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  • How to add a slot to my main window in Qt builder?

    - by George Edison
    I am using Qt Builder to create a simple window. I used the menu editor to add a menu. Now, I figured out how to connect one of the menu items to the close() method of the main window. My problem is how to add a slot to the main window. Here is what I have: private slots: void OnAbout(); However, I can't get this method to show up in the 'Signals and Slots Editor'. How can I get it to show up?

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  • How to delete Document Workspace sub folders with Sharepoint web services?

    - by pclem12
    I'm trying to delete a sub folder in a dws. This is the code I've got: SharepointDocs.DwsSoapClient dws = new SharepointDocs.DwsSoapClient(); dws.DeleteFolderCompleted += dws_DeleteFolderCompleted; dws.DeleteFolderAsync(DWSname+'/'+folderName); In the call back for completion I get no error codes only the message "<Results/>" On the msdn site here, it says this empty message signals a success. However, the folder is still there. Any ideas what could be the problem?

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  • how to call a function to refresh GUI

    - by SWKK
    Hi Guys, I am refactoring some code to decouple GUI from some state. #include <StateObject> Class GUI{ ... StateObject A; void doSomething() { A->hullaballoo();} **void ReFreshMyGui() { //take state A and redraw }** }; State object is being shared by multiple classes to update the state but this Gui Object specializes in displaying the state. So I would like to call the Refresh function via StateObject whenever its modified. I am not sure how or if signals will provide the solution. Any hints?

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  • send() always interrupted by EPIPE

    - by Manuel Abeledo
    I've this weird behaviour in a multithreaded server programmed in C under GNU/Linux. While it's sending data, eventually will be interrupted by SIGPIPE. I managed to ignore signals in send() and treat errno after each action because of it. So, it has two individual sending methods, one that sends a large amount of data at once (or at least tries to), and another that sends a nearly similar amount and slices it in little chunks. Finally, I tried with this to keep it sending data. do { total_bytes_sent += send(client_sd, output_buf + total_bytes_sent, output_buf_len - total_bytes_sent, MSG_NOSIGNAL); } while ((total_bytes_sent < output_buf_len) && (errno != EPIPE)); This ugly piece of code does its work in certain situations, but not always. I'm pretty sure it's not a hardware or ISP problem, as this server is running in six european servers, four in Germany and two in France. Any ideas? Thanks in advance.

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  • GTK+ (2.0) - signal "clicked" on GtkEntry?

    - by Lght
    i'm testing some signals with Gtk+ 2.0. Actually, i'm looking for a way to get the signal emitted when i click on a GtkEntry. if (widgets_info[i].action & IG_INPUT) { widget->frame[i] = gtk_entry_new_with_max_length(MAX_INPUT_LENGTH); gtk_entry_set_text(widget->frame[i], widgets_info[i].text); catch_signal(widget->frame[i], MY_SIGNAL, &change_entry, widget); } I have a pre-selected text in my entry (widgets_info[i].text) and i want this text to disappear if the user click on my GtkEntry. Does someone knows what is this signal ? Sincerely, Lght (sorry for my english)

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  • How to implement low pass filter using java

    - by chai
    Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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  • Get binary data from audio impulses

    - by Timo
    I have IR sensor which have TRS plug and I can record my remotes signals into audio. Now I want to control my computer with TV remote, but I don't have any clue how to compare audio input with pre-recorded audio. But after I realized that these audio waves contains only some kind data (binary) I can turn these into binary or hex, so it is much easier to compare. Waves look just like this: http://i.imgur.com/lCIyl.png And this: ttp://i.imgur.com/goJ6d.png These are records of "OK" button, sometimes there are some impulses on right channel too and I don't know why, it seems like connections in sensor are damaged maybe. Ok thats not matter, anyway I need help with python program which read these impulses and turn these into binary, in realtime from audio input(mic). I know it's sounds like "Do it for me, while I enjoy my life", but I don't have experiences with sound transforming/reading... I've looking for python examples for recording and reading audio, but unsuccessfully.

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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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  • Regular expression one or more times JAVA

    - by user1381564
    Hi i am trying to match a string against a pattern this is the possible string signal CS, NS, dl: stateType := writeOrRead0; signal CS, pS : stateType := writeOrRead0; signal dS : stateType := writeOrRead0; i am only concerned with the pattern as far as the first colon. but the number of signals define can be more than one it could be three or four even this is the regular expression i have ^signal\\s*(\\w+),*\\s*(\\w+)\\s*: it will pick up the second two signal but and for the second one it picks up CS and pS and but the d and S in the next signal when i use matcher.group() come up seperately Can anyone give me an expression that will pick up all signal names whether there is one two three or more?

