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• "Inlining" (kind of) functions at runtime in C

  - by fortran

  Hi, I was thinking about a typical problem that is very JIT-able, but hard to approach with raw C. The scenario is setting up a series of function pointers that are going to be "composed" (as in maths function composition) once at runtime and then called lots and lots of times. Doing it the obvious way involves many virtual calls, that are expensive, and if there are enough nested functions to fill the CPU branch prediction table completely, then the performance with drop considerably. In a language like Lisp, I could probably process the code and substitute the "virtual" call by the actual contents of the functions and then call compile to have an optimized version, but that seems very hacky and error prone to do in C, and using C is a requirement for this problem ;-) So, do you know if there's a standard, portable and safe way to achieve this in C? Cheers

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• A strange error in java generic.

  - by ???

  This is ok: Class<? extends String> stringClass = "a".getClass(); But this gets error: <T> void f(T obj) { Class<? extends T> objClass = obj.getClass(); } I know I can cast it like: <T> void f(T obj) { @SuppressWarnings("unchecked") Class<? extends T> objClass = (Class<? extends T>) obj.getClass(); } But why the previous error? Will the next release of Java 7 will support such usage?

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• Does SetThreadPriority cause thread reschedulling?

  - by Suma

  Consider following situation, assuming single CPU system: thread A is running with a priority THREAD_PRIORITY_NORMAL, signals event E thread B with a priority THREAD_PRIORITY_LOWEST is waiting for an event E (Note: at this point the thread is not scheduled because it is runnable, but A is higher priority and runnable as well) thread A calls SetThreadPriority(B, THREAD_PRIORITY_ABOVE_NORMAL) Is thread B re-scheduled immediately to run, or is thread A allowed to continue until current time-slice is over, and B is scheduled only once a new time-slice has begun? I would be interested to know the answer for WinXP, Vista and Win7, if possible. Note: the scenario above is simplified from my real world code, where multiple threads are running on multiple cores, but the main object of the question stays: does SetThreadPriority cause thread scheduling to happen?

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• How to keep a floating div centered on window resize (jQuery/CSS)

  - by Jimbo

  Is there a way (without binding to the window.resize event) to force a floating DIV to re-center itself when the browser window is resized? To help explain, I imagine the pseudocode would look something like: div.left = 50% - (div.width / 2) div.top = 50% - (div.height / 2) UPDATE My query having been answered below, I wanted to post the final outcome of my quest - a jQuery extension method allowing you to center any block element - hope it helps someone else too. jQuery.fn.center = function() { var container = $(window); var top = -this.height() / 2; var left = -this.width() / 2; return this.css('position', 'absolute').css({ 'margin-left': left + 'px', 'margin-top': top + 'px', 'left': '50%', 'top': '50%' }); } Usage: $('#mydiv').center();

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• Should I put a try-finally block after every Object.Create?

  - by max

  I have a general question about best practice in OO Delphi. Currently, I put try-finally blocks anywhere I create an object to free that object after usage (to avoid memory leaks). E.g.: aObject := TObject.Create; try aOBject.AProcedure(); ... finally aObject.Free; end; instead of: aObject := TObject.Create; aObject.AProcedure(); .. aObject.Free; Do you think it is good practice, or too much overhead? And what about the performance?

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• strategy to allocate/free lots of small objects

  - by aaa

  hello I am toying with certain caching algorithm, which is challenging somewhat. Basically, it needs to allocate lots of small objects (double arrays, < 256 elements), with objects accessible through mapped value, map[key] = array. time to initialized array may be quite large, generally more than 10 thousand cpu cycles. By lots I mean around gigabyte in total. objects may need to be popped/pushed as needed, generally in random places, one object at a time. lifetime of an object is generally long, minutes or more, however, object may be subject to allocation/deallocation several times during duration of program. What would be good strategy to avoid memory fragmentation, while still maintaining reasonable allocate deallocate speed? I am using C++, so I can use new and malloc. Thanks. I know there a similar questions on website, http://stackoverflow.com/questions/2156745/efficiently-allocating-many-short-lived-small-objects, are somewhat different, thread safety is not immediate issue for me.

