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• Test tomcat for ssl renegotiation vulnerability

  - by Jim

  How can I test if my server is vulnerable for SSL renegotiation? I tried the following (using OpenSSL 0.9.8j-fips 07 Jan 2009: openssl s_client -connect 10.2.10.54:443 I see it connects, it brings the certificate chain, it shows the server certificate, and last: SSL handshake has read 2275 bytes and written 465 bytes --- New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA Server public key is 1024 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 Cipher : DHE-RSA-AES256-SHA Session-ID: 50B4839724D2A1E7C515EB056FF4C0E57211B1D35253412053534C4A20202020 Session-ID-ctx: Master-Key: 7BC673D771D05599272E120D66477D44A2AF4CC83490CB3FDDCF62CB3FE67ECD051D6A3E9F143AE7C1BA39D0BF3510D4 Key-Arg : None Start Time: 1354008417 Timeout : 300 (sec) Verify return code: 21 (unable to verify the first certificate) What does Secure Renegotiation IS supported mean? That SSL renegotiation is allowed? Then I did but did not get an exception or get the certificate again: verify error:num=20:unable to get local issuer certificate verify return:1 verify error:num=27:certificate not trusted verify return:1 verify error:num=21:unable to verify the first certificate verify return:1 HTTP/1.1 200 OK Server: Apache-Coyote/1.1 Content-Type: text/html;charset=ISO-8859-1 Content-Length: 174 Date: Tue, 27 Nov 2012 09:13:14 GMT Connection: close So is the server vulnerable to SSL renegotiation or not?

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• Simple dig output?

  - by knocte

  In a script I want to be able to write an IP address to somewhere easily, so I thought using dig (or a similar command) with back-ticks. However the simplest output I've been able to come up to wrt dig parameters is > dig -t A +noall +answer www.google.com www.google.com. 300 IN A 173.194.66.106 www.google.com. 300 IN A 173.194.66.104 Any way (extra arg, different tool instead of dig?) to get rid of the junk apart from the IP address?? (And please don't tell me to use sed.) Thanks

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• How do functional languages handle a mocking situation when using Interface based design?

  - by Programmin Tool

  Typically in C# I use dependency injection to help with mocking; public void UserService { public UserService(IUserQuery userQuery, IUserCommunicator userCommunicator, IUserValidator userValidator) { UserQuery = userQuery; UserValidator = userValidator; UserCommunicator = userCommunicator; } ... public UserResponseModel UpdateAUserName(int userId, string userName) { var result = UserValidator.ValidateUserName(userName) if(result.Success) { var user = UserQuery.GetUserById(userId); if(user == null) { throw new ArgumentException(); user.UserName = userName; UserCommunicator.UpdateUser(user); } } ... } ... } public class WhenGettingAUser { public void AndTheUserDoesNotExistThrowAnException() { var userQuery = Substitute.For<IUserQuery>(); userQuery.GetUserById(Arg.Any<int>).Returns(null); var userService = new UserService(userQuery); AssertionExtensions.ShouldThrow<ArgumentException>(() => userService.GetUserById(-121)); } } Now in something like F#: if I don't go down the hybrid path, how would I test workflow situations like above that normally would touch the persistence layer without using Interfaces/Mocks? I realize that every step above would be tested on its own and would be kept as atomic as possible. Problem is that at some point they all have to be called in line, and I'll want to make sure everything is called correctly.

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• Why does my Visual Studio 2010 default to a horizontal windows split if I quit then reopen it?

  - by Martin Doms

  I use Visual Studio 2010 Professional at work and up until a couple of weeks ago I have had no problems. But now whenever I open an instance of VS 2010 it defaults to horizontal split. I never split my windows horizontally, so this is very annoying. It happens consistently, every time on every project. Here is how VS2010 looked before I closed the window: I close it and reopen in that project, and: Arg! The only plugin I use is ReSharper, in case it's relevant.

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• Why is `cmd /C` living after it did its job?

  - by acidzombie24

  My question is why does "cmd" exist (idle) in my process after i update my exe? In my code i run this code to update myself and launch var args = string.Format(@"/C ping 1.1.1.1 -n 1 -w 3000 & move /Y ""{0}"" ""{1}"" & ""{1}"" {2}", updateFn, fn, exeargs); new Process() { StartInfo = new ProcessStartInfo(@"cmd", args) { CreateNoWindow = true, UseShellExecute = false } }.Start(); Environment.Exit(0); The idea is i exit right away and have ping stall for 3seconds before trying to replace my current exe with my updated exe. Then i launch with the necessary args The full arg for cmd looks like this /C ping 1.1.1.1 -n 1 -w 3000 & move /Y "c:\path\update" "c:\path\my.exe" & "c:\path\my.exe" exeargs Everything works fine however i see cmd in the taskmanager (looks to be idle) after my process is launched and correctly working. Why?

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• Why are Full GCs not running on my gcInterval I set?

  - by Brad Wood

  ColdFusion 10 Update 10 Windows Server 2008 R2 Java 1.7.0_21 I am trying to figure Full GCs to run every 10 minutes. I have used the gcInterval JVM arg in the past on earlier versions of ColdFusion with success, but I have confirmed with verbose GC logs that Full GCs are still happening on the hour (Unless the Old Gen gets so full that it forces a full collection). Here are the full JVM args from ColdFusion10\cfusion\bin\jvm.config (line breaks added for readability) Is there something else I need to be doing to get this working on ColdFusion 10? java.args= -server -Xms4072m -Xmx4072m -XX:PermSize=512m -XX:MaxPermSize=512m -Dsun.rmi.dgc.client.gcInterval=600000 -Dsun.rmi.dgc.server.gcInterval=600000 -XX:+UseParallelGC -XX:+UseParallelOldGC -Xloggc:gc.log -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=5 -XX:GCLogFileSize=1024K -Xbatch -Dcoldfusion.home={application.home} -Dcoldfusion.rootDir={application.home} -Dcoldfusion.libPath={application.home}/lib -Dorg.apache.coyote.USE_CUSTOM_STATUS_MSG_IN_HEADER=true -Dcoldfusion.jsafe.defaultalgo=FIPS186Random -Dcoldfusion.classPath={application.home}/lib/updates,{application.home}/lib,{application.home}/lib/axis2,{application.home}/gateway/lib/,{application.home}/wwwroot/WEB-INF/flex/jars,{application.home}/wwwroot/WEB-INF/cfform/jars

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• boost::asio::async_read_until problem

  - by user368831

  I'm trying to modify the echo server example from boost asio and I'm running into problem when I try to use boost::asio::async_read_until. Here's the code: #include <cstdlib> #include <iostream> #include <boost/bind.hpp> #include <boost/asio.hpp> using boost::asio::ip::tcp; class session { public: session(boost::asio::io_service& io_service) : socket_(io_service) { } tcp::socket& socket() { return socket_; } void start() { std::cout<<"starting"<<std::endl; boost::asio::async_read_until(socket_, boost::asio::buffer(data_, max_length), ' ', boost::bind(&session::handle_read, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); } void handle_read(const boost::system::error_code& error, size_t bytes_transferred) { std::cout<<"handling read"<<std::endl; if (!error) { boost::asio::async_write(socket_, boost::asio::buffer(data_, bytes_transferred), boost::bind(&session::handle_write, this, boost::asio::placeholders::error)); } else { delete this; } } void handle_write(const boost::system::error_code& error) { if (!error) { /* socket_.async_read_some(boost::asio::buffer(data_, max_length), boost::bind(&session::handle_read, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred)); */ } else { delete this; } } private: tcp::socket socket_; enum { max_length = 1024 }; char data_[max_length]; }; class server { public: server(boost::asio::io_service& io_service, short port) : io_service_(io_service), acceptor_(io_service, tcp::endpoint(tcp::v4(), port)) { session* new_session = new session(io_service_); acceptor_.async_accept(new_session->socket(), boost::bind(&server::handle_accept, this, new_session, boost::asio::placeholders::error)); } void handle_accept(session* new_session, const boost::system::error_code& error) { if (!error) { new_session->start(); new_session = new session(io_service_); acceptor_.async_accept(new_session->socket(), boost::bind(&server::handle_accept, this, new_session, boost::asio::placeholders::error)); } else { delete new_session; } } private: boost::asio::io_service& io_service_; tcp::acceptor acceptor_; }; int main(int argc, char* argv[]) { try { if (argc != 2) { std::cerr << "Usage: async_tcp_echo_server <port>\n"; return 1; } boost::asio::io_service io_service; using namespace std; // For atoi. server s(io_service, atoi(argv[1])); io_service.run(); } catch (std::exception& e) { std::cerr << "Exception: " << e.what() << "\n"; } return 0; } The problem is when I try to compile I get this weird error: server.cpp: In member function ‘void session::start()’: server.cpp:27: error: no matching function for call to ‘async_read_until(boost::asio::basic_stream_socket &, boost::asio::mutable_buffers_1, char, boost::_bi::bind_t, boost::_bi::list3, boost::arg<1 ()(), boost::arg<2 ()() )’ Can someone please explain what's going on? From what I can tell the arguments to async_read_until are correct. Thanks!

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• Why is my spawned process still causing IntelliJ to wait?