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  • Can jquery capture the dynamic dom events and perform actions

    - by Zombie15
    I just wanted to know if something like this is possible. Jquery should fire some action on certian custom event. Like Whenever a new row is added to dom dynamically to table then i have certain action like change the background color to example red. That should work across the whole site. Somethings like Event listeners in Doctrine2 or Signals in Django EDIT: Basically i want some thing like where i can create custom event $.AddnewEvent(newRowAdded); Then i can customise that event with my own functions like $.newRowAdded(function(){ blah blah });

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  • Oracle Unveils Oracle Social Relationship Management Suite at Oracle OpenWorld

    - by Richard Lefebvre
    New Service Enables Companies to Listen, Engage, Create, Market and Analyze Interactions across Multiple Social Platforms in Real-Time During his keynote presentation, Oracle CEO Larry Ellison announced the Oracle Social Relationship Management (SRM) Suite.   Oracle Social Relationship Management Suite is an integrated enterprise service that enables companies to listen, engage, create, market, and analyze interactions across multiple social platforms in real-time providing a holistic view of the consumer.   Oracle Social Relationship Management Suite is integrated with Oracle’s enterprise applications, including Oracle Fusion Marketing, Oracle Fusion Sales Catalog, Oracle ATG Web Commerce, and Oracle Enterprise Resource Planning (ERP), allowing organizations to use social to transform their corporate business processes and systems.   Additionally, Oracle Social Relationship Management Suite is integrated with Oracle Platform Services, including Oracle Java Cloud Service and Oracle Database Cloud Service, enabling marketing teams to integrate social with their custom Web pages, landing pages and marketing tools. Unleashing the Power of Social • Providing a holistic view of consumer interactions, Oracle Social Relationship Management Suite includes: Oracle Social Network (OSN): Provides a secure collaboration platform that supports real-time collaboration and networking for users inside and outside the organization. Oracle Social Marketing: Enables marketers to centrally create, publish, moderate, manage, measure and report across multiple social campaigns and platforms. It also helps marketers publish social content, engage fans and customize their brand's look and feel. Oracle Social Engagement & Monitoring Cloud Service: Enables organizations to analyze social media interactions while also empowering customer service and sales teams to effectively engage with customers and prospects. It gives organizations the tools they need to understand customers and take the appropriate actions by monitoring, listening, learning, and responding to signals and trends across the social web. Oracle Social Sites: provides brands and agencies a powerful and rich editing experience that end users can leverage to dynamically develop and launch social sites. Oracle Data and Insights. A service that caters to a growing enterprise need for externally information by providing information, directory and insights about common business entities. Supporting Quote “By fundamentally changing the way organizations connect with their different stakeholders, social is changing the rules of business,” said Thomas Kurian, executive vice president, Oracle Product Development. “With the Oracle Social Relationship Management Suite we are empowering our customers to embrace this change by integrating the tools required to listen, engage, create, market and analyze social interactions into existing applications and services.”

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  • How to upgrade boost lib using apt-get?

