Starting and destroying Singleton Single Selenium Server process for C # DLL lifespan

Question

I have a Selenium Test.DLL that loads using NUnit.

I run the required Selenium Java Server silently hidden in the process when starting the test.

However, currently start the server when the test starts and it when the test stops . Kill()

This causes the selenium server to start / stop for each test .

---

I want the Selenium Server process:

• Run either in the loading / initialization of the DLL , or the first time you run the test
• Be ed on Death DLL or Garbage Collection Kill()

---

I read that C # does not support the DLL initialization trap and call code. (I am wrong?)

My idea was to host the Selenium server in a singleton class and initialize it the first time the test is run. Then I left it in the garbage collector to call the Dispose method through the deconstructor. I currently have the following code for hosting a selenium server:

namespace Tests.Server
{
    using System;
    using System.Diagnostics;
    using System.IO;
    using System.Security;
    using System.Windows.Forms;
    using Microsoft.Win32;

    /// <summary>
    /// A singleton class to host and control the selenium server.
    /// </summary>
    public class SeleniumServer : IDisposable
    {
        #region Fields
        /// <summary>
        /// The singleton instance
        /// </summary>
        private static volatile SeleniumServer instance;

        /// <summary>
        /// An object to perform double-check locking upon instance creation to 
        /// avoid dead-locks. 
        /// See <see href="SeleniumServer.Instance"/> for more information.
        /// </summary>
        private static object syncRoot = new Object();

        /// <summary>
        /// The current selenium server.
        /// </summary>
        private Process seleniumServer = null;

        /// <summary>
        /// A flag for the disposal of the class.
        /// </summary>
        private bool isDisposed = false;
        #endregion

        #region Constructor
        /// <summary>
        /// Initializes a new instance of the SeleniumServer class.  Starts the 
        /// Selenium Java server in a background hidden thread.
        /// </summary>
        private SeleniumServer()
        {
            // Get the java install folder.
            string javaFileLocation = this.GetJavaFileLocation();

            // Get the selenium server java executable
            string jarFileLocation = '"' + Directory.GetCurrentDirectory() + @"\SeleniumServer\selenium-server.jar""";

            // Start the selenium server
            seleniumServer = new Process();
            seleniumServer.StartInfo.FileName = javaFileLocation;
            seleniumServer.StartInfo.Arguments = " -jar " + jarFileLocation + " -browserSessionReuse -trustAllSSLCertification";
            seleniumServer.StartInfo.WorkingDirectory = jarFileLocation.Substring(0, jarFileLocation.LastIndexOf("\\"));
            seleniumServer.StartInfo.UseShellExecute = true;
            seleniumServer.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
            seleniumServer.Start();
        }
        #endregion

        #region Deconstructor
        ~SeleniumServer()
        {
            Dispose(false);
        }
        #endregion

        #region Properties
        /// <summary>
        /// A thread safe
        /// </summary>
        public static SeleniumServer Instance
        {
            get
            {
                // This approach ensures that only one instance is created and 
                // only when the instance is needed. Also, the variable is 
                // declared to be volatile to ensure that assignment to the 
                // instance variable completes before the instance variable can 
                // be accessed. Lastly, this approach uses a syncRoot instance 
                // to lock on, rather than locking on the type itself, to avoid 
                // deadlocks.
                // This double-check locking approach solves the thread 
                // concurrency problems while avoiding an exclusive lock in 
                // every call to the Instance property method. It also allows 
                // you to delay instantiation until the object is first 
                // accessed. In practice, an application rarely requires this 
                // type of implementation. In most cases, the static 
                // initialization approach is sufficient.
                if (instance == null)
                {
                    lock (syncRoot)
                    {
                        if (instance == null)
                        {
                            instance = new SeleniumServer();
                        }
                    }
                }

                return instance;
            }
        }
        #endregion

        #region Methods
        /// <summary>
        /// Stops the process.
        /// </summary>   
        protected void Dispose(bool disposing)
        {
            if (disposing)
            {
                // Code to dispose the managed resources of the class
                // Not needed right now.
            }