  - by itsadok

  I'm trying to start a server as part of an Ant artifact. Here are the relevant lines: <exec dir="." executable="cmd.exe" spawn="true"> <arg line="/c c:\Java\james-2.3.2\bin\debug.bat" /> </exec> If I start it with ant from the command line, a process is spawned and I get a command prompt and everything seems fine. However, if I start it from IntelliJ 6, my IDE, the build stays alive until I kill the server. Here's the line IntelliJ uses to start ant: C:\Java\jdk1.6.0_02\bin\java -Xmx128m -Dant.home=C:\Java\apache-ant-1.7.1 -Dfile.encoding=UTF-8 -classpath "C:\Java\apache-ant-1.7.1\lib\ant-antlr.jar;C:\Java\apache-ant-1.7.1\lib\ant-apache-bcel.jar;C:\Java\apache-ant-1.7.1\lib\ant-apache-bsf.jar;C:\Java\apache-ant-1.7.1\lib\ant-apache-log4j.jar;C:\Java\apache-ant-1.7.1\lib\ant-apache-oro.jar;C:\Java\apache-ant-1.7.1\lib\ant-apache-regexp.jar;C:\Java\apache-ant-1.7.1\lib\ant-apache-resolver.jar;C:\Java\apache-ant-1.7.1\lib\ant-commons-logging.jar;C:\Java\apache-ant-1.7.1\lib\ant-commons-net.jar;C:\Java\apache-ant-1.7.1\lib\ant-jai.jar;C:\Java\apache-ant-1.7.1\lib\ant-javamail.jar;C:\Java\apache-ant-1.7.1\lib\ant-jdepend.jar;C:\Java\apache-ant-1.7.1\lib\ant-jmf.jar;C:\Java\apache-ant-1.7.1\lib\ant-jsch.jar;C:\Java\apache-ant-1.7.1\lib\ant-junit.jar;C:\Java\apache-ant-1.7.1\lib\ant-launcher.jar;C:\Java\apache-ant-1.7.1\lib\ant-netrexx.jar;C:\Java\apache-ant-1.7.1\lib\ant-nodeps.jar;C:\Java\apache-ant-1.7.1\lib\ant-starteam.jar;C:\Java\apache-ant-1.7.1\lib\ant-stylebook.jar;C:\Java\apache-ant-1.7.1\lib\ant-swing.jar;C:\Java\apache-ant-1.7.1\lib\ant-testutil.jar;C:\Java\apache-ant-1.7.1\lib\ant-trax.jar;C:\Java\apache-ant-1.7.1\lib\ant-weblogic.jar;C:\Java\apache-ant-1.7.1\lib\ant.jar;C:\Java\apache-ant-1.7.1\lib\xercesImpl.jar;C:\Java\apache-ant-1.7.1\lib\xml-apis.jar;C:\Java\jdk1.6.0_02\lib\tools.jar;C:\Program Files\JetBrains\IntelliJ IDEA 6.0\lib\idea_rt.jar" com.intellij.rt.ant.execution.AntMain2 -logger com.intellij.rt.ant.execution.IdeaAntLogger2 -inputhandler com.intellij.rt.ant.execution.IdeaInputHandler -buildfile C:\Java\Projects\CcMailer\ccmailer.xml jar I suspect the inputhandler parameter has something to do with the problem, but if I run it myself the problem is not reproduced. Either way, I have only limited control over what IntelliJ does. My question is: how does IntelliJ even know the process is running? The Ant process is long gone. Is there a way to start a subprocess in a more sneaky way, so that IntelliJ won't even know there's anything to wait around for? Here's what I've tried so far: I tried using the start command, like this: <exec dir="." executable="cmd.exe" spawn="true"> <arg line="/c start cmd /c c:\Java\james-2.3.2\bin\debug.bat" /> </exec> I also tried using python, with code like this: import os.path import subprocess subprocess.Popen(["cmd.exe", "/c", "debug.bat"], stdin=open(os.path.devnull), stdout=open(os.path.devnull, "w"), stderr=subprocess.STDOUT) To no avail. The build window always stays up until I kill the server. Any ideas?

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• Partial Trust in WPF 4

  - by Hadi Eskandari

  I've started a new project in WPF 4 (.NET 4) and trying to see if I can run it in xbap mode. I need to run the application in Full Trust with the new mode made available in .NET 4 which asks the end user if the full trust application should be run. I've set the "Security" mode to "Full Trust" application, and it builds just fine. When I run it, an exception is thrown and IE error message shows the following error. Any ways around it?? Startup URI: T:\projects\Hightech Sources\PayRoll\PayRoll.Web\publish\PayRoll.Web.xbap Application Identity: file:///T:/projects/Hightech%20Sources/PayRoll/PayRoll.Web/publish/PayRoll.Web.xbap#PayRoll.Web.xbap, Version=1.0.0.0, Culture=neutral, PublicKeyToken=1d910f49755d2c97, processorArchitecture=msil/PayRoll.Web.exe, Version=1.0.0.0, Culture=neutral, PublicKeyToken=1d910f49755d2c97, processorArchitecture=msil, type=win32 System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.FileIOPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed. at System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet) at System.Security.CodeAccessSecurityEngine.Check(CodeAccessPermission cap, StackCrawlMark& stackMark) at System.Security.CodeAccessPermission.Demand() at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection, Boolean suppressSecurityChecks) at System.Reflection.RuntimeAssembly.InternalLoadFrom(String assemblyFile, Evidence securityEvidence, Byte[] hashValue, AssemblyHashAlgorithm hashAlgorithm, Boolean forIntrospection, Boolean suppressSecurityChecks, StackCrawlMark& stackMark) at System.Reflection.Assembly.LoadFrom(String assemblyFile) at PayRoll.Web.App.SelectAssemblies() at Caliburn.PresentationFramework.ApplicationModel.CaliburnApplication..ctor() at PayRoll.Web.App..ctor() at PayRoll.Web.App.Main() at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.AppDomain.nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel) at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly() at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData) at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext) at System.Windows.Interop.PresentationApplicationActivator.CreateInstance(ActivationContext actCtx) at System.Activator.CreateInstance(ActivationContext activationContext) at System.AppDomain.Setup(Object arg) at System.AppDomain.nCreateInstance(String friendlyName, AppDomainSetup setup, Evidence providedSecurityInfo, Evidence creatorsSecurityInfo, IntPtr parentSecurityDescriptor) at System.Runtime.Hosting.ApplicationActivator.CreateInstanceHelper(AppDomainSetup adSetup) at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData) at System.Windows.Interop.PresentationApplicationActivator.CreateInstance(ActivationContext actCtx) at System.Activator.CreateInstance(ActivationContext activationContext) at System.Deployment.Application.DeploymentManager.ExecuteNewDomain() at System.Deployment.Application.InPlaceHostingManager.Execute() at MS.Internal.AppModel.XappLauncherApp.ExecuteDownloadedApplication() at System.Windows.Interop.DocObjHost.RunApplication(ApplicationRunner runner) at MS.Internal.AppModel.XappLauncherApp.XappLauncherApp_Exit(Object sender, ExitEventArgs e) at System.Windows.Application.OnExit(ExitEventArgs e) at System.Windows.Application.DoShutdown() at System.Windows.Application.ShutdownImpl() at System.Windows.Application.ShutdownCallback(Object arg) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Threading.DispatcherOperation.Invoke() at System.Windows.Threading.Dispatcher.ProcessQueue() at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.Run() at System.Windows.Application.RunDispatcher(Object ignore) at System.Windows.Application.StartDispatcherInBrowser(Object unused) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.DispatcherOperation.InvokeImpl() at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Threading.DispatcherOperation.Invoke() at System.Windows.Threading.Dispatcher.ProcessQueue() at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) The action that failed was: Demand The type of the first permission that failed was: System.Security.Permissions.FileIOPermission

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• HOWTO: disable jmx in activemq network of brokers (spring, xbean)

  - by subes

  Since I've struggled a lot with this problem, I am posting my solution. Disabling jmx in an activemq network of brokers removes race conditions about the registration of the jmx connector. When starting multiple activemq servers on the same machine: Failed to start jmx connector: Cannot bind to URL [rmi://localhost:1099/jmxrmi]: javax.naming.NameAlreadyBoundException: jmxrmi [Root exception is java.rmi.AlreadyBoundException: jmxrmi] Another problem with this is, that even if you don't cause a race condition, this exception can still occur. Even when starting one broker after another while waiting for them to initialize properly in between. If one process is run by root as the first instance and the other as a normal user, somehow the user process tries to register its own jmx connector, though there already is one. Or another exception which happens when the broker that successfully registered the jmx connector goes down: Failed to start jmx connector: Cannot bind to URL [rmi://localhost:1099/jmxrmi]: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: java.net.ConnectException: Connection refused] Those exceptions cause the network of brokers to stop working, or to not work at all. The trick to disable jmx was, that jmx had to be disabled in the connectionfactory aswell. The documentation http://activemq.apache.org/jmx.html does not say that this is needed explicitly. So I had to struggle for 2 days until I found the solution: <beans xmlns="http://www.springframework.org/schema/beans" xmlns:amq="http://activemq.apache.org/schema/core" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://activemq.apache.org/schema/core http://activemq.apache.org/schema/core/activemq-core-5.3.1.xsd"> <!-- Spring JMS Template --> <bean id="jmsTemplate" class="org.springframework.jms.core.JmsTemplate"> <constructor-arg ref="connectionFactory" /> </bean> <!-- Caching, sodass das jms template überhaupt nutzbar ist in sachen performance --> <bean id="connectionFactory" class="org.springframework.jms.connection.CachingConnectionFactory"> <constructor-arg ref="amqConnectionFactory" /> <property name="exceptionListener" ref="jmsExceptionListener" /> <property name="sessionCacheSize" value="1" /> </bean> <!-- Jeder Client verbindet sich mit seinem eigenen broker, broker sind untereinander vernetzt. Nur wenn hier nochmals jmx deaktiviert wird, bleibt es auch deaktiviert... --> <amq:connectionFactory id="amqConnectionFactory" brokerURL="vm://broker:default?useJmx=false" /> <!-- Broker suchen sich einen eigenen Port und sind gegenseitig verbunden, ergeben dadurch ein Grid. Dies zwar etwas langsamer, aber dafür ausfallsicherer. Siehe http://activemq.apache.org/networks-of-brokers.html --> <amq:broker useJmx="false" persistent="false"> <!-- Wird benötigt um JMX endgültig zu deaktivieren --> <amq:managementContext> <amq:managementContext connectorHost="localhost" createConnector="false" /> </amq:managementContext> <!-- Nun die normale Konfiguration für Network of Brokers --> <amq:networkConnectors> <amq:networkConnector networkTTL="1" duplex="true" dynamicOnly="true" uri="multicast://default" /> </amq:networkConnectors> <amq:persistenceAdapter> <amq:memoryPersistenceAdapter /> </amq:persistenceAdapter> <amq:transportConnectors> <amq:transportConnector uri="tcp://localhost:0" discoveryUri="multicast://default" /> </amq:transportConnectors> </amq:broker> With this, there is no need to specify -Dcom.sun.management.jmxremote=false for the jvm. Which somehow also didn't work for me, because the connectionfactory started the jmx connector.

