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• Can SHA-1 algorithm be computed on a stream? With low memory footprint?

  - by raoulsson

  I am looking for a way to compute SHA-1 checksums of very large files without having to fully load them into memory at once. I don't know the details of the SHA-1 implementation and therefore would like to know if it is even possible to do that. If you know the SAX XML parser, then what I look for would be something similar: Computing the SHA-1 checksum by only always loading a small part into memory at a time. All the examples I found, at least in Java, always depend on fully loading the file/byte array/string into memory. If you even know implementations (any language), then please let me know!

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• Where are the static methods in gcc's dump file.c.135r.jump

  - by Customizer

  When I run gcc with the parameter -fdump-rtl-jump, I get a dump file with the name file.c.135r.jump, where I can read some information about the intermediate representation of the methods in my C or C++ file. I just recently discovered, that the static methods of a project are missing in this dump file. Do you know, why they are missing in that representation and if there is a possibility to include the static methods in this file, too. Update (some additional information): The test program, I'm using here, is the Hybrid OpenMP MPI Benchmark. Update2: I just reproduced the problem with a serial application, so it has nothing to do with parallel sections.

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• How can I use Amazon's API in PHP to search for books?

  - by TerranRich

  I'm working on a Facebook app for book sharing, reviewing, and recommendations. I've scoured the web, searched Google using every search phrase I could think of, but I could not find any tutorials on how to access the Amazon.com API for book information. I signed up for an AWS account, but even the tutorials on their website didn't help me one bit. They're all geared toward using cloud computing for file storage and processing, but that's not what I want. I just want to access their API to search info on books. Kind of like how http://openlibrary.org/ does it, where it's a simple URL call to get information on a book (but their databases aren't nearly as populated as Amazon's). Why is it so damned hard to find the information I need on Amazon's AWS site? If anybody could help, I would greatly appreciate it.

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• RewriteCond to change displayed host, but not server

  - by coneybeare

  Typing out the title to this leads me to believe this might not be possible due to security concerns, but I will ask anyway. I have shortcode support running on my server, lets call it xx.yy I want it so when a user sends a request to xx.yy, it just changes the displayed host to another valid domain running on the same box. I have this so far (lets the server know to accept requests from xx.yy): RewriteCond %{HTTP_HOST} ^.*xx.yy [NC] RewriteRule ^/(.*)$ http://127.0.0.1:<PORT_OMITTED>%{REQUEST_URI} [P,QSA,L] RewriteCond %{HTTP_HOST} ^.*mysite.com [NC] RewriteRule ^/(.*)$ http://127.0.0.1:<PORT_OMITTED>%{REQUEST_URI} [P,QSA,L] It works, and it directs the traffic into my app, but the url says http://xx.yy when I would rather it say http://mysite.com I know i could redirect to http://mysite.com instead of 127.0.0.1, but I have 4 parallel boxes of mysite.com and going back out to DNS to maybe go to another box seems like a waste when I am already here. Also, I am not sure how POST requests would work like that. What can I do?

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• How does one modify the thread scheduling behavior when using Threading Building Blocks (TBB)?

  - by J Teller

  Does anyone know how to modify the thread scheduling (specifically affinity) when using TBB? Doing a high level analysis on a simple parallel-for application, it seems like TBB is specifying the underlying threads' affinity in a way that reduces performance. Specifically, the cores I'm running on have hyper-threading enabled, and it looks like TBB is affinitizing threads to the same core even if there is a different core left completely unloaded. FWIW, I realize it's likely that TBB is doing the "right thing" and that changing the threads' affinity will only reduce performance. I'd just like to experiment with it to see if that's really the case.

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• Oracle Sql Query taking a day long to return results using dblink

  - by Suresh S

  Guys i have the following oracle sql query that gives me the monthwise report between the dates. Basically for nov month i want sum of values between the dates 01nov to 30 nov. The table tha is being queried is residing in another database and accesssed using dblink. The DT columns is of NUMBER type (for ex 20101201) .The execution of the query is taking a day long and not completed. kindly suggest me , if their is any optimisation that can be suggested to my DBA on the dblink, or any tuning that can be done on the query , or rewriting the same. SELECT /*+ PARALLEL (A 8) */ TO_CHAR(TRUNC(TRUNC(SYSDATE,'MM')- 1,'MM'),'MONYYYY') "MONTH", TYPE AS "TYPE", COLUMN, COUNT (DISTINCT A) AS "A_COUNT", COUNT (COLUMN) AS NO_OF_COLS, SUM (DURATION) AS "SUM_DURATION", SUM (COST) AS "COST" FROM **A@LN_PROD A** WHERE DT >=TO_NUMBER(TO_CHAR(TRUNC(TRUNC(SYSDATE,'MM')-1,'MM'),'YYYYMMDD')) AND DT < TO_NUMBER(TO_CHAR(TRUNC(TRUNC(SYSDATE,'MM'),'MM'),'YYYYMMDD')) GROUP BY TYPE, COLUMN

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• signed angle between two 3d vectors with same origin within the same plane? recipe?

