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  • Able to ping but cannot browse after several hours running of my python program

    - by Shane
    It's a GUI program I wrote in python checking website/server status running on my XP SP3, multi threads are used to check different site/server. After several hours running, the program starts to get urlopen error timed out all the time, and this always happens right after a POST request from a server(not a certain one, might be A or B or C), and it's also not the first POST request causing the problem, normally after several hours running and it happens to make a POST request at an unknown moment, all you get from then on is urlopen error timed out. I'm still able to ping but cannot browse any site, once the program closed everything's fine. It's definitely the program causing this problem, well I just don't know how to debug/check what the problem is, also don't know if it's from OS side or my program wasting too many resources/connections(are you still able to ping when too many connections used?), would anybody please help me out?

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  • How to get Acknowlegement in TCP communication in Java

    - by Sunil Kumar Sahoo
    I have written a socket program in Java. Both server and client can sent/receive data to each other. But I found that if client sends data to server using TCP then internally TCP sends acknowledgement to the client once the data is received by the server. I want to detect or handle that acknowledgement. How can I read or write data in TCP so that I can handle TCP acknowledgement. Thanks Sunil Kumar Sahoo

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  • Scalaz: request for use case for Cokleisli composition

    - by oxbow_lakes
    This question isn't meant as flame-bait! As it might be apparent, I've been looking at Scalaz recently. I'm trying to understand why I need some of the functionality that the library provides. Here's something: import scalaz._ import Scalaz._ type NEL[A] = NonEmptyList[A] val NEL = NonEmptyList I put some println statements in my functions to see what was going on (aside: what would I have done if I was trying to avoid side effects like that?). My functions are: val f: NEL[Int] => String = (l: NEL[Int]) => {println("f: " + l); l.toString |+| "X" } val g: NEL[String] => BigInt = (l: NEL[String]) => {println("g: " + l); BigInt(l.map(_.length).sum) } Then I combine them via a cokleisli and pass in a NEL[Int] val k = cokleisli(f) =>= cokleisli(g) println("RES: " + k( NEL(1, 2, 3) )) What does this print? f: NonEmptyList(1, 2, 3) f: NonEmptyList(2, 3) f: NonEmptyList(3) g: NonEmptyList(NonEmptyList(1, 2, 3)X, NonEmptyList(2, 3)X, NonEmptyList(3)X) RES: 57 The RES value is the character count of the (String) elements in the final NEL. Two things occur to me: How could I have known that my NEL was going to be reduced in this manner from the method signatures involved? (I wasn't expecting the result at all) What is the point of this? Can a reasonably simple and easy-to-follow use case be distilled for me? This question is a thinly-veiled plea for some lovely person like retronym to explain how this powerful library actually works.

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  • J: Self-reference in bubble sort tacit implementation

    - by Yasir Arsanukaev
    Hello people! Since I'm beginner in J I've decided to solve a simple task using this language, in particular implementing the bubblesort algorithm. I know it's not idiomatically to solve such kind of problem in functional languages, because it's naturally solved using array element transposition in imperative languages like C, rather than constructing modified list in declarative languages. However this is the code I've written: (((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # Let's apply it to an array: (((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # 5 3 8 7 2 2 3 5 7 8 The thing that confuses me is $: referring to the statement within the outermost parentheses. Help says that: $: denotes the longest verb that contains it. The other book (~ 300 KiB) says: 3+4 7 5*20 100 Symbols like + and * for plus and times in the above phrases are called verbs and represent functions. You may have more than one verb in a J phrase, in which case it is constructed like a sentence in simple English by reading from left to right, that is 4+6%2 means 4 added to whatever follows, namely 6 divided by 2. Let's rewrite my code snippet omitting outermost ()s: ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) ^: # 5 3 8 7 2 2 3 5 7 8 Reuslts are the same. I couldn't explain myself why this works, why only ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) is treated as the longest verb for $: but not the whole expression ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) ^: # and not just (<./@(2&{.)), $:@((>./@(2&{.)),2&}.), because if ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) is a verb, it should also form another verb after conjunction with #, i. e. one might treat the whole sentence (first snippet) as a verb. Probably there's some limit for the verb length limited by one conjunction. Look at the following code (from here): factorial =: (* factorial@<:) ^: (1&<) factorial 4 24 factorial within expression refers to the whole function, i. e. (* factorial@<:) ^: (1&<). Following this example I've used a function name instead of $:: bubblesort =: (((<./@(2&{.)), bubblesort@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # bubblesort 5 3 8 7 2 2 3 5 7 8 I expected bubblesort to refer to the whole function, but it doesn't seem true for me since the result is correct. Also I'd like to see other implementations if you have ones, even slightly refactored. Thanks.

