    Map session = ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: The method put(Object, Object) belongs to the raw type Map. References to generic type Map should be parameterized. Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: Unchecked cast from Map to Map. The getSession method belongs to Struts2 so I can't modify it. I would like to avoid using @SuppressWarnings because other warnings can be useful. I guess all Struts2 users in the world faced the same problem... is there an elegant solution?

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  • Delphi - Proper way to page though data.

    - by Brad
    I have a string list (TStrings) that has a couple thousand items in it. I need to process them in groups of 100. I basically want to know what the best way to do the loop is in Delphi. I'm hitting a brick wall when I'm trying to figure it out. Thanks unit Unit2; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TForm2 = class(TForm) Memo1: TMemo; Memo2: TMemo; Button1: TButton; procedure Button1Click(Sender: TObject); private { Private declarations } public { Public declarations } end; var Form2: TForm2; implementation Uses math; {$R *.dfm} procedure TForm2.Button1Click(Sender: TObject); var I:Integer; pages:Integer; str:string; begin pages:= ceil(memo1.Lines.Count/100) ; memo2.Lines.add('Total Pages: '+inttostr(pages)); memo2.Lines.add('Total Items: '+inttostr(memo1.Lines.Count)); // Should just do in batches of 100 VS entire list for I := 0 to memo1.lines.Count - 1 do begin if str '' then str:= str+#10+ memo1.Lines.Strings[i] else str:= memo1.Lines.Strings[i]; end; //I need to stop here every 100 items, then process the items. memo2.Lines.Add(str); end; end. Example form object Form2: TForm2 Left = 0 Top = 0 Caption = 'Form2' ClientHeight = 245 ClientWidth = 527 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = 'Tahoma' Font.Style = [] OldCreateOrder = False PixelsPerInch = 96 TextHeight = 13 object Memo1: TMemo Left = 16 Top = 8 Width = 209 Height = 175 Lines.Strings = ( '4xlt columbia thunder storm jacket' '5 things about thunder storms' 'a thunder storm with a lot of thunder ' 'and lighting sccreensaver' 'a thunder storm with a lot of thunder ' 'and lighting screensaver with no nag ' 'screens' 'all about thunder storms' 'all about thunderstorms for kids' 'amazing tornado videos and ' 'thunderstorm videos' 'are thunder storms louder in ohio?' 'bad thunder storms' 'bathing in thunder storm' 'best thunderstorm pictures' 'cartoon thunder storms' 'celtic thunder storm' 'central valley thunder storm' 'chicago thunderstorm pictures' 'cool thunderstorm pictures' 'current thunderstorm warnings' 'does thunder storms in december mean ' 'snow will be coming' 'facts about thunderstorms for kids' 'facts on thunderstorms for kids' 'fedex thunderstorm video' 'florida thunderstorms facts' 'free relaxing thunderstorm music' 'free soothing thunderstorm sounds ' 'online' 'free thunderstorm mp3' 'free thunderstorm mp3 download' 'free thunderstorm mp3 downloads' 'free thunderstorm mp3s' 'free thunderstorm music' 'free thunderstorm pictures' 'free thunderstorm sound effects' 'free thunderstorm sounds' 'free thunderstorm sounds cd' 'free thunderstorm sounds mp3' 'free thunderstorm sounds online' 'free thunderstorm soundscape' 'free thunderstorm video' 'free thunderstorm video download' 'free thunderstorm videos' 'god of storm and thunder' 'horses storm thunder rain' 'how do thunder storms form' 'how far away is a thunder storm' 'how long do thunder storms last' 'ice cube in a thunder storm' 'indoor thunderstorm safety tips' 'information about thunderstorms for kids' 'interesting thunderstorm facts' 'is it dangerous to shower during thunder ' 'storm' 'is there frequently thunder during snow ' 'storms' 'isolated thunderstorms' 'it'#39's just