    - by sam
    I use ubuntu 11.04. My boost version: sam@sam:~/code/ros/pcl$ apt-cache showpkg libboost-all-dev Package: libboost-all-dev Versions: 1.42.0.1ubuntu1 (/var/lib/apt/lists/tw.archive.ubuntu.com_ubuntu_dists_natty_universe_binary-amd64_Packages) (/var/lib/dpkg/status) Description Language: File: /var/lib/apt/lists/tw.archive.ubuntu.com_ubuntu_dists_natty_universe_binary-amd64_Packages MD5: 72efad05a3c79394c125b79e1d4eb3a7 Reverse Depends: libvtk5-dev,libboost-all-dev libfeel++-dev,libboost-all-dev Dependencies: 1.42.0.1ubuntu1 - libboost-dev (0 (null)) libboost-date-time-dev (0 (null)) libboost-filesystem-dev (0 (null)) libboost-graph-dev (0 (null)) libboost-iostreams-dev (0 (null)) libboost-math-dev (0 (null)) libboost-program-options-dev (0 (null)) libboost-python-dev (0 (null)) libboost-regex-dev (0 (null)) libboost-serialization-dev (0 (null)) libboost-signals-dev (0 (null)) libboost-system-dev (0 (null)) libboost-test-dev (0 (null)) libboost-thread-dev (0 (null)) libboost-wave-dev (0 (null)) Provides: 1.42.0.1ubuntu1 - Reverse Provides: sam@sam:~/code/ros/pcl$ How to upgrade boost to 1.44+ by using apt tools? Thank you~ When I run apt-add-repository,it shows: sam@sam:~/code/ros/pcl$ sudo apt-add-repository ppa:timklingt/ppa Error reading https://launchpad.net/api/1.0/~timklingt/+archive/ppa: GnuTLS recv error (-9): A TLS packet with unexpected length was received. sam@sam:~/code/ros/pcl$ How to fix it? Thank you~ I try to install libboost1.46-all-dev: sam@sam:~/code/ros/pcl$ sudo apt-get install libboost1.46-all-dev Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: libboost1.46-all-dev : Depends: libboost1.46-dev but it is not going to be installed Depends: libboost-date-time1.46-dev but it is not going to be installed Depends: libboost-filesystem1.46-dev but it is not going to be installed Depends: libboost-graph1.46-dev but it is not going to be installed Depends: libboost-iostreams1.46-dev but it is not going to be installed Depends: libboost-math1.46-dev but it is not going to be installed Depends: libboost-program-options1.46-dev but it is not going to be installed Depends: libboost-python1.46-dev but it is not going to be installed Depends: libboost-regex1.46-dev but it is not going to be installed Depends: libboost-serialization1.46-dev but it is not going to be installed Depends: libboost-signals1.46-dev but it is not going to be installed Depends: libboost-system1.46-dev but it is not going to be installed Depends: libboost-test1.46-dev but it is not going to be installed Depends: libboost-thread1.46-dev but it is not going to be installed Depends: libboost-wave1.46-dev but it is not going to be installed E: Broken packages sam@sam:~/code/ros/pcl$ What's these error means? And how to solve it? Thank you~

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  • Using MVP, how to create a view from another view, linked with the same model object

    - by Dinaiz
    Background We use the Model-View-Presenter design pattern along with the abstract factory pattern and the "signal/slot" pattern in our application, to fullfill 2 main requirements Enhance testability (very lightweight GUI, every action can be simulated in unit tests) Make the "view" totally independant from the rest, so we can change the actual view implementation, without changing anything else In order to do so our code is divided in 4 layers : Core : which holds the model Presenter : which manages interactions between the view interfaces (see bellow) and the core View Interfaces : they define the signals and slots for a View, but not the implementation Views : the actual implementation of the views When the presenter creates or deals with views, it uses an abstract factory and only knows about the view interfaces. It does the signal/slot binding between views interfaces. It doesn't care about the actual implementation. In the "views" layer, we have a concrete factory which deals with implementations. The signal/slot mechanism is implemented using a custom framework built upon boost::function. Really, what we have is something like that : http://martinfowler.com/eaaDev/PassiveScreen.html Everything works fine. The problem However, there's a problem I don't know how to solve. Let's take for example a very simple drag and drop example. I have two ContainersViews (ContainerView1, ContainerView2). ContainerView1 has an ItemView1. I drag the ItemView1 from ContainerView1 to ContainerView2. ContainerView2 must create an ItemView2, of a different type, but which "points" to the same model object as ItemView1. So the ContainerView2 gets a callback called for the drop action with ItemView1 as a parameter. It calls ContainerPresenterB passing it ItemViewB In this case we are only dealing with views. In MVP-PV, views aren't supposed to know anything about the presenter nor the model, right ? How can I create the ItemView2 from the ItemView1, not knowing which model object is ItemView1 representing ? I thought about adding an "itemId" to every view, this id being the id of the core object the view represents. So in pseudo code, ContainerPresenter2 would do something like itemView2=abstractWidgetFactory.createItemView2(); this.add(itemView2,itemView1.getCoreObjectId()) I don't get too much into details. That just work. The problem I have here is that those itemIds are just like pointers. And pointers can be dangling. Imagine that by mistake, I delete itemView1, and this deletes coreObject1. The itemView2 will have a coreObjectId which represents an invalid coreObject. Isn't there a more elegant and "bulletproof" solution ? Even though I never did ObjectiveC or macOSX programming, I couldn't help but notice that our framework is very similar to Cocoa framework. How do they deal with this kind of problem ? Couldn't find more in-depth information about that on google. If someone could shed some light on this. I hope this question isn't too confusing ...

