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• How to setup matlabpool for multiple processors?

  - by JohnIdol

  I just setup a Extra Large Heavy Computation EC2 instance to throw it at my Genetic Algorithms problem, hoping to speed up things. This instance has 8 Intel Xeon processors (around 2.4Ghz each) and 7 Gigs of RAM. On my machine I have an Intel Core Duo, and matlab is able to work with my two cores just fine by runinng: matlabpool open 2 On the EC2 instance though, matlab only is capable of detecting 1 out of 8 processors, and if I try running: matlabpool open 8 I get an error saying that the ClusterSize is 1 since there's only 1 core on my CPU. True, there is only 1 core on each CPU, but I have 8 CPUs on the given EC2 instance! So the difference from my machine and the ec2 instance is that I have my 2 cores on a single processor locally, while the EC2 instance has 8 distinct processors. My question is, how do I get matlab to work with those 8 processors? I found this paper, but it seems related to setting up matlab with multiple EC2 instances (not related to multiple processors on the same instance, EC2 or not), which is not my problem. Any help appreciated!

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• Binding a member signal to a function

  - by the_drow

  This line of code compiles correctly without a problem: boost::bind(boost::ref(connected_), boost::dynamic_pointer_cast<session<version> >(shared_from_this()), boost::asio::placeholders::error); However when assigning it to a boost::function or as a callback like this: socket_->async_connect(connection_->remote_endpoint(), boost::bind(boost::ref(connected_), boost::dynamic_pointer_cast<session<version> >(shared_from_this()), boost::asio::placeholders::error)); I'm getting a whole bunch of incomprehensible errors (linked since it's too long to fit here). On the other hand I have succeeded binding a free signal to a boost::function like this: void print(const boost::system::error_code& error) { cout << "session connected"; } int main() { boost::signal<void(const boost::system::error_code &)> connected_; connected_.connect(boost::bind(&print, boost::asio::placeholders::error)); client<>::connection_t::socket_ptr socket_(new client<>::connection_t::socket_t(conn->service())); // shared_ptr of a tcp socket socket_->async_connect(conn->remote_endpoint(), boost::bind(boost::ref(connected_), boost::asio::placeholders::error)); conn->service().run(); // io_service.run() return 0; } This works and prints session connected correctly. What am I doing wrong here?

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• Matlab crashes on library initialize when called from Java

  - by David Sauter

  Hello everyone. The setup I have is I'm using a Java application to call native C-code with JNI, which in turn starts up the MATLAB runtime and calls functions on it (I know there are other solutions to call MATLAB methods from Java). The problem is that the MATLAB engine crashes at some point during the initialization and I don't know what's causing it exactly. The crash causes my jvm to terminate, I assume it's some kind of memory corruption. The C++ code calling MATLAB functions that is actually crashing is JNIEXPORT void JNICALL some_jni_vodoo_initializeLibrary(JNIEnv* env, jclass thisClass) { try { if (!mclInitializeApplication(NULL, 0)) { THROW_EXCEPTION(env, "Could not initialize the application properly."); return; } if (!<library>Initialize()) { THROW_EXCEPTION(env, "Could not initialize the library."); return; } } ... The function <library>Initialize() crashes here, the Java error log reads Stack Trace: [0] jmi.dll:0x793f4175(0x7934cdca, 1, 0x7937e67c "à;.y`[email protected] in C:\BUILD_ARE..", 0x792d6a32) [1] jvm.dll:0x792df9a5(0xc0000005, 0x79356791, 0x4961b400 "Ð\8y", 0x6d8b29de) [2] jvm.dll:0x792e0431(0x8b515008, 0x70f0e8ce, 0x8b5ffffa, 0xc25d5ec6) ------------------------------------------------------------------------ Fatal Java Exception detected at Fri Apr 30 11:08:08 2010 ------------------------------------------------------------------------ Configuration: MATLAB Version: 7.8.0.347 (R2009a) MATLAB License: unknown Operating System: Microsoft Windows Vista Window System: Version 6.0 (Build 6002: Service Pack 2) Processor ID: x86 Family 6 Model 10 Stepping 5, GenuineIntel Virtual Machine: Java is not enabled Default Encoding: windows-1252 Java is not enabled I really have no idea what could be wrong. Is there not enough memory from the jvm? I guess the problem is somehow related to Java, since calling the JNI functions from a simple test C++ program works fine... Thanks

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• Can I make a "TCP packet modifier" using tun/tap and raw sockets?