a thunder storm baby there is ' 'nothing you should fear lyrics' 'lightning & thunder storm safety' 'lightning and thunderstorm facts' 'lightning and thunderstorms facts' 'lightning and thunderstorms for kids' 'listen to thunderstorm sounds online' 'mississauga thunder storm' 'nature sounds free mp3 thunder storm' 'only about thunderstorms facts' 'original storm deep thunderstick' 'phone use during thunder storms' 'pictures of thunderstorms' 'pocono thunder storm' 'posters of thunder storms' 'power rangers ninja storm' 'power rangers thunder storm' 'power rangers thunder storm cast' 'power rangers thunder storm games' 'power rangers thunder storm morphers' 'power rangers thunder storm part 1' 'power rangers thunder storm part 2' 'power rangers thunderstorm' 'power rangers thunderstorm cannon' 'power rangers thunderstorm deluxe ' 'megazord' 'power rangers thunderstorm games' 'power rangers thunderstorm megazord' 'power rangers thunderstorm part 2' 'power rangers thunderstorm pictures' 'power rnager ninja storm thunder staff' 'powerful thunder and lightning storms' 'precambrian thunder storms' 'rain thunderstorm mp3' 'rain thunderstorm pictures' 'relaxing thunderstorm music' 'reminds me of ohio river thunder lighten ' 'storms' 'sacramento thunder storm' 'safety tips for when your caught in a ' 'thunder storm' 'scattered thunderstorms' 'schemer puts his head in the thunder ' 'storm' 'sedative thunder storm' 'server thunder storms' 'severe supercell thunderstorm pictures' 'severe thunder storm pictures' 'severe thunder storms' 'severe thunderstorm facts' 'severe thunderstorm pictures' 'severe thunderstorm pictures hail' 'severe thunderstorm pictures in alberta' 'severe thunderstorm pictures tornado' 'severe thunderstorm safety' 'severe thunderstorm safety tips' 'severe thunderstorm videos' 'severe thunderstorm warning' 'severe thunderstorm warning los ' 'angeles' 'severe thunderstorm warning signs' 'severe thunderstorm warnings' 'severe thunderstorms' 'severe thunderstorms facts' 'shakespeare use thunder storm for ' 'cosmic disorder julius caesar' 'soothing thunderstorm sounds online' 'sound effects of severe thunder storm' 'sound of rain storm finger snapping ' 'thunder chorus' 'split thunder storm' 'storm 3d thunder power' 'storm dark thunder' 'storm dark thunder bowling ball' 'storm dark thunder bowling ball sale' 'storm dark thunder for sale' 'storm dark thunder pearl' 'storm dark thunder pearl bowling ball' 'storm dark thunder review' 'storm dark thunder shirt' 'storm dark thunderball' 'storm deep thunder' 'storm deep thunder 11' 'storm deep thunder 15' 'storm deep thunder 15 lure' 'storm deep thunder 2' 'storm deep thunder lures' 'storm deep thunderstick' 'storm deep thunderstick crankbaits' 'storm deep thunderstick dts09' 'storm deep thunderstick jr' 'storm deep thunderstick lures' 'storm deep thundersticks' 'storm rolling thunder 3 ball roller' 'storm rolling thunder bowling bag' 'storm rolling thunder three ball bowling ' 'bag' 'storm shallow thunder' 'storm shallow thunder 15' 'storm thunder claw' 'storm thunder craw' 'storm watches thunder' 'storms with constant lightning and ' 'thunder non-stop' 'supercell thunder storms' 'supercell thunderstorm pictures' 'supercell thunderstorms' 'swimming pools thunder storms' 'tampa + lightning strikes + thunder ' 'storms' 'texas thunderstorm pictures' 'texas thunderstorm warnings' 'thunder and lightning storm' 'thunder and lighting storms' 'thunder and lightning storms' 'thunder bay snow storm video' 'thunder storm' 'thunder storm and windmill' 'thunder storm cd' 'thunder storm cloud' 'thunder storm clouds' 'thunder storm dog peppermint oil' 'thunder storm in winter' 'thunder storm in winter and weather ' 'prediction' 'thunder storm lx-3 & road blaster psx ' 'download' 'thunder storm occurances' 'thunder