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  • Going Metro

    - by Tony Davis
    When it was announced, I confess was somewhat surprised by the striking new "Metro" User Interface for Windows 8, based on Swiss typography, Bauhaus design, tiles, touches and gestures, and the new Windows Runtime (WinRT) API on which Metro apps were to be built. It all seemed to have come out of nowhere, like field mushrooms in the night and seemed quite out-of-character for a company like Microsoft, which has hung on determinedly for over twenty years to its quaint Windowing system. Many were initially puzzled by the lack of support for plug-ins in the "Metro" version of IE10, which ships with Win8, and the apparent demise of Silverlight, Microsoft's previous 'radical new framework'. Win8 signals the end of the road for Silverlight apps in the browser, but then its importance here has been waning for some time, anyway, now that HTML5 has usurped its most compelling use case, streaming video. As Shawn Wildermuth and others have noted, if you're doing enterprise, desktop development with Silverlight then nothing much changes immediately, though it seems clear that ultimately Silverlight will die off in favor of a single WPF/XAML framework that supports those technologies that were pioneered on the phones and tablets. There is a mystery here. Is Silverlight dead, or merely repurposed? The more you look at Metro, the more it seems to resemble Silverlight. A lot of the philosophies underpinning Silverlight applications, such as the fundamentally asynchronous nature of the design, have moved wholesale into Metro, along with most the Microsoft Silverlight dev team. As Simon Cooper points out, "Silverlight developers, already used to all the principles of sandboxing and separation, will have a much easier time writing Metro apps than desktop developers". Metro certainly has given the framework formerly known as Silverlight a new purpose. It has enabled Microsoft to bestow on Windows 8 a new "duality", as both a traditional desktop OS supporting 'legacy' Windows applications, and an OS that supports a new breed of application that can share functionality such as search, that understands, and can react to, the full range of gestures and screen-sizes, and has location-awareness. It's clear that Win8 is developed in the knowledge that the 'desktop computer' will soon be a very large, tilted, touch-screen monitor. Windows owes its new-found versatility to the lessons learned from Windows Phone, but it's developed for the big screen, and with full support for familiar .NET desktop apps as well as the new Metro apps. But the old mouse-driven Windows applications will soon look very passé, just as MSDOS character-mode applications did in the nineties. Cheers, Tony.

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  • Going Inside the Store

    - by David Dorf
    Location was the first "killer-tech" for smartphones, and innovators have found several ways to use it. For retail, apps exist to find nearby stores, provide coupons, and give directions to the front door. But once you enter the store, location-finding ceases to work. That's because your location is usually found by finding GPS satellites in they sky, and the store's roof blocks the signal. But it won't take technology long to solve that problem. The first problem to solve is a lack of indoor maps. Navteq and others provide very accurate maps of the outdoors, enabling navigation for cars and pedestrians. Micello is building a business creating digital maps of indoor locations like malls, convention centers, office buildings. They have over 500 live maps, including maps of IKEA stores. They claim it took them only four hours to create a map of the Stanford Shopping Center in Palo Alto with its 1.4 million square feet and 140 retail stores. And within stores, retailers are producing more accurate plan-o-grams. I'm always impressed watching demos of our space planning from AVT. It uses CAD software to allow you to walk the virtual store and see products on the shelves. The second problem is being able to determine location inside the store so it can be overlayed on the map. There are several goals for this endeavor. Your smartphone might direct you straight to particular products, it might summon a sales associate to your location for immediate assistance, and it might send you coupons based on the aisle you're viewing. Companies like Nearbuy, ZuluTime, and Skyhook are working to master indoor location using a combination of GPS signals, WiFi, and cell tower positioning to calculate a location. (Skyhook calls this WPS, as depicted in the chart.) Today they can usually hit 10 meters accuracy, but that number is improving all the time. When it gets inside 3 meters some the goals mentioned earlier will be in easy reach. I for one can't wait until the time my iPhone leads me directly to the sprinkler heads in Lowes and Home Depot.

