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• Is there a Java equivalent to libevent?

  - by JoelPM

  I've written a high-throughput server that handles each request in its own thread. For requests coming in it is occasionally necessary to do RPCs to one or more back-ends. These back-end RPCs are handled by a separate queue and thread-pool, which provides some bounding on the number of threads created and the maximum number of connections to the back-end (it does some caching to reuse clients and save the overhead of constantly creating connections). Having done all this, though, I'm beginning to think an event-based architecture would be more efficient. In searching around I haven't found any equivalents to libevent for Java, but maybe I'm not looking in the right place? Mina-statemachine from Apache was the closest thing I found, but it looks more verbose than I need and there's no real release available. Any suggestions?

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• Broadcast-style Bluetooth using Sockets on the iPhone?

  - by Kyle

  Is there any way to open a broadcast bluetooth socket, take a listen and send replies? I want a proper peer to peer system where I broadcast and listen for broadcasts in an area. That way, variable clients can mingle. Is this possible? My theory is this: If GameKit can sit around wasting 25 seconds of the users time whilst having access to a broadcast socket, can't I? Or, must I be in kernel mode for such access? I'm not really sure where the proper bluetooth headers are as well. Thanks for reading!

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• Tricking a Unix Commandline Program into Accepting a File Stream

  - by Alan Storm

  Hypothetical situation. I have a command line program in *nix (linux, BSD, etc.). It was written so that you pass it a text file as an argument $ program file.txt Run the program, it looks at the text in file.txt. Is it possible to "trick" this program into accepting input from a file stream rather than reading a file via disk? I'm pretty comfortable using unix pipes to do stuff, but there's still something a little mysterious about their internals that make it so I can't say (definitively) yes or not to the above question.

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• Efficient algorithm to generate all solutions of a linear diophantine equation with ai=1

  - by Ben

  I am trying to generate all the solutions for the following equations for a given H. With H=4 : 1) ALL solutions for x_1 + x_2 + x_3 + x_4 =4 2) ALL solutions for x_1 + x_2 + x_3 = 4 3) ALL solutions for x_1 + x_2 = 4 4) ALL solutions for x_1 =4 For my problem, there are always 4 equations to solve (independently from the others). There are a total of 2^(H-1) solutions. For the previous one, here are the solutions : 1) 1 1 1 1 2) 1 1 2 and 1 2 1 and 2 1 1 3) 1 3 and 3 1 and 2 2 4) 4 Here is an R algorithm which solve the problem. library(gtools) H<-4 solutions<-NULL for(i in seq(H)) { res<-permutations(H-i+1,i,repeats.allowed=T) resum<-apply(res,1,sum) id<-which(resum==H) print(paste("solutions with ",i," variables",sep="")) print(res[id,]) } However, this algorithm makes more calculations than needed. I am sure it is possible to go faster. By that, I mean not generating the permutations for which the sums is H Any idea of a better algorithm for a given H ?

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• Interacting with system commands using a web dev language

  - by Jamie

  Hi all, First of all, sorry for the vague title. Let me explain. At work we're currently using SunGrid I've been assigned a project to create a web interface wrapper for interacting with the engine. i.e. displaying users jobs, submitting jobs via a nice GUI etc. (most of the sgrid commands output xml which is nice) My question for you chaps is the following: What web dev language would you use to interact with the system? i.e. use the language to do a system call and evaluate the response. I'm not after an argument on which language is best, I just would like to know which language is specifically good for interacting with the system and is also good for web dev.

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• Confusion regarding laziness

  - by Abhinav Kaushik

  I have a function myLength = foldl (\ x _ -> x + 1) 0 which fails with stack overflow with input around 10^6 elements (myLength [1..1000000] fails). I believe that is due to the thunk build up since when I replace foldl with foldl', it works. So far so good. But now I have another function to reverse a list : myReverse = foldl (\ acc x -> x : acc) [] which uses the lazy version foldl (instead of foldl') When I do myLength . myReverse $ [1.1000000]. This time it works fine. I fail to understand why foldl works for the later case and not for former?

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• Sharepoint hit counter is not displayed.

  - by stckvrflw

  I followed the instructions here http://support.microsoft.com/kb/825532 After that when I preview my page, I can't see the hitcounter. I learned that it may be related to permissions of the site but I couldn't find how to do it. Is it realy related to permissions ? If so what should I do to ? And any external solution (except this one: http://hitcounter.codeplex.com/) would help, the one in pharanthesis, I couldn't make it work.