  - by benhoyt

  I have a Linux application that talks TCP, and to help with analysis and statistics, I'd like to modify the data in some of the TCP packets that it sends out. I'd prefer to do this without hacking the Linux TCP stack. The idea I have so far is to make a bridge which acts as a "TCP packet modifier". My idea is to connect to the application via a tun/tap device on one side of the bridge, and to the network card via raw sockets on the other side of the bridge. My concern is that when you open a raw socket it still sends packets up to Linux's TCP stack, and so I couldn't modify them and send them on even if I wanted to. Is this correct? A pseudo-C-code sketch of the bridge looks like: tap_fd = open_tap_device("/dev/net/tun"); raw_fd = open_raw_socket(); for (;;) { select(fds = [tap_fd, raw_fd]); if (FD_ISSET(tap_fd, &fds)) { read_packet(tap_fd); modify_packet_if_needed(); write_packet(raw_fd); } if (FD_ISSET(raw_fd, &fds)) { read_packet(raw_fd); modify_packet_if_needed(); write_packet(tap_fd); } } Does this look possible, or are there other better ways of achieving the same thing? (TCP packet bridging and modification.)

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• FOR BOUNTY: "QFontEngine(Win) GetTextMetrics failed ()" error on 64-bit Windows

  - by David Murdoch

  I'll add a large bounty to this when Stack Overflow lets me. I'm using wkhtmltopdf to convert HTML web pages to PDFs. This works perfectly on my 32-bit dev server [unfortunately, I can't ship my machine :-p ]. However, when I deploy to the web application's 64-bit server the following errors are displayed: C:\>wkhtmltopdf http://www.google.com google.pdf Loading pages (1/5) QFontEngine::loadEngine: GetTextMetrics failed () ] 10% QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngine::loadEngine: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngine::loadEngine: GetTextMetrics failed () ] 36% QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () // ...etc.... and the PDF is created and saved... just WITHOUT text. All form-fields, images, borders, tables, divs, spans, ps, etc are rendered accurately...just void of any text at all. Server information: Windows edition: Windows Server Standard Service Pack 2 Processor: Intel Xeon E5410 @ 2.33GHz 2.33 GHz Memory: 8.00 GB System type: 64-bit Operating System Can anyone give me a clue as to what is happening and how I can fix this? Also, I wasn't sure what to tag/title this question with...so if you can think of better tags/title comment them or edit the question. :-)

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• Connection aborted.

  - by Pinu

  I am getting this error when i am trying to upload a file of 3mb or more on my WCF client application. SocketException (0x2745): An established connection was aborted by the software in your host machine] System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags) +73 System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size) +131 [IOException: Unable to read data from the transport connection: An established connection was aborted by the software in your host machine.] System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size) +294 System.Net.PooledStream.Read(Byte[] buffer, Int32 offset, Int32 size) +26 System.Net.Connection.SyncRead(HttpWebRequest request, Boolean userRetrievedStream, Boolean probeRead) +297 [WebException: The underlying connection was closed: An unexpected error occurred on a receive.] System.Net.HttpWebRequest.GetResponse() +5314029 System.ServiceModel.Channels.HttpChannelRequest.WaitForReply(TimeSpan timeout) +54 [CommunicationException: An error occurred while receiving the HTTP response to http://localhost:4649/Service1.svc. This could be due to the service endpoint binding not using the HTTP protocol. This could also be due to an HTTP request context being aborted by the server (possibly due to the service shutting down). See server logs for more details.] System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) +7596735 System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) +275 SmartConnectClient.SmartConnect.IService1.OrderCertMail(OrderCertMailResponse OrderCertMail1) +0 SmartConnectClient.SmartConnect.Service1Client.OrderCertMail(OrderCertMailResponse OrderCertMail1) in c:\documents and settings\pkale\my documents\visual studio 2008\projects\smartconnectclient\smartconnectclient\service references\smartconnect\reference.cs:1939 SmartConnectClient.Test_CertMail_Order.Page_Load(Object sender, EventArgs e) in C:\Documents and Settings\pkale\My Documents\Visual Studio 2008\Projects\SmartConnectClient\SmartConnectClient\Test_CertMail_Order.aspx.cs:40 System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14 System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35 System.Web.UI.Control.OnLoad(EventArgs e) +99 System.Web.UI.Control.LoadRecursive() +50 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627 enter code here

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• What is the best way to send structs containing enum values via sockets in C.