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  • Beat detection and FFT

    - by Quincy
    So I am working on a platformer game which includes music with beat detection. I am currently using a simple if the energy that is stored in the history buffer is smaller then the current energy there is a beat. The problem with this is that ofcourse if you use songs like rock songs where you have a pretty steady amplitude this isn't going to work. So I looked further and found algorithms splitting the sound into multiple bands using FFT. I then found this : http://en.literateprograms.org/Cooley-Tukey_FFT_algorithm_(C) The only problem I'm having is that I am quite new to audio and I have no idea how to use that to split the signal up into multiple signals. So my question is : How do you use a FFT to split a signal into multiple bands ? Also for the guys interested, this is my algorithm in c# : // C = threshold, N = size of history buffer / 1024 public void PlaceBeatMarkers(float C, int N) { List<float> instantEnergyList = new List<float>(); short[] samples = soundData.Samples; float timePerSample = 1 / (float)soundData.SampleRate; int sampleIndex = 0; int nextSamples = 1024; // Calculate instant energy for every 1024 samples. while (sampleIndex + nextSamples < samples.Length) { float instantEnergy = 0; for (int i = 0; i < nextSamples; i++) { instantEnergy += Math.Abs((float)samples[sampleIndex + i]); } instantEnergy /= nextSamples; instantEnergyList.Add(instantEnergy); if(sampleIndex + nextSamples >= samples.Length) nextSamples = samples.Length - sampleIndex - 1; sampleIndex += nextSamples; } int index = N; int numInBuffer = index; float historyBuffer = 0; //Fill the history buffer with n * instant energy for (int i = 0; i < index; i++) { historyBuffer += instantEnergyList[i]; } // If instantEnergy / samples in buffer < instantEnergy for the next sample then add beatmarker. while (index + 1 < instantEnergyList.Count) { if(instantEnergyList[index + 1] > (historyBuffer / numInBuffer) * C) beatMarkers.Add((index + 1) * 1024 * timePerSample); historyBuffer -= instantEnergyList[index - numInBuffer]; historyBuffer += instantEnergyList[index + 1]; index++; } }

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  • Is this Ubuntu One DBus signal connection code correct?

    - by Chris Wilson
    This is my first time using DBus so I'm not entirely sure if I'm going about this the right way. I'm attempting to connect the the Ubuntu One DBus service and obtain login credentials for my app, however the slots I've connected to the DBus return signals detailed here never seem to be firing, despite a positive result being returned during the connection. Before I start looking for errors in the details relating to this specific service, could someone please tell me if this code would even work in the first place, or if I'm done something wrong here? int main() { UbuntuOneDBus *u1Dbus = new UbuntuOneDBus; if( u1Dbus->init() ){ qDebug() << "Message queued"; } } UbuntuOneDBus::UbuntuOneDBus() { service = "com.ubuntuone.Credentials"; path = "/credentials"; interface = "com.ubuntuone.CredentialsManagement"; method = "register"; signature = "a{ss} (Dict of {String, String})"; connectReturnSignals(); } bool UbuntuOneDBus::init() { QDBusMessage message = QDBusMessage::createMethodCall( service, path, interface, method ); bool queued = QDBusConnection::sessionBus().send( message ); return queued; } void UbuntuOneDBus::connectReturnSignals() { bool connectionSuccessful = false; connectionSuccessful = QDBusConnection::sessionBus().connect( service, path, interface, "CredentialsFound", "a{ss} (Dict of {String, String})", this, SLOT( credentialsFound() ) ); if( ! connectionSuccessful ) qDebug() << "Connection to DBus::CredentialsFound signal failed"; connectionSuccessful = QDBusConnection::systemBus().connect( service, path, interface, "CredentialsNotFound", "(nothing)", this, SLOT( credentialsNotFound() ) ); if( ! connectionSuccessful ) qDebug() << "Connection to DBus::CredentialsNotFound signal failed"; connectionSuccessful = QDBusConnection::systemBus().connect( service, path, interface, "CredentialsError", "a{ss} (Dict of {String, String})", this, SLOT( credential if( ! connectionSuccessful ) qDebug() << "Connection to DBus::CredentialsError signal failed"; } void UbuntuOneDBus::credentialsFound() { std::cout << "Credentials found" << std::endl; } void UbuntuOneDBus::credentialsNotFound() { std::cout << "Credentials not found" << std::endl; } void UbuntuOneDBus::credentialsError() { std::cout << "Credentials error" << std::endl; }

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  • How to remove the boundary effects arising due to zero padding in scipy/numpy fft?