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• Pattern Matching in Scheme

  - by kunjaan

  How do I accept the following input? (list of 0 or more charcters and ends with 3) or (list of 1 or more characters 4 and 0 or more characters after 4) something like (match ( list 3)) -> #t (match ( list 1 2 3)) -> #t (match (list 1 2 3 4)) -> #t (match (list 1 2 3 4 5)) -> #t (match (list 4)) -> #f EDIT: THIS IS NOT MY HOMEWORK. I trying to write something like ELIZA from PAIP but I know only how to write a pattern that begins with a word.

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• SocketTimeOutException while creating socket, java

  - by Sunil Kumar Sahoo

  Hi All, I have created a sample java socket application. I used Socket s = new Socket(ip, port) Now it works fine. but when my internet connection is very slow that time after a long interval (even if sometimes after 2 minutes) i used to get SocketTimeOutException in that line. means it gives that error while creating socket. I want the exception should be handled properly means if internet connection is very slow then if that error occurs it happens very late now . I want if this type of error occurs then it should be caught very fast means the error should not come at such a delay interval of time rather it should come immediately. How to achieve this. Thanks Sunil Kumar Sahoo

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• How to counter the "one true language" perspective?

  - by Rob Wells

  How do you work with someone when they haven't been able to see that there is a range of other languages out there beyond "The One True Path"? I mean someone who hasn't realised that the modern software professional has a range of tools in his toolbox. The person whose knee jerk reaction is, for example, "We must do this is C++!" "Everything must be done in C++!" What's the best approach to open people up to the fact that "not everything is a nail"? How may I introduce them to having a well-equipped toolbox, selecting the best tool for the job at hand?

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• iPhone - Browsing iPhone files through computer

  - by quano

  I want to be able to send files from an iPhone app to a computer. What would be the easiest way of doing this? I've made simple server client programs before, but in those, the client has always needed to connect to the server before being able to receive messages from it. There is an app for the iPhone called iSimulate, where you put a server on a Mac (the iPhone simulator), and then you use the iSimulate app of an iTouch or iPhone to send touch events to the server. This app does not require you to type in an ip-address. Instead it presents a list of available computers that have this server up and running. How exactly is this being done? Can a server broadcast a message over a network, w/o anyone being connected to the server? How does that work? How does a client listen for that broadcast? Here's a video of the app I'm talking about: http://www.youtube.com/watch?v=N3Qpd1ycZh4

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• side effect gotchas in python/numpy? horror stories and narrow escapes wanted

  - by shabbychef

  I am considering moving from Matlab to Python/numpy for data analysis and numerical simulations. I have used Matlab (and SML-NJ) for years, and am very comfortable in the functional environment without side effects (barring I/O), but am a little reluctant about the side effects in Python. Can people share their favorite gotchas regarding side effects, and if possible, how they got around them? As an example, I was a bit surprised when I tried the following code in Python: lofls = [[]] * 4 #an accident waiting to happen! lofls[0].append(7) #not what I was expecting... print lofls #gives [[7], [7], [7], [7]] #instead, I should have done this (I think) lofls = [[] for x in range(4)] lofls[0].append(7) #only appends to the first list print lofls #gives [[7], [], [], []] thanks in advance

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• Known "Z notation" applications ?

  - by Amadeus45

  I was just remembering back my university classes and was wondering to know if anyone out here even used the "Z notation" in a professional environment. I honestly must say that it was the single most boring class that I have ever attended in my life. Maybe because of the teacher, but at the time we really all thought it was a big waste of time. I might have been wrong, which is why I'd like to hear you about it. If you are using it or some derived language (Z++), I'd just like to know how is it useful for you. Just curious to know some commonly-known applications of Z or your application. For those who are not familiar : http://staff.washington.edu/jon/z/z-examples.html

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• n++ vs n=n+1. Which one is faster

  - by piemesons

  Somebody asked me Is n++ faster than n=n+1? My answer:-- ++ is a unary operator in C which(n++) takes only one machine instruction to execute while n=n+1 takes more than one machine instructions to execute. Anyone correct me if I am wrong, but in Assembler it take something like this: n++: inc n n = n + 1; mov ax n add ax 1 mov n ax its not exactli this, but it's near it.but in most cases a good compiler will change n = n + 1 to ++n.So A good compiler will generate same code for both and hence the same time to execute.