  - by Axel

  I've lots of different structs containing enum members that I have to transmit via TCP/IP. While the communication endpoints are on different operating systems (Windows XP and Linux) meaning different compilers (gcc 4.x.x and MSVC 2008) both program parts share the same header files with type declarations. For performance reasons, the structures should be transmitted directly (see code sample below) without expensively serializing or streaming the members inside. So the question is how to ensure that both compilers use the same internal memory representation for the enumeration members (i.e. both use 32-bit unsigned integers). Or if there is a better way to solve this problem... //type and enum declaration typedef enum { A = 1, B = 2, C = 3 } eParameter; typedef enum { READY = 400, RUNNING = 401, BLOCKED = 402 FINISHED = 403 } eState; #pragma pack(push,1) typedef struct { eParameter mParameter; eState mState; int32_t miSomeValue; uint8_t miAnotherValue; ... } tStateMessage; #pragma pack(pop) //... send via socket tStateMessage msg; send(iSocketFD,(void*)(&msg),sizeof(tStateMessage)); //... receive message on the other side tStateMessage msg_received; recv(iSocketFD,(void*)(&msg_received),sizeof(tStateMessage)); Additionally... Since both endpoints are little endian maschines, endianess is not a problem here. And the pack #pragma solves alignment issues satisfactorily. Thx for your answers, Axel

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• Oracle performance problems with large batch of XSL operations

  - by FrustratedWithFormsDesigner

  I have a system that is performing many XSL transformations on XMLType objects. The problem is that the system gradually slows down over time, and sometimes crashes when it runs out of memory. It seems that the slow down (and possibly memory crash) is around the dbms_xslprocessor.processXSL function call, which gradually takes longer and longer to complete. The code looks like this: v_doc dbms_xmldom.DOMDocument; v_transformer dbms_xmldom.DOMDocument; v_XSLprocessor dbms_xslprocessor.Processor; v_stylesheet dbms_xslprocessor.Stylesheet; v_clob clob; ... transformer := PKG_STUFF.getXSL(); v_transformer := dbms_xmldom.newDOMDocument(transformer); v_XSLprocessor := Dbms_Xslprocessor.newProcessor; v_stylesheet := dbms_xslprocessor.newStylesheet(v_transformer, ''); ... for source_data in (select id in source_tbl) loop begin v_doc := PKG_CONVERT.convert(in_id => source_data.id); --start time of operation v_begin_op_time := dbms_utility.get_time; --reset the CLOB v_clob := ' '; --Apply XSL Transform dbms_xslprocessor.processXSL(p => v_XSLprocessor, ss => v_stylesheet, xmldoc => v_Doc, cl => v_clob); v_doc := dbms_xmldom.newDOMDocument(XMLType(v_clob)); --end time v_end_op_time := dbms_utility.get_time; --calculate duration v_time_taken := (((v_end_op_time - v_begin_op_time))); --log the duration PKG_LOG.log_message('Time taken to transform XML: '||v_time_taken); ... ... DBMS_XMLDOM.freeDocument(v_Doc); DBMS_LOB.freetemporary(lob_loc => v_clob); end loop; The time taken to transform the XML is slowly creeping up (I suppose it might also be the call to dbms_xmldom.newDOMDocument, but I had thought that to be fairly straightforward). I have no idea why.... :( (Oracle 10g)

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• while(1) block my recv thread

  - by zp26

  Hello. I have a problem with this code. As you can see a launch with an internal thread recv so that the program is blocked pending a given but will continue its execution, leaving the task to lock the thread. My program would continue to receive the recv data socket new_sd and so I entered an infinite loop (the commented code). The problem is that by entering the while (1) my program block before recv, but not inserting it correctly receives a string, but after that stop. Someone could help me make my recv always waiting for information? Thanks in advance for your help. -(IBAction)Chat{ [NSThread detachNewThreadSelector:@selector(riceviDatiServer) toTarget:self withObject:nil]; } -(void)riceviDatiServer{ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init]; labelRicevuti.text = [[NSString alloc] initWithFormat:@"In attesa di ricevere i dati"]; char datiRicevuti[500]; int ricevuti; //while(1){ ricevuti = recv(new_sd, &datiRicevuti, 500, 0); labelRicevuti.text = [[NSString alloc] initWithFormat:@"%s", datiRicevuti]; //} [pool release]; }