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• How to use pthread_atfork() and pthread_once() to reinitialize mutexes in child processes

  - by Blair Zajac

  We have a C++ shared library that uses ZeroC's Ice library for RPC and unless we shut down Ice's runtime, we've observed child processes hanging on random mutexes. The Ice runtime starts threads, has many internal mutexes and keeps open file descriptors to servers. Additionally, we have a few of mutexes of our own to protect our internal state. Our shared library is used by hundreds of internal applications so we don't have control over when the process calls fork(), so we need a way to safely shutdown Ice and lock our mutexes while the process forks. Reading the POSIX standard on pthread_atfork() on handling mutexes and internal state: Alternatively, some libraries might have been able to supply just a child routine that reinitializes the mutexes in the library and all associated states to some known value (for example, what it was when the image was originally executed). This approach is not possible, though, because implementations are allowed to fail *_init() and *_destroy() calls for mutexes and locks if the mutex or lock is still locked. In this case, the child routine is not able to reinitialize the mutexes and locks. On Linux, the this test C program returns EPERM from pthread_mutex_unlock() in the child pthread_atfork() handler. Linux requires adding _NP to the PTHREAD_MUTEX_ERRORCHECK macro for it to compile. This program is linked from this good thread. Given that it's technically not safe or legal to unlock or destroy a mutex in the child, I'm thinking it's better to have pointers to mutexes and then have the child make new pthread_mutex_t on the heap and leave the parent's mutexes alone, thereby having a small memory leak. The only issue is how to reinitialize the state of the library and I'm thinking of reseting a pthread_once_t. Maybe because POSIX has an initializer for pthread_once_t that it can be reset to its initial state. #include <pthread.h> #include <stdlib.h> #include <string.h> static pthread_once_t once_control = PTHREAD_ONCE_INIT; static pthread_mutex_t *mutex_ptr = 0; static void setup_new_mutex() { mutex_ptr = malloc(sizeof(*mutex_ptr)); pthread_mutex_init(mutex_ptr, 0); } static void prepare() { pthread_mutex_lock(mutex_ptr); } static void parent() { pthread_mutex_unlock(mutex_ptr); } static void child() { // Reset the once control. pthread_once_t once = PTHREAD_ONCE_INIT; memcpy(&once_control, &once, sizeof(once_control)); setup_new_mutex(); } static void init() { setup_new_mutex(); pthread_atfork(&prepare, &parent, &child); } int my_library_call(int arg) { pthread_once(&once_control, &init); pthread_mutex_lock(mutex_ptr); // Do something here that requires the lock. int result = 2*arg; pthread_mutex_unlock(mutex_ptr); return result; } In the above sample in the child() I only reset the pthread_once_t by making a copy of a fresh pthread_once_t initialized with PTHREAD_ONCE_INIT. A new pthread_mutex_t is only created when the library function is invoked in the child process. This is hacky but maybe the best way of dealing with this skirting the standards. If the pthread_once_t contains a mutex then the system must have a way of initializing it from its PTHREAD_ONCE_INIT state. If it contains a pointer to a mutex allocated on the heap than it'll be forced to allocate a new one and set the address in the pthread_once_t. I'm hoping it doesn't use the address of the pthread_once_t for anything special which would defeat this. Searching comp.programming.threads group for pthread_atfork() shows a lot of good discussion and how little the POSIX standards really provides to solve this problem. There's also the issue that one should only call async-signal-safe functions from pthread_atfork() handlers, and it appears the most important one is the child handler, where only a memcpy() is done. Does this work? Is there a better way of dealing with the requirements of our shared library?

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• Loading a PyML multiclass classifier... why isn't this working?

  - by Michael Aaron Safyan

  This is a followup from "Save PyML.classifiers.multi.OneAgainstRest(SVM()) object?". I am using PyML for a computer vision project (pyimgattr), and have been having trouble storing/loading a multiclass classifier. When attempting to load one of the SVMs in a composite classifier, with loadSVM, I am getting: ValueError: invalid literal for float(): rest Note that this does not happen with the first classifier that I load, only with the second. What is causing this error, and what can I do to get around this so that I can properly load the classifier? Details To better understand the trouble I'm running into, you may want to look at pyimgattr.py (currently revision 11). I am invoking the program with "./pyimgattr.py train" which trains the classifier (invokes train on line 571, which trains the classifier with trainmulticlassclassifier on line 490 and saves it with storemulticlassclassifier on line 529), and then invoking the program with "./pyimgattr.py test" which loads the classifier in order to test it with the testing dataset (invokes test on line 628, which invokes loadmulticlassclassifier on line 549). The multiclass classifier consists of several one-against-rest SVMs which are saved individually. The loadmulticlassclassifier function loads these individually by calling loadSVM() on several different files. It is in this call to loadSVM (done indirectly in loadclassifier on line 517) that I get an error. The first of the one-against-rest classifiers loads successfully, but the second one does not. A transcript is as follows: $ ./pyimgattr.py test [INFO] pyimgattr -- Loading attributes from "classifiers/attributes.lst"... [INFO] pyimgattr -- Loading classnames from "classifiers/classnames.lst"... [INFO] pyimgattr -- Loading dataset "attribute_data/apascal_test.txt"... [INFO] pyimgattr -- Loaded dataset "attribute_data/apascal_test.txt". [INFO] pyimgattr -- Loading multiclass classifier from "classifiers/classnames_from_attributes"... [INFO] pyimgattr -- Constructing object into which to store loaded data... [INFO] pyimgattr -- Loading manifest data... [INFO] pyimgattr -- Loading classifier from "classifiers/classnames_from_attributes/aeroplane.svm".... scanned 100 patterns scanned 200 patterns read 100 patterns read 200 patterns {'50': 38, '60': 45, '61': 46, '62': 47, '49': 37, '52': 39, '53': 40, '24': 16, '25': 17, '26': 18, '27': 19, '20': 12, '21': 13, '22': 14, '23': 15, '46': 34, '47': 35, '28': 20, '29': 21, '40': 32, '41': 33, '1': 1, '0': 0, '3': 3, '2': 2, '5': 5, '4': 4, '7': 7, '6': 6, '8': 8, '58': 44, '39': 31, '38': 30, '15': 9, '48': 36, '16': 10, '19': 11, '32': 24, '31': 23, '30': 22, '37': 29, '36': 28, '35': 27, '34': 26, '33': 25, '55': 42, '54': 41, '57': 43} read 250 patterns in LinearSparseSVModel done LinearSparseSVModel constructed model [INFO] pyimgattr -- Loaded classifier from "classifiers/classnames_from_attributes/aeroplane.svm". [INFO] pyimgattr -- Loading classifier from "classifiers/classnames_from_attributes/bicycle.svm".... label at None delimiter , Traceback (most recent call last): File "./pyimgattr.py", line 797, in sys.exit(main(sys.argv)); File "./pyimgattr.py", line 782, in main return test(attributes_file,classnames_file,testing_annotations_file,testing_dataset_path,classifiers_path,logger); File "./pyimgattr.py", line 635, in test multiclass_classnames_from_attributes_classifier = loadmulticlassclassifier(classnames_from_attributes_folder,logger); File "./pyimgattr.py", line 529, in loadmulticlassclassifier classifiers.append(loadclassifier(os.path.join(filename,label+".svm"),logger)); File "./pyimgattr.py", line 502, in loadclassifier result=loadSVM(filename,datasetClass = SparseDataSet); File "/Library/Python/2.6/site-packages/PyML/classifiers/svm.py", line 328, in loadSVM data = datasetClass(fileName, **args) File "/Library/Python/2.6/site-packages/PyML/containers/vectorDatasets.py", line 224, in __init__ BaseVectorDataSet.__init__(self, arg, **args) File "/Library/Python/2.6/site-packages/PyML/containers/baseDatasets.py", line 214, in __init__ self.constructFromFile(arg, **args) File "/Library/Python/2.6/site-packages/PyML/containers/baseDatasets.py", line 243, in constructFromFile for x in parser : File "/Library/Python/2.6/site-packages/PyML/containers/parsers.py", line 426, in next x = [float(token) for token in tokens[self._first:self._last]] ValueError: invalid literal for float(): rest

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• Why wont this JS code work if its all on the same line?

