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  • What about parallelism across network using multiple PCs?

    - by MainMa
    Parallel computing is used more and more, and new framework features and shortcuts make it easier to use (for example Parallel extensions which are directly available in .NET 4). Now what about the parallelism across network? I mean, an abstraction of everything related to communications, creation of processes on remote machines, etc. Something like, in C#: NetworkParallel.ForEach(myEnumerable, () => { // Computing and/or access to web ressource or local network database here }); I understand that it is very different from the multi-core parallelism. The two most obvious differences would probably be: The fact that such parallel task will be limited to computing, without being able for example to use files stored locally (but why not a database?), or even to use local variables, because it would be rather two distinct applications than two threads of the same application, The very specific implementation, requiring not just a separate thread (which is quite easy), but spanning a process on different machines, then communicating with them over local network. Despite those differences, such parallelism is quite possible, even without speaking about distributed architecture. Do you think it will be implemented in a few years? Do you agree that it enables developers to easily develop extremely powerfull stuff with much less pain? Example: Think about a business application which extracts data from the database, transforms it, and displays statistics. Let's say this application takes ten seconds to load data, twenty seconds to transform data and ten seconds to build charts on a single machine in a company, using all the CPU, whereas ten other machines are used at 5% of CPU most of the time. In a such case, every action may be done in parallel, resulting in probably six to ten seconds for overall process instead of forty.

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  • Using items in a list as arguments

    - by Travis Brown
    Suppose I have a function with the following type signature: g :: a -> a -> a -> b I also have a list of as—let's call it xs—that I know will contain at least three items. I'd like to apply g to the first three items of xs. I know I could define a combinator like the following: ($$$) :: (a -> a -> a -> b) -> [a] -> b f $$$ (x:y:z:_) = f x y z Then I could just use g $$$ xs. This makes $$$ a bit like uncurry, but for a function with three arguments of the same type and a list instead of a tuple. Is there a way to do this idiomatically using standard combinators? Or rather, what's the most idiomatic way to do this in Haskell? I thought trying pointfree on a non-infix version of $$$ might give me some idea of where to start, but the output was an abomination with 10 flips, a handful of heads and tails and aps, and 28 parentheses. (NB: I know this isn't a terribly Haskelly thing to do in the first place, but I've come across a couple of situations where it seems like a reasonable solution, especially when using Parsec. I'll certainly accept "don't ever do this in real code" if that's the best answer, but I'd prefer to see some clever trick involving the ((->) r) monad or whatever.)

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  • How much one can trust the information published in the wikipedia? [closed]

    - by AKN
    Wikipedia has answers for many question almost in all categories. Let it be Technical Sports Personalities Important events (this day, that day) Scientific terms etc... I know the source of contents are from volunteers (Please correct me if I'm wrong here). But what measures they have to ensure that contents are properly written. Even if they have admin/moderator and all that, they may not be experts in all areas. So how do they validate the appropriateness of the content?

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  • Is there any data missing?

    - by smwikipedia
    Hi experts, Here is some code quoted from Douglas.E.Comer's < Computer Networks and Internets 4th edition. This program will send back any data it received. ... while((len = recv(conn, buff, BUFFERSIZE,0)) >0) // receive data send(conn, buff, len, 0); // send it back ... I am wondering, what if some data arrived when the code is executing in send(..) function, will it miss that data? Because the recv() function is not being executed. If no data is missed, where is the data kept? And by whom? Thanks...

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  • Avoiding dependency carrying

    - by dotnetdev
    When coding, I often come across the following pattern: -A method calls another method (Fine), but the method being called/callee takes parameters, so in the wrapping method, I pass in parameters. Problem is, this dependency carrying can go on and on. How could I avoid this (any sample code appreciated)? Thanks

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  • How do I use Declarations (type, inline, optimize) in Scheme?

    - by kunjaan
    How do I declare the types of the parameters in order to circumvent type checking? How do I optimize the speed to tell the compiler to run the function as fast as possible like (optimize speed (safety 0))? How do I make an inline function in Scheme? How do I use an unboxed representation of a data object? And finally are any of these important or necessary? Can I depend on my compiler to make these optimizations? thanks, kunjaan.