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• Flush kernel's TCP buffer with `MSG_MORE`-flagged packets

  - by timn

  send()'s man page reveals the MSG_MORE flag which is asserted to act like TCP_CORK. I have a wrapper function around send(): int SocketConnection_Write(SocketConnection *this, void *buf, int len) { errno = 0; int sent = send(this->fd, buf, len, MSG_NOSIGNAL); if (errno == EPIPE || errno == ENOTCONN) { throw(exc, &SocketConnection_NotConnectedException); } else if (errno == ECONNRESET) { throw(exc, &SocketConnection_ConnectionResetException); } else if (sent != len) { throw(exc, &SocketConnection_LengthMismatchException); } return sent; } Assuming I want to use the kernel buffer, I could go with TCP_CORK, enable whenever it is necessary and then disable it to flush the buffer. But on the other hand, thereby the need for an additional system call arises. Thus, the usage of MSG_MORE seems more appropriate to me. I'd simply change the above send() line to: int sent = send(this->fd, buf, len, MSG_NOSIGNAL | MSG_MORE); According to lwm.net, packets will be flushed automatically if they are large enough: If an application sets that option on a socket, the kernel will not send out short packets. Instead, it will wait until enough data has shown up to fill a maximum-size packet, then send it. When TCP_CORK is turned off, any remaining data will go out on the wire. But this section only refers to TCP_CORK. Now, what is the proper way to flush MSG_MORE packets? I can only think of two possibilities: Call send() with an empty buffer and without MSG_MORE being set Re-apply the TCP_CORK option as described on this page Unfortunately the whole topic is very poorly documented and I couldn't find much on the Internet. I am also wondering how to check that everything works as expected? Obviously running the server through strace' is not an option. So the only simplest way would be to usenetcat' and then look at its `strace' output? Or will the kernel handle traffic differently transmitted over a loopback interface?

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• saxon java xpath exception :

  - by changed

  Hi I am trying to read XPath queries from a file and run it against a xml data file. I am doing it through Saxon Xpath processor. But i keep getting this error. Code i am using is from sample code provided with the library. Error i am getting is : Exception in thread "main" javax.xml.xpath.XPathExpressionException: Supplied node must be built using the same or a compatible Configuration at net.sf.saxon.xpath.XPathExpressionImpl.evaluate(XPathExpressionImpl.java:283) at net.sf.saxon.xpath.XPathExpressionImpl.evaluate(XPathExpressionImpl.java:375) at edu.xml.XPathExample.go(XPathExample.java:81) at edu.xml.XPathExample.main(XPathExample.java:42) - public void go(String filename) throws Exception { XPathExpression findLine = null; String readLine = null; Object document = new XPathEvaluator().setSource(new StreamSource(new File(dataPath))); System.setProperty("javax.xml.xpath.XPathFactory:" + NamespaceConstant.OBJECT_MODEL_SAXON, "net.sf.saxon.xpath.XPathFactoryImpl"); XPathFactory xpf = XPathFactory.newInstance(NamespaceConstant.OBJECT_MODEL_SAXON); XPath xpe = xpf.newXPath(); if (filename != null) { this.queryPath = filename; } try { fileReader = new BufferedReader(new FileReader(queryPath)); } catch (FileNotFoundException ex) { System.out.println("File not found: " + ex.getMessage()); } xpe.setXPathVariableResolver(this); while (true) { try { readLine = fileReader.readLine(); } catch (IOException ex) { System.out.println("Error while reading file: " + ex.getMessage()); } if (readLine == null) { break; } findLine = xpe.compile(readLine); String resultString = findLine.evaluate(document); System.out.println("<output>"); System.out.println("String Value => " + resultString); System.out.println("</output>"); } }

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• Custom SSL handling stopped working on Android 2.2 FroYo