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• CUDA Global Memory, Where is it?

  - by gamerx

  I understand that in CUDA's memory hierachy, we have things like shared memory, texture memory, constant memory, registers and of course the global memory which we allocate using cudaMalloc(). I've been searching through whatever documentations I can find but I have yet to come across any that explicitly explains what is the global memory. I believe that the global memory allocated is on the GDDR of graphics card itself and not the RAM that is shared with the CPU since one of the documentations did state that the pointer cannot be dereferenced by the host side. Am I right?

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• this.Dispose() Don't release memory used by Form after Closing it .

  - by Ehab Sutan

  Hello, in C# Application. I've a windows form application in which clicking certain button make object from a 2nd Form. On closing this 2nd From by user Memory used by this form not released (from Task Manager). I Tried using this.dispose() on exit button ,tried this.close() , tried form2 =null in the main code ,and tried clearing all controls from this form by code before Disposing and every time the clicks the button memory usage by the application increases more and memory used by previous instance not released. What shall i use to solve this problem ?

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• How to find out how libraries work together?

  - by Eric

  I'm tasked to replicate a few functionnalities from an existing application. This application rely on .NET managed assemblies accessible from C#. I can import those DLLs in my new C# project but there is no documentation on how to use them. Yes, this is labeled as an "SDK", but does not contain examples or documentation. Any pointers on how I should procceed? I thought about creating stubs assemblies and monitor their usage by the original application but this involves a lot of code, maybe a tool could do it for me?

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• Make object by it's name

  - by Ockonal

  Hello, is it possible to return exemplar of object using passed type name (string) in c++? I have some base abstract class Base and a few derivates. Example code: class Base { /* ... */ }; class Der1 : public Base { /* ... */ }; class Der2 : public Base { /* ... */ }; And I need function like: Base *objectByType(const std::string &name); Number of derivates classes are changeable and I don't want to make something like switching of name and returning by hands new object type. Is it possible in c++ to do that automatically anyway? p.s. usage should looks like: dynamic_cast<Der1>(objectByType("Der1")); I need pure c++ code (crossplatform). Using boost is permissible.

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• Java concurrency - Should block or yield?

  - by teto

  Hi, I have multiple threads each one with its own private concurrent queue and all they do is run an infinite loop retrieving messages from it. It could happen that one of the queues doesn't receive messages for a period of time (maybe a couple seconds), and also they could come in big bursts and fast processing is necessary. I would like to know what would be the most appropriate to do in the first case: use a blocking queue and block the thread until I have more input or do a Thread.yield()? I want to have as much CPU resources available as possible at a given time, as the number of concurrent threads may increase with time, but also I don't want the message processing to fall behind, as there is no guarantee of when the thread will be reescheduled for execution when doing a yield(). I know that hardware, operating system and other factors play an important role here, but setting that aside and looking at it from a Java (JVM?) point of view, what would be the most optimal?

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• When is a program limited by the memory bandwidth?

  - by hanno

  I want to know if a program that I am using and which requires a lot of memory is limited by the memory bandwidth. When do you expect this to happen? Did it ever happen to you in a real life scenario? I found several articles discussing this issue, including http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node12.html http://www.cs.virginia.edu/~mccalpin/papers/bandwidth/node13.html http://ispass.org/ucas5/session2_3_ibm.pdf The first link is a bit old, but suggests that you need to perform less than about 1-40 floating point operations per floating point variable in order to see this effect (correct me if I'm wrong). How can I measure the memory bandwidth that a given program is using and how do I measure the (peak) bandwidth that my system can offer? I don't want to discuss any complicated cache issues here. I'm only interested in the communication between the CPU and the memory.

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• How can I optimize this code?

