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• Why does the the Java VM not recover after "Too many open files" errors?

  - by Michael

  In certain well-understood circumstances, our application will open too many sockets (database connections) and reach the maximum open files that the OS allows. We understand this; we are fixing the issue and also bumping up the limit. What we can't explain is why parts of our application don't recover even after the number of connections abates and we're well within the limit. In this case, it's an application running under Tomcat. When this happens, we first start seeing "Too many open files" errors: SEVERE: Socket accept failed java.net.SocketException: Too many open files at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:390) at java.net.ServerSocket.implAccept(ServerSocket.java:453) at java.net.ServerSocket.accept(ServerSocket.java:421) at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:61) at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:310) at java.lang.Thread.run(Thread.java:619) Eventually, we start seeing NoClassDefFoundErrors inside an application thread that's trying to open HTTP connections: java.lang.NoClassDefFoundError: org/apache/commons/httpclient/protocol/ControllerThreadSocketFactory at org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:128) at org.apache.commons.httpclient.HttpConnection.open(HttpConnection.java:707) at org.apache.commons.httpclient.MultiThreadedHttpConnectionManager$HttpConnectionAdapter.open(MultiThreadedHttpConnectionManager.java:1349) [...] Caused by: java.lang.ClassNotFoundException: org.apache.commons.httpclient.protocol.ControllerThreadSocketFactory at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1387) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1233) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) ... 8 more When the errant connections go away, the server starts accepting connections again, and everything seems ok, but we're left with the latter error constantly being spewed to stderr. Although the application typically logs unloaded classes to stdout, I don't see any such logs just before, during or after the "Too many open files" errors. My initial theory was that the Hotspot JVM would unload seemingly unused classes when it encounters "Too many open files," but if so, it doesn't log the fact. I'd also expect it to recover if that were the case. Platform details: Java(TM) SE Runtime Environment (build 1.6.0_14-b08) Java HotSpot(TM) 64-Bit Server VM (build 14.0-b16, mixed mode) Apache Tomcat Version 6.0.18

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• Best method of achieving bi-directional communication between Apple iPad "clients" and a Windows Ser

  - by user361910

  We are currently starting to build a client-server system which will see 10 or more Apple iPad client devices communicating to a central Windows server over a wireless LAN. We wanted to some existing plumbing (.NET remoting/WCF/web services/etc) that would allow us to implement a reliable, secure solution without having to start at a low level (e.g. sockets) and recreate the wheel. One of the major requirements that complicates this scenario is that unlike a traditional web service, the windows server needs to be able to arbitrarily notify the clients whenever certain events occur -- so it is not a simple request/response scenario like the web. Initially, we were going to use Windows clients, so our plan was to use the full-duplex mode of .NET WCF over HTTP|TCP. But now using the iPad, we don't have any of the WCF infrastructure. So my question is: what is the best way to allow an iPad and a Windows server to (securely) communicate over a LAN, with each device able to initiate communication to the other? Am I stuck writing low-level socket code? Thanks!

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• Use UdpClient with IPv4 and IPv6?