  - by Eric

  For my app, Transdroid, I am connecting to remote servers via HTTP and optionally securely via HTTPS. For these HTTPS connections with the HttpClient I am using a custom SSL socket factory implementation to make sure self-signed certificates are working. Basically, I accept everything and ignore every checking of any certificate. This has been working fine for some time now, but it no longer work for Android 2.2 FroYo. When trying to connect, it will return an exception: java.io.IOException: SSL handshake failure: I/O error during system call, Broken pipe Here is how I initialize the HttpClient: SchemeRegistry registry = new SchemeRegistry(); registry.register(new Scheme("http", new PlainSocketFactory(), 80)); registry.register(new Scheme("https", (trustAll ? new FakeSocketFactory() : SSLSocketFactory.getSocketFactory()), 443)); client = new DefaultHttpClient(new ThreadSafeClientConnManager(httpParams, registry), httpParams); I make use of a FakeSocketFactory and FakeTrustManager, of which the source can be found here: http://code.google.com/p/transdroid/source/browse/#svn/trunk/src/org/transdroid/util Again, I don't understand why it suddenly stopped work, or even what the error 'Broken pipe' means. I have seen messages on Twitter that Seesmic and Twidroid fail with SSL enabled on FroYo as well, but am unsure if it's related. Thanks for any directions/help!

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• "Work stealing" vs. "Work shrugging (tm)"?

  - by John

  Why is it that I can find lots of information on "work stealing" and nothing on a "work shrugging(tm)" as a load-balancing strategy? I am surprised because work-stealing seems to me to have an inherent weakness when implementating efficient fine-grained load-balancing. Vis:- Relying on consumer processors to implement distribution (by actively stealing) begs the question of what these processors do when they find no work? None of the work-stealing references and implementations I have come across so far address this issue satisfactorarily for me. They either:- 1) Manage not to disclose what they do with idle processors! [Cilk] (?anyone know?) 2) Have all idle processors sleep and wake periodically and scatter messages to the four winds to see if any work has arrived [e.g. JAWS] (= way too latent & inefficient for me). 3) Assume that it is acceptable to have processors "spinning" looking for work ( = non-starter for me!) Unless anyone thinks there is a solution for this I will move on to consider a "Work Shrugging(tm)" strategy. Having the task-producing processor distribute excess load seems to me inherently capable of a much more efficient implementation. However a quick google didn't show up anything under the heading of "Work Shrugging" so any pointers to prior-art would be welcome. tx Tags I would have added if I was allowed to [work-stealing]

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• MySQL Access denied error

  - by dancingbush

  I am trying to install mySQL on a Mac OS 10.8 and set up a user account. NOTE I am a abs beginner when it comes to using the command line in Terminal window. I used these instructions to install: http://www.macminivault.com/mysql-mountain-lion/ I set my own password for all users here: GRANT ALL ON *.* TO 'root'@'localhost' IDENTIFIED BY 'mypass' WITH GRANT OPTION; quit Every time i try to execute mySQL as a root user on the command line i get this: Ciarans-MacBook-Pro:~ callanmooneys$ mysql -u root ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO) I read around on the net and tried various things including tried this to change password: mysqladmin -u root -pyourcurrentmysqlrootpassword password yournewmysqlrootpassword, it returns -> -> USE mysql -> If i simply type 'mysql' and launch the mySQL monitor then try to crete a user account: mysql> USE mysql ERROR 1044 (42000): Access denied for user ''@'localhost' to database 'mysql' mysql> Also tried answers on forum: access is denied for user 'root'@localhost mysql error 1045 returned '[email protected] command not found And MySQL - ERROR 1045 - Access denied: Ciarans-MacBook-Pro:~ callanmooneys$ mysqld_safe --skip-grant-tables 131105 21:44:41 mysqld_safe Logging to '/usr/local/mysql/data/Ciarans-MacBook-Pro.local.err'. 131105 21:44:41 mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data /usr/local/mysql/bin/mysqld_safe: line 129: /usr/local/mysql/data/Ciarans-MacBook-Pro.local.err: Permission denied /usr/local/mysql/bin/mysqld_safe: line 166: /usr/local/mysql/data/Ciarans-MacBook-Pro.local.err: Permission denied 131105 21:44:41 mysqld_safe mysqld from pid file /usr/local/mysql/data/Ciarans-MacBook-Pro.local.pid ended /usr/local/mysql/bin/mysqld_safe: line 129: /usr/local/mysql/data/Ciarans-MacBook-Pro.local.err: Permission denied Ciarans-MacBook-Pro:~ callanmooneys$ mysql -u root ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2) Ciarans-MacBook-Pro:~ callanmooneys$ Feedback appreciated.