    - by Omkar
    I have made a python code to smoothen a given signal using the Weierstrass transform, which is basically the convolution of a normalised gaussian with a signal. The code is as follows: #Importing relevant libraries from __future__ import division from scipy.signal import fftconvolve import numpy as np def smooth_func(sig, x, t= 0.002): N = len(x) x1 = x[-1] x0 = x[0] # defining a new array y which is symmetric around zero, to make the gaussian symmetric. y = np.linspace(-(x1-x0)/2, (x1-x0)/2, N) #gaussian centered around zero. gaus = np.exp(-y**(2)/t) #using fftconvolve to speed up the convolution; gaus.sum() is the normalization constant. return fftconvolve(sig, gaus/gaus.sum(), mode='same') If I run this code for say a step function, it smoothens the corner, but at the boundary it interprets another corner and smoothens that too, as a result giving unnecessary behaviour at the boundary. I explain this with a figure shown in the link below. Boundary effects This problem does not arise if we directly integrate to find convolution. Hence the problem is not in Weierstrass transform, and hence the problem is in the fftconvolve function of scipy. To understand why this problem arises we first need to understand the working of fftconvolve in scipy. The fftconvolve function basically uses the convolution theorem to speed up the computation. In short it says: convolution(int1,int2)=ifft(fft(int1)*fft(int2)) If we directly apply this theorem we dont get the desired result. To get the desired result we need to take the fft on a array double the size of max(int1,int2). But this leads to the undesired boundary effects. This is because in the fft code, if size(int) is greater than the size(over which to take fft) it zero pads the input and then takes the fft. This zero padding is exactly what is responsible for the undesired boundary effects. Can you suggest a way to remove this boundary effects? I have tried to remove it by a simple trick. After smoothening the function I am compairing the value of the smoothened signal with the original signal near the boundaries and if they dont match I replace the value of the smoothened func with the input signal at that point. It is as follows: i = 0 eps=1e-3 while abs(smooth[i]-sig[i])> eps: #compairing the signals on the left boundary smooth[i] = sig[i] i = i + 1 j = -1 while abs(smooth[j]-sig[j])> eps: # compairing on the right boundary. smooth[j] = sig[j] j = j - 1 There is a problem with this method, because of using an epsilon there are small jumps in the smoothened function, as shown below: jumps in the smooth func Can there be any changes made in the above method to solve this boundary problem?

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  • Why is multithreading often preferred for improving performance?

    - by user1849534
    I have a question, it's about why programmers seems to love concurrency and multi-threaded programs in general. I'm considering 2 main approaches here: an async approach basically based on signals, or just an async approach as called by many papers and languages like the new C# 5.0 for example, and a "companion thread" that manages the policy of your pipeline a concurrent approach or multi-threading approach I will just say that I'm thinking about the hardware here and the worst case scenario, and I have tested this 2 paradigms myself, the async paradigm is a winner at the point that I don't get why people 90% of the time talk about multi-threading when they want to speed up things or make a good use of their resources. I have tested multi-threaded programs and async program on an old machine with an Intel quad-core that doesn't offer a memory controller inside the CPU, the memory is managed entirely by the motherboard, well in this case performances are horrible with a multi-threaded application, even a relatively low number of threads like 3-4-5 can be a problem, the application is unresponsive and is just slow and unpleasant. A good async approach is, on the other hand, probably not faster but it's not worst either, my application just waits for the result and doesn't hangs, it's responsive and there is a much better scaling going on. I have also discovered that a context change in the threading world it's not that cheap in real world scenario, it's in fact quite expensive especially when you have more than 2 threads that need to cycle and swap among each other to be computed. On modern CPUs the situation it's not really that different, the memory controller it's integrated but my point is that an x86 CPUs is basically a serial machine and the memory controller works the same way as with the old machine with an external memory controller on the motherboard. The context switch is still a relevant cost in my application and the fact that the memory controller it's integrated or that the newer CPU have more than 2 core it's not bargain for me. For what i have experienced the concurrent approach is good in theory but not that good in practice, with the memory model imposed by the hardware, it's hard to make a good use of this paradigm, also it introduces a lot of issues ranging from the use of my data structures to the join of multiple threads. Also both paradigms do not offer any security abut when the task or the job will be done in a certain point in time, making them really similar from a functional point of view. According to the X86 memory model, why the majority of people suggest to use concurrency with C++ and not just an async approach ? Also why not considering the worst case scenario of a computer where the context switch is probably more expensive than the computation itself ?