            // Code to dispose the un-managed resources of the class
            // TODO: Handle the exceptions
            Instance.seleniumServer.Kill();

            // All done!
            isDisposed = true;
        }

        /// <summary>
        /// Dispose of the class and stop the Selenium server process.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Stops the Selenium Server.
        /// </summary>
        public void Stop()
        {
            this.Dispose();
        }

        /// <summary>
        /// Attempts to get the Java installation folder from the registry.  If 
        /// it cannot be found the default installation folder is checked before 
        /// failing.
        /// </summary>
        /// <returns>The Java executable file path.</returns>
        /// <exception cref="System.Exception">
        /// Thrown when the user does not have permission to access the 
        /// registry.
        /// </exception>
        /// <exception cref="System.ObjectDisposedException">
        /// Thrown if the registry key object is disposed of.
        /// </exception>
        /// <exception cref="System.IOException">
        /// Thrown if the registry key object is marked for deletion.
        /// </exception>
        private string GetJavaFileLocation()
        {
            string javaFileLocation = string.Empty;
            RegistryKey regKey = Registry.LocalMachine;
            RegistryKey subKey = null;
            try
            {
                // Check for Java in the native bitness
                string javaRegistryLocation = @"SOFTWARE\JavaSoft\Java Runtime Environment\";
                subKey = regKey.OpenSubKey(javaRegistryLocation);

                // Check if we are running in WOW64 and only 32 bit Java is installed.
                if (subKey == null)
                {
                    javaRegistryLocation = @"SOFTWARE\Wow6432Node\JavaSoft\Java Runtime Environment\";
                    subKey = regKey.OpenSubKey(javaRegistryLocation);
                }

                // If Java was not found in either of these location the user 
                // needs to install it.  Note that Java 32 bit is a prerequisite 
                // for the installer so should always be installed.
                if (subKey == null)
                {
                    MessageBox.Show(
                        "You must have Java installed to run the commands server. This allows browser commands to be routed to the browser window.\n\nPlease visit: http://www.java.com/ to download.",
                        "Please Install Java",
                        MessageBoxButtons.OK,
                        MessageBoxIcon.Information);

                    throw new Exception("No installation of Java was detected to run the selenium server.");
                }

                // Get all the sub keys (could be multiple versions of Java 
                // installed) and get the most recent (last one)
                string[] subKeyNames = subKey.GetSubKeyNames();
                subKey = regKey.OpenSubKey(javaRegistryLocation + subKeyNames[subKeyNames.Length - 1]);

                // Specify the java executable location
                javaFileLocation = subKey.GetValue("JavaHome").ToString() + @"\bin\java.exe";
            }
            catch (SecurityException e)
            {
                // Attempt to find the java executable at the default location.
                javaFileLocation = @"C:\Program Files\Java\jre6\bin\java.exe";
                if (!File.Exists(javaFileLocation))
                {
                    MessageBox.Show(
                        "The program did not have permission to access the registry to obtain the installation folder of Java.\n\nThe default location (" + javaFileLocation + ") of Java was used and the Java executable was not found.\n\nPlease install Java in this folder or see the help under the RegistryKey.OpenSubKey method on MSDN.",
                        "Java Executable Not Found",
                        MessageBoxButtons.OK,
                        MessageBoxIcon.Error);

                    throw new Exception("The program did not have permission to access the registry to obtain the installation folder of Java.", e);
                }
            }
            catch (UnauthorizedAccessException e)
            {
                // Attempt to find the java executable at the default location.
                javaFileLocation = @"C:\Program Files\Java\jre6\bin\java.exe";
                if (!File.Exists(javaFileLocation))
                {
                    MessageBox.Show(
                        "The user does not have the necessary registry rights to obtain the installation folder of Java.\n\nThe default location (" + javaFileLocation + ") of Java was used and the Java executable was not found.\n\nPlease install Java in this folder or see the help under the RegistryKey.OpenSubKey method on MSDN.",
                        "Java Executable Not Found",
                        MessageBoxButtons.OK,
                        MessageBoxIcon.Error);