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  • Is the IP from the source or target in this System.Net.Sockets.SocketException?

    - by Jeremy Mullin
    I'm making an outbound connection using a DNS name to a server other than the localhost, and I get this exception: System.Net.WebException: Unable to connect to the remote server --- System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 127.0.0.1:5555 The text implies that the TARGET machine refused the connection, but the IP address and port are from the localhost, which is kind of confusing. So is that IP address really the outgoing IP and port, even though the exception was caused by the target refusing the connection? Or is the exception from the local firewall blocking the outgoing connection?

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  • Recommended Math textbooks for programmers

    - by Tony
    I learned math in a non-English environment, I recently read some books about algorithm analysis, I found some math concepts were confusing, and seemed not the same as what I've learned. What math textbooks would you recommend that covers math concepts from the scratch and suitable for self-learning ?

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  • Data Collection (Offline - no internet) and then syncing it to generate reports from server

    - by Nishant
    So, I have a new project I am planning on taking, and needed to know what skills will be required to achieve this project. The project is to do intensive data collection in the field where they don't have internet access. As part of the data collection, images will be uploaded as part of the data collection which will have to be resized, etc. Once the data collection occurs, this data needs to be consolidated and reported on. I am thinking there are two ways of generating the report. 1. Into a PDF that can be designed. 2. Is there a way to generate an executable file (since the PDF will be huge due to multiple images, etc) and the executable file is navigation friendly with drop-downs etc. It might not be an executable file, but could be a web page or some way that this can be delivered to the client in a friendly professional way. The PDF will have to be generated somehow so that it can be printed as a hard copy. What languages and skill sets will I need to accomplish this project?

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  • How should I go about implementing a points-to analysis in Maude?

    - by reprogrammer
    I'm going to implement a points-to analysis algorithm. I'd like to implement this analysis mainly based on the algorithm by Whaley and Lam. Whaley and Lam use a BDD based implementation of Datalog to represent and compute the points-to analysis relations. The following lists some of the relations that are used in a typical points-to analysis. Note that D(w, z) :- A(w, x),B(x, y), C(y, z) means D(w, z) is true if A(w, x), B(x, y), and C(y, z) are all true. BDD is the data structure used to represent these relations. Relations input vP0 (variable : V, heap : H) input store (base : V, field : F, source : V) input load (base : V, field : F, dest : V) input assign (dest : V, source : V) output vP (variable : V, heap : H) output hP (base : H, field : F, target : H) Rules vP(v, h) :- vP0(v, h) vP(v1, h) :- assign(v1, v2), vP(v2, h) hP(h1, f,h2) :- store(v1, f, v2), vP(v1, h1), vP(v2, h2) vP(v2, h2) :- load(v1, f, v2), vP(v1, h1), hP(h1, f, h2) I need to understand if Maude is a good environment for implementing points-to analysis. I noticed that Maude uses a BDD library called BuDDy. But, it looks like that Maude uses BDDs for a different purpose, i.e. unification. So, I thought I might be able to use Maude instead of a Datalog engine to compute the relations of my points-to analysis. I assume Maude propagates independent information concurrently. And this concurrency could potentially make my points-to analysis faster than sequential processing of rules. But, I don't know the best way to represent my relations in Maude. Should I implement BDD in Maude myself, or Maude's internal unification based on BDD has the same effect?

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  • Why doesn't Python require exactly four spaces per indentation level?