  - by culov

  I'm writing HTML code for a java servlet. i first write the code in html/js so i can debug what im working on, and then ill make it a java string and put it in my servlet. My problem is that the code is working fine when i view it in ff from a local html file, but when i view it on my java servlet, it doesnt work because the js isnt getting called. what I did was format the html that my servlet generated so that its not all on a single line and ran the code again. This time it worked. I copied this working code into a browser address bar so that it will all be on a single line, and copied that code back into the script in my html file. Now, when the previously working code is on a single line, it doesnt work. Here's the formatted JS: var sMax var holder; var preSet; var rated; var request; function rating(num){ sMax = 0; for(n=0; n<num.parentNode.childNodes.length; n++){ if(num.parentNode.childNodes[n].nodeName == "A"){ sMax++; } } if(!rated){ s = num.id.replace("_", ''); a = 0; for(i=1; i<=sMax; i++){ if(i<=s){ document.getElementById("_"+i).className = "on"; document.getElementById("rateStatus").innerHTML = num.title; holder = a+1; a++; }else{ document.getElementById("_"+i).className = ""; } } } } function off(me){ if(!rated){ if(!preSet){ for(i=1; i<=sMax; i++){ document.getElementById("_"+i).className = ""; document.getElementById("rateStatus").innerHTML = me.parentNode.title; } }else{ rating(preSet); document.getElementById("rateStatus").innerHTML = document.getElementById("ratingSaved").innerHTML; } } } function rateIt(me){ if(!rated){ document.getElementById("rateStatus").innerHTML = document.getElementById("ratingSaved").innerHTML + " "+me.title; preSet = me; rated=1; sendRate(me); rating(me); } } function sendRate(sel){ alert("Your rating was: "+sel.title); addRating("rating", "?truck=kogibbq?rating="+ sel.id); } function addRating(servletName, servletArguments){ var servlet = servletName; var arg = servletArguments var req = servlet + arg; alert(req); addrequest(req); request.onreadystatechange = function(){ alert("response received"); } } function addrequest(req) { try { request = new XMLHttpRequest(); }catch (e) { try { request = new ActiveXObject("Microsoft.XMLHTTP"); }catch (e) { alert("XMLHttpRequest error: " + e); } } request.open("GET", element, true); request.send(null); return request; } Thanks.

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• C - circular character buffer w/ pthreads

  - by Matt

  I have a homework assignment where I have to implement a circular buffer and add and remove chars with separate threads: #include <pthread.h> #include <stdio.h> #define QSIZE 10 pthread_cond_t full,/* count == QSIZE */ empty,/* count == 0 */ ready; pthread_mutex_t m, n; /* implements critical section */ unsigned int iBuf, /* tail of circular queue */ oBuf; /* head of circular queue */ int count; /* count characters */ char buf [QSIZE]; /* the circular queue */ void Put(char s[]) {/* add "ch"; wait if full */ pthread_mutex_lock(&m); int size = sizeof(s)/sizeof(char); printf("size: %d", size); int i; for(i = 0; i < size; i++) { while (count >= QSIZE) pthread_cond_wait(&full, &m);/* is there empty slot? */ buf[iBuf] = s[i]; /* store the character */ iBuf = (iBuf+1) % QSIZE; /* increment mod QSIZE */ count++; if (count == 1) pthread_cond_signal(&empty);/* new character available */ } pthread_mutex_unlock(&m); } char Get() {/* remove "ch" from queue; wait if empty */ char ch; pthread_mutex_lock(&m); while (count <= 0) pthread_cond_wait(&empty, &m);/* is a character present? */ ch = buf[oBuf]; /* retrieve from the head of the queue */ oBuf = (oBuf+1) % QSIZE; count--; if (count == QSIZE-1) pthread_cond_signal(&full);/* signal existence of a slot */ pthread_mutex_unlock(&m); return ch; } void * p1(void *arg) { int i; for (i = 0; i < 5; i++) { Put("hella"); } } void * p2(void *arg) { int i; for (i = 0; i < 5; i++) { Put("goodby"); } } int main() { pthread_t t1, t2; void *r1, *r2; oBuf = 0; iBuf = 0; count=0; /* all slots are empty */ pthread_cond_init(&full, NULL); pthread_cond_init(&empty, NULL); pthread_mutex_init(&m, NULL); pthread_create(&t1, NULL, p1, &r1); pthread_create(&t2, NULL, p2, &r2); printf("Main"); char c; int i = 0; while (i < 55) { c = Get(); printf("%c",c); i++; } pthread_join(t1, &r1); pthread_join(t2, &r2); return 0; } I shouldn't have to change the logic much at all, the requirements are pretty specific. I think my problem lies in the Put() method. I think the first thread is going in and blocking the critical section and causing a deadlock. I was thinking I should make a scheduling attribute? Of course I could be wrong. I am pretty new to pthreads and concurrent programming, so I could really use some help spotting my error.

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• Performance issues with jms and spring integration. What is wrong with the following configuration?

  - by user358448

  I have a jms producer, which generates many messages per second, which are sent to amq persistent queue and are consumed by single consumer, which needs to process them sequentially. But it seems that the producer is much faster than the consumer and i am having performance and memory problems. Messages are fetched very very slowly and the consuming seems to happen on intervals (the consumer "asks" for messages in polling fashion, which is strange?!) Basically everything happens with spring integration. Here is the configuration at the producer side. First stake messages come in stakesInMemoryChannel, from there, they are filtered throw the filteredStakesChannel and from there they are going into the jms queue (using executor so the sending will happen in separate thread) <bean id="stakesQueue" class="org.apache.activemq.command.ActiveMQQueue"> <constructor-arg name="name" value="${jms.stakes.queue.name}" /> </bean> <int:channel id="stakesInMemoryChannel" /> <int:channel id="filteredStakesChannel" > <int:dispatcher task-executor="taskExecutor"/> </int:channel> <bean id="stakeFilterService" class="cayetano.games.stake.StakeFilterService"/> <int:filter input-channel="stakesInMemoryChannel" output-channel="filteredStakesChannel" throw-exception-on-rejection="false" expression="true"/> <jms:outbound-channel-adapter channel="filteredStakesChannel" destination="stakesQueue" delivery-persistent="true" explicit-qos-enabled="true" /> <task:executor id="taskExecutor" pool-size="100" /> The other application is consuming the messages like this... The messages come in stakesInputChannel from the jms stakesQueue, after that they are routed to 2 separate channels, one persists the message and the other do some other stuff, lets call it "processing". <bean id="stakesQueue" class="org.apache.activemq.command.ActiveMQQueue"> <constructor-arg name="name" value="${jms.stakes.queue.name}" /> </bean> <jms:message-driven-channel-adapter channel="stakesInputChannel" destination="stakesQueue" acknowledge="auto" concurrent-consumers="1" max-concurrent-consumers="1" /> <int:publish-subscribe-channel id="stakesInputChannel" /> <int:channel id="persistStakesChannel" /> <int:channel id="processStakesChannel" /> <int:recipient-list-router id="customRouter" input-channel="stakesInputChannel" timeout="3000" ignore-send-failures="true" apply-sequence="true" > <int:recipient channel="persistStakesChannel"/> <int:recipient channel="processStakesChannel"/> </int:recipient-list-router> <bean id="prefetchPolicy" class="org.apache.activemq.ActiveMQPrefetchPolicy"> <property name="queuePrefetch" value="${jms.broker.prefetch.policy}" /> </bean> <bean id="connectionFactory" class="org.springframework.jms.connection.CachingConnectionFactory"> <property name="targetConnectionFactory"> <bean class="org.apache.activemq.ActiveMQConnectionFactory"> <property name="brokerURL" value="${jms.broker.url}" /> <property name="prefetchPolicy" ref="prefetchPolicy" /> <property name="optimizeAcknowledge" value="true" /> <property name="useAsyncSend" value="true" /> </bean> </property> <property name="sessionCacheSize" value="10"/> <property name="cacheProducers" value="false"/> </bean>

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• How do you send a named pipe string from umnanaged to managed code space?