  - by mazzzzz

  A little while ago I created a class to deal with my LAN networking programs. I recently upgraded one of my laptops to windows 7 and relized that windows 7 (or at least the way I have it set up) only supports IPv6, but my desktop is still back in the Windows xp days, and only uses IPv4. The class I created uses the UdpClient class, and is currently setup to only work with IPv4.. Is there a way to modify my code to allow sending and receiving of IPv6 and IPv4 packets?? It would be hard to scrap the classes code, a lot of my programs rely on this class. I would like to keep the class as close to its original state, so I don't need to modify my older programs, only switch out the old class for the updated one. Thanks for any and all help, Max Send: using System.Net.Sockets;UdpClient tub = new UdpClient (); tub.Connect ( new IPEndPoint ( ToIP, ToPort ) ); UdpState s = new UdpState (); s.client = tub; s.endpoint = new IPEndPoint ( ToIP, ToPort ); tub.BeginSend ( data, data.Length, new AsyncCallback ( SendCallBack ),s); private void SendCallBack ( IAsyncResult result ) { UdpClient client = (UdpClient)( (UdpState)( result.AsyncState ) ).client; IPEndPoint endpoint = (IPEndPoint)( (UdpState)( result.AsyncState ) ).endpoint; client.EndSend ( result ); } Receive: UdpClient tub = new UdpClient (ReceivePort); UdpState s = new UdpState (); s.client = tub; s.endpoint = new IPEndPoint ( ReceiveIP, ReceivePort ); s.callback = cb; tub.BeginReceive ( new AsyncCallback ( receivedPacket ), s ); public void receivedPacket (IAsyncResult result) { UdpClient client = (UdpClient)( (UdpState)( result.AsyncState ) ).client; IPEndPoint endpoint = (IPEndPoint)( (UdpState)( result.AsyncState ) ).endpoint; Byte[] receiveBytes = client.EndReceive ( result, ref endpoint ); ReceivedPacket = new Packet ( receiveBytes ); client.Close(); //Do what ever with the packets now }

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• cannot receive UDP broadcast packets

  - by user292792

  Hello I have 2 boxes: - an embedded device (ARM Omap with linux) which I'll call "Omap". - a PC (can either be Windows or linux). Scenario 1 Both boxes are in the same network (example: my office). The Omap gets its address from a DHCP server (ex: 192.168.10.110). The PC has always the same address (ex. 192.168.10.104). I can successfully exchange UDP broadcast packets on any port. Success. Scenario 2 The 2 boxes are in a network withOUT a DHCP server. The PC has a static IP address (example: 10.10.10.20). The Omap boots, looks for a DHCP server, doesn't find it, and is in what I call "bad IP address" state. Now... Broadcasting UDP packets from the Omap works: the PC can see them. The opposite doesn't work: UDP packets broadcasted by the PC are not seen by the Omap. I am using Wireshark on another PC to verify that the packets are being sent. Failure. I tried to change the Omap ip address (with ifconfig)... no luck. What am I missing? To complete the picture, when the Omap is in Scenario 2, if I run udhcpc ... it can communicate with the DHCP server and get an IP address. I also see the packets with Wireshark. So this means that the DHCP client is able to broadcast UDP packets. (Yes, I tried to use DHCP ports 67/68 but it doesn't work). I am using Boost C++ Asio UDP sockets. Specifically, I took the multicast examples and changed them to do broadcasting. Any help is appreciated. Thanks, Benedetto

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• When using SendKeys()-InvalidOperationException: Undo Operation encountered...

  - by M0DC0M

  Here is my code public void KeyPress() { //Finds the target window and sends a key command to the application Process[] processes = Process.GetProcessesByName("calc"); IntPtr calculatorHandle; foreach (Process proc in processes) { calculatorHandle = proc.MainWindowHandle; if (calculatorHandle == IntPtr.Zero) { MessageBox.Show("Calculator is not running."); return; } SetForegroundWindow(calculatorHandle); break; } SendKeys.SendWait("1"); } After Executing this code I recieve an Error, i know the source is the SendKeys. Here is the full error I am Receiving System.InvalidOperationException was unhandled Message="The Undo operation encountered a context that is different from what was applied in the corresponding Set operation. The possible cause is that a context was Set on the thread and not reverted(undone)." Source="mscorlib" StackTrace: at System.Threading.SynchronizationContextSwitcher.Undo() at System.Threading.ExecutionContextSwitcher.Undo() at System.Threading.ExecutionContext.runFinallyCode(Object userData, Boolean exceptionThrown) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteBackoutCodeHelper(Object backoutCode, Object userData, Boolean exceptionThrown) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Net.ContextAwareResult.Complete(IntPtr userToken) at System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken) at System.Net.Sockets.BaseOverlappedAsyncResult.CompletionPortCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP) InnerException: I'm not sure what the problem is, The number will appear in my calculator but that error pops up

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• According to MSDN ReadFile() Win32 function may incorrectly report read operation completion. When?

