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  • Better algorithm for estimating download time

    - by Scott Smith
    We've all seen the download time running estimate that initially says something like "7 days", but keeps dropping wildly (e.g. "23 hours", "45 minutes", "1 min. 50 sec", etc) with each successive estimation as the chunks are downloaded. To avoid these initial (alarming) estimates, there are techniques one could try like suppressing display of the first n estimates, or waiting for the delta between estimates to drop below some threshold before you start displaying them, but these don't seem like a general, robust solution. There are corner cases involving too few samples, or samples that actually are wildly varying... I think I recall a general solution for this kind of thing in mathematics (statistics?) that reduced or eliminated these wild values. Does anyone know?

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  • How to sum up an array of integers in C#

    - by Filburt
    Is there a better shorter way than iterating over the array? int[] arr = new int[] { 1, 2, 3 }; int sum = 0; for (int i = 0; i < arr.Length; i++) { sum += arr[i]; } clarification: Better primary means cleaner code but hints on performance improvement are also welcome. (Like already mentioned: splitting large arrays). It's not like I was looking for killer performance improvement - I just wondered if this very kind of syntactic sugar wasn't already available: "There's String.Join - what the heck about int[]?".

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  • Comparison of collection datatypes in C#

    - by Joel in Gö
    Does anyone know of a good overview of the different C# collection types? I am looking for something showing which basic operations such as Add, Remove, RemoveLast etc. are supported, and giving the relative performance. It would be particularly interesting for the various generic classes - and even better if it showed eg. if there is a difference in performance between a List<T> where T is a class and one where T is a struct. A start would be a nice cheat-sheet for the abstract data structures, comparing Linked Lists, Hash Tables etc. etc. Thanks!

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  • New instruction sets in CPU

    - by Tomek Tarczynski
    Every new generation of CPU introduces some sets of new instruction, ie.: MMX,3DNOW,SSE and so on. I've got few general questions about them: 1) If some program uses for example SSE instruction can it be run on CPU that doesn't support SSE? 2) If yes , does it mean that those instuction will be changed to some greater number of simpler instuctions? 3) If not, does it mean that the real perfomance impact of such new instructions will be after few years when most CPU will support such technology (so there won't be any incompatibilities)? 4) When I compile a C++ program with optimizations does it mean that it'll use some of this new instructions? (I know that it depends on many factors, especcialy on the code, but I want some general answer) Or are they reserved mostly for programs written in asm?

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  • Inline function and calling cost in C

    - by Eonil
    I'm making a vector/matrix library. (GCC, ARM NEON, iPhone) typedef struct{ float v[4]; } Vector; typedef struct{ Vector v[4]; } Matrix; I passed struct data as pointer to avoid performance degrade from data copying when calling function. So I thought designed function like this: void makeTranslation(const Vector* factor, Matrix* restrict result); But, if function is inline, is there any reason to pass values as pointer for performance? Do those variables copied too? How about register and caches? inline Matrix makeTranslation(Vector factor) __attribute__ ((always_inline)); How do you think about calling costs of each cases?

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  • Do you know Best Practise and Design Patterns for Adobe Air/Flex Applications?

    - by Julian
    I'm going to write an application with the Air/Flex-Framework. I'm looking for Best Practise and general Design Patterns for designing software especially in Air/Flex. I have experience with this framework but never had the pleasure to write a piece of software from scratch. For instance: I stumbled across lots of software written in Air/Flex with nearly infinity global vars :-) Most of the software I saw was not object-oriented How can I pack the asynchronous method calls nicely? I'm familiar with general design patterns by gamma. I'm looking more for advise in designing good quality software with Adobe Air/Flex.

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  • Why do people still use C these days? [closed]

    - by Joshua
    C++ is clearly a far superior language than C, since it has many features that C lacks (although, C++'s object model isn't as ideal as say C#'s). With the coming off the new C++0x standard, why hasn't C been phased out to obscurity? C++ has been around for so long, since the '80s. The Linux kernel has already been ported to C++ with negligible performance differences. I believe, with no evidence, that larger program structures benefit in performance if written in C++ than in C, if only because of object interaction. Don't get me started on "objects-in-C!" libraries, which are all a terrible hack. (Not that C++'s object model is the most ideal, but it is almost up to snuff with C# using common ad-hoc techniques.)

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  • Haskell maps returning a monad

    - by sabauma
    The lookup function in Data.Map and Data.IntMap currently return values wrapped in Maybe with the type signature lookup :: Ord k => k -> Map k a -> Maybe a It used to have the more general type of lookup :: (Monad m, Ord k) => k -> Map k a -> m a I realize the former likely reduces the need of extra type specification, but the latter would make it much more general and allow lookup to be used in list comprehensions. Is there any way to mimic this behavior with the newer version, or would I have to use an older version of the library?