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  • My python program always brings down my internet connection after several hours running, how do I debug and fix this problem?

    - by Shane
    I'm writing a python script checking/monitoring several server/websites status(response time and similar stuff), it's a GUI program and I use separate thread to check different server/website, and the basic structure of each thread is using an infinite while loop to request that site every random time period(15 to 30 seconds), once there's changes in website/server each thread will start a new thread to do a thorough check(requesting more pages and similar stuff). The problem is, my internet connection always got blocked/jammed/messed up after several hours running of this script, the situation is, from my script side I got urlopen error timed out each time it's requesting a page, and from my FireFox browser side I cannot open any site. But the weird thing is, the moment I close my script my Internet connection got back on immediately which means now I can surf any site through my browser, so it must be the script causing all the problem. I've checked the program carefully and even use del to delete any connection once it's used, still get the same problem. I only use urllib2, urllib, mechanize to do network requests. Anybody knows why such thing happens? How do I debug this problem? Is there a tool or something to check my network status once such situation occurs? It's really bugging me for a while... By the way I'm behind a VPN, does it have something to do with this problem? Although I don't think so because my network always get back on once the script closed, and the VPN connection never drops(as it appears) during the whole process.

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  • inode_operations , warning: initialization from incompatible pointer type

    - by djTeller
    Hi everyone, I'm trying to compile a simple Kernel program that read and write from a proc file. I'm trying to set permission to that file by overriding the permission fp in inode_operations struct (.permission) static int module_permission(struct inode *inode, int op, struct nameidata *foo) { . . . } static struct inode_operations Inode_Ops_4_Our_Proc_File = { .permission = module_permission, /* check for permissions */ }; Our_Proc_File->proc_iops = &Inode_Ops_4_Our_Proc_File; For some reason, when I compile this i get - warning: initialization from incompatible pointer type on the following line: .permission = module_permission, /* check for permissions */ Any idea how to solve this? Thanks!

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  • How to implement a list fold in Java

    - by Peter Kofler
    I have a List and want to reduce it to a single value (functional programing term "fold", Ruby term "inject"), like Arrays.asList("a", "b", "c") ... fold ... "a,b,c" As I am infected with functional programing ideas (Scala), I am looking for an easier/shorter way to code it than sb = new StringBuilder for ... { append ... } sb.toString

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  • Hold a network connection although IP address change

    - by rursw1
    Hi, Is it possible to hold an open TCP connection with a client, while the IP address of the client is externally changed? For example, the connection is establishes against address X, but somewhen while the connection is open, the client-side user asks for IP renew and gets another IP address. Can the connection remains alive in this case? Thanks in advance.

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  • Function templates for arbitrary STL containers containing arbitrary types.

    - by Chad Brewbaker
    I have an arbitrary STL container C, which contains elements of an arbitrary type T. I want to create an std::vector that has a copy of all the elements. What is the cleanest way to do this? template <typename C> void myfunction(C container){ /*Derive the type T of elements within the container*/ std::vector<T> mystack; /* Iterate over container and push_back() the elements into mystack*/ }

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  • PHP string to object name.

    - by Smickie
    Ok I have a string... $a_string = "Product"; and I want to use this string in a call to a object like this: $this->$a_string->some_function(); How the dickens do I dynamically call that object? (don't think Im on php 5 mind)

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  • recv receiving not whole data sometime

    - by milo
    hi all, i have following issue: here is the chunk of code: void get_all_buf(int sock, std::string & inStr) { int n = 1; char c; char temp[1024*1024]; bzero(temp, sizeof(temp)); n = recv(sock, temp, sizeof(temp), 0); inStr = temp; }; but sometimes recv returning not whole data (data length always less then sizeof(temp)), only it's part. write side always sends me whole data (i got it with sniffer). what matter? thx. P.S. i know, good manner suggests me to check n (if (n < 0) perror ("error while receiving data), but it doesn't matter now - it's not reason of my problem. P.S.2 i've forgot - it's blocking socket.