  - by Martin Dobšík

  The MSDN states in its description of ReadFile() function (http://msdn.microsoft.com/en-us/library/aa365467%28VS.85%29.aspx): “If hFile is opened with FILE_FLAG_OVERLAPPED, the lpOverlapped parameter must point to a valid and unique OVERLAPPED structure, otherwise the function can incorrectly report that the read operation is complete.” I have some applications that are violating the above recommendation and I would like to know the severity of the problem. I mean the program uses named pipe that has been created with FILE_FLAG_OVERLAPPED, but it reads from it using the following call: ReadFile(handle, &buf, n, &n_read, NULL); That means it passes NULL as the lpOverlapped parameter. That call should not work correctly in some circumstances according to documentation. I have spent a lot of time trying to reproduce the problem, but I was unable to! I always got all data in right place at right time. I was testing only Named Pipes though. Would anybody know when can I expect that ReadFile() will incorrectly return and report successful completion even the data are not yet in the buffer? What would have to happen in order to reproduce the problem? Does it happen with files, pipes, sockets, consoles, or other devices? Do I have to use particular version of OS? Or particular version of reading (like register the handle to I/O completion port)? Or particular synchronization of reading and writing processes/threads? Or when would that fail? It works for me :/ Please help! With regards Martin

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• Java NIO (Netty): How does Encryption or GZIPping work in theory (with filters)

  - by Tom

  Hello Experts, i would be very thankfull if you can explain to me, how in theory the "Interceptor/Filter" Pattern in ByteStreams (over Sockets/Channels) work (in Asynchronous IO with netty) in regard to encryption or compression of data. Given I have a Filter that does GZIPPING. How is this internally implemented? Does the Filter "collect" so many bytes form the channel, that this is a usefull number of bytes that can then be en/decoded? What is in general the minimal "blocksize(data to encode/decode in a chunk)" of socket based gzipping? Does this "blocksize" have to be negotiated in advance between server and client? What happens if the client does not send enough data to "fill" the blocksize (due to a network conquestion) but does not close the connection. Does this mean the other side will simply wait until it gets enough bytes to decode or until a timeout occoures...How is the Filter pattern the applied? The compression filter will de/compress the blocksize of bytes and then store them again in the same buffer would (in the case of netty) i normally be using the ChannelHanlderContext to pass the de/encoded data to the next filter?... Any explanations/links/tutorials (for beginners;-) will be very much appreciated to help me understand how for example encryption/compressing are implemented in socket based communication with filters/interceptor pattern. thank you very much tom

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• Java Server Client Program I/O Exception

  - by AjayP

  I made this program: http://java.sun.com/docs/books/tutorial/networking/sockets/clientServer.html And it works perfectly if I put the server's hostname as 127.0.0.1 or my computers name (Ajay-PC). However these 2 methods are LAN or local only not internet. So I changed it to my internet ip. 70.128.xxx.xxx etc. But it didn't work. I checked: canyouseeme.org and it said 4444 was CLOSED. So I did a quick port forward. Portforward: Name: My Java Program Start Port: 4444 End Port: 4444 Server IP: 10.0.0.12 <-- (Yeah this is my Local IP I checked) then I tried canyouseeme.org AGAIN: and it said 4444 was OPEN I ran my server client program and it yet to work. So my problem is the client server program is not working on the internet just locally. So something is blocking it and I don't know what. Computer: Windows Vista x64 Norton AntiVirus 2010 Thanks! I'll give best answer or whatever to who ever answers the best ;) :)

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• Windows could not start the Apache2 on Local Computer - problem