  - by Advanced Customer

  Was looking through the web for an answer but it seems like there is no clear recipe for it. What I need is a signed angle of rotation between two vectors Va and Vb lying within the same 3D plane and having the same origin knowing that: the plane contatining both vectors is an arbitrary and is not parallel to XY or any other of cardinal planes Vn - is a plane normal both vectors along with the normal have the same origin O = { 0, 0, 0 } Va - is a reference for measuring the left handed rotation at Vn The angle should be measured in such a way so if the plane would be XY plane the Va would stand for X axis unit vector of it. I guess I should perform a kind of coordinate space transformation by using the Va as the X-axis and the cross product of Vb and Vn as the Y-axis and then just using some 2d method like with atan2() or something. Any ideas? Formulas?

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• Mahout Recommendations on Binary data

  - by Pranay Kumar

  Hi, I'm a newbie to mahout.My aim is to produce recommendations on binary user purchased data.So i applied item-item similarity model in computing top N recommendations for movie lens data assuming 1-3 ratings as a 0 and 4-5 ratings as a 1.Then i tried evaluating my recommendations with the ratings in the test-data but hardly there have been two or three matches from my top 20 recommendations to the top rated items in test data and no match for most users. So are my recommendations totally bad by nature or do i need to go for a different measure for evaluating my recommendations ? Please help me ! Thanks in advance. Pranay, 2nd yr ,UG student.

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• No method 'get' on backbone model save

  - by user888734

  I'm using backbone for a reasonably complicated form. I have a number of nested models, and have been computing other variables in the parent model like so: // INSIDE PARENT MODEL computedValue: function () { var value = this.get('childModel').get('childModelProperty'); return value; } This seems to work fine for keeping my UI in sync, but as soon as I call .save() on the parent model, I get: Uncaught TypeError: Object #<Object> has no method 'get' It seems that the child model kind of temporarily stops responding. Am I doing something inherently wrong? EDIT: The stack trace is: Uncaught TypeError: Object #<Object> has no method 'get' publish.js:90 Backbone.Model.extend.neutralDivisionComputer publish.js:90 Backbone.Model.extend.setNeutralComputed publish.js:39 Backbone.Events.trigger backbone.js:163 _.extend.change backbone.js:473 _.extend.set backbone.js:314 _.extend.save.options.success backbone.js:385 f.Callbacks.o jquery.min.js:2 f.Callbacks.p.fireWith jquery.min.js:2 w jquery.min.js:4 f.support.ajax.f.ajaxTransport.send.d

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• My Thread Programs Crash

  - by zp26

  I have a problem with threads objectiveC. The line of code below contains the recv block the program waiting for a datum. My intention is to launch a thread parallel to the program so that this statement does not block any application. I put this code in my program but when active switch the program crashes. Enter the code. -(IBAction)Chat{ if(switchChat.on){ buttonInvio.enabled = TRUE; fieldInvio.enabled = TRUE; [NSThread detachNewThreadSelector:@selector(riceviDatiServer) toTarget:self withObject:nil]; } else { buttonInvio.enabled = FALSE; fieldInvio.enabled = FALSE; } -(void)riceviDatiServer{ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init]; int ricevuti; NSString *datiRicevuti; ricevuti = recv(temp, &datiRicevuti, datiRicevuti.length, 0); labelRicezione.text = [[NSString alloc] initWithFormat:@"%s.... %d", datiRicevuti, ricevuti]; [pool release]; }

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• starting 64 Bit Windows Application Development

  - by user173438

  I intend to start writing a 64 Bit Scientific Computing Application (signal processing) for Windows using Microsoft Visual Studio 2008. What should I have ready as far as a development platform is concerned? How would it be different from 32 Bit development? What could be the porting issues for a 32 Bit version that I already have (ok - this might too early to ask.. even before I start compiling)? As you might have guessed, I am looking for general directions. All pointers would be much appreciated! :) Thanks in advance..

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• Long running, polling, queueing process for Python. What's the best stuff to use?