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  • Haskell map function with predicate

    - by Paul
    I feel like this should be fairly obvious, or easy, but I just can't get it. What I want to do is apply a function to a list (using map) but only if a condition is held. Imagine you only wanted to divide the numbers which were even: map (`div` 2) (even) [1,2,3,4] And that would give out [1,1,3,2] since only the even numbers would have the function applied to them. Obviously this doesn't work, but is there a way to make this work without having to write a seperate function that you can give to map? Filter is almost there, except I also want to keep the elements which the condition doesn't hold for, and just not apply the function to them. Thanks

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  • Additional concerns when compiling for x64

    - by dotnetdev
    I know that the additional consideratiosn when compiling for x64 is that some data types, like ints, can hold larger values. Are there any concerns? VS2010, released a few days ago, can support compiling for x64 and x32, just like VS2008. The app is x32/86 only. I keep thinking that the app needs to be 64 bit however. What am I missing? Obviously this is not the case. Thanks

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  • Which OS the binary was build

    - by Prakash
    We have recently installed RHEL 5.4 on some existing 6.2 OS and migrated our code from RH 6.2 to RHEL 5.4. We are facing a difficulty that given a binary (on both OS they have same name) how can we distinguish that which gcc and OS it was build as there are some minor differences in between binary respectively made. Please help

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  • java statistics collection for performance evaluation

    - by user384706
    What is the most efficient way to collect and report performance statistic analysis from an application? If I have an application that uses a series of network apis, and I want to report statistics at runtime, e.g. Method doA() was called 3 times and consumed on avg 500ms Method doB() was called 5 times and consumed on avg 1200ms etc Then, I thought of using a well defined data structure (of collection) that each thread updates per remote call, and this can be used for the report. But I think that it will make the performance worse, for the time spend for statistics collection. Am I correct? How would I procceed if I used a background thread for this, and the other threads that did the remote calls were unaware of this collection gathering? Thanks

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  • When will a TCP network packet be fragmented at the application layer?

    - by zooropa
    When will a TCP packet be fragmented at the application layer? When a TCP packet is sent from an application, will the recipient at the application layer ever receive the packet in two or more packets? If so, what conditions cause the packet to be divided. It seems like a packet won't be fragmented until it reaches the Ethernet (at the network layer) limit of 1500 bytes. But, that fragmentation will be transparent to the recipient at the application layer since the network layer will reassemble the fragments before sending the packet up to the next layer, right?

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  • Mapping over multiple Seq in Scala

    - by bsdfish
    Suppose I have val foo : Seq[Double] = ... val bar : Seq[Double] = ... and I wish to produce a seq where the baz(i) = foo(i) + bar(i). One way I can think of to do this is val baz : Seq[Double] = (foo.toList zip bar.toList) map ((f: Double, b : Double) => f+b) However, this feels both ugly and inefficient -- I have to convert both seqs to lists (which explodes with lazy lists), create this temporary list of tuples, only to map over it and let it be GCed. Maybe streams solve the lazy problem, but in any case, this feels like unnecessarily ugly. In lisp, the map function would map over multiple sequences. I would write (mapcar (lambda (f b) (+ f b)) foo bar) And no temporary lists would get created anywhere. Is there a map-over-multiple-lists function in Scala, or is zip combined with destructuring really the 'right' way to do this?

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  • using Python reduce over a list of pairs

    - by user248237
    I'm trying to pair together a bunch of elements in a list to create a final object, in a way that's analogous to making a sum of objects. I'm trying to use a simple variation on reduce where you consider a list of pairs rather than a flat list to do this. I want to do something along the lines of: nums = [1, 2, 3] reduce(lambda x, y: x + y, nums) except I'd like to add additional information to the sum that is specific to each element in the list of numbers nums. For example for each pair (a,b) in the list, run the sum as (a+b): nums = [(1, 0), (2, 5), (3, 10)] reduce(lambda x, y: (x[0]+x[1]) + (y[0]+y[1]), nums) This does not work: >>> reduce(lambda x, y: (x[0]+x[1]) + (y[0]+y[1]), nums) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 1, in <lambda> TypeError: 'int' object is unsubscriptable Why does it not work? I know I can encode nums as a flat list - that is not the point - I just want to be able to create a reduce operation that can iterate over a list of pairs, or over two lists of the same length simultaneously and pool information from both lists. thanks.

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