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• Java memory mapped files and swap

  - by MarkS

  I'm looking at some memory mapped files in Java. Let's say I have a heap size set to 2gb, and I memory map a file that is 50gb - far more than the physical memory on the machine. The OS will cache parts of that 50gb file in the os file cache, the java process will have 2gb of heap space. What I'm curious about is how does the OS decide how much of the 50gb file to cache? For instance, if I have another java process, also with a 2gb heap size, will that 2gb be swapped out to allow the os to cache parts of the memory mapped file? Will parts of the heap space of the first process be swapped out to allow the OS to cache? Is there any way to tell the OS not to swap heap space for OS caching? If the OS doesn't swap out main processes, how does it determine how big its file cache should be?

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• Get enum by it's inner field

  - by zeroed

  Hi! Have enum with inner fields, kind of map. Now I need to get enum by it's inner field. Wrote this: package test; /** * Test enum to test enum =) */ public enum TestEnum { ONE(1), TWO(2), THREE(3); private int number; TestEnum(int number) { this.number = number; } public TestEnum findByKey(int i) { TestEnum[] testEnums = TestEnum.values(); for (TestEnum testEnum : testEnums) { if (testEnum.number == i) { return testEnum; } } return null; } } But it's not very efficient to look up through all enums each time I need to find appropriate instance. Is there any other way to do the same?

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• How do I find the top N batters per year?

  - by Drew Stephens

  I'm playing around with the Lahman Baseball Database in a MySQL instance. I want to find the players who topped home runs (HR) for each year. The Batting table has the following (relevant parts) of its schema: +-----------+----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------+----------------------+------+-----+---------+-------+ | playerID | varchar(9) | NO | PRI | | | | yearID | smallint(4) unsigned | NO | PRI | 0 | | | HR | smallint(3) unsigned | YES | | NULL | | +-----------+----------------------+------+-----+---------+-------+ For each year, every player has an entry (between hundreds and 12k per year, going back to 1871). Getting the top N hitters for a single year is easy: SELECT playerID,yearID,HR FROM Batting WHERE yearID=2009 ORDER BY HR DESC LIMIT 3; +-----------+--------+------+ | playerID | yearID | HR | +-----------+--------+------+ | pujolal01 | 2009 | 47 | | fieldpr01 | 2009 | 46 | | howarry01 | 2009 | 45 | +-----------+--------+------+ But I'm interested in finding the top 3 from every year. I've found solutions like this, describing how to select the top from a category and I've tried to apply it to my problem, only to end up with a query that never returns: SELECT b.yearID, b.playerID, b.HR FROM Batting AS b LEFT JOIN Batting b2 ON (b.yearID=b2.yearID AND b.HR <= b2.HR) GROUP BY b.yearID HAVING COUNT(*) <= 3; Where have I gone wrong?

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• [C++] instantiating bitset using hex character.

  - by bndz

  Hey, I'm trying to figure out how to instantiate a 4 bit bitset based on a hex character. For instance, If I have a character with value 'F', I want to create a bitset of size 4 initialized to 1111 or if it is A, i want to initialize it to 1010. I could use a bunch of if statements like so: fn(char c) { bitset<4 temp; if(c == 'F') temp.set(); //... if(c == '9') { temp.set(1); temp.set(3); } //... } This isn't efficient, is there a way of easily converting the string to a decimal integer and constructing the bitset using the last 4 bits of the int? Thanks for any help.

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• validates_uniqueness_of...limiting scope - How do I restrict someone from creating a certain number

  - by bgadoci

  I have the following code: class Like < ActiveRecord::Base belongs_to :site validates_uniqueness_of :ip_address, :scope => [:site_id] end Which limits a person from "liking" a site more than one time based on a remote ip request. Essentially when someone "likes" a site, a record is created in the Likes table and I use a hidden field to request and pass their ip address to the :ip_address column in the like table. With the above code I am limiting the user to one "like" per their ip address. I would like to limit this to a certain number for instance 10. My initial thought was do something like this: validates_uniqueness_of :ip_address, :scope => [:site_id, :limit => 10] But that doesn't seem to work. Is there a simple syntax here that will allow me to do such a thing?