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  • Custom onsynctopreference for XUL textbox

    - by Alexey Romanov
    I wanted to enable custom shortcuts in my Firefox extension. The idea is that the user just focuses on a textbox, presses key combination, and it's shown in the textbox and saved to a preference. However, I couldn't get it to work. With this XUL <?xml version="1.0"?> <?xml-stylesheet href="chrome://global/skin/" type="text/css"?> <?xml-stylesheet href="chrome://mozapps/skin/pref/pref.css" type="text/css"?> <!DOCTYPE window SYSTEM "chrome://nextplease/locale/nextplease.dtd"> <prefwindow id="nextpleaseprefs" title="&options.title;" buttons="accept, cancel" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"> <prefpane id="nextplease.general" label="&options.general.title;" image="chrome://nextplease/skin/Sound Mixer.png"> <preferences> <preference id="nextkey" name="nextplease.nextkey" type="int"/> </preferences> <vbox flex="1"> <hbox align="center"> <label value="&options.general.nextKey;" /> <textbox id="nextkey" flex="1" editable="false" onkeyup="return nextplease.handleKeySelection(this, event);" preference-editable="true" preference="nextkey" onsynctopreference="alert('syncing'); return nextplease.syncKeySelector(this);"/> </hbox> </vbox> </prefpane> <script type="application/x-javascript" src="chrome://nextplease/content/nextpleaseCommon.js" /> <script type="application/x-javascript" src="chrome://nextplease/content/nextpleaseOptions.js" /> </prefwindow> the event in onkeyup works. But when I click the OK button, I don't see a "syncing" alert. Why isn't onsynctopreference working? Is it impossible to have custom onsynctopreference attribute for a textbox?

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  • Remove items from SWT tables

    - by Dima
    This is more of an answer I'd like to share for the problem I was chasing for some time in RCP application using large SWT tables. The problem is the performance of SWT Table.remove(int start, int end) method. It gives really bad performance - about 50msec per 100 items on my Windows XP. But the real show stopper was on Vista and Windows 7, where deleting 100 items would take up to 5 seconds! Looking into the source code of the Table shows that there are huge amount of windowing events flying around in this call.. That brings the windowing system to its knees. The solution was to hide the damn thing during this call: table.setVisible(false); table.remove(from, to); table.setVisible(true); That does wonders - deleting 500 items on both XP & Windows7 takes ~15msec, which is just an overhead for printing out time stamps I used. nice :)

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  • How to integrate access control with my ORM in a .net windows form application?

    - by Ying
    I am developing a general database query tools, a .Net 3.5 Windows Form application. In order to make the presentation layer is independent of the database layer. I use an ORM framework, XPO from DevExpress. But, I have no access control function built in. I surfed Internet and I found in WCF Data Services, there is an interesting concept, Interceptor, which is following AOP(Aspect Oriented Programming). I am wondering who has such an experience to build access control in ORM. My basic requirement is : It should be a general method and controlled by users in runtime. So any hard coding is not acceptable. It could be based on attribute, database table, or even an external assembly. I am willing to buy a ready solution. According to the idea of AOP, an access control function can be integrated with existing functions easily and nearly not knowingly to the previous developer;) Any suggestions are welcome.

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  • Is there a module that implements an efficient array type in Erlang?

    - by dsmith
    I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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  • Database indexes and their Big-O notation

    - by miket2e
    I'm trying to understand the performance of database indexes in terms of Big-O notation. Without knowing much about it, I would guess that: Querying on a primary key or unique index will give you a O(1) lookup time. Querying on a non-unique index will also give a O(1) time, albeit maybe the '1' is slower than for the unique index (?) Querying on a column without an index will give a O(N) lookup time (full table scan). Is this generally correct ? Will querying on a primary key ever give worse performance than O(1) ? My specific concern is for SQLite, but I'd be interested in knowing to what extent this varies between different databases too.

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  • Emails, a different 'reply to' address then sender address.

    - by dcrodjer
    I have a contact form on a website (a general form: name, email, subject, message) in which mails are sent using google apps smtp to the admins. Currently if an administrator wants to reply to the mail directly selecting the reply option, the person's reply's To field will be filled by the sender's address automatically. What I wan't to ask is, Is there any standardized way to pass on some additional info with the mail which would define any reply to the mail should go to this address instead of the sender's? It does seems that there is a little chance for this option as it may lead to some problems due to spammers (They may define a custom reply field in their mail and a general user might not look where they are replying). So as an alternative what I thought is to find a way to create a filter with sender's account which figures out the reply email address from the format and forwards the mail (Doesn't seems like a good solution and I have no idea how to achieve this). I have tagged django, though this is not directly related with this, as I will finally implement this through django.