storm photos' 'thunder storm poems' 'thunder storm safety' 'thunder storm sign' 'thunder storm sounds' 'thunder storms' 'thunder storms and deaths' 'thunder storms and ilghting' 'thunder storms and lighting' 'thunder storms cd' 'thunder storms in the arctic arctic ' 'weather' 'thunder storms in winter' 'thunder storms on you tub' 'thunder storms pics' 'thunder storms with rain' 'thunderstorm' 'thunderstorm backgrounds' 'thunderstorm capital' 'thunderstorm capital 2008 dorfman' 'thunderstorm capital in boston' 'thunderstorm capital llc' 'thunderstorm capital of canada' 'thunderstorm capital of the us' 'thunderstorm capital of the world' 'thunderstorm facts' 'thunderstorm facts for kids' 'thunderstorm facts hail' 'thunderstorm facts tornadoes' 'thunderstorm mp3' 'thunderstorm mp3 download' 'thunderstorm mp3 download free' 'thunderstorm mp3 downloads' 'thunderstorm mp3 downloads free' 'thunderstorm mp3 files' 'thunderstorm mp3 free' 'thunderstorm mp3 free download' 'thunderstorm mp3 free downloads' 'thunderstorm mp3 torrent' 'thunderstorm mp3s' 'thunderstorm music' 'thunderstorm music cd' 'thunderstorm music downloads' 'thunderstorm music free' 'thunderstorm music playlists' 'thunderstorm music rain' 'thunderstorm pics' 'thunderstorm pictures' 'thunderstorm pictures for kids' 'thunderstorm safety' 'thunderstorm safety for kids' 'thunderstorm safety precautions' 'thunderstorm safety procedures' 'thunderstorm safety rules' 'thunderstorm safety tips' 'thunderstorm safety tips for kids' 'thunderstorm safety tips shelter' 'thunderstorm safety tips trees' 'thunderstorm sound effects' 'thunderstorm sound effects cd' 'thunderstorm sound effects download' 'thunderstorm sound effects free' 'thunderstorm sound effects free ' 'download' 'thunderstorm sound effects free music ' 'feature audio' 'thunderstorm sound effects mp3' 'thunderstorm sound effects rain' 'thunderstorm sounds' 'thunderstorm sounds cd' 'thunderstorm sounds download' 'thunderstorm sounds for sleep' 'thunderstorm sounds for sleeping' 'thunderstorm sounds free' 'thunderstorm sounds free download' 'thunderstorm sounds free downloads' 'thunderstorm sounds mp3' 'thunderstorm sounds mp3 download' 'thunderstorm sounds mp3 free' 'thunderstorm sounds online' 'thunderstorm sounds online for free' 'thunderstorm sounds online free' 'thunderstorm sounds sleep' 'thunderstorm sounds streaming' 'thunderstorm sounds torrent' 'thunderstorm soundscape' 'thunderstorm soundscapes' 'thunderstorm video' 'thunderstorm video clips' 'thunderstorm video download' 'thunderstorm video downloads' 'thunderstorm videos' 'thunderstorm videos for kids' 'thunderstorm videos lightning' 'thunderstorm videos online' 'thunderstorm wallpaper' 'thunderstorm warning' 'thunderstorm warning brisbane' 'thunderstorm warning definition' 'thunderstorm warning los angeles' 'thunderstorm warning san diego' 'thunderstorm warning san mateo county' 'thunderstorm warning santa barbara' 'thunderstorm warning santa clara' 'thunderstorm warning santa clara ' 'county' 'thunderstorm warning signal' 'thunderstorm warning signs' 'thunderstorm warning vs watch' 'thunderstorm warnings' 'thunderstorm warnings and watches' 'thunderstorm warnings for nj' 'thunderstorm warnings qld' 'thunderstorms' 'thunderstorms facts' 'thunderstorms facts for kids' 'thunderstorms for kids' 'tornados and thunder storms animated' 'understanding thunderstorms for kids' 'watch thunderstorm videos' 'weather underground forecast ' 'thunderstorms' 'what causes thunder storms' 'what is a thunder storm' 'where d thunder storms occur') TabOrder = 0 end object Memo2: TMemo Left = 240 Top = 8 Width = 265 Height = 129 Lines.Strings = ( 'Memo2') TabOrder = 1 end object Button1: TButton Left = 384 Top = 184 Width = 75 Height = 25 Caption = 'Button1' TabOrder = 2 OnClick = Button1Click end end