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• Populate properties decorated with an attribute

  - by PUT

  Are there any frameworks that assist me with this: (thinking that perhaps StructureMap can help me) Whenever I create a new instance of "MyClass" or any other class that inherits from IMyInterface I want all properties decorated with [MyPropertyAttribute] to be populated with values from a database or some other data storage using the property Name in the attribute. public class MyClass : IMyInterface { [MyPropertyAttribute("foo")] public string Foo { get; set; } } [AttributeUsage(AttributeTargets.Property)] public sealed class MyPropertyAttribute : System.Attribute { public string Name { get; private set; } public MyPropertyAttribute(string name) { Name = name; } }

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• How can I change or remove HttpRequest input arguments in a HttpModule

  - by Eric Gunn

  Is it possible to change or remove http request form inputs in an httpmodule? My goal is to create a security IHttpmodule that will check the request for reasonable values, such as limits on acceptable input and query parameter length, or use the AntiXSS Sanitizer to remove threats, log potential hack attempts, etc. before a request is passed on to a processor. Because this is a cross cutting concern I'd prefer to find a solution that applies to all requests and affects all ways request values could be accessed, Reqest.Form, Action(model), Action(FormCollection), HttpContext.Current.Request.Form, etc. I'm using MVC and have considered creating custom model binders to clean the data before creating the model instance. But that would be application specific, require remembering to register every model binder and only apply to Action(model).

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• Is str.replace(..).replace(..) ad nauseam a standard idiom in Python?

  - by meeselet

  For instance, say I wanted a function to escape a string for use in HTML (as in Django's escape filter): def escape(string): """ Returns the given string with ampersands, quotes and angle brackets encoded. """ return string.replace('&', '&amp;').replace('<', '&lt;').replace('>', '&gt;').replace("'", '&#39;').replace('"', '&quot;') This works, but it gets ugly quickly and appears to have poor algorithmic performance (in this example, the string is repeatedly traversed 5 times). What would be better is something like this: def escape(string): """ Returns the given string with ampersands, quotes and angle brackets encoded. """ # Note that ampersands must be escaped first; the rest can be escaped in # any order. return replace_multi(string.replace('&', '&amp;'), {'<': '&lt;', '>': '&gt;', "'": '&#39;', '"': '&quot;'}) Does such a function exist, or is the standard Python idiom to use what I wrote before?

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• Why state cannot be part of Presenter in MVP?

  - by rFactor

  I read http://www.codeproject.com/KB/architecture/MVC_MVP_MVVM_design.aspx and it said: As powerful as they are, both MVC and MVP have their problems. One of them is persistence of the View’s state. For instance, if the Model, being a domain object, does not know anything about the UI, and the View does not implement any business logic, then where would we store the state of the View’s elements such as selected items? Fowler comes up with a solution in the form of a Presentation Model pattern. I wonder why Presenter can't hold View state? It already holds all View logic. As far as I understand, in MVC and MVP the state is kept in View. In PM and MVVM the state is kept in the Presentation Model. Why can't Presenter follow PM in this particular case and contain the state of the view? Here is another article which says Presenter does not hold View state, instead the view does: http://www.codeproject.com/KB/aspnet/ArchitectureComparison.aspx

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• Class variable defined at @implementation rather than @interface?

  - by bitcruncher

  Hello. I'm new to Objective-C, but I am curious about something that I haven't really seen addressed anywhere else. Could anyone tell me what is the difference between a private variable that is declared at the @interface block versus a variable that is declared within the @implementation block outside of the class methods, i.e: @interface Someclass : NSObject { NSString *forExample; } @end vs. @implementation Someclass NSString *anotherExample; -(void)methodsAndSuch {} @end It seems both variables ( forExample, anotherExample ) are equally accessible throughout the class and I can't really find a difference in their behaviour. Is the second form also called an instance variable?

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• code throws std::bad_alloc, not enough memory or can it be a bug?

  - by Andreas

  I am parsing using a pretty large grammar (1.1 GB, it's data-oriented parsing). The parser I use (bitpar) is said to be optimized for highly ambiguous grammars. I'm getting this error: 1terminate called after throwing an instance of 'std::bad_alloc' what(): St9bad_alloc dotest.sh: line 11: 16686 Aborted bitpar -p -b 1 -s top -u unknownwordsm -w pos.dfsa /tmp/gsyntax.pcfg /tmp/gsyntax.lex arbobanko.test arbobanko.results Is there hope? Does it mean that it has ran out of memory? It uses about 15 GB before it crashes. The machine I'm using has 32 GB of RAM, plus swap as well. It crashes before outputting a single parse tree. The parser is an efficient CYK chart parser using bit vector representations; I presume it is already near the limit of memory efficiency. If it really requires too much memory I could sample from the grammar rules, but this will decrease parse accuracy of course.