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• Why is WMDC/ActiveSync so flaky?

  - by Ira Rainey

  I'm developing a Windows Mobile app using the .NET Compact Framework 3.5 and VS2008, and for debugging using the Device Emulator V3, on Win7, and seem to have constant problems with Windows Mobile Device Centre (6.1) connecting. Using the Emulator Manager (9.0.21022.8) I cradle the device using DMA in WMDC. The problem is it's so flaky at actually connecting that it's becoming a pain. I find that when I turn my computer on, before I can get it to connect I have to open up WMDC, disable Connect over DMA, close WMDC down, reopen it again, and then it might cradle. Often I have to do this twice before it will cradle. Once it's cradled it's generally fine, but nothing seems consistent in getting it to connect. Connecting with physical devices is often better, although not always. If I plug a PDA into a USB socket other than the one it was originally plugged into then it won't connect at all. Often the best/most reliable connection method seems to be over Bluetooth, but that's quite slow. Anybody got any tips or advice?

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• "QFontEngine(Win) GetTextMetrics failed ()" error on 64-bit Windows

  - by David Murdoch

  I'll add 500 of my own rep as a bounty when SO lets me. I'm using wkhtmltopdf to convert HTML web pages to PDFs. This works perfectly on my 32-bit dev server [unfortunately, I can't ship my machine :-p ]. However, when I deploy to the web application's 64-bit server the following errors are displayed: C:\>wkhtmltopdf http://www.google.com google.pdf Loading pages (1/5) QFontEngine::loadEngine: GetTextMetrics failed () ] 10% QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngine::loadEngine: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () QFontEngine::loadEngine: GetTextMetrics failed () ] 36% QFontEngineWin: GetTextMetrics failed () QFontEngineWin: GetTextMetrics failed () // ...etc.... and the PDF is created and saved... just WITHOUT text. All form-fields, images, borders, tables, divs, spans, ps, etc are rendered accurately...just void of any text at all. Server information: Windows edition: Windows Server Standard Service Pack 2 Processor: Intel Xeon E5410 @ 2.33GHz 2.33 GHz Memory: 8.00 GB System type: 64-bit Operating System Can anyone give me a clue as to what is happening and how I can fix this? Also, I wasn't sure what to tag/title this question with...so if you can think of better tags/title comment them or edit the question. :-)

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• Learning about the low level

  - by Anoners

  I'm interested in learning more about the PC from a lower (machine) level. I graduated from a school which taught us concepts using the Java language which abstracted out that level almost completely. As a result I only learned a bit from the one required assembly language course. In order to cram in ASM and quite a few details about architecture, it was hard to get a very deep picture of what is going on there. At work I focus on unix socket programming in C, so i'm much closer to the hardware now, but I feel I should learn a bit more about what streams really are, how memory management and paging works, what goes on when you call "paint()" on a graphics buffer, etc. I missed out on a lot of this and i'm looking for a good resource to get me started. I've heard a lot about the "Pink Book" by Peter Norton (Programmer's Guide to the IBM PC, Programmer's Guide to inside the PC, etc). It seems like this is on the right track, however the original is quite out dated and the newer ones have had conflicting reviews, with many people saying to stay away from it. I'm not sure what the SO crowd thinks about this book or if they have some suggestions for similar books, online resources, etc that may be good primers for this sort of thing. Any suggestions would be appreciated.

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• P6 Architecture - Register renaming aside, does the limited user registers result in more ops spent

  - by mrjoltcola

  I'm studying JIT design with regard to dynamic languages VM implementation. I haven't done much Assembly since the 8086/8088 days, just a little here or there, so be nice if I'm out of sorts. As I understand it, the x86 (IA-32) architecture still has the same basic limited register set today that it always did, but the internal register count has grown tremendously, but these internal registers are not generally available and are used with register renaming to achieve parallel pipelining of code that otherwise could not be parallelizable. I understand this optimization pretty well, but my feeling is, while these optimizations help in overall throughput and for parallel algorithms, the limited register set we are still stuck with results in more register spilling overhead such that if x86 had double, or quadruple the registers available to us, there may be significantly less push/pop opcodes in a typical instruction stream? Or are there other processor optmizations that also optimize this away that I am unaware of? Basically if I've a unit of code that has 4 registers to work with for integer work, but my unit has a dozen variables, I've got potentially a push/pop for every 2 or so instructions. Any references to studies, or better yet, personal experiences?