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  • is there some lightweight tecnique for adding type safety to identifier properties?

    - by shoren
    After using C++ I got used to the concept of Identifier which can be used with a class for the type, provides type safety and has no runtime overhead (the actual size is the size of the primitive). I want to do something like that, so I will not make mistakes like: personDao.find(book.getId());//I want compilation to fail personDao.find(book.getOwnerId());//I want compilation to succeed Possible solutuions that I don't like: For every entity have an entity id class wrapping the id primitive. I don't like the code bloat. Create a generic Identifier class. Code like this will not compile: void foo(Identifier book); void foo(Identifier person); Does anyone know of a better way? Is there a library with a utility such as this? Is implementing this an overkill? And the best of all, can this be done in Java without the object overhead like in C++?

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  • Fill data gaps - UNION, PARTITION BY, or JOIN?

    - by Dave Jarvis
    Problem There are data gaps that need to be filled. Would like to avoid UNION or PARTITION BY if possible. Query Statement The select statement reads as follows: SELECT count( r.incident_id ) AS incident_tally, r.severity_cd, r.incident_typ_cd FROM report_vw r GROUP BY r.severity_cd, r.incident_typ_cd ORDER BY r.severity_cd, r.incident_typ_cd Data Sources The severity codes and incident type codes are from: severity_vw incident_type_vw The columns are: incident_tally severity_cd incident_typ_cd Actual Result Data 36 0 ENVIRONMENT 1 1 DISASTER 27 1 ENVIRONMENT 4 2 SAFETY 1 3 SAFETY Required Result Data 36 0 ENVIRONMENT 0 0 DISASTER 0 0 SAFETY 27 1 ENVIRONMENT 0 1 DISASTER 0 1 SAFETY 0 2 ENVIRONMENT 0 2 DISASTER 4 2 SAFETY 0 3 ENVIRONMENT 0 3 DISASTER 1 3 SAFETY Question How would you use UNION, PARTITION BY, or LEFT JOIN to fill in the zero counts?

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  • Concurrent Programming:Should I write a sequential program first, then add thread safety?

    - by evthim
    I'm working on a project where we have to create a number of threads(actual number will be inputted in by testers (TA's)). I'm having trouble not only with the programming but also with the design, I can't wrap my head around all of the threads that will be invoked and where I might cause errors. The project is due soon so I don't want to waste time on this if it'll actually set me back, but I was wondering if I should write the program like only one thread will be running and everything should be sequential and then later go back and try to add the thread safety parts of the code? Would that take twice the original amount of time? Project Description: Note:I'm going to be as vague as possible so I don't violate any honor codes, sorry :( your program should accept n number of objectA threads, m number of objectB threads, and r number of objectC objectB threads interact with code in objectA. objectA threads interact with code in objectB and objectC objectB and objectC don't directly interact, but do so indirectly through objectA -ex: objectB needs something from objectA. objectA gets the result for that something by calling objectC my confusion stems mostly from the fact that all of this interactions will be done by m+n threads and there are various restrictions throughout the descriptions, like objectB can request something from objectA, and objectA has to wait for objectC to finish that something before returning it to objectB. Also each objectA thread can only work on one instruction from objectB at a time, etc. etc. I just want to know if I write the code so that there is only 1 objectA, 1 objectB and 1 object C, can I go back and easily modify it so that those 1's can be changed to m, n and r? Sorry again, if my description is a little bit confusing.