  - by vaske

  During the installation of Apache2 I got the following message into cmd window: Installing the Apache2.2 service The Apache2.2 service is successfully installed. Testing httpd.conf.... Errors reported here must be corrected before the service can be started. httpd.exe: Could not reliably determine the server's fully qualified domain name , using 192.168.1.3 for ServerName (OS 10048)Only one usage of each socket address (protocol/network address/port) is normally permitted. : make_sock: could not bind to address 0.0.0.0:80 no listening sockets available, shutting down Unable to open logs Note the errors or messages above, and press the key to exit. 24... and after installing everything look fine, but it isn't. If I try to start service I got the following message: Windows could not start the Apache2 on Local Computer. For more information, review the System Event Log. If this is a non-Micorsoft service, contact the service vendor, and refer to service-specific error code 1. Apach2 version is 2.2.9 Does anyone have the same problem, or could help me.

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• What AOP tools exist for doing aspect-oriented programming at the assembly language level against x8

  - by JohnnySoftware

  Looking for a tool I can use to do aspect-oriented programming at the assembly language level. For experimentation purposes, I would like the code weaver to operate native application level executable and dynamic link libraries. I have already done object-oriented AOP. I know assembly language for x86 and so forth. I would like to be able to do logging and other sorts of things using the familiar before/after/around constructs. I would like to be able to specify certain instructions or sequences/patterns of consecutive instructions as what to do a pointcut on since assembly/machine language is not exactly the most semantically rich computer language on the planet. If debugger and linker symbols are available, naturally, I would like to be able to use them to identify subroutines' entry points , branch/call/jump target addresses, symbolic data addresses, etc. I would like the ability to send notifications out to other diagnostic tools. Thus, support for sending data through connection-oriented sockets and datagrams is highly desirable. So is normal logging to files, UI, etc. This can be done using the action part of an aspect to make a function call, but then there are portability issues so the tool needs to support a flexible, well-abstracted logging/notifying mechanism with a clean, simple yet flexible. The goal is rapid-QA. The idea is to be able to share aspect source code braodly within communties as well as publicly. So, there needs to be a declarative security policy file that users can share. This insures that nothing untoward that is hidden directly or indirectly in an aspect source file slips by the execution manager. The policy file format needs to be simple to read, write, modify, understand, type-in, edit, and generate. Sort of like Java .policy files. Think the exact opposite of anything resembling XML Schema files and you get the idea. Is there such a tool in existence already?

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• ASP MVC: Sending an E-mail

  - by wh0emPah

  Okay I'm kindoff new to the .NET platform. And currently i'm learning ASP MVC. I want to send an e-mail from my program and i have the following code: public void sendVerrificationEmail() { //create the mail message MailMessage mail = new MailMessage(); //set the addresses mail.From = new MailAddress("[email protected]"); mail.To.Add("[email protected]"); //set the content mail.Subject = "This is an email"; mail.Body = "this is a sample body with html in it. <b>This is bold</b> <font color=#336699>This is blue</font>"; mail.IsBodyHtml = true; //send the message SmtpClient smtp = new SmtpClient("127.0.0.1"); smtp.Send(mail); } Now when i execute this code i'll get the following exception: System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 127.0.0.1:25 Now i'm very very new to the IIS manager & stuff. so there is probably something wrong there. Do i need to install a virtual smtp server or something?. Currently i have following settings (sorry not allowed to uplaod images yet =) ): http://img153.imageshack.us/img153/695/capture2p.png I've been looking for a few hours now but i can't seem to find a working solution. Help would be appreciated! Tyvm.