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  • Traditional POS is Dead

    - by David Dorf
    Traditional POS is dead -- I've heard that one before. Here's an excerpt from Joe Skorupa's blog over at RIS where he relayed ten trends that were presented at NRF. 7. Mobile POS signals death of traditional POS. Shoppers don't love self-checkout, but they prefer it to long queues or dealing with associates. Fixed POS is expensive and bulky. Mobile POS frees floor space for other purposes and converts associates from being cashiers to being sales assistants that provide new levels of customer service and incremental basket sales. In addition to unplugging the POS, new alternatives are starting to take hold - thin client, POS as a service, and replacing POS software with e-commerce platforms. I'll grant that in some situations for some retailers there might be an opportunity to to ditch the traditional POS, but for the majority of retailers that's just not practical. Take it from a guy that had to wake up at 3am after every Thanksgiving to monitor POS systems across the US on Black Friday. If a retailer's website goes down on Black Friday, they will take a significant hit. If a retailer's chain-wide POS system goes down on Black Friday, that retailer will cease to exist. Mobile POS works great for Apple because the majority of purchases are one or two big-ticket items that don't involve cash. There's still a traditional POS in every store to fall back on (its just hidden). Try this at home: Choose your favorite e-commerce site and add an item to the cart while timing how long it takes. Now multiply that by 15 to represent the 15 items you might buy at store like Target. The user interface isn't optimized for bulk purchases, and that's how it should be. The webstore and POS are designed for different purposes. Self-checkout is a great addition to POS and so is mobile checkout. But they add capabilities to POS, not replace it. Centralized architectures, even those based in the cloud, are quite viable as long as there's resiliency in the registers. You cannot assume perfect access to the network, so a POS must always be able to sell regardless of connectivity. Clearly the different selling channels should be sharing common functionality. Things like calculating tax, accepting coupons, and processing electronic payments can be shared, usually through a service-oriented architecture. This lowers costs and providers greater consistency, both of which help retailers. On paper these technologies look really good and we should continue to push boundaries, but I'm not ready to call the patient dead just yet.

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  • Why C++ people loves multithreading when it comes to performances?

    - by user1849534
    I have a question, it's about why programmers seems to love concurrency and multi-threaded programs in general. I'm considering 2 main approach here: an async approach basically based on signals, or just an async approach as called by many papers and languages like the new C# 5.0 for example, and a "companion thread" that maanges the policy of your pipeline a concurrent approach or multi-threading approach I will just say that I'm thinking about the hardware here and the worst case scenario, and I have tested this 2 paradigms myself, the async paradigm is a winner at the point that I don't get why people 90% of the time talk about concurrency when they wont to speed up things or make a good use of their resources. I have tested multi-threaded programs and async program on an old machine with an Intel quad-core that doesn't offer a memory controller inside the CPU, the memory is managed entirely by the motherboard, well in this case performances are horrible with a multi-threaded application, even a relatively low number of threads like 3-4-5 can be a problem, the application is unresponsive and is just slow and unpleasant. A good async approach is, on the other hand, probably not faster but it's not worst either, my application just waits for the result and doesn't hangs, it's responsive and there is a much better scaling going on. I have also discovered that a context change in the threading world it's not that cheap in real world scenario, it's infact quite expensive especially when you have more than 2 threads that need to cycle and swap among each other to be computed. On modern CPUs the situation it's not really that different, the memory controller it's integrated but my point is that an x86 CPUs is basically a serial machine and the memory controller works the same way as with the old machine with an external memory controller on the motherboard. The context switch is still a relevant cost in my application and the fact that the memory controller it's integrated or that the newer CPU have more than 2 core it's not bargain for me. For what i have experienced the concurrent approach is good in theory but not that good in practice, with the memory model imposed by the hardware, it's hard to make a good use of this paradigm, also it introduces a lot of issues ranging from the use of my data structures to the join of multiple threads. Also both paradigms do not offer any security abut when the task or the job will be done in a certain point in time, making them really similar from a functional point of view. According to the X86 memory model, why the majority of people suggest to use concurrency with C++ and not just an async aproach ? Also why not considering the worst case scenario of a computer where the context switch is probably more expensive than the computation itself ?

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  • Error In centos6 while compiling java classes,in tomcat6

    - by AJIT RANA
    I am newbie to Linux and Centos6. I bought server just now and want to deploy my web app in it. I am getting error while I am compiling my servlet classes. It showing me bash: javac: command not found when I try to compile my classes. But when I checked my class in '/usr/lib/jvm/java-1.6.0/bin .'I found my javac there. Then I checked javac with the help of command ./javac i got ERROR.. [root:ip_address.com]# ./javac There is insufficient memory for the Java Runtime Environment to continue. pthread_getattr_np Error occurred during initialization of VM java.lang.OutOfMemoryError: unable to create new native thread I followed the step as shown in "" Java outofmemoryerror when creating <100 threads "" which shows me command to get limits.. '[root:ipaddress.com]# ulimit -a core file size (blocks, -c) unlimited data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 278528 max locked memory (kbytes, -l) 32 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited' [root:ipaddress.com]# top bash: top: command not found link :- http://stackoverflow.com/q/12913857/1746764

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  • What is the best keyboard for typing speed (not layouts)