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• What are some programming questions (or mistakes) you get wrong only as you get better?

  - by BlueRaja

  In programming, as many professions, there are mistakes you'll make now that you may not have made as a beginner. For instance, consider pointers: In C++, is there any difference between arrays and pointers? The beginner will say yes, they are two completely different concepts, and treat them as such. The intermediate programmer (having learned that arrays are pointers internally) will tell you no, they are the same thing, and may miss some crucial bugs by interchanging them all willy-nilly. The expert, however, will again say they are different things (ex. see here or here). What other questions/mistakes are like this?

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• Expression.Call() to String.Equals() throws error

  - by Sam

  The following code: var constant = Expression.Constant("find me", typeof(string)); // memberExpression evaluates to a string var predicate = Expression.Call(memberExpression, "Equals", null, constant); is throwing the error More than one method 'Equals' on type 'System.String' is compatible with the supplied arguments. I'm guessing that's because there's Equals(Object) and Equals(String) - is there any way for me to specify which method I mean to use via the overload of Expression.Call() that takes an instance method name as a string? Or do I have to make a special case for calls to Equals() to take a MethodInfo instead?

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• CPU/GPU Monitering. (Tempature, current speed, etc) in C#

  - by Tommy

  Im looking for a way to moniter system statistics, here are my main points of interest: CPU Tempature CPU speed, (Cycles per second) CPU Load (Idle percent) GPU Tempature Some other points of interest: Memory useage Network Load (Traffic Up/Down) My ultimate goal is to write an application that can be used for easily running in the backround, and allow setting many events fr certain actions, for instance When processer temp gets to 56C -> Do _Blank_ etc. So this leaves me two main points. Is there a framework already out there for this sort of thing? If No to #1, How can i go about doing this?

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• How to share a variable between two classes?

  - by Altefquatre

  How would you share the same object between two other objects? For instance, I'd like something in that flavor: class A { private string foo_; // It could be any other class/struct too (Vector3, Matrix...) public A (string shared) { this.foo_ = shared; } public void Bar() { this.foo_ = "changed"; } } ... // inside main string str = "test"; A a = new A(str); Console.WriteLine(str); // "test" a.Bar(); Console.WriteLine(str); // I get "test" instead of "changed"... :( I read there is some ref/out stuff, but I couldn't get what I'm asking here. I could only apply some changes in the methods scope where I was using ref/out arguments... I also read we could use pointers, but is there no other way to do it?

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• Returning values from Swing using invokeAndWait

  - by Joonas Pulakka

  I've been using the following approach to create components and return values from Swing to/from outside the EDT. For instance, the following method could be an extension to JFrame, to create a JPanel and add it to the parent JFrame: public JPanel threadSafeAddPanel() { final JPanel[] jPanel = new JPanel[1]; try { EventQueue.invokeAndWait(new Runnable() { public void run() { jPanel[0] = new JPanel(); add(jPanel[0]); } }); } catch (InterruptedException ex) { } catch (InvocationTargetException ex) { } return jPanel[0]; } The local 1-length array is used to transfer the "result" from inside the Runnable, which is invoked in the EDT. Well, it looks "a bit" hacky, and so my questions: Does this make sense? Is anybody else doing something like this? Is the 1-length array a good way of transferring the result? Is there an easier way to do this?

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• Single database with multiple instances of Django

  - by jwesonga

  I have a Django project where the company will have a main site like www.ourcompany.org and a bunch of sub-domains like project.ourcompany.org. Content appearing in the sub-domains like case studies should also appear in the main site. I've decided to use multiple instances of Django BUT one database for each sub-domain so that I can have some flexibility and take advantage of the Sites framework. What I'm not sure of is how to access the models across the multiple instances. If I have a model: class CaseStudy(models.Model): title=models.CharField(max_length=100) site=models.ManyToMany(Site) Do I need to create this model in every instance so that I can have access to the object?