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  • Fill data gaps without UNION

    - by Dave Jarvis
    Problem There are data gaps that need to be filled, possibly using PARTITION BY. Query Statement The select statement reads as follows: SELECT count( r.incident_id ) AS incident_tally, r.severity_cd, r.incident_typ_cd FROM report_vw r GROUP BY r.severity_cd, r.incident_typ_cd ORDER BY r.severity_cd, r.incident_typ_cd Code Tables The severity codes and incident type codes are from: severity_vw incident_type_vw Actual Result Data 36 0 ENVIRONMENT 1 1 DISASTER 27 1 ENVIRONMENT 4 2 SAFETY 1 3 SAFETY Required Result Data 36 0 ENVIRONMENT 0 0 DISASTER 0 0 SAFETY 27 1 ENVIRONMENT 0 1 DISASTER 0 1 SAFETY 0 2 ENVIRONMENT 0 2 DISASTER 4 2 SAFETY 0 3 ENVIRONMENT 0 3 DISASTER 1 3 SAFETY Any ideas how to use PARTITION BY (or JOINs) to fill in the zero counts?

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  • Safety concerns on allowing connections to MySQL with no password on localhost?

    - by ÉricO
    In the case of a Linux system, is there any security concern to let MySQL users with standard privileges (that is, not the root users) connect to the database with no password from localhost? I think that enforcing a password even for localhost can add a layer of protection, since, with no password the database access would be compromised if the SSH access is itself compromised. Considering that, would it be less safe to allow no password connection to MySQL than having the same password for SSH and for MySQL? I don't know if that is to be taken into account, but we also use phpMyAdmin to let users administrate their own database. I am asking because I kinda dislike having to put our database passwords unencrypted in the source or configuration files of our applications, where they can easily be leaked unintentionally. Since our servers are configured to run our applications as the Linux user the application belongs to, I was considering allowing no password from localhost as a simple solution. So, would that be a very bad idea or not?

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  • How to address thread-safety of service data used for maintaining static local variables in C++?

    - by sharptooth
    Consider the following scenario. We have a C++ function with a static local variable: void function() { static int variable = obtain(); //blahblablah } the function needs to be called from multiple threads concurrently, so we add a critical section to avoid concurrent access to the static local: void functionThreadSafe() { CriticalSectionLockClass lock( criticalSection ); static int variable = obtain(); //blahblablah } but will this be enough? I mean there's some magic that makes the variable being initialized no more than once. So there's some service data maintained by the runtime that indicates whether each static local has already been initialized. Will the critical section in the above code protect that service data as well? Is any extra protection required for this scenario?

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  • How long will a "safely stored" Solid-State-Drive (SSD) keep its data? (e.g. bank safety-deposit box)

    - by user31575
    Here's my usecase: once-and-only-once copy off photos/videos to an internal SATA Solid State Drive (SSD) put this drive in a well-ventilated, air-conditioned bank "safety deposit box" for safe keeping The question: How long can I safely store a solid-state-drive in such an environment? i.e. 0% bitrot, 100% success when "plugged in" Are some SSD drives more reliable than other for this usecase? (e.g. smaller size vs larger size, SLC vs MLC, different brands, etc) More fodder: I have read that solid state memory cards (e..g compactflash, or sd cards) have much longer durability than other media (DVD's, CD's, hard drives) for this usecase (guaranteed against bitrot/other dysfunction on the order of ~ a decades vs a year ). I don't know if this applies to "SSD hard drives". Copying to one 500Gb ssd vs 8 64gb flash drives is easier SSD SATA hard drives have no moving parts, but they have more "visible electronics" than a compact flash card. I don't know if this "visible electronics" can fail, i.e. in contr I know many will point to carbonite, other cloud backup stuff, but I like the simplicity of having physical copies and wanted to understand the risks/implications thanks,

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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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  • Subterranean IL: Generics and array covariance