    - by Gapton
    So I am a programmer, and I like playing typing speed games. My typing speed is, for common English words, 85 to 90 wpm, max 95. I type on various devices, my laptop, desktop, office pc.... they all have slightly different keyboards. Being a curious programmer, I wonder what types of keyboard is used for the highest possible typing speed. Or let me phrase it in another way, what is the type of keyboards that people use in typing speed contest? Here is something I know that I feel like I can share: It must be a wired keyboard, I can feel the lag as I am typing this on my wireless keyboard, even if it is a slightly more expensive model which claims to have zero lag. I know people prefer a mechanical keyboard, for the hepatic feedback, however I have not tried one. It lasts longer and is noisy, it also does not have the problem of normal keyboards where you press many keys at a time the signals will get all jammed and the computer will only receive one or two keys. I personally prefer those "thin profile" keyboards. I type a lot, and 95 wpm put me in the top 5%, this is of course just on a gaming site. However when I type on the fat keyboards, my fingers have to travel a much longer distance before the keys actually click. This is where I find myself typing much faster with those thin profile keyboards found on my laptop. Because my fingers only hover on the keys and I only need to press a short distance, each stroke takes less force and light rapid strokes is what makes me type fast. When I type on a fat keyboard, I was forced to use heavy strokes, and this slows me down. There must be some people out there who are keyboard scientists, who actually do experiments and user tests with different setups. It would be interesting to understand more about the things we use everyday for not just work but a majority of our communications. P.S. this is about hardware and not about switching keyboard layouts to dvorak

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  • What DBus signal is sent on system suspend?

    - by Paul Robinson
    Hello, I need to detect when a machine is going to sleep in Ubuntu 9.10 and Fedora 13. Both use UPower, so I've been looking on the "org.freedesktop.UPower" DBus bus for such signals. I've been listening for the "sleeping" signal on the UPower bus with the following command: dbus-monitor --system "type='signal',interface='org.freedesktop.UPower',member='Sleeping'" When I sleep the machine (either by closing the lid, selecting "shutdown - suspend" or sending a DBus message) I don't see a "sleeping" event. I notice that the "Sleeping" event is sent when the "org.freedesktop.UPower.AboutToSleep" method is invoked. I can do this manually by calling: dbus-send --print-reply --system --dest=org.freedesktop.UPower /org/freedesktop/UPower org.freedesktop.UPower.AboutToSleep And I notice the "sleeping" signal is fired. My understanding is that anything that sleeps the PC must send the "AboutToSleep" signal before hand. It doesn't seem like this is happening. I've tried these steps on both Fedora 13 and Ubuntu 9.10 and I see the same results. Can anyone explain what's happening or provide me with an alternative DBus signal to listen for? Many thanks, Paul

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  • 613 threads limit on debian

    - by Joel
    When running this program thread-limit.c on my dedicated debian server, the output says that my system can't create more than around 600 threads. I need to create more threads, and fix my system misconfiguration. Here are a few informations about my dedicated server: de801:/# uname -a Linux de801.ispfr.net 2.6.18-028stab085.5 #1 SMP Thu Apr 14 15:06:33 MSD 2011 x86_64 GNU/Linux de801:/# java -version java version "1.6.0_26" Java(TM) SE Runtime Environment (build 1.6.0_26-b03) Java HotSpot(TM) 64-Bit Server VM (build 20.1-b02, mixed mode) de801:/# ldd $(which java) linux-vdso.so.1 => (0x00007fffbc3fd000) libpthread.so.0 => /lib/libpthread.so.0 (0x00002af013225000) libjli.so => /usr/lib/jvm/java-6-sun-1.6.0.26/jre/bin/../lib/amd64/jli/libjli.so (0x00002af013441000) libdl.so.2 => /lib/libdl.so.2 (0x00002af01354b000) libc.so.6 => /lib/libc.so.6 (0x00002af013750000) /lib64/ld-linux-x86-64.so.2 (0x00002af013008000) de801:/# cat /proc/sys/kernel/threads-max 1589248 de801:/# ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 794624 max locked memory (kbytes, -l) 32 max memory size (kbytes, -m) unlimited open files (-n) 10240 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 128 cpu time (seconds, -t) unlimited max user processes (-u) unlimited virtual memory (kbytes, -v) unlimited file locks (-x) unlimited Here is the output of the C program de801:/test# ./thread-limit Creating threads ... Address of c = 1061520 KB Address of c = 1081300 KB Address of c = 1080904 KB Address of c = 1081168 KB Address of c = 1080508 KB Address of c = 1080640 KB Address of c = 1081432 KB Address of c = 1081036 KB Address of c = 1080772 KB 100 threads so far ... 200 threads so far ... 300 threads so far ... 400 threads so far ... 500 threads so far ... 600 threads so far ... Failed with return code 12 creating thread 637. Any ideas how to fix this please ?

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