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• Sync Vs. Async Sockets Performance in .NET

  - by Michael Covelli

  Everything that I read about sockets in .NET says that the asynchronous pattern gives better performance (especially with the new SocketAsyncEventArgs which saves on the allocation). I think this makes sense if we're talking about a server with many client connections where its not possible to allocate one thread per connection. Then I can see the advantage of using the ThreadPool threads and getting async callbacks on them. But in my app, I'm the client and I just need to listen to one server sending market tick data over one tcp connection. Right now, I create a single thread, set the priority to Highest, and call Socket.Receive() with it. My thread blocks on this call and wakes up once new data arrives. If I were to switch this to an async pattern so that I get a callback when there's new data, I see two issues The threadpool threads will have default priority so it seems they will be strictly worse than my own thread which has Highest priority. I'll still have to send everything through a single thread at some point. Say that I get N callbacks at almost the same time on N different threadpool threads notifying me that there's new data. The N byte arrays that they deliver can't be processed on the threadpool threads because there's no guarantee that they represent N unique market data messages because TCP is stream based. I'll have to lock and put the bytes into an array anyway and signal some other thread that can process what's in the array. So I'm not sure what having N threadpool threads is buying me. Am I thinking about this wrong? Is there a reason to use the Async patter in my specific case of one client connected to one server?

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• Compiler optimization causing the performance to slow down

  - by aJ

  I have one strange problem. I have following piece of code: template<clss index, class policy> inline int CBase<index,policy>::func(const A& test_in, int* srcPtr ,int* dstPtr) { int width = test_in.width(); int height = test_in.height(); double d = 0.0; //here is the problem for(int y = 0; y < height; y++) { //Pointer initializations //multiplication involving y //ex: int z = someBigNumber*y + someOtherBigNumber; for(int x = 0; x < width; x++) { //multiplication involving x //ex: int z = someBigNumber*x + someOtherBigNumber; if(soemCondition) { // floating point calculations } *dstPtr++ = array[*srcPtr++]; } } } The inner loop gets executed nearly 200,000 times and the entire function takes 100 ms for completion. ( profiled using AQTimer) I found an unused variable double d = 0.0; outside the outer loop and removed the same. After this change, suddenly the method is taking 500ms for the same number of executions. ( 5 times slower). This behavior is reproducible in different machines with different processor types. (Core2, dualcore processors). I am using VC6 compiler with optimization level O2. Follwing are the other compiler options used : -MD -O2 -Z7 -GR -GX -G5 -X -GF -EHa I suspected compiler optimizations and removed the compiler optimization /O2. After that function became normal and it is taking 100ms as old code. Could anyone throw some light on this strange behavior? Why compiler optimization should slow down performance when I remove unused variable ? Note: The assembly code (before and after the change) looked same.

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• Memory mapped files and "soft" page faults. Unavoidable?

  - by Robert Oschler

  I have two applications (processes) running under Windows XP that share data via a memory mapped file. Despite all my efforts to eliminate per iteration memory allocations, I still get about 10 soft page faults per data transfer. I've tried every flag there is in CreateFileMapping() and CreateFileView() and it still happens. I'm beginning to wonder if it's just the way memory mapped files work. If anyone there knows the O/S implementation details behind memory mapped files I would appreciate comments on the following theory: If two processes share a memory mapped file and one process writes to it while another reads it, then the O/S marks the pages written to as invalid. When the other process goes to read the memory areas that now belong to invalidated pages, this causes a soft page fault (by design) and the O/S knows to reload the invalidated page. Also, the number of soft page faults is therefore directly proportional to the size of the data write. My experiments seem to bear out the above theory. When I share data I write one contiguous block of data. In other words, the entire shared memory area is overwritten each time. If I make the block bigger the number of soft page faults goes up correspondingly. So, if my theory is true, there is nothing I can do to eliminate the soft page faults short of not using memory mapped files because that is how they work (using soft page faults to maintain page consistency). What is ironic is that I chose to use a memory mapped file instead of a TCP socket connection because I thought it would be more efficient. Note, if the soft page faults are harmless please note that. I've heard that at some point if the number is excessive, the system's performance can be marred. If soft page faults intrinsically are not significantly harmful then if anyone has any guidelines as to what number per second is "excessive" I'd like to hear that. Thanks.