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• Using Unix Process Controll Methods in Ruby

  - by John F. Miller

  Ryan Tomayko touched off quite a fire storm with this post about using Unix process control commands. We should be doing more of this. A lot more of this. I'm talking about fork(2), execve(2), pipe(2), socketpair(2), select(2), kill(2), sigaction(2), and so on and so forth. These are our friends. They want so badly just to help us. I have a bit of code (a delayed_job clone for DataMapper that I think would fit right in with this, but I'm not clear on how to take advantage of the listed commands. Any Ideas on how to improve this code? def start say "*** Starting job worker #{@name}" t = Thread.new do loop do delay = Update.work_off(self) break if $exit sleep delay break if $exit end clear_locks end trap('TERM') { terminate_with t } trap('INT') { terminate_with t } trap('USR1') do say "Wakeup Signal Caught" t.run end end

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• What languages have a while-else type control structure, and how does it work?

  - by Dan

  A long time ago, I thought I saw a proposal to add an else clause to for or while loops in C or C++... or something like that. I don't remember how it was supposed to work -- did the else clause run if the loop exited normally but not via a break statement? Anyway, this is tough to search for, so I thought maybe I could get some CW answers here for various languages. What languages support adding an else clause to something other than an if statement? What is the meaning of that clause? One language per answer please.

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• FTP to SFTP in shell scripting

  - by Kimi

  This script is to connect to different servers and copy a file from a loaction defined. It is mandatory to use sftp and not ftp. #!/usr/bin/ksh -xvf Detail="jyotibo|snv4915|/tlmusr1/tlm/rt/jyotibo/JyotiBo/ jyotibo|snv4915|/tlmusr1/tlm/rt/jyotibo/JyotiBo/" password=Unix11! c_filename=import.log localpath1=`pwd` for i in $Detail do echo $i UserName=`echo $i | cut -d'|' -f1` echo $UserName remotehost=`echo $i | cut -d'|' -f2` echo $remotehost remote_path=`echo $i | cut -d'|' -f3` echo $remote_path { echo "open $remotehost user $UserName $password lcd $localpath1 cd $remote_path bi prompt mget $c_filename prompt " } |ftp -i -n -v 2>&1 done I want to do the similar thing using sftp instead of ftp.

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• 0xDEADBEEF equivalent for 64-bit development?

  - by Peter Mortensen

  For C++ development for 32-bit systems (be it Linux, Mac OS or Windows, PowerPC or x86) I have initialised pointers that would otherwise be undefined (e.g. they can not immediately get a proper value) like so: int *pInt = reinterpret_cast<int *>(0xDEADBEEF); (To save typing and being DRY the right-hand side would normally be in a constant, e.g. BAD_PTR.) If pInt is dereferenced before it gets a proper value then it will crash immediately on most systems (instead of crashing much later when some memory is overwritten or going into a very long loop). Of course the behavior is dependent on the underlying hardware (getting a 4 byte integer from the odd address 0xDEADBEEF from a user process may be perfectly valid), but the crashing has been 100% reliable for all the systems I have developed for so far (Mac OS 68xxx, Mac OS PowerPC, Linux Redhat Pentium, Windows GUI Pentium, Windows console Pentium). For instance on PowerPC it is illegal (bus fault) to fetch a 4 byte integer from an odd address. What is a good value for this on 64-bit systems?

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• Effects of the `extern` keyword on C functions

  - by Elazar Leibovich

  In C I did not notice any effect of the extern keyword used before function declaration. At first I thougth that when defining extern int f(); in a single file forces you to implement it outside of the files scope, however I found out that both extern int f(); int f() {return 0;} And extern int f() {return 0;} Compiles just fine, with no warnings from gcc. I used gcc -Wall -ansi, he wouldn't even accept // comments. Are there any effects for using extern before function definitions? Or is it just an optional keyword with no side effects for functions. In the latter case I don't understand why did the standard designers chose to litter the grammar with superfluous keywords. EDIT: to clarify, I know there's usage for extern in variables, but I'm only asking about extern in functions.

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• How do we, as a community, help encourage programming in public schools? (Or state Schools for the U