  - by billmcf

  I appear to have a named pipes 101 issue. I have a very simple set up to connect a simplex named pipe transmitting from a C++ unmanaged app to a C# managed app. The pipe connects, but I cannot send a "message" through the pipe unless I close the handle which appears to flush the buffer and pass the message through. It's like the message is blocked. I have tried reversing the roles of client/server and invoking them with different Flag combinations without any luck. I can easily send messages in the other direction from C# managed to C++ unmanaged. Does anyone have any insight. Can any of you guys successfully send messages from C++ unmanaged to C# managed? I can find plenty of examples of intra amanged or unmanaged pipes but not inter managed to/from unamanged - just claims to be able to do it. In the listings, I have omitted much of the wrapper stuff for clarity. The key bits I believe that are relevant are the pipe connection/creation/read and write methods. Don't worry too much about blocking/threading here. C# Server side // This runs in its own thread and so it is OK to block private void ConnectToClient() { // This server will listen to the sending client if (m_InPipeStream == null) { m_InPipeStream = new NamedPipeServerStream("TestPipe", PipeDirection.In, 1); } // Wait for client to connect to our server m_InPipeStream.WaitForConnection(); // Verify client is running if (!m_InPipeStream.IsConnected) { return; } // Start listening for messages on the client stream if (m_InPipeStream != null && m_InPipeStream.CanRead) { ReadThread = new Thread(new ParameterizedThreadStart(Read)); ReadThread.Start(m_InPipeStream); } } // This runs in its own thread and so it is OK to block private void Read(object serverObj) { NamedPipeServerStream pipeStream = (NamedPipeServerStream)serverObj; using (StreamReader sr = new StreamReader(pipeStream)) { while (true) { string buffer = "" ; try { // Blocks here until the handle is closed by the client-side!! buffer = sr.ReadLine(); // <<<<<<<<<<<<<< Sticks here } catch { // Read error break; } // Client has disconnected? if (buffer == null || buffer.Length == 0) break; // Fire message received event if message is non-empty if (MessageReceived != null && buffer != "") { MessageReceived(buffer); } } } } C++ client side // Static - running in its own thread. DWORD CNamedPipe::ListenForServer(LPVOID arg) { // The calling app (this) is passed as the parameter CNamedPipe* app = (CNamedPipe*)arg; // Out-Pipe: connect as a client to a waiting server app->m_hOutPipeHandle = CreateFile("\\\\.\\pipe\\TestPipe", GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL); // Could not create handle if (app->m_hInPipeHandle == NULL || app->m_hInPipeHandle == INVALID_HANDLE_VALUE) { return 1; } return 0; } // Sends a message to the server BOOL CNamedPipe::SendMessage(CString message) { DWORD dwSent; if (m_hOutPipeHandle == NULL || m_hOutPipeHandle == INVALID_HANDLE_VALUE) { return FALSE; } else { BOOL bOK = WriteFile(m_hOutPipeHandle, message, message.GetLength()+1, &dwSent, NULL); //FlushFileBuffers(m_hOutPipeHandle); // <<<<<<< Tried this return (!bOK || (message.GetLength()+1) != dwSent) ? FALSE : TRUE; } } // Somewhere in the Windows C++/MFC code... ... // This write is non-blocking. It just passes through having loaded the pipe. m_pNamedPipe->SendMessage("Hi de hi"); ...

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• Can i create different observables and different corresponding observers in java?

  - by mithun1538

  Hello everyone, Currently, I have one observable and many observers. What i need is different observables, and depending on the observable, different observers. How do I achieve this? ( For understanding, assume I have different apples - say apple1 apple2... I have observer_1 observing apple1, observer_2 observing apple2, observer_3 observing apple 2 and so on..). I tried creating different objects of the Observable class, but since observers are observing the same class of observable, I don't know how to access a particular instance of the Observable. I have included the following servlet code that contains Observer and Observable classes: public class CustomerServlet extends HttpServlet { public String getNextMessage() { // Create a message sink to wait for a new message from the // message source. return new MessageSink().getNextMessage(source); } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream()); String recMSG = getNextMessage(); dout.writeObject(recMSG); dout.flush(); } public void broadcastMessage(String message) { // Send the message to all the HTTP-connected clients by giving the // message to the message source source.sendMessage(message); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try { ObjectInputStream din= new ObjectInputStream(request.getInputStream()); String message = (String)din.readObject(); ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream()); dout.writeObject("1"); dout.flush(); if (message != null) { broadcastMessage(message); } // Set the status code to indicate there will be no response response.setStatus(response.SC_NO_CONTENT); } catch (Exception e) { e.printStackTrace(); } } @Override public String getServletInfo() { return "Short description"; }// </editor-fold> MessageSource source = new MessageSource(); } class MessageSource extends Observable { public void sendMessage(String message) { setChanged(); notifyObservers(message); } } class MessageSource extends Observable { public void sendMessage(String message) { setChanged(); notifyObservers(message); } } class MessageSink implements Observer { String message = null; // set by update() and read by getNextMessage() // Called by the message source when it gets a new message synchronized public void update(Observable o, Object arg) { // Get the new message message = (String)arg; // Wake up our waiting thread notify(); } // Gets the next message sent out from the message source synchronized public String getNextMessage(MessageSource source) { // Tell source we want to be told about new messages source.addObserver(this); // Wait until our update() method receives a message while (message == null) { try { wait(); } catch (Exception e) { System.out.println("Exception has occured! ERR ERR ERR"); } } // Tell source to stop telling us about new messages source.deleteObserver(this); // Now return the message we received // But first set the message instance variable to null // so update() and getNextMessage() can be called again. String messageCopy = message; message = null; return messageCopy; } }

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• Understanding C# async / await (1) Compilation

  - by Dixin

  Now the async / await keywords are in C#. Just like the async and ! in F#, this new C# feature provides great convenience. There are many nice documents talking about how to use async / await in specific scenarios, like using async methods in ASP.NET 4.5 and in ASP.NET MVC 4, etc. In this article we will look at the real code working behind the syntax sugar. According to MSDN: The async modifier indicates that the method, lambda expression, or anonymous method that it modifies is asynchronous. Since lambda expression / anonymous method will be compiled to normal method, we will focus on normal async method. Preparation First of all, Some helper methods need to make up. internal class HelperMethods { internal static int Method(int arg0, int arg1) { // Do some IO. WebClient client = new WebClient(); Enumerable.Repeat("http://weblogs.asp.net/dixin", 10) .Select(client.DownloadString).ToArray(); int result = arg0 + arg1; return result; } internal static Task<int> MethodTask(int arg0, int arg1) { Task<int> task = new Task<int>(() => Method(arg0, arg1)); task.Start(); // Hot task (started task) should always be returned. return task; } internal static void Before() { } internal static void Continuation1(int arg) { } internal static void Continuation2(int arg) { } } Here Method() is a long running method doing some IO. Then MethodTask() wraps it into a Task and return that Task. Nothing special here. Await something in async method Since MethodTask() returns Task, let’s try to await it: internal class AsyncMethods { internal static async Task<int> MethodAsync(int arg0, int arg1) { int result = await HelperMethods.MethodTask(arg0, arg1); return result; } } Because we used await in the method, async must be put on the method. Now we get the first async method. According to the naming convenience, it is called MethodAsync. Of course a async method can be awaited. So we have a CallMethodAsync() to call MethodAsync(): internal class AsyncMethods { internal static async Task<int> CallMethodAsync(int arg0, int arg1) { int result = await MethodAsync(arg0, arg1); return result; } } After compilation, MethodAsync() and CallMethodAsync() becomes the same logic. This is the code of MethodAsyc(): internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MethodAsync(int arg0, int arg1) { MethodAsyncStateMachine methodAsyncStateMachine = new MethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; methodAsyncStateMachine.Builder.Start(ref methodAsyncStateMachine); return methodAsyncStateMachine.Builder.Task; } } It just creates and starts a state machine MethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Result; private TaskAwaiter<int> awaitor; void IAsyncStateMachine.MoveNext() { try { if (this.State != 0) { this.awaitor = HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaitor.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaitor, ref this); return; } } else { this.State = -1; } this.Result = this.awaitor.GetResult(); } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); return; } this.State = -2; this.Builder.SetResult(this.Result); } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine param0) { this.Builder.SetStateMachine(param0); } } The generated code has been cleaned up so it is readable and can be compiled. Several things can be observed here: The async modifier is gone, which shows, unlike other modifiers (e.g. static), there is no such IL/CLR level “async” stuff. It becomes a AsyncStateMachineAttribute. This is similar to the compilation of extension method. The generated state machine is very similar to the state machine of C# yield syntax sugar. The local variables (arg0, arg1, result) are compiled to fields of the state machine. The real code (await HelperMethods.MethodTask(arg0, arg1)) is compiled into MoveNext(): HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(). CallMethodAsync() will create and start its own state machine CallMethodAsyncStateMachine: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(CallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> CallMethodAsync(int arg0, int arg1) { CallMethodAsyncStateMachine callMethodAsyncStateMachine = new CallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; callMethodAsyncStateMachine.Builder.Start(ref callMethodAsyncStateMachine); return callMethodAsyncStateMachine.Builder.Task; } } CallMethodAsyncStateMachine has the same logic as MethodAsyncStateMachine above. The detail of the state machine will be discussed soon. Now it is clear that: async /await is a C# level syntax sugar. There is no difference to await a async method or a normal method. A method returning Task will be awaitable. State machine and continuation To demonstrate more details in the state machine, a more complex method is created: internal class AsyncMethods { internal static async Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; } } In this method: There are multiple awaits. There are code before the awaits, and continuation code after each await After compilation, this multi-await method becomes the same as above single-await methods: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; multiCallMethodAsyncStateMachine.Builder.Start(ref multiCallMethodAsyncStateMachine); return multiCallMethodAsyncStateMachine.Builder.Task; } } It creates and starts one single state machine, MultiCallMethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Arg2; public int Arg3; public int ResultOfAwait1; public int ResultOfAwait2; public int ResultToReturn; private TaskAwaiter<int> awaiter; void IAsyncStateMachine.MoveNext() { try { switch (this.State) { case -1: HelperMethods.Before(); this.awaiter = AsyncMethods.MethodAsync(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 0: this.ResultOfAwait1 = this.awaiter.GetResult(); HelperMethods.Continuation1(this.ResultOfAwait1); this.awaiter = AsyncMethods.MethodAsync(this.Arg2, this.Arg3).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 1; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 1: this.ResultOfAwait2 = this.awaiter.GetResult(); HelperMethods.Continuation2(this.ResultOfAwait2); this.ResultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; this.State = -2; this.Builder.SetResult(this.ResultToReturn); break; } } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); } } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { this.Builder.SetStateMachine(stateMachine); } } The above code is already cleaned up, but there are still a lot of things. More clean up can be done, and the state machine can be very simple: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { // State: // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End public int State; public TaskCompletionSource<int> ResultToReturn; // int resultToReturn ... public int Arg0; // int Arg0 public int Arg1; // int arg1 public int Arg2; // int arg2 public int Arg3; // int arg3 public int ResultOfAwait1; // int resultOfAwait1 ... public int ResultOfAwait2; // int resultOfAwait2 ... private Task<int> currentTaskToAwait; /// <summary> /// Moves the state machine to its next state. /// </summary> void IAsyncStateMachine.MoveNext() { try { switch (this.State) { // Orginal code is splitted by "case"s: // case -1: // HelperMethods.Before(); // MethodAsync(Arg0, arg1); // case 0: // int resultOfAwait1 = await ... // HelperMethods.Continuation1(resultOfAwait1); // MethodAsync(arg2, arg3); // case 1: // int resultOfAwait2 = await ... // HelperMethods.Continuation2(resultOfAwait2); // int resultToReturn = resultOfAwait1 + resultOfAwait2; // return resultToReturn; case -1: // -1 is begin. HelperMethods.Before(); // Code before 1st await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg0, this.Arg1); // 1st task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 0. this.State = 0; IAsyncStateMachine this1 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => this1.MoveNext()); // Callback break; case 0: // Now 1st await is done. this.ResultOfAwait1 = this.currentTaskToAwait.Result; // Get 1st await's result. HelperMethods.Continuation1(this.ResultOfAwait1); // Code after 1st await and before 2nd await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg2, this.Arg3); // 2nd task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 1. this.State = 1; IAsyncStateMachine this2 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => this2.MoveNext()); // Callback break; case 1: // Now 2nd await is done. this.ResultOfAwait2 = this.currentTaskToAwait.Result; // Get 2nd await's result. HelperMethods.Continuation2(this.ResultOfAwait2); // Code after 2nd await. int resultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; // Code after 2nd await. // End with resultToReturn. this.State = -2; // -2 is end. this.ResultToReturn.SetResult(resultToReturn); break; } } catch (Exception exception) { // End with exception. this.State = -2; // -2 is end. this.ResultToReturn.SetException(exception); } } /// <summary> /// Configures the state machine with a heap-allocated replica. /// </summary> /// <param name="stateMachine">The heap-allocated replica.</param> [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { // No core logic. } } Only Task and TaskCompletionSource are involved in this version. And MultiCallMethodAsync() can be simplified to: [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync_(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, ResultToReturn = new TaskCompletionSource<int>(), // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End State = -1 }; (multiCallMethodAsyncStateMachine as IAsyncStateMachine).MoveNext(); // Original code are in this method. return multiCallMethodAsyncStateMachine.ResultToReturn.Task; } Now the whole state machine becomes very clear - it is about callback: Original code are split into pieces by “await”s, and each piece is put into each “case” in the state machine. Here the 2 awaits split the code into 3 pieces, so there are 3 “case”s. The “piece”s are chained by callback, that is done by Builder.AwaitUnsafeOnCompleted(callback), or currentTaskToAwait.ContinueWith(callback) in the simplified code. A previous “piece” will end with a Task (which is to be awaited), when the task is done, it will callback the next “piece”. The state machine’s state works with the “case”s to ensure the code “piece”s executes one after another. Callback Since it is about callback, the simplification  can go even further – the entire state machine can be completely purged. Now MultiCallMethodAsync() becomes: internal static Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { TaskCompletionSource<int> taskCompletionSource = new TaskCompletionSource<int>(); try { // Oringinal code begins. HelperMethods.Before(); MethodAsync(arg0, arg1).ContinueWith(await1 => { int resultOfAwait1 = await1.Result; HelperMethods.Continuation1(resultOfAwait1); MethodAsync(arg2, arg3).ContinueWith(await2 => { int resultOfAwait2 = await2.Result; HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; // Oringinal code ends. taskCompletionSource.SetResult(resultToReturn); }); }); } catch (Exception exception) { taskCompletionSource.SetException(exception); } return taskCompletionSource.Task; } Please compare with the original async / await code: HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; Yeah that is the magic of C# async / await: Await is literally pretending to wait. In a await expression, a Task object will be return immediately so that caller is not blocked. The continuation code is compiled as that Task’s callback code. When that task is done, continuation code will execute. Please notice that many details inside the state machine are omitted for simplicity, like context caring, etc. If you want to have a detailed picture, please do check out the source code of AsyncTaskMethodBuilder and TaskAwaiter.