    - by Simon Cooper
    Arrays in .NET are curious beasts. They are the only built-in collection types in the CLR, and SZ-arrays (single dimension, zero-indexed) have their own commands and IL syntax. One of their stranger properties is they have a kind of built-in covariance long before generic variance was added in .NET 4. However, this causes a subtle but important problem with generics. First of all, we need to briefly recap on array covariance. SZ-array covariance To demonstrate, I'll tweak the classes I introduced in my previous posts: public class IncrementableClass { public int Value; public virtual void Increment(int incrementBy) { Value += incrementBy; } } public class IncrementableClassx2 : IncrementableClass { public override void Increment(int incrementBy) { base.Increment(incrementBy); base.Increment(incrementBy); } } In the CLR, SZ-arrays of reference types are implicitly convertible to arrays of the element's supertypes, all the way up to object (note that this does not apply to value types). That is, an instance of IncrementableClassx2[] can be used wherever a IncrementableClass[] or object[] is required. When an SZ-array could be used in this fashion, a run-time type check is performed when you try to insert an object into the array to make sure you're not trying to insert an instance of IncrementableClass into an IncrementableClassx2[]. This check means that the following code will compile fine but will fail at run-time: IncrementableClass[] array = new IncrementableClassx2[1]; array[0] = new IncrementableClass(); // throws ArrayTypeMismatchException These checks are enforced by the various stelem* and ldelem* il instructions in such a way as to ensure you can't insert a IncrementableClass into a IncrementableClassx2[]. For the rest of this post, however, I'm going to concentrate on the ldelema instruction. ldelema This instruction pops the array index (int32) and array reference (O) off the stack, and pushes a pointer (&) to the corresponding array element. However, unlike the ldelem instruction, the instruction's type argument must match the run-time array type exactly. This is because, once you've got a managed pointer, you can use that pointer to both load and store values in that array element using the ldind* and stind* (load/store indirect) instructions. As the same pointer can be used for both input and output to the array, the type argument to ldelema must be invariant. At the time, this was a perfectly reasonable restriction, and maintained array type-safety within managed code. However, along came generics, and with it the constrained callvirt instruction. So, what happens when we combine array covariance and constrained callvirt? .method public static void CallIncrementArrayValue() { // IncrementableClassx2[] arr = new IncrementableClassx2[1] ldc.i4.1 newarr IncrementableClassx2 // arr[0] = new IncrementableClassx2(); dup newobj instance void IncrementableClassx2::.ctor() ldc.i4.0 stelem.ref // IncrementArrayValue<IncrementableClass>(arr, 0) // here, we're treating an IncrementableClassx2[] as IncrementableClass[] dup ldc.i4.0 call void IncrementArrayValue<class IncrementableClass>(!!0[],int32) // ... ret } .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } And the result: Unhandled Exception: System.ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array. at IncrementArrayValue[T](T[] arr, Int32 index) at CallIncrementArrayValue() Hmm. We're instantiating the generic method as IncrementArrayValue<IncrementableClass>, but passing in an IncrementableClassx2[], hence the ldelema instruction is failing as it's expecting an IncrementableClass[]. On features and feature conflicts What we've got here is a conflict between existing behaviour (ldelema ensuring type safety on covariant arrays) and new behaviour (managed pointers to object references used for every constrained callvirt on generic type instances). And, although this is an edge case, there is no general workaround. The generic method could be hidden behind several layers of assemblies, wrappers and interfaces that make it a requirement to use array covariance when calling the generic method. Furthermore, this will only fail at runtime, whereas compile-time safety is what generics were designed for! The solution is the readonly. prefix instruction. This modifies the ldelema instruction to ignore the exact type check for arrays of reference types, and so it lets us take the address of array elements using a covariant type to the actual run-time type of the array: .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 readonly. ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } But what about type safety? In return for ignoring the type check, the resulting controlled mutability pointer can only be used in the following situations: As the object parameter to ldfld, ldflda, stfld, call and constrained callvirt instructions As the pointer parameter to ldobj or ldind* As the source parameter to cpobj In other words, the only operations allowed are those that read from the pointer; stind* and similar that alter the pointer itself are banned. This ensures that the array element we're pointing to won't be changed to anything untoward, and so type safety within the array is maintained. This is a typical example of the maxim that whenever you add a feature to a program, you have to consider how that feature interacts with every single one of the existing features. Although an edge case, the readonly. prefix instruction ensures that generics and array covariance work together and that compile-time type safety is maintained. Tune in next time for a look at the .ctor generic type constraint, and what it means.

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