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• RDP through TCP Proxy

  - by johng100

  Hi, First time in Stackoverflow and I'm hoping someone can help me. I'm looking at a proof of concept to pass RDP traffic through a TCP Proxy/tunnel which will pass through firewalls using HTTPS. The problem has to do with deploying images to machines and so it can't be assumed that the .NET framework will be present, so C++ is being used at the deployment end of a connection. The basic system I have at present is a program which listens for client connections on a port then passes any data to a WCF service which stores it as a byte array. A deployment machine (using GSoap and C++) polls the WCF service for messages and if it finds them then passes the data onto the target server process via sockets. I know this sounds horrible, but it works for simple test clients and server passing data to and from simple test client and server programs via this WCF/C++/C# proxy layer. But I have to support traffic from RDP, VNC and possibly others, so I need a transparent proxy to do this and am wondering whether the above approach is worth pursuing. I've read up on SSH tunneling and that seems a possibility. My basic question is is it possible to tunnel RDP traffic over HTTPS using custom code. Thanks John

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• Service php-fpm does not support chkconfig

  - by ychian

  Everything is working fine. Just that when i chkconfig –add php-fpm It throws me an error Service php-fpm does not support chkconfig php-5.2.13 php-5.2.13-fpm-0.5.13.diff.gz Below is the configuration i use ./configure --enable-fastcgi --enable-fpm --build=x86_64-redhat-linux-gnu --host=x86_64-redhat-linux-gnu --target=x86_64-redhat-linux-gnu --program-prefix= --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --cache-file=../config.cache --with-libdir=lib64 --with-config-file-path=/etc --with-config-file-scan-dir=/etc/php.d --disable-debug --with-pic --disable-rpath --with-pear --with-bz2 --with-curl --with-exec-dir=/usr/bin --with-freetype-dir=/usr --with-png-dir=/usr --enable-gd-native-ttf --without-gdbm --with-gettext --with-gmp --with-iconv --with-jpeg-dir=/usr --with-openssl --with-png --with-expat-dir=/usr --with-pcre-regex=/usr --with-zlib --with-layout=GNU --enable-exif --enable-ftp --enable-magic-quotes --enable-sockets --enable-sysvsem --enable-sysvshm --enable-sysvmsg --enable-track-vars --enable-trans-sid --enable-yp --enable-wddx --with-kerberos --enable-ucd-snmp-hack --with-unixODBC=shared,/usr --enable-memory-limit --enable-shmop --enable-calendar --enable-dbx --enable-dio --with-mime-magic=/usr/share/file/magic.mime --without-sqlite --with-libxml-dir=/usr --with-xml --with-system-tzdata --without-mysql --without-gd --without-odbc --disable-dom --disable-dba --without-unixODBC --disable-pdo --disable-xmlreader --disable-xmlwriter

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• NSMutableURLRequest wont turn on 3G

  - by Kyle

  I won't bother posting any code because my code works fine when I launch Safari or something that turns on the 3G connection first. When I put it Airport mode, then put back OFF, I will get the behavior of a connection error saying No internet connection with NSMutableURLRequest. I've personally mailed apple about how the Ant gets turned on and off, and they said anything that uses their base CFSocketStream object will turn on the Ant, and I quote: "such as NSURLRequest".. BSD Sockets do not, just so everyone knows.. However, I assumed NSMutableURLRequest would fall into the category of 'Does', but it seems like it doesnt. It never succeeds for me when I cycle Airport or have the phone idle for a long time. It will ALWAYS succeed when I open any other network app first to turn the Ant on. Shall I be forced to do a dummy NSURLRequest call to turn this on; or has anyone been able to get this class working just fine? Remember this is just an implementation of NSMutableURLRequest to upload a file Async, and no other Network operations are performed anywhere; no ads, no version checks, no nothing.

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• Terminal / Panel PC - Single Server Solution: Client/Server or RDP?

  - by StillLearning

  Hi, Our current setup involves a touch screen panel pc with embedded windows, that is connected via network to a server / dedicated pc, within the same physical location. Each of our 'units' has this hardware setup. For a quick resolution we deploy our application to the dedicated pc, and have the panel pc remote desktop to an account which then activates the application. This works but seems a little clunky / rough approach. We did this because the panel pc is rather limited. Now that we have more time, I was wondering if I should separate the application into a gui / application. Deploy the gui logic on the panel pc, and the business/database logic on the dedicated pc. The app is in Java so I was wondering what technology would be best? I was thinking of using RMI, but its not really a client/server app, as there is only one client. Should I stick with RMI, or use Sockets or something else? It will be easy to implement as the application is old, and manually wraps and unwraps data which passes through one class / method call to remote services. All I would have to do is 'RMI' this one method call, and the app will do its own stuff. Cheers.