  - by Bialecki

  Feel free to close and/or redirect if this has been asked, but here's my situation: I've got an application that will require doing a bunch of small units of work (polling a web service until something is done, then parsing about 1MB worth of XML and putting it in a database). I want to have a simple async queueing mechanism that'll poll for work to do in a queue, execute the units of work that need to be done, and have the flexibility to allow for spawning multiple worker processes so these units of work can be done in parallel. (Bonus if there's some kind of event framework that would also me to listen for when work is complete.) I'm sure there is stuff to do this. Am I describing Twisted? I poked through the documentation, I'm just not sure exactly how my problems maps onto their framework, but I haven't spent much time with it. Should I just look at the multiprocess libraries in Python? Something else?

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• Android Service Multiple Thread Design

  - by Gernot

  Hello, A new question about android and services. Currently I'm developing a App that should send images to a server. It should also be possible to send more images parallel. I made a service that creates for every image a new image. The activity can bind to that service and gather information about the progress. I want to show the current status for every image in a notification (and when the user clicks a notification, an activity with the progress for that image should be shown). But I get several problems with that approach. There are errors with binding, the notification pending event starts the activity completly new, so I lose information about currently sending images and so on. Can someone plase tell me, how I could design such a problem in a appropriate way. thx

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• Svn merging trunk and branches

  - by Darko Petreski

  Hi All, I have a huge project. I need to make a branch - this will be version 2 of the project, but I also need to keep the trunk and change it in parallel with the branch 1 as bug fix to the version 1. I need to merge bug fixes from the trunk to the branch 1 while adding new features to the branch. At the end I need to merge all changes back in the trunk and make new tag from it. So I need bug fix for version 1, new branch for version 2 and of course merging bug fixes in the version 2. I am using svn but the svn makes problems all the time. I cannot merge anything without conflicts. Can someone give me an advice what to do? Regards

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• Is Work Stealing always the most appropriate user-level thread scheduling algorithm?

  - by Il-Bhima

  I've been investigating different scheduling algorithms for a thread pool I am implementing. Due to the nature of the problem I am solving I can assume that the tasks being run in parallel are independent and do not spawn any new tasks. The tasks can be of varying sizes. I went immediately for the most popular scheduling algorithm "work stealing" using lock-free deques for the local job queues, and I am relatively happy with this approach. However I'm wondering whether there are any common cases where work-stealing is not the best approach. For this particular problem I have a good estimate of the size of each individual task. Work-stealing does not make use of this information and I'm wondering if there is any scheduler which will give better load-balancing than work-stealing with this information (obviously with the same efficiency). NB. This question ties up with a previous question.

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• In Javascript, by what mechanism does setting an Image src property trigger an image load?

  - by brainjam

  One of the things you learn early on when manipulating a DOM using Javascript is the following pattern: var img = new Image(); // Create new Image object img.onload = function(){ // execute drawImage statements here } img.src = 'myImage.png'; // Set source path As far as I know, in general when you set an object property there are no side effects. So what is the mechanism for triggering an image load? Is it just magic? Or can I use a similar mechanism to implement a class Foo that supports a parallel pattern? var foo = new Foo(); // Create new object foo.barchanged = function(){ // execute something after side effect has completed } foo.bar = 'whatever'; // Assign something to 'bar' property I'm vaguely aware of Javascript getters and setters. Is this how Image.src triggers a load?

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• How to do concurrent modification testing for grails application

  - by werner5471

  I'd like to run tests that simulate users modifying certain data at the same time for a grails application. Are there any plug-ins / tools / mechanisms I can use to do this efficiently? They don't have to be grails specific. It should be possible to fire multiple actions in parallel. I'd prefer to run the tests on functional level (so far I'm using Selenium for other tests) to see the results from the user perspective. Of course this can be done in addition to integration testing if you'd recommend to run concurrent modification tests on integration level as well.

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• BizTalk Server Threading in Receive Pipelines

  - by ToxicAvenger

  I am building custom pipeline components for receive pipelines in BizTalk Server (2006 and 2009). I am building the components in a streaming fashion. My question: for any single inbound message, if I have a disassembling component, when I create n messages from a single inbound message, will the message agent always use a single thread when reading the (body) streams and persisting the messages to the message box? I would think so, but confirmation would be helpful. Say if I create five messages in the disassembler, will any of these messages be persisted sequentially from the same thread? Or could these messages be processed in parallel?

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• A simple algorithm for polygon intersection

  - by Elazar Leibovich

  I'm looking for a very simple algorithm for computing the polygon intersection/clipping. That is, given polygons P, Q, I wish to find polygon T which is contained in P and in Q, and I wish T to be maximal among all possible polygons. I don't mind the run time (I have a few very small polygons), I can also afford getting an approximation of the polygons' intersection (that is, a polygon with less points, but which is still contained in the polygons' intersection). But it is really important for me that the algorithm will be simple (cheaper testing) and preferably short (less code). edit: please note, I wish to obtain a polygon which represent the intersection. I don't need only a boolean answer to the question of whether the two polygons intersect.