  - by loop0

  Hi, I'm developing a logger daemon to squid to grab the logs on a mongodb database. But I'm experiencing too much cpu utilization. How can I optimize this code? from sys import stdin from pymongo import Connection connection = Connection() db = connection.squid logs = db.logs buffer = [] a = 'timestamp' b = 'resp_time' c = 'src_ip' d = 'cache_status' e = 'reply_size' f = 'req_method' g = 'req_url' h = 'username' i = 'dst_ip' j = 'mime_type' L = 'L' while True: l = stdin.readline() if l[0] == L: l = l[1:].split() buffer.append({ a: float(l[0]), b: int(l[1]), c: l[2], d: l[3], e: int(l[4]), f: l[5], g: l[6], h: l[7], i: l[8], j: l[9] } ) if len(buffer) == 1000: logs.insert(buffer) buffer = [] if not l: break connection.disconnect()

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• why does InnoDB keep on growing without for every update?

  - by Akash Kava

  I have a table which consists of heavy blobs, and I wanted to conduct some tests on it. I know deleted space is not reclaimed by innodb, so I decided to reuse existing records by updating its own values instead of createing new records. But I noticed, whether I delete and insert a new entry, or I do UPDATE on existing ROW, InnoDB keeps on growing. Assuming I have 100 Rows, each Storing 500KB of information, My InnoDB size is 10MB, now when I call UPDATE on all rows (no insert/ no delete), the innodb grows by ~8MB for every run I do. All I am doing is I am storing exactly 500KB of data in each row, with little modification, and size of blob is fixed. What can I do to prevent this? I know about optimize table, but I cant do it because on regular usage, the table is going to be 60-100GB big, and running optimize will just stall entire server.

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• Persistent UDP sessions on Android

  - by Wedgeski

  I have a client-server app which requires me to maintain a persistent session over UDP. The goal is to maintain a path from the server to the mobile Android device no matter what route it has to the internet (WiFi or mobile network). This is achieved using a proprietary, well-tested session-management protocol over UDP. I need the phone to be able to maintain, say, a five-minute keep-alive with the server at all times. Ideally I would like to do this without maintaining any wake-locks on the device. I don't want the screen to light up every time I send a UDP to the server, for example, and I don't want to have a damaging effect on battery usage. Has anyone addressed this problem?

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• How to select random image of specific size using Django / Python?

  - by Jonathan

  I've been using this little snippet to select random images. However I would like to change it to select only images of a certain size. I'm running into trouble checking against image size. If I use get_image_dimensions() I need to use a conditional statement, which then requires that I allow exceptions. So, I guess I need some pointers on just limiting by image dimensions. Thanks. import os import random import posixpath from django import template from django.conf import settings register = template.Library() def is_image_file(filename): """Does `filename` appear to be an image file?""" img_types = [".jpg", ".jpeg", ".png", ".gif"] ext = os.path.splitext(filename)[1] return ext in img_types @register.simple_tag def random_image(path): """ Select a random image file from the provided directory and return its href. `path` should be relative to MEDIA_ROOT. Usage: <img src='{% random_image "images/whatever/" %}'> """ fullpath = os.path.join(settings.MEDIA_ROOT, path) filenames = [f for f in os.listdir(fullpath) if is_image_file(f)] pick = random.choice(filenames) return posixpath.join(settings.MEDIA_URL, path, pick)

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• Mongodb, simple IN problem

  - by afvasd

  Hi everyone I am new to mongo, this is my db design: product := { name: str group: ref, comments: [ ref, ref, ref, ref ] } comments := { ... a bunch of comments stuff } tag := { _id: int, #Need this for online requests tag: str, products: [ {product: ref, score: float}, ... ], comments: [ {comment: ref, score: float}, ...], } So my usage pattern is: GIVEN a product, find comments that have certain tag and sort them accordingly. My current approach involves: Look for that tag object that has tag=myTag pull all the comments out, sorted look for that product where product.name=myProduct pull all the comments out (which are dbrefs by the way) loop through the result of 2, and checking if they are in 4, (this I can do a limit 10) etc. It's pretty inefficient. Any better methods?

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• iPhone real memory climbs when interacting with UI

  - by Scott Gress

  I've been using the Activity Monitor to check the memory usage of my iPhone apps. I've noticed that the Real Memory climbs whenever I interact with the UI in any way, even if there's no code being called. For example, I can create a brand new View-Based application and run it, and as I click or drag in the empty window the Real Memory increases even though the app isn't responding in any way. I get that the view controller is doing some stuff in the background to interpret my interactions, but it seems like the memory should go back down after a second or so. Instead, it keeps going up and up and up as long as I keep clicking or dragging. I can wait forever and it never decreases. This is a little disturbing. Am I missing something?