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• Understanding C# async / await (1) Compilation

  - by Dixin

  Now the async / await keywords are in C#. Just like the async and ! in F#, this new C# feature provides great convenience. There are many nice documents talking about how to use async / await in specific scenarios, like using async methods in ASP.NET 4.5 and in ASP.NET MVC 4, etc. In this article we will look at the real code working behind the syntax sugar. According to MSDN: The async modifier indicates that the method, lambda expression, or anonymous method that it modifies is asynchronous. Since lambda expression / anonymous method will be compiled to normal method, we will focus on normal async method. Preparation First of all, Some helper methods need to make up. internal class HelperMethods { internal static int Method(int arg0, int arg1) { // Do some IO. WebClient client = new WebClient(); Enumerable.Repeat("http://weblogs.asp.net/dixin", 10) .Select(client.DownloadString).ToArray(); int result = arg0 + arg1; return result; } internal static Task<int> MethodTask(int arg0, int arg1) { Task<int> task = new Task<int>(() => Method(arg0, arg1)); task.Start(); // Hot task (started task) should always be returned. return task; } internal static void Before() { } internal static void Continuation1(int arg) { } internal static void Continuation2(int arg) { } } Here Method() is a long running method doing some IO. Then MethodTask() wraps it into a Task and return that Task. Nothing special here. Await something in async method Since MethodTask() returns Task, let’s try to await it: internal class AsyncMethods { internal static async Task<int> MethodAsync(int arg0, int arg1) { int result = await HelperMethods.MethodTask(arg0, arg1); return result; } } Because we used await in the method, async must be put on the method. Now we get the first async method. According to the naming convenience, it is named MethodAsync. Of course a async method can be awaited. So we have a CallMethodAsync() to call MethodAsync(): internal class AsyncMethods { internal static async Task<int> CallMethodAsync(int arg0, int arg1) { int result = await MethodAsync(arg0, arg1); return result; } } After compilation, MethodAsync() and CallMethodAsync() becomes the same logic. This is the code of MethodAsyc(): internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MethodAsync(int arg0, int arg1) { MethodAsyncStateMachine methodAsyncStateMachine = new MethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; methodAsyncStateMachine.Builder.Start(ref methodAsyncStateMachine); return methodAsyncStateMachine.Builder.Task; } } It just creates and starts a state machine, MethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Result; private TaskAwaiter<int> awaitor; void IAsyncStateMachine.MoveNext() { try { if (this.State != 0) { this.awaitor = HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaitor.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaitor, ref this); return; } } else { this.State = -1; } this.Result = this.awaitor.GetResult(); } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); return; } this.State = -2; this.Builder.SetResult(this.Result); } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine param0) { this.Builder.SetStateMachine(param0); } } The generated code has been refactored, so it is readable and can be compiled. Several things can be observed here: The async modifier is gone, which shows, unlike other modifiers (e.g. static), there is no such IL/CLR level “async” stuff. It becomes a AsyncStateMachineAttribute. This is similar to the compilation of extension method. The generated state machine is very similar to the state machine of C# yield syntax sugar. The local variables (arg0, arg1, result) are compiled to fields of the state machine. The real code (await HelperMethods.MethodTask(arg0, arg1)) is compiled into MoveNext(): HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(). CallMethodAsync() will create and start its own state machine CallMethodAsyncStateMachine: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(CallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> CallMethodAsync(int arg0, int arg1) { CallMethodAsyncStateMachine callMethodAsyncStateMachine = new CallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; callMethodAsyncStateMachine.Builder.Start(ref callMethodAsyncStateMachine); return callMethodAsyncStateMachine.Builder.Task; } } CallMethodAsyncStateMachine has the same logic as MethodAsyncStateMachine above. The detail of the state machine will be discussed soon. Now it is clear that: async /await is a C# language level syntax sugar. There is no difference to await a async method or a normal method. As long as a method returns Task, it is awaitable. State machine and continuation To demonstrate more details in the state machine, a more complex method is created: internal class AsyncMethods { internal static async Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; } } In this method: There are multiple awaits. There are code before the awaits, and continuation code after each await After compilation, this multi-await method becomes the same as above single-await methods: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; multiCallMethodAsyncStateMachine.Builder.Start(ref multiCallMethodAsyncStateMachine); return multiCallMethodAsyncStateMachine.Builder.Task; } } It creates and starts one single state machine, MultiCallMethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Arg2; public int Arg3; public int ResultOfAwait1; public int ResultOfAwait2; public int ResultToReturn; private TaskAwaiter<int> awaiter; void IAsyncStateMachine.MoveNext() { try { switch (this.State) { case -1: HelperMethods.Before(); this.awaiter = AsyncMethods.MethodAsync(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 0: this.ResultOfAwait1 = this.awaiter.GetResult(); HelperMethods.Continuation1(this.ResultOfAwait1); this.awaiter = AsyncMethods.MethodAsync(this.Arg2, this.Arg3).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 1; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 1: this.ResultOfAwait2 = this.awaiter.GetResult(); HelperMethods.Continuation2(this.ResultOfAwait2); this.ResultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; this.State = -2; this.Builder.SetResult(this.ResultToReturn); break; } } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); } } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { this.Builder.SetStateMachine(stateMachine); } } Once again, the above state machine code is already refactored, but it still has a lot of things. More clean up can be done if we only keep the core logic, and the state machine can become very simple: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { // State: // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End public int State; public TaskCompletionSource<int> ResultToReturn; // int resultToReturn ... public int Arg0; // int Arg0 public int Arg1; // int arg1 public int Arg2; // int arg2 public int Arg3; // int arg3 public int ResultOfAwait1; // int resultOfAwait1 ... public int ResultOfAwait2; // int resultOfAwait2 ... private Task<int> currentTaskToAwait; /// <summary> /// Moves the state machine to its next state. /// </summary> public void MoveNext() // IAsyncStateMachine member. { try { switch (this.State) { // Original code is split by "await"s into "case"s: // case -1: // HelperMethods.Before(); // MethodAsync(Arg0, arg1); // case 0: // int resultOfAwait1 = await ... // HelperMethods.Continuation1(resultOfAwait1); // MethodAsync(arg2, arg3); // case 1: // int resultOfAwait2 = await ... // HelperMethods.Continuation2(resultOfAwait2); // int resultToReturn = resultOfAwait1 + resultOfAwait2; // return resultToReturn; case -1: // -1 is begin. HelperMethods.Before(); // Code before 1st await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg0, this.Arg1); // 1st task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 0. this.State = 0; MultiCallMethodAsyncStateMachine that1 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => that1.MoveNext()); break; case 0: // Now 1st await is done. this.ResultOfAwait1 = this.currentTaskToAwait.Result; // Get 1st await's result. HelperMethods.Continuation1(this.ResultOfAwait1); // Code after 1st await and before 2nd await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg2, this.Arg3); // 2nd task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 1. this.State = 1; MultiCallMethodAsyncStateMachine that2 = this; this.currentTaskToAwait.ContinueWith(_ => that2.MoveNext()); break; case 1: // Now 2nd await is done. this.ResultOfAwait2 = this.currentTaskToAwait.Result; // Get 2nd await's result. HelperMethods.Continuation2(this.ResultOfAwait2); // Code after 2nd await. int resultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; // Code after 2nd await. // End with resultToReturn. this.State = -2; // -2 is end. this.ResultToReturn.SetResult(resultToReturn); break; } } catch (Exception exception) { // End with exception. this.State = -2; // -2 is end. this.ResultToReturn.SetException(exception); } } /// <summary> /// Configures the state machine with a heap-allocated replica. /// </summary> /// <param name="stateMachine">The heap-allocated replica.</param> [DebuggerHidden] public void SetStateMachine(IAsyncStateMachine stateMachine) // IAsyncStateMachine member. { // No core logic. } } Only Task and TaskCompletionSource are involved in this version. And MultiCallMethodAsync() can be simplified to: [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, ResultToReturn = new TaskCompletionSource<int>(), // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End State = -1 }; multiCallMethodAsyncStateMachine.MoveNext(); // Original code are moved into this method. return multiCallMethodAsyncStateMachine.ResultToReturn.Task; } Now the whole state machine becomes very clean - it is about callback: Original code are split into pieces by “await”s, and each piece is put into each “case” in the state machine. Here the 2 awaits split the code into 3 pieces, so there are 3 “case”s. The “piece”s are chained by callback, that is done by Builder.AwaitUnsafeOnCompleted(callback), or currentTaskToAwait.ContinueWith(callback) in the simplified code. A previous “piece” will end with a Task (which is to be awaited), when the task is done, it will callback the next “piece”. The state machine’s state works with the “case”s to ensure the code “piece”s executes one after another. Callback If we focus on the point of callback, the simplification  can go even further – the entire state machine can be completely purged, and we can just keep the code inside MoveNext(). Now MultiCallMethodAsync() becomes: internal static Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { TaskCompletionSource<int> taskCompletionSource = new TaskCompletionSource<int>(); try { // Oringinal code begins. HelperMethods.Before(); MethodAsync(arg0, arg1).ContinueWith(await1 => { int resultOfAwait1 = await1.Result; HelperMethods.Continuation1(resultOfAwait1); MethodAsync(arg2, arg3).ContinueWith(await2 => { int resultOfAwait2 = await2.Result; HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; // Oringinal code ends. taskCompletionSource.SetResult(resultToReturn); }); }); } catch (Exception exception) { taskCompletionSource.SetException(exception); } return taskCompletionSource.Task; } Please compare with the original async / await code: HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; Yeah that is the magic of C# async / await: Await is not to wait. In a await expression, a Task object will be return immediately so that execution is not blocked. The continuation code is compiled as that Task’s callback code. When that task is done, continuation code will execute. Please notice that many details inside the state machine are omitted for simplicity, like context caring, etc. If you want to have a detailed picture, please do check out the source code of AsyncTaskMethodBuilder and TaskAwaiter.