  - by NoMoreZealots

  PRIMARY MOTIVATION My office gets involved with the "First Robotics" competitions and one thing that lingers year to year is the students typically have no preparation for doing even simple programming as part of the public schools system. While the science classes provide some basic grasp of mechanical and electrical concepts, by in large computer programming gets no coverage from the curriculum. (This my be different in other areas of the country/world.) What makes it worse is there is only a short period of time you have to prepare the student's and help them design the robot. Talking to some professors from local colleges, it's a problem because you can't assume even the most basic understanding for freshman CS majors. Languages like Python, Lua and BASIC are simple enough for at least high school level students, if not younger. SCOPE So how do you get public schools to support a programming, at least to the level of "Try it in BASIC" examples that used to be at the end of a chapter in my Algebra book? At least enough to prepare them for event's such as the FIRST Robotic competitions. Which the primary objectives are to teach problem solving and team work, and to possible foster an interest in Math, Science and Engineering in general. (Not force feed to them, as some people her seem to be implying.) Edit: Why teach kids: (Since 2000 CS enrollment in US colleges has decreased by 70% while college enrollment has increased, this is a PROBLEM.) Saying there is no value in teaching someone programming in Jr./High school because they might think "they know programming." Is like saying there's no value in teaching High school science and physics, because they might decide they "know physics." Leading to abuse like: "I passed a high school physics class, I'm going to develop a Unified Quantum Gravitational Theory." Better Prepared students are better students. Instead it would allows college programs to raise the bar on the entry level courses, allowing students to be weeded out based on their understanding of more advanced material. Plus people who did poorly in that in topic in High school aren't as likely to say "I think there's money in computer's so I'll computer science." Plus if people take it in high school and decide THEN that it's not for them, it's better than them wasting their money to PAY a college to figure that out. The result is that people who take the degree are more likely to succeed and be there for the RIGHT reasons. (i.e. It's what they REALLY want to do. And that's REALLY the key to being good at anything.) Programming is like anything else, the more practice and genuine interest you have the better you get. If you start them later, they get less practice. The earlier give them the opportunity to start, the more practice they will get. All other things equal, the more practice the better the programmer.

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• A question for retrieve minix os version

  - by majnun

  Hi guys i'm having a project for the university in which (above others ) i have to get the minix os version from kernell call.I'm not a very experienced programmer so this is what i have come to (with some help ) int main (int argc, char *argv[] ) { char M3ca1[23]; message ml; m.m_u.m_m1.m3ca1= OS_VERSION; char temp=_syscall(MM,69,&m); printf("the os version is %c\n",temp); return 0; } and i get multiple errors.IF you have any ideas it would be greatly appreciated.

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• Make a function which returns the original list except the argument

  - by Alex

  I want make a function which takes a list of string and a string and returns NONE if there is no string in the string list, otherwise it returns SOME of the list of string which is the same as the original list of string except it doesn't contain the initial string (pattern): fun my_function (pattern, source_list) = case source_list of [] => NONE | [x] => if pattern = x then SOME [] else NONE | x::xs => if pattern = x then SOME (xs) else SOME (x) :: my_function (pattern, xs) (* this is wrong, what to do here?*) val a = my_function ("haha", ["12", "aaa", "bbb", "haha", "ccc", "ddd"]) (* should be SOME ["12", "aaa", "bbb", "ccc", "ddd"]*) val a2 = my_function ("haha2", ["123", "aaa", "bbb", "haha", "ccc"]) (*should be NONE*) val a3 = my_function ("haha3", ["haha3"]) (* should be SOME []*) I'm confused by the 3rd case: x::xs => .... What should do there? Note that I'd like not to use any sml library function.

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• What are all the disadvantages of using files as a means of communicating between two processes?

  - by Manny

  I have legacy code which I need to improve for performance reasons. My application comprises of two executables that need to exchange certain information. In the legacy code, one exe writes to a file ( the file name is passed as an argument to exe) and the second executable first checks if such a file exists; if does not exist checks again and when it finds it, then goes on to read the contents of the file. This way information in transferred between the two executables. The way the code is structured, the second executable is successful on the first try itself. Now I have to clean this code up and was wondering what are the disadvantages of using files as a means of communication rather than some inter-process communication like pipes.Is opening and reading a file more expensive than pipes? Are there any other disadvantages? And how significant do you think would be the performance degradation. The legacy code is run on both windows and linux.

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• How to acces File over the Network

  - by Polo

  Hi! I am having a hard time on this one, I have à folder over the network wit public accès (no credential restriction). I am trying to do à File.Exist or Directory.Exist and I keep on having a exception. Can somewone tell me the good way to do IO over the network. EDIT 1 FOR DETAILS: if i do execture = \agoodip\Public\test.txt I get the file etc etc In my code it look like a basic Directory.Exist(@"\agoodip\Public") or File.exist(@"\agoodip\Public\test.txt") The exception I get is Path not found. Thanks!

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• What are the best programming websites on the web?

  - by lajoo

  Ok,lets have a big list here,write about the best programming websites you have approached and a description of them and they'll be added here.i'll write some websites for now: UVA Online Judge a bunch of useful programming problems are there that you could use to improve your programming. Prgrammers Heven Resources for different programming languages. SourceForge This site Has lots of open source programs available for download,it's a must-go site for a programmer. W3Schools This Websites has all you need to learn about Web-designing Languages like Java Script,Css,PHP,HTML,.... Note:This is not an advertising topic,it's just a guide for programmers to find what they need.

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