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• VS2008 is very slow on a specific large C++ solution

  - by VioletRose

  I have a solution with 21 C++ projects and 1 VB.NET project. The IDE responds very slowly when I simply move the carret in a file or try to open the menu. The process seems to take 50% of CPU for each movement. It only happens with this solution and only on my machine. The solution has total of 2380 source and header files, of which 1280 are header files. I tried to remove all connection to the source control (Perforce) but it didn't help. Also, I have Visual Assist installed but even after removing it (uninstall), the same behavior continued. Any idea?

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• Empty files generated from running `mysqldump` using PHP

  - by alex

  I keep getting empty files generated from running $command = 'mysqldump --opt -h localhost -u username -p \'password\' dbname > \'backup 2009-04-15 09-57-13.sql\''; command($command); Anyone know what might be causing this? My password has strange characters in it, but works fine with connecting to the db. I've ran exec($command, $return) and outputted the $return array and it is finding the command. I've also ran it with mysqldump > file.sql and the file contains Usage: mysqldump [OPTIONS] database [tables] OR mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...] OR mysqldump [OPTIONS] --all-databases [OPTIONS] For more options, use mysqldump --help So it would seem like the command is working.

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• How to determine bandwidth used by cron job?

  - by Lost_in_code

  I'm not a unix guy. CPanel does a good job of managing cronjobs and that is what I used to run dozens of cronjobs. All of them combined run more than 5000 times every day. Every cron makes a call to an external API. How can I check how much bandwidth are all the cron jobs eating? For my website I use awstats and that shows bandwidth usage et al. Another thing is that I dont want the admins to ban the cron jobs because they are using too much bandwidth (and CPU), more than what is allocated in my web hosting package.

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• Import external dll based on 64bit or 32bit OS

  - by Mike_G

  I have a dll that comes in both 32bit and 64bit version. My .NET WinForm is configured for "Any CPU" and my boss will not let us have separate installs for the different OS versions. So I am wondering: if I package both dlls in the install, then is there a way to have the WinForm determine if its 64bit/32bit and load the proper dll. I found this article for determining version. But i am not sure how to inject the proper way to define the DLLImport attribute on the methods i wish to use. Any ideas?

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• Problem in populating a dictionary object using Enumerable.Range() (C#3.0)

  - by Newbie

  If I do for (int i = 0; i < appSettings.Count; i++) { string key = appSettings.Keys[i]; euFileDictionary.Add(key, appSettings[i]); } It is working fine. When I am trying the same thing using Enumerable.Range(0, appSettings.Count).Select(i => { string Key = appSettings.Keys[i]; string Value = appSettings[i]; euFileDictionary.Add(Key, Value); }).ToDictionary<string,string>(); I am getting a compile time error The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly. Any idea? Using C#3.0 Thanks

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• How to get just free heap size (not together w stack/method mem) in Java?

  - by Pentium10

  I want to calculate the heap usage for my app. I would like to get a procent value of Heap size only. How do I get the value in code for the current running app? EDIT The upvoted answer is NOT complete/correct. The values returned by those methods include stack and method area too, and I need to monitor only heap size. With that code I got HeapError exception when I reached 43%, so I can't use those methods to monitor just heap.

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• If I had to create a server farm what should I do? (how others companies work?)

  - by Michel

  I have a business idea but this is not really my field so I'm trying to understand what I'm really dealing with. I have a general understanding of how a web farm works, I'm a web developer and I understand the technology behind it, but I'm curious to know specifically how a web farm is set up and which professionals are involved. Things to consider probably are the hardware, the power supply, the software managment, the cooling system and if possible the usage of green technology/power recycling. Basically, can you explain me how a web hosting company is structured and how it works? A big question, I know, but from what I already read here about the subject a lot of you know this stuff. Thanks for your time guys!

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