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  • which is better, creating a materialized view or a new table?

    - by Carson
    I have some demanding mysql queries that are needed to grap same up-to-date datasets from 5-7 mysql tables. I am thinking of creating a table or materialized view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create materialized view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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  • Extract a sentence out of sentences separated by delimitors

    - by Laura
    Below is a sample line I have extracted from a website: below a satisfactory level; &quot;an off year for tennis&quot;; &quot;his performance was off&quot; The output displays as: below a satisfactory level; "an off year for tennis"; "his performance was off" I want to get only the first sentence "below a satisfactory level"; Here is the code I have tried after exploring many stackoverflow posts: $data=explode('; ',$str); echo $data[0]; But somehow it is not working. Thanks in advance.

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  • CLI design and implementation?

    - by Majid
    I am developing a time management tool for my personal use. I prefer using keyboard over mouse, and on the interface have a general purpose text box which will act like a command line. I have just started thinking about what commands I need, what to use for the command names, how to pass in switches and parameters, and so forth. I wonder if some of you have come across a good read along these lines; something that describes the choices you have for designing a cli, and how those affect the complexity of the interpreter, and extendability of the commands. It makes no difference if the descriptions are language-specific or in general terms. However, my implementation will be with javascript. Thank you.

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  • What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

    - by Robert S. Barnes
    Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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  • What tricks can be used to type and edit code faster?

    - by Thomas
    As Jeff Atwood noted, we are typists first, programmers second. Fast typing and editing may not be essential to be a good programmer, but it certainly helps. I noticed that I consciously and subconsciously use various tricks to get my intent across to the computer as fast as possible. What tricks can be used to type and edit code faster? I'm hoping to collect a nice list here that we can all learn from, so that we can be ever so slightly more productive. One trick per answer please! (This is not about typing speed in general. There are other questions about that. It's also not about general answers like "learn your editor's shortcut keys". Think of this topic as micro-optimizations for specific cases. See my own answers for examples of what I mean.)

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  • Combining FileStream and MemoryStream to avoid disk accesses/paging while receiving gigabytes of data?

    - by w128
    I'm receiving a file as a stream of byte[] data packets (total size isn't known in advance) that I need to store somewhere before processing it immediately after it's been received (I can't do the processing on the fly). Total received file size can vary from as small as 10 KB to over 4 GB. One option for storing the received data is to use a MemoryStream, i.e. a sequence of MemoryStream.Write(bufferReceived, 0, count) calls to store the received packets. This is very simple, but obviously will result in out of memory exception for large files. An alternative option is to use a FileStream, i.e. FileStream.Write(bufferReceived, 0, count). This way, no out of memory exceptions will occur, but what I'm unsure about is bad performance due to disk writes (which I don't want to occur as long as plenty of memory is still available) - I'd like to avoid disk access as much as possible, but I don't know of a way to control this. I did some testing and most of the time, there seems to be little performance difference between say 10 000 consecutive calls of MemoryStream.Write() vs FileStream.Write(), but a lot seems to depend on buffer size and the total amount of data in question (i.e the number of writes). Obviously, MemoryStream size reallocation is also a factor. Does it make sense to use a combination of MemoryStream and FileStream, i.e. write to memory stream by default, but once the total amount of data received is over e.g. 500 MB, write it to FileStream; then, read in chunks from both streams for processing the received data (first process 500 MB from the MemoryStream, dispose it, then read from FileStream)? Another solution is to use a custom memory stream implementation that doesn't require continuous address space for internal array allocation (i.e. a linked list of memory streams); this way, at least on 64-bit environments, out of memory exceptions should no longer be an issue. Con: extra work, more room for mistakes. So how do FileStream vs MemoryStream read/writes behave in terms of disk access and memory caching, i.e. data size/performance balance. I would expect that as long as enough RAM is available, FileStream would internally read/write from memory (cache) anyway, and virtual memory would take care of the rest. But I don't know how often FileStream will explicitly access a disk when being written to. Any help would be appreciated.

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  • What is the optimal number of threads for performing IO operations in java?

    - by marc
    In Goetz's "Java Concurrency in Practice", in a footnote on page 101, he writes "For computational problems like this that do not I/O and access no shared data, Ncpu or Ncpu+1 threads yield optimal throughput; more threads do not help, and may in fact degrade performance..." My question is, when performing I/O operations such as file writing, file reading, file deleting, etc, are there guidelines for the number of threads to use to achieve maximum performance? I understand this will be just a guide number, since disk speeds and a host of other factors play into this. Still, I'm wondering: can 20 threads write 1000 separate files to disk faster than 4 threads can on a 4-cpu machine?

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