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• com.jcraft.jsch.JSchException: UnknownHostKey

  - by Alex

  I don't know how SSH works and I think that's a simple question. How do I fix that exception: com.jcraft.jsch.JSchException: UnknownHostKey: mywebsite.com. RSA key fingerprint is 22:fb:ee:fe:18:cd:aa:9a:9c:78:89:9f:b4:78:75:b4 I know I should verify that key or something, but there is like zero documentation for Jsch. Here is my code it's really straightforward: import com.jcraft.jsch.JSch; import com.jcraft.jsch.Session; public class ssh{ public static void main(String[] arg){ try{ JSch jsch = new JSch(); //create SSH connection String host = "mywebsite.com"; String user = "username"; String password = "123456"; Session session = jsch.getSession(user, host, 22); session.setPassword(password); session.connect(); } catch(Exception e){ System.out.println(e); } } }

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• How to configure LocalSessionFactoryBean to release connections after transaction end?

  - by peter

  I am testing an application (Spring 2.5, Hibernate 3.5.0 Beta, Atomikos 3.6.2, and Postgreql 8.4.2) with the configuration for the DAO listed below. The problem that I see is that the pool of 10 connections with the dataSource gets exhausted after the 10's transaction. I know 'hibernate.connection.release_mode' has no effect unless the session is obtained with openSession rather then using a contextual session. I am wandering if anyone has found a way to configure the LocalSessionFactoryBean to release connections after any transaction. Thank you Peter <bean id="dataSource" class="com.atomikos.jdbc.AtomikosDataSourceBean" init-method="init" destroy-method="close"> <property name="uniqueResourceName"><value>XADBMS</value></property> <property name="xaDataSourceClassName"> <value>org.postgresql.xa.PGXADataSource</value> </property> <property name="xaProperties"> <props> <prop key="databaseName">${jdbc.name}</prop> <prop key="serverName">${jdbc.server}</prop> <prop key="portNumber">${jdbc.port}</prop> <prop key="user">${jdbc.username}</prop> <prop key="password">${jdbc.password}</prop> </props> </property> <property name="poolSize"><value>10</value></property> </bean> <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource"> <ref bean="dataSource" /> </property> <property name="mappingResources"> <list> <value>Abc.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</prop> <prop key="hibernate.show_sql">on</prop> <prop key="hibernate.format_sql">true</prop> <prop key="hibernate.connection.isolation">3</prop> <prop key="hibernate.current_session_context_class">jta</prop> <prop key="hibernate.transaction.factory_class">org.hibernate.transaction.JTATransactionFactory</prop> <prop key="hibernate.transaction.manager_lookup_class">com.atomikos.icatch.jta.hibernate3.TransactionManagerLookup</prop> <prop key="hibernate.connection.release_mode">auto</prop> <prop key="hibernate.transaction.auto_close_session">true</prop> </props> </property> </bean> <!-- Transaction definition here --> <bean id="userTransactionService" class="com.atomikos.icatch.config.UserTransactionServiceImp" init-method="init" destroy-method="shutdownForce"> <constructor-arg> <props> <prop key="com.atomikos.icatch.service"> com.atomikos.icatch.standalone.UserTransactionServiceFactory </prop> </props> </constructor-arg> </bean> <!-- Construct Atomikos UserTransactionManager, needed to configure Spring --> <bean id="AtomikosTransactionManager" class="com.atomikos.icatch.jta.UserTransactionManager" init-method="init" destroy-method="close" depends-on="userTransactionService"> <property name="forceShutdown" value="false" /> </bean> <!-- Also use Atomikos UserTransactionImp, needed to configure Spring --> <bean id="AtomikosUserTransaction" class="com.atomikos.icatch.jta.UserTransactionImp" depends-on="userTransactionService"> <property name="transactionTimeout" value="300" /> </bean> <!-- Configure the Spring framework to use JTA transactions from Atomikos --> <bean id="txManager" class="org.springframework.transaction.jta.JtaTransactionManager" depends-on="userTransactionService"> <property name="transactionManager" ref="AtomikosTransactionManager" /> <property name="userTransaction" ref="AtomikosUserTransaction" /> </bean> <!-- the transactional advice (what 'happens'; see the <aop:advisor/> bean below) --> <tx:advice id="txAdvice" transaction-manager="txManager"> <tx:attributes> <!-- all methods starting with 'get' are read-only --> <tx:method name="get*" read-only="true" propagation="REQUIRED"/> <!-- other methods use the default transaction settings (see below) --> <tx:method name="*" propagation="REQUIRED"/> </tx:attributes> </tx:advice> <aop:config> <aop:advisor pointcut="execution(* *.*.AbcDao.*(..))" advice-ref="txAdvice"/> </aop:config> <!-- DAO objects --> <bean id="abcDao" class="test.dao.impl.HibernateAbcDao" scope="singleton"> <property name="sessionFactory" ref="sessionFactory"/> </bean>

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• MSBuild cannot find SGen when compiling a solution