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• Algorithm to distribute objects in a box (like InDesign, Illustrator, Draw!)

  - by Rafael Almeida

  I have a set of rectangles with their corresponding positions and a big rectangle which serves as the 'bounding box' for these rectangles. I would like to know of an algorithm that would 'distribute the free space' evenly among the rectangles. Some of you may be familiar with the Distribute Spacing option in Adobe InDesign and similar layout-oriented apps. That would be what I'm looking for. I did try looking it up, but I'm not familiar with 'graphical' algorithms terminology and trying only terms relating to 'distribute' mainly yields results about Distributed Computing. So, even the names of the algorithms or better terms to look up would be a big help. Finally, the algorithm doesn't need to be rigorously the same as InDesign's one: pretty much any algorithm that 'distributes' objects inside a region will work fine. In fact, since I'm striving for visual appeal mainly, the more suggestions the better. =D

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• Configurability for windows application built in C#

  - by Sam

  Hi, I am working on a windows application which is developed in C#. I am kinda new in windows world. I want to restrict number of parallel threads running for this application at a given point of time. This number can be changed by user on a beefier machine. What is the best way to do this configuration and how it can be achieved. I can think of following approaches. 1. Use ConfigurationManager to read the configuration value. If user exists more than N number of threads show a message and give option there to modify the value of N. 2. Use registery entry? Thanks in Advance! Sam

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• Efficiently compute the row sums of a 3d array in R

  - by Gavin Simpson

  Consider the array a: > a <- array(c(1:9, 1:9), c(3,3,2)) > a , , 1 [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9 , , 2 [,1] [,2] [,3] [1,] 1 4 7 [2,] 2 5 8 [3,] 3 6 9 How do we efficiently compute the row sums of the matrices indexed by the third dimension, such that the result is: [,1] [,2] [1,] 12 12 [2,] 15 15 [3,] 18 18 ?? The column sums are easy via the 'dims' argument of colSums(): > colSums(a, dims = 1) but I cannot find a way to use rowSums() on the array to achieve the desired result, as it has a different interpretation of 'dims' to that of colSums(). It is simple to compute the desired row sums using: > apply(a, 3, rowSums) [,1] [,2] [1,] 12 12 [2,] 15 15 [3,] 18 18 but that is just hiding the loop. Are there other efficient, truly vectorised, ways of computing the required row sums?

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• Php efficiency question --> Database call vs. File Write vs. Calling C++ executable

  - by JP19

  Hi, What I wish to achieve is - log all information about each and every visit to every page ofmy website (like ip address, browser, referring page, etc). Now this is easy to do. What I am interested is doing this in a way so as to cause minimum overhead (runtime) in the php scripts. What is the best approach for this efficiency-wise: 1) Log all information to a database table 2) Write to a file (from php directly) 3) Call a C++ executable, that will write this info to a file in parallel [so the script can continue execution without waiting for the file write to occur ...... is this even possible] I may be trying to optimize unnecessarily/prematurely, but still - any thoughts / ideas on this would be appreciated. (I think efficiency of file write/logging can really be a concern if I have say 100 visits per minute...) Thanks & Regards, JP

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• Tuning JVM (GC) for high responsive server application

  - by elgcom

  I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory. The server must be highly responsive. After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak) After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html I use these JVM options -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly. How can I further improve or tune the JVM? larger heap size? but will it take more time for GC? larger NewSize and MaxNewSize (for young generation)? other collector? parallel GC? is it a good idea to let major GC take place more often? and how?

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• Count of memory copies in *nix systems between packet at NIC and user application?

  - by Michael_73

  Hi there, This is just a general question relating to some high-performance computing I've been wondering about. A certain low-latency messaging vendor speaks in its supporting documentation about using raw sockets to transfer the data directly from the network device to the user application and in so doing it speaks about reducing the messaging latency even further than it does anyway (in other admittedly carefully thought-out design decisions). My question is therefore to those that grok the networking stacks on Unix or Unix-like systems. How much difference are they likely to be able to realise using this method? Feel free to answer in terms of memory copies, numbers of whales rescued or areas the size of Wales ;) Their messaging is UDP-based, as I understand it, so there's no problem with establishing TCP connections etc. Any other points of interest on this topic would be gratefully thought about! Best wishes, Mike

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