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• Proper use of the IDisposable interface

  - by cwick

  I know from reading the MSDN documentation that the "primary" use of the IDisposable interface is to clean up unmanaged resources http://msdn.microsoft.com/en-us/library/system.idisposable.aspx. To me, "unmanaged" means things like database connections, sockets, window handles, etc. But, I've seen code where the Dispose method is implemented to free managed resources, which seems redundant to me, since the garbage collector should take care of that for you. For example: public class MyCollection : IDisposable { private List<String> _theList = new List<String>(); private Dictionary<String, Point> _theDict = new Dictionary<String, Point>(); // Die, you gravy sucking pig dog! public void Dispose() { _theList.clear(); _theDict.clear(); _theList = null; _theDict = null; } My question is, does this make the garbage collector free memory used by MyCollection any faster than it normally would? edit: So far people have posted some good examples of using IDisposable to clean up unmanaged resources such as database connections and bitmaps. But suppose that _theList in the above code contained a million strings, and you wanted to free that memory now, rather than waiting for the garbage collector. Would the above code accomplish that?

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• Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (104)

  - by user309670

  Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for multiplexing connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on their port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR?), which in the network context suggests that ...'the connection was reset by peer'; or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? I use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right, but of course in series not parallel. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. Any ideas? I cannot figure-out whatever is wrong even with Valgrind, GDB or much logging. Kindly help where you can.

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• yet another question about migrating to Java

  - by aloneguid

  Hi, There are plenty similar questions, but maybe responses to this one will save a developer's life :) I want to migrate to Java. The reasons are very clear: all the .NET vacancies are client and windows oriented (Silverlight developer, ASP.NET developer, WPF developer etc.) and none of them are any interest to me. I worked with .NET since it's beginning as our company decided to invest in .NET having C++ stack and all the natual problems, so I was just blindly following and actually enjoyed it as the products were mostly server oriented with mixed C++/C# code. Today I have beforementioned problem - can't find an inspiring job. I'd rather kill myself than start working on a Silverlight or WPF project. Searching Java vacancies shows promising results, however they all require a huge java-related technology stack and experience. The question is is there any chance to find a job quickly and without dramatic salary drop (I know that Java guys are usually better paid, so there must be a kind of a credit) and if not, how must time and effort does it take to migrate (my .NET knowledge mostly includes server-oriented technologies like NHibernate, WCF, threading, sockets, ASP.NET web services, Enterprise Library, NInject etc etc etc, and (still) some C++ leftovers). Thanks!

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• moving audio over a local network using GStreamer

  - by James Turner

  I need to move realtime audio between two Linux machines, which are both running custom software (of mine) which builds on top of Gstreamer. (The software already has other communication between the machines, over a separate TCP-based protocol - I mention this in case having reliable out-of-band data makes a difference to the solution). The audio input will be a microphone / line-in on the sending machine, and normal audio output as the sink on the destination; alsasrc and alsasink are the most likely, though for testing I have been using the audiotestsrc instead of a real microphone. GStreamer offers a multitude of ways to move data round over networks - RTP, RTSP, GDP payloading, UDP and TCP servers, clients and sockets, and so on. There's also many examples on the web of streaming both audio and video - but none of them seem to work for me, in practice; either the destination pipeline fails to negotiate caps, or I hear a single packet and then the pipeline stalls, or the destination pipeline bails out immediately with no data available. In all cases, I'm testing on the command-line just gst-launch. No compression of the audio data is required - raw audio, or trivial WAV, uLaw or aLaw encoding is fine; what's more important is low-ish latency.