  - by Jaxidian

  I've looked at several other SGen-related questions on here and either their answers don't apply or their answers don't fix this for me. I have installed several SDKs to fix this issue with no luck. Reference types should not be changed since this is the only place this is a problem. Once suggestion is to put SGen.exe into the C:\Windows\Microsoft.NET\Framework\v3.5 folder, but that's not been done on the box where this is not a problem. In this scenario, SGen.exe actually exists and is right where it's supposed to be, but MSBuild still is having issues with finding it for some reason! Background: We have a NAnt script that automates our builds. In this scenario, NAnt is calling MSBuild and MSBuild is generating the error claiming to be unable to find SGen. The project is .NET 3.5-based. I have my primary dev environment (64-bit Vista Ultimate) where the script works perfectly and I am attempting to duplicate it in a VM (64-bit Win 7 Ultimate). I THINK I have everything to the point where I should be good-to-go but this fails on the Win7 box (works perfectly on the Vista box). I have done some comparisons between the two boxes and they both look identical in this regard, but it still fails. For example, the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework's sdkInstallRootv2.0 value is set to C:\Program Files\Microsoft.NET\SDK\v2.0 64bit\ on both machines. In both machines, SGen.exe is in that path's bin subdirectory. NAnt Script: <target name="report-installer" depends="fail-if-environment-not-set"> <exec program="MSBuild.exe" basedir="${framework35.directory}"> <arg value="${tools.directory.current}\ReportInstaller\ReportInstaller.sln" /> <arg value="/p:Configuration=${buildconfiguration.current}" /> </exec> </target> The error message I get is this: report-installer: [exec] Microsoft (R) Build Engine Version 3.5.30729.4926 [exec] [Microsoft .NET Framework, Version 2.0.50727.4927] [exec] Copyright (C) Microsoft Corporation 2007. All rights reserved. [exec] [exec] Build started 4/8/2010 11:28:23 AM. [exec] Project "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.sln" on node 0 (default targets). [exec] Building solution configuration "Release|Any CPU". [exec] Project "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.sln" (1) is building "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.csproj" (2) on node 0 (default targets). [exec] Could not locate the .NET Framework SDK. The task is looking for the path to the .NET Framework SDK at the location specified in the SDKInstallRootv2.0 value of the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework. You may be able to solve the problem by doing one of the following: 1.) Install the .NET Framework SDK. 2.) Manually set the above registry key to the correct location. [exec] CoreCompile: [exec] Skipping target "CoreCompile" because all output files are up-to-date with respect to the input files. [exec] C:\Windows\Microsoft.NET\Framework\v2.0.50727\Microsoft.Common.targets(1902,9): error MSB3091: Task failed because "sgen.exe" was not found, or the .NET Framework SDK v2.0 is not installed. The task is looking for "sgen.exe" in the "bin" subdirectory beneath the location specified in the SDKInstallRootv2.0 value of the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework. You may be able to solve the problem by doing one of the following: 1.) Install the .NET Framework SDK v2.0. 2.) Manually set the above registry key to the correct location. 3.) Pass the correct location into the "ToolPath" parameter of the task. [exec] Done Building Project "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.csproj" (default targets) -- FAILED. [exec] Done Building Project "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.sln" (default targets) -- FAILED. [exec] [exec] Build FAILED. [exec] [exec] "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.sln" (default target) (1) -> [exec] "C:\Projects\Production\Tools\ReportInstaller\ReportInstaller.csproj" (default target) (2) -> [exec] (GenerateSerializationAssemblies target) -> [exec] C:\Windows\Microsoft.NET\Framework\v2.0.50727\Microsoft.Common.targets(1902,9): error MSB3091: Task failed because "sgen.exe" was not found, or the .NET Framework SDK v2.0 is not installed. The task is looking for "sgen.exe" in the "bin" subdirectory beneath the location specified in the SDKInstallRootv2.0 value of the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework. You may be able to solve the problem by doing one of the following: 1.) Install the .NET Framework SDK v2.0. 2.) Manually set the above registry key to the correct location. 3.) Pass the correct location into the "ToolPath" parameter of the task. [exec] [exec] 0 Warning(s) [exec] 1 Error(s) [exec] [exec] Time Elapsed 00:00:00.24 [call] C:\Projects\Production\Source\reports.build(15,4): [call] External Program Failed: C:\Windows\Microsoft.NET\Framework\v3.5\MSBuild.exe (return code was 1) What am I doing wrong here that is causing MSBuild to STILL be unable to find SGen?

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• Looping to provide multiple lines in linechart (django-googlecharts)

  - by mighty_bombero

  Hi, I'm trying to generate some charts using django-googlecharts. This works fine for rather static data but in one case I would like to render a different number of lines, based on a variable. I tried this: {% chart %} {% for line in line_data %} {% chart-data line %} {% endfor %} {% chart-size "390x200" %} {% chart-type "line" %} {% chart-labels days %} {% endchart %} Line data is a list containing lists. The template code fails with "Caught an exception while rendering: max() arg is an empty sequence". I guess the problem is that I try to loop over templatetags. What approach could be used here? Or am I completely missing something? Is this doable using inclusion tags? Thanks for your help.

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• Exception while exposing a bean in webservice using spring mvc

  - by Ajay

  Hi, I am using Spring 3.0.5.Release MVC for exposing a webservice and below is my servlet.xml <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <!-- To enable @RequestMapping process on type level and method level --> <context:component-scan base-package="com.pyramid.qls.progressReporter.service" /> <bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" /> <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"> <property name="messageConverters"> <list> <ref bean="marshallingConverter" /> <ref bean="atomConverter" /> <ref bean="jsonConverter" /> </list> </property> </bean> <bean id="marshallingConverter" class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"> <constructor-arg ref="jaxbMarshaller" /> <property name="supportedMediaTypes" value="application/xml"/> </bean> <bean id="atomConverter" class="org.springframework.http.converter.feed.AtomFeedHttpMessageConverter"> <property name="supportedMediaTypes" value="application/atom+xml" /> </bean> <bean id="jsonConverter" class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter"> <property name="supportedMediaTypes" value="application/json" /> </bean> <!-- Client --> <bean id="restTemplate" class="org.springframework.web.client.RestTemplate"> <property name="messageConverters"> <list> <ref bean="marshallingConverter" /> <ref bean="atomConverter" /> <ref bean="jsonConverter" /> </list> </property> </bean> <bean id="jaxbMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller"> <property name="classesToBeBound"> <list> <value>com.pyramid.qls.progressReporter.impl.BatchProgressMetricsImpl</value> <value>com.pyramid.qls.progressReporter.datatype.InstrumentStats</value> <value>com.pyramid.qls.progressReporter.datatype.InstrumentInfo</value> <value>com.pyramid.qls.progressReporter.datatype.LoadOnConsumer</value> <value>com.pyramid.qls.progressReporter.datatype.HighLevelTaskStats</value> <value>com.pyramid.qls.progressReporter.datatype.SessionStats</value> <value>com.pyramid.qls.progressReporter.datatype.TaskStats</value> <value>com.pyramid.qls.progressReporter.datatype.ComputeStats</value> <value>com.pyramid.qls.progressReporter.datatype.DetailedInstrumentStats</value> <value>com.pyramid.qls.progressReporter.datatype.ImntHistoricalStats</value> </list> </property> </bean> <bean id="QPRXmlView" class="org.springframework.web.servlet.view.xml.MarshallingView"> <constructor-arg ref="jaxbMarshaller" /> </bean> <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"> <property name="mediaTypes"> <map> <entry key="xml" value="application/xml"/> <entry key="html" value="text/html"/> </map> </property> <property name="viewResolvers"> <list> <bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/> <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </list> </property> </bean> <bean id="QPRController" class="com.pyramid.qls.progressReporter.service.QPRController"> <property name="jaxb2Mashaller" ref="jaxbMarshaller" /> </bean> </beans> Following is what i am doing in controller (QPRController) @RequestMapping(value = "/clientMetrics/{clientId}", method = RequestMethod.GET) public ModelAndView getBatchProgressMetrics(@PathVariable String clientId) { List<BatchProgressMetrics> batchProgressMetricsList = null; batchProgressMetricsList = batchProgressReporter.getBatchProgressMetricsForClient(clientId); ModelAndView mav = new ModelAndView("QPRXmlView", BindingResult.MODEL_KEY_PREFIX + "batchProgressMetrics", batchProgressMetricsList); return mav; } And i get the following: SEVERE: Servlet.service() for servlet rest threw exception javax.servlet.ServletException: Unable to locate object to be marshalled in model: {org.springframework.validation.BindingResult.batchProgressMetrics= Note that BatchProgressMetrics is an interface so my MAV is returning list of BatchProgressMetrics objects and i have entry for its impl in classes to be bound in servlet.xml. Can you please help me as to what i am doing wrong. And yes if i send just batchProgressMetricsList.get(0) in MAV it just works fine.

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• Java - short and casting

  - by chr1s

  Hi all, I have the following code snippet. public static void main(String[] args) { short a = 4; short b = 5; short c = 5 + 4; short d = a; short e = a + b; // does not compile (expression treated as int) short z = 32767; short z_ = 32768; // does not compile (out of range) test(a); test(7); // does not compile (not applicable for arg int) } public static void test(short x) { } Is the following summary correct (with regard to only the example above using short)? direct initializations without casting is only possible using literals or single variables (as long as the value is in the range of the declared type) if the rhs of an assignment deals with expressions using variables, casting is necessary But why exactly do I need to cast the argument of the second method call taking into account the previous summary?

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