    - by knorv
    Whitespace is signification in Python in that code blocks are defined by their indentation. Furthermore, Guido van Rossum recommends using four spaces per indentation level (see PEP 8: Style Guide for Python Code). What was the reasoning behind not requiring exactly four spaces per indentation level as well? Are there any technical reasons? It seems like all the arguments that can be made for making whitespace define code blocks can also be used to argument for setting an exact whitespace length for one indentation level (say four spaces).

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  • C# StreamReader.EndOfStream produces IOException

    - by Ziplin
    I'm working on an application that accepts TCP connections and reads in data until an </File> marker is read and then writes that data to the filesystem. I don't want to disconnect, I want to let the client sending the data to do that so they can send multiple files in one connection. I'm using the StreamReader.EndOfStream around my outter loop, but it throws an IOException when the client disconnects. Is there a better way to do this? private static void RecieveAsyncStream(IAsyncResult ar) { TcpListener listener = (TcpListener)ar.AsyncState; TcpClient client = listener.EndAcceptTcpClient(ar); // init the streams NetworkStream netStream = client.GetStream(); StreamReader streamReader = new StreamReader(netStream); StreamWriter streamWriter = new StreamWriter(netStream); while (!streamReader.EndOfStream) // throws IOException { string file= ""; while (file!= "</File>" && !streamReader.EndOfStream) { file += streamReader.ReadLine(); } // write file to filesystem } listener.BeginAcceptTcpClient(RecieveAsyncStream, listener); }

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  • FireLog: proper installation...

    - by kent
    I have installed the firewiresdk26 on my dev mac... and in the Tools/ directory is FireLog. I have run the FireLog 2.0.0.pkg installer on my dev mac, but the payload it deploys is installed in my /System/Library tree, as opposed to my /Developer/SDKs tree. so when I try to include the header iokit/firewire/FireLog.h it does not get found. am I missing something? or doing something wrong? or is this an error in the installer (either FW26 or FireLog installers?) I realize that the FireLog installer is intended to be run on the machine to be debugged remotely and thus it makes sense that the framework is placed in the /System/Library path, however none of the installers gets it into my developer path... I guess I just have to move it over there by hand, but before I do that I wanted to see if I'm just overlooking something silly and need to read the docs with more concentration or something... anyone run into this before? [thx]

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  • Linux Kernel - traverse to buffer heads

    - by CodeRanger
    In the Linux kernel, is there a way to traverse down to the buffer_heads from within a module? I can see how to get to struct bio (task_struct macro: current-bio). But how can I get to the buffer heads? The buffer_head struct holds some information I'd like to obtain at any point regarding physical block numbers.

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  • Dynamics of the using keyword

    - by AngryHacker
    Consider the following code: // module level declaration Socket _client; void ProcessSocket() { _client = GetSocketFromSomewhere(); using (_client) { DoStuff(); // receive and send data Close(); } } void Close() { _client.Close(); _client = null; } Given that that the code calls the Close() method, which closes the _client socket and sets it to null, while still inside the `using' block, what exactly happens behind the scenes? Does the socket really get closed? Are there side effects? P.S. This is using C# 3.0 on the .NET MicroFramework, but I suppose the c#, the language, should function identically. The reason i am asking is that occasionally, very rarely, I run out of sockets (which is a very precious resource on a .NET MF devices).

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  • Javascript comma operator

    - by Claudiu
    When combining assignment with comma (something that you shouldn't do, probably), how does javascript determine which value is assigned? Consider these two snippets: function nl(x) { document.write(x + "<br>"); } var i = 0; nl(i+=1, i+=1, i+=1, i+=1); nl(i); And: function nl(x) { document.write(x + "<br>"); } var i = 0; nl((i+=1, i+=1, i+=1, i+=1)); nl(i); The first outputs 1 4 while the second outputs 4 4 What are the parentheses doing here?

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  • Apache HttpClient CoreConnectionPNames.CONNECTION_TIMEOUT does nothing ?