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• C++ Serialization Clean XML Similar to XSTREAM

  - by disown

  I need to write a linux c++ app which saves it settings in XML format (for easy hand editing) and also communicates with existing apps through XML messages over sockets and HTTP. Problem is that I haven't been able to find any intelligent libs to help me, I don't particular feel like writing DOM or SAX code just to write and read some very simple messages. Boost Serialization was almost a match, but it adds a lot of boost-specific data to the xml it generates. This obviously doesn't work well for interchange formats. I'm wondering if it is possible to make Boost Serialization or some other c++ serialization library generate clean xml. I don't mind if there are some required extra attributes - like a version attribute, but I'd really like to be able to control their naming and also get rid of 'features' that I don't use - tracking_level and class_id for instance. Ideally I would just like to have something similar to xstream in Java. I am aware of the fact that c++ lacks introspection and that it is therefore necessary to do some manual coding - but it would be nice if there was a clean solution to just read and write simple XML without kludges! If this cannot be done I am also interested in tools where the XML schema is the canonical resource (contract first) - a good JAXB alternative to C++. So far I have only found commercial solutions like CodeSynthesis XSD. I would prefer open source solutions. I have tried gSoap - but it generates really ugly code and it is also SOAP-specific. In desperation I also started looking at alternative serialization formats for protobuffers. This exists - but only for Java! It really surprises me that protocol buffers seems to be a better supported data interchange format than XML. I'm going mad just finding libs for this app and I really need some new ideas. Anyone?

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• Writing fortran robust and "modern" code

  - by Blklight

  In some scientific environments, you often cannot go without FORTRAN as most of the developers only know that idiom, and there is lot of legacy code and related experience. And frankly, there are not many other cross-platform options for high performance programming ( C++ would do the task, but the syntax, zero-starting arrays, and pointers are too much for most engineers ;-) ). I'm a C++ guy but I'm stuck with some F90 projects. So, let's assume a new project must use FORTRAN (F90), but I want to build the most modern software architecture out of it. while being compatible with most "recent" compilers (intel ifort, but also including sun/HP/IBM own compilers) So I'm thinking of imposing: global variable forbidden, no gotos, no jump labels, "implicit none", etc. "object-oriented programming" (modules with datatypes + related subroutines) modular/reusable functions, well documented, reusable libraries assertions/preconditions/invariants (implemented using preprocessor statements) unit tests for all (most) subroutines and "objects" an intense "debug mode" (#ifdef DEBUG) with more checks and all possible Intel compiler checks possible (array bounds, subroutine interfaces, etc.) uniform and enforced legible coding style, using code processing tools C stubs/wrappers for libpthread, libDL (and eventually GPU kernels, etc.) C/C++ implementation of utility functions (strings, file operations, sockets, memory alloc/dealloc reference counting for debug mode, etc.) ( This may all seem "evident" modern programming assumptions, but in a legacy fortran world, most of these are big changes in the typical programmer workflow ) The goal with all that is to have trustworthy, maintainable and modular code. Whereas, in typical fortran, modularity is often not a primary goal, and code is trustworthy only if the original developer was very clever, and the code was not changed since then ! (i'm a bit joking here, but not much) I searched around for references about object-oriented fortran, programming-by-contract (assertions/preconditions/etc.), and found only ugly and outdated documents, syntaxes and papers done by people with no large-scale project involvement, and dead projects. Any good URL, advice, reference paper/books on the subject?

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• How to make a small flash swf with ComboBox in Actionscript 3?