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• Singleton array deallocated? EXC_BAD_ACCESS

  - by lclaud

  Ok, so I have this singleton object and in it is an array that needs to be shown in a tableview. The thing is that it deallocates and after the first show, i get EXC_BAD_ACCESS in cellForRowAtIndexPath - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return [[dataBase shareddataBase].dateActive count]; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { UITableViewCell *cell=[tableView dequeueReusableCellWithIdentifier:@"celula"]; int i; i=indexPath.row; if (cell==nil) { cell=[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:@"celula"]; } count sent to dealocated instance of CFArray .. in cellForRowAtIndexPath.. WHAT is deallocating it? why? it's declarea as an NSMutableArray and has a (nonatomic,retain) property defined .. if ((i<[[dataBase shareddataBase].dateActive count])&&(i>=0)) { NSDictionary *d=[[dataBase shareddataBase].dateActive objectAtIndex:i]; cell.textLabel.text=[d objectForKey:@"detaliu"]; } return cell; }

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• Can anyone tell me what's wrong in this part of code

  - by Mobin

  string name = ((DateTimePicker)sender).Name.ToString(); name = name.Substring(0, name.Length - 1); name = name + "4"; TimeSpan duration = new TimeSpan(); duration = ((DateTimePicker)sender).Value - ((DateTimePicker)panel2.Controls[name]).Value; name = name.Substring(0, name.Length - 1); name = name + "6"; ((MaskedTextBox)panel2.Controls[name]).Text = duration.ToString(); On execution it gives me Object reference not set to instance of an object similar functionality is used on other places but I can't find out what I have to reinitialize here :$ The casting for datetimepicker is fine I have to get a name for the datetiempicker to identify the row it's on in my form and the picker before that to calculate their differences and then print that difference in a maskedtext box from the control whose name I make using names of two datetimepickers but when I access controls in the error line I get this message.

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• drupal body class

  - by anru

  drupal version is 6. just want to know where are those $body_classes comes form. I knew in template_preprocess_page , there is a variable called 'body_classes'. but my problem is, not all body_classes are come from preprocess page. for instance: I have a term named 'activities and attractions', then in my page.tpl.php, there is a class 'page-activities and attractions' in my tag. looks like taxonomy module generates a body_class, but i could find it after search seource code of taxonomy module.

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• A controller method that calls a different method on the same controller

  - by justSteve

  I have a controller method: public ActionResult Details(int id) { Order order = OrderFacade.Instance.Load(id); return View(order); } that is used for 95% of possible invocations. For the other 5% i need to manipulate the value of id before passing to the facade. I'd like to create a separate method within this same controller that executes that manipulation and then calls this (Details) method. What would the signature of that method look like? What is the syntax to call the main Details method? public ??? ManipulatorMethod(int id) { [stuff that manipulates id] [syntax to call Details(manipulatedID)] } mny thx

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• New to C/C++ Using Android NDK to port Legacy code, getting compile errors

  - by Donal Rafferty

  I have been trying to take some old Symbian C++ code over to Android today using the NDK. I have little to no C or C++ knowledge so its been a chore, however has to be done. My main issue is that I'm having trouble porting what I believe is Symbian specifi code to work using the small C/C++ subset that is available with the Android NDK. Here is a picture of the compilation errors I'm getting using cygwin I was wondering if anyone could point me in the right direction on how to deal with these errors? For instance is TBool/Int/TUint/RPointerArray/RSocket a Symbian primitive and thats why it wont compile or is it something else? Also what is ISO C++? Any tutorials, guides or tips and help would be greatly appreciated.

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• Is an ORM redundant with a NoSQL API?

  - by Earlz

  Hello, with MongoDB (and I assume other NoSQL database APIs worth their salt) the ways of querying the database are much more simplistic than SQL. There is no tedious SQL queries to generate and such. For instance take this from mongodb-csharp: using MongoDB.Driver; Mongo db = new Mongo(); db.Connect(); //Connect to localhost on the default port. Document query = new Document(); query["field1"] = 10; Document result = db["tests"]["reads"].FindOne(query); db.Disconnect(); How could an ORM even simplify that? Is an ORM or other "database abstraction device" required on top of a decent NoSQL API?

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• Clean bindings with structs

  - by andyvn22

  I have a model class for which it makes quite a lot of sense to have NSSize and NSPoint instance variables. This is lovely. I'm trying to create an editing interface for this object. I'd like to bind to size.width and whatnot. This, of course, doesn't work. What's the cleanest, most Cocoa-y solution to this problem? Of course I could write separate accessors for the individual members of every struct I use, but it seems like there should be a better solution.

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• vector<string> or vector<char *>?

  - by Aaron

  Question: What is the difference between: vector<string> and vector<char *>? How would I pass a value of data type: string to a function, that specifically accepts: const char *? For instance: vector<string> args(argv, argv + argc); vector<string>::iterator i; void foo (const char *); //*i I understand using vector<char *>: I'll have to copy the data, as well as the pointer Edit: Thanks for input!

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