    - by Maxim Veksler
    Hi, I'm testing some result from HttpClient that looks irrational. It seems that setting CoreConnectionPNames.CONNECTION_TIMEOUT = 1 has no effect because send request to different host return successfully with connect timeout 1 which IMHO can't be the case (1ms to setup TCP handshake???) Am I misunderstood something or is something very strange going on here? The httpclient version I'm using as can be seen in this pom.xml is <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>4.0.1</version> <type>jar</type> </dependency> Here is the code: import java.io.IOException; import java.util.Random; import org.apache.http.HttpEntity; import org.apache.http.HttpResponse; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.client.methods.HttpUriRequest; import org.apache.http.impl.client.DefaultHttpClient; import org.apache.http.params.CoreConnectionPNames; import org.apache.http.util.EntityUtils; import org.apache.log4j.Logger; public class TestNodeAliveness { private static Logger log = Logger.getLogger(TestNodeAliveness.class); public static boolean nodeBIT(String elasticIP) throws ClientProtocolException, IOException { try { HttpClient client = new DefaultHttpClient(); // The time it takes to open TCP connection. client.getParams().setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 1); // Timeout when server does not send data. client.getParams().setParameter(CoreConnectionPNames.SO_TIMEOUT, 5000); // Some tuning that is not required for bit tests. client.getParams().setParameter(CoreConnectionPNames.STALE_CONNECTION_CHECK, false); client.getParams().setParameter(CoreConnectionPNames.TCP_NODELAY, true); HttpUriRequest request = new HttpGet("http://" + elasticIP); HttpResponse response = client.execute(request); HttpEntity entity = response.getEntity(); if(entity == null) { return false; } else { System.out.println(EntityUtils.toString(entity)); } // Close just in case. request.abort(); } catch (Throwable e) { log.warn("BIT Test failed for " + elasticIP); e.printStackTrace(); return false; } return true; } public static void main(String[] args) throws ClientProtocolException, IOException { nodeBIT("google.com?cant_cache_this=" + (new Random()).nextInt()); } } Thank you.

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  • Do Scala and Erlang use green threads?

    - by CHAPa
    I've been reading a lot about how Scala and Erlang does lightweight threads and their concurrency model (actors). However, I have my doubts. Do Scala and Erlang use an approach similar to the old thread model used by Java (green threads) ? For example, suppose that there is a machine with 2 cores, so the Scala/Erlang environment will fork one thread per processor? The other threads will be scheduled by user-space (Scala VM / Erlang VM ) environment. Is this correct? Under the hood, how does this really work?

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  • Why is Haskell used so little in the industry?

    - by bugspy.net
    It is a wonderful, very fast, mature and complete language. It exists for a very long time and has a big set of libraries. Yet, it appears not to be widely used. Why ? I suspect it is because it is pretty rough and unforgiving for beginners, and maybe because its lazy execution makes it even harder

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  • In what areas might the use of F# be more appropriate than C#?

    - by Peter McGrattan
    Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#. EDIT: Edited based on feedback from close votes with the intent of reducing perceived ambiguity.

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  • How do I make a module in PLT Scheme?

    - by kunjaan
    I tried doing this: #lang scheme (module duck scheme/base (provide num-eggs quack) (define num-eggs 2) (define (quack n) (unless (zero? n) (printf "quack\n") (quack (sub1 n))))) But I get this error: module: illegal use (not at top-level) in: (module duck scheme/base (provide num-eggs quack) (define num-eggs 2) (define (quack n) (unless (zero? n) (printf "quack\n") (quack (sub1 n))))) what is the correct way?

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  • Self Assessment Tests for Programmers

    - by THX1138.6
    I want to help the Dev team identify areas of knowledge (practical and theoretical) that they can work on. Though I am big believer in focusing on people's strengths being a good programmer requires (I think) being challenged by concepts and ideas that don't always come naturally. We work largely in the web app space using PHP & MySQL but better skills in data modelling, query optimisation, use of MVC and OOP etc. would help the team and the company a lot. I want to help the Dev team manage their careers, explore and expand their skills sets. Be all they can be and better than they were previously. I know its an idealistic goal but work must be about more than simply getting the work done. There should be some time to review, to learn, to grow and get better. Any thoughts, ideas, opinions and directions to tests or similar resources would be greatly appreciated.

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