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• Java: volatile guarantees and out-of-order execution

  - by WizardOfOdds

  Note that this question is solely about the volatile keyword and the volatile guarantees: it is not about the synchronized keyword (so please don't answer "you must use synchronize" for I don't have any issue to solve: I simply want to understand the volatile guarantees (or lack of guarantees) regarding out-of-order execution). Say we have an object containing two volatile String references that are initialized to null by the constructor and that we have only one way to modify the two String: by calling setBoth(...) and that we can only set their references afterwards to non-null reference (only the constructor is allowed to set them to null). For example (it's just an example, there's no question yet): public class SO { private volatile String a; private volatile String b; public SO() { a = null; b = null; } public void setBoth( @NotNull final String one, @NotNull final String two ) { a = one; b = two; } public String getA() { return a; } public String getB() { return b; } } In setBoth(...), the line assigning the non-null parameter "a" appears before the line assigning the non-null parameter "b". Then if I do this (once again, there's no question, the question is coming next): if ( so.getB() != null ) { System.out.println( so.getA().length ); } Am I correct in my understanding that due to out-of-order execution I can get a NullPointerException? In other words: there's no guarantee that because I read a non-null "b" I'll read a non-null "a"? Because due to out-of-order (multi)processor and the way volatile works "b" could be assigned before "a"? volatile guarantees that reads subsequent to a write shall always see the last written value, but here there's an out-of-order "issue" right? (once again, the "issue" is made on purpose to try to understand the semantics of the volatile keyword and the Java Memory Model, not to solve a problem).

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• Using jQuery delay() with separate elements

  - by boomturn

  I want to fake a simple animation on page load by sequentially revealing several pngs, each appearing instantly but with unique, precisely timed delay before the next one. Using the latest version of jQuery (1.4.2 at writing), which provides a delay method. My first (braindead) impulse was: $('#image1').show('fast').delay(800); $('#image2').show('fast').delay(1200); $('#image3').show('fast'); Of course all come up simultaneously. jQuery doc examples refer to a single item being chained, not handling multiple items. OK... try again using nested callbacks from show(): $('#image1').show('fast', function() { $('#image2').show('fast', function() { $('#image3').show('fast', function() { }); }); }); Looks ugly (imagine doing 10, also wonder what processor hit would be) but hey, it works sequentially! Without delay though. So... chain delay() after show() using a callback function from it (not even sure if it supports one): $('#image1').show('fast').delay(800, function() { $('#image2').show('fast').delay(1200, function() { $('#image3').show('fast'); }); }); Hm. Opposite result of what I thought might happen: the callback works, but still no delay. So... should I be using some combination of queue and delay instead of nested callbacks? jQuery doc examples for queue again only use one element for example. Guessing this would involve using a custom queue, but am uncertain how to implement this. Or maybe I'm missing a simple way? (For a simple problem!)

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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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• java.net.SocketException: Software caused connection abort: recv failed; Causes and cures?

  - by IVR Avenger

  Hi, all. I've got an application running on Apache Tomcat 5.5 on a Win2k3 VM. The application serves up XML to be consumed by some telephony appliances as part of our IVR infrastructure. The application, in turn, receives its information from a handful of SOAP services. This morning, the SOAP services were timing out intermittently, causing all sorts of Exceptions. Once these stopped, I noticed that our application was still performing very slowly, in that it took it a long time to render and deliver pages. This sluggishness was noticed both on the appliances that consume the Tomcat output, and from a simple test of requesting some static documents from my web browser. Restarting Tomcat immediately resolved the issue. Cracking open the localhost log, I see a ton of these errors, right up until I restarted Tomcat: WARNING: Exception thrown whilst processing POSTed parameters java.net.SocketException: Software caused connection abort: recv failed After a big of Googling, my working theory is that the SOAP issue caused my users to get errors, which caused them to make more requests, which put an increased load on the application. This caused it to run out of available sockets to handle incoming requests. So, here's my quandary: 1. Is this a valid hypothesis, or am I just in over my head with HTTP and Tomcat? 2. If this is a valid hypothesis, is there a way to increase the size of the "socket queue", so that this doesn't happen in the future? Thanks! IVR Avenger

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