  - by Sint

  I have a pure Actionscript 3 project, using flash.* libraries, compiles down to about 6k (using mxmlc). Program handles about 1k shapes, a few sprites, a sockets connection, works great (tastes less filling). Now, how would I add a ComboBox control without incurring excessive bloat? More specificially, I would like to keep the size under 100k. So far I have tried: Adobe mx.controls ComboBoxexample - simple mxml example compiles to 200+k both on my main Linux Box using mxmlc and in Windows using Flash Builder 4 Yahoo Astra - uses mx libraries underneath(so as bloated as Adobe?), plus does not contain exact ComboBox Keith Peter's MinimalComps - seems small, but far from providing ComboBox functionality SPAS (Swing Package for Actionscript) - compiles to 130k, but alpha version of ComboBox does not let me adjust height... asuilib - compiles to 40k, unfortunately this ComboBox does not provide for scrolling items...if it does not fit on screen no way to scroll to it Now my questions: Is there a way to lower size for projects importing mx.controls ? Maybe there is a way to fix SPAS or asuilib ComboBoxes? Perhaps, there are some other libraries which provide a ComboBox(or DropList)?

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• Invalid argument in sendfile() with two regular files

  - by Daniel Hershcovich

  I'm trying to test the sendfile() system call under Linux 2.6.32 to zero-copy data between two regular files. As far as I understand, it should work: ever since 2.6.22, sendfile() has been implemented using splice(), and both the input file and the output file can be either regular files or sockets. The following is the content of sendfile_test.c: #include <sys/sendfile.h> #include <fcntl.h> #include <stdio.h> int main(int argc, char **argv) { int result; int in_file; int out_file; in_file = open(argv[1], O_RDONLY); out_file = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644); result = sendfile(out_file, in_file, NULL, 1); if (result == -1) perror("sendfile"); close(in_file); close(out_file); return 0; } And when I'm running the following commands: $ gcc sendfile_test.c $ ./a.out infile The output is sendfile: Bad file descriptor Which means that the system call resulted in errno = -EINVAL, I think. What am I doing wrong?

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• F# Async problem.

  - by chrisdew

  Hi, I've written a dummy http server as an exercise in F#. I'm using Mono 2.4.4 on Ubuntu 10.04 x86_64, with MonoDevelop. The following code fails to compile with the error: Error FS0039: The field, constructor or member 'Spawn' is not defined (FS0039) Could someone try this in VisualStudio please, I don't know whether this is a Mono problem, or my problem. I have tried several Async examples from the F# book, and they also all produce similar messages about Async.* methods. Thanks, Chris. #light open System open System.IO open System.Threading open System.Net open System.Net.Sockets open Microsoft.FSharp.Control.CommonExtensions printfn "%s" "Hello World!" let headers = System.Text.Encoding.ASCII.GetBytes("HTTP/1.0 200 OK\r\nContent-Type: text/html; charset=UTF-8\r\nContent-Length: 37\r\nDate: Sun, 13 Jun 2010 05:30:00 GMT\r\nServer: FSC/0.0.1\r\n\r\n") let content = System.Text.Encoding.ASCII.GetBytes("<html><body>Hello World</body></html>") let serveAsync (client : TcpClient) = async { let out = client.GetStream() do! out.AsyncWrite(headers) do! Async.Sleep 3000 do! out.AsyncWrite(content) do out.Close() } let http_server (ip, port) = let server = new TcpListener(IPAddress.Parse(ip),port) server.Start() while true do let client = server.AcceptTcpClient() printfn "new client" Async.Spawn (serveAsync client) http_server ("0.0.0.0", 1234)

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• Two objects with dependencies for each other. Is that bad?

  - by Kasper Grubbe

  Hi SO. I am learning a lot about design patterns these days. And I want to ask you about a design question that I can't find an answer to. Currently I am building a little Chat-server using sockets, with multiple Clients. Currently I have three classes. Person-class which holds information like nick, age and a Room-object. Room-class which holds information like room-name, topic and a list of Persons currently in that room. Hotel-class which have a list of Persons and a list of Rooms on the server. I have made a diagram to illustrate it (Sorry for the big size!): http://i.imgur.com/Kpq6V.png I have a list of players on the server in the Hotel-class because it would be nice to keep track of how many there are online right now (Without having to iterate through all of the rooms). The persons live in the Hotel-class because I would like to be able to search for a specific Person without searching the rooms. Is this bad design? Is there another way of achieve it? Thanks.

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