                    throw new Exception("The user does not have the necessary registry rights to obtain the installation folder of Java.", e);
                }
            }
            catch (ObjectDisposedException e)
            {
                // This hopefully shouldn't happen so ask the user to report it.
                MessageBox.Show(
                    "The Java registry object was closed, resulting in the Java server not being started.  Please report this error.",
                    "Error",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                throw new ObjectDisposedException("The Java registry object was closed.  Please report this error.", e);
            }
            catch (IOException e)
            {
                // This hopefully shouldn't happen so ask the user to report it.
                MessageBox.Show(
                    "The Java registry object was marked for deletion, resulting in the Java server not being started.  Please report this error.",
                    "Error",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                throw new ObjectDisposedException("The Java registry object was marked for deletion.  Please report this error.", e);
            }

            return javaFileLocation;
        }
        #endregion
    }
}

---

My questions:

• Is this a smart way to host a process for a DLL's life?
• How do I configure this class from my code? Does it need static / global? Any good singleton usage examples you know about?
• Will garbage collection recycle this singleton when unloading a DLL?
• DLL, DLL , NUnit DLL ?

Answer 1

:

// <copyright file="SeleniumServer.cs" company="Your Company">
// Copyright (c) 2010 All Right Reserved
// </copyright>
// <summary>
// Provides a singleton class for hosting and running the selenium server.
// </summary>

namespace YourCompany.Tests.Server
{
    using System;
    using System.Diagnostics;
    using System.IO;
    using System.Security;
    using System.Windows.Forms;
    using Microsoft.Win32;

    /// <summary>
    /// A singleton class to host and control the selenium server.
    /// </summary>
    public sealed class SeleniumServer : IDisposable
    {
        #region Fields
        /// <summary>
        /// The singleton instance
        /// </summary>
        private static volatile SeleniumServer instance;

        /// <summary>
        /// An object to perform double-check locking upon instance creation to 
        /// avoid dead-locks. 
        /// See <see href="SeleniumServer.Instance"/> for more information.
        /// </summary>
        private static object syncRoot = new object();

        /// <summary>
        /// The current selenium server.
        /// </summary>
        private Process seleniumServer = null;

        /// <summary>
        /// A flag for the disposal of the class.
        /// </summary>
        private bool isDisposed = false;
        #endregion

        #region Constructor
        /// <summary>
        /// Prevents a default instance of the SeleniumServer class from being created.  Starts the Selenium Java server in a background hidden thread.
        /// </summary>
        private SeleniumServer()
        {
            // Get the java install folder.
            string javaFileLocation = this.GetJavaFileLocation();

            // Get the selenium server java executable
            string jarFileLocation = '"' + Directory.GetCurrentDirectory() + @"\SeleniumServer\selenium-server.jar""";

            // Start the selenium server
            this.seleniumServer = new Process();
            this.seleniumServer.StartInfo.FileName = javaFileLocation;
            this.seleniumServer.StartInfo.Arguments = " -jar " + jarFileLocation + " -browserSessionReuse -trustAllSSLCertificates";
            this.seleniumServer.StartInfo.WorkingDirectory = jarFileLocation.Substring(0, jarFileLocation.LastIndexOf("\\"));
            this.seleniumServer.StartInfo.UseShellExecute = true;
            this.seleniumServer.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
            this.seleniumServer.Start();

            // The class is no long disposed
            this.isDisposed = false;
        }
        #endregion

        #region Deconstructor
        /// <summary>
        /// Finalizes an instance of the SeleniumServer class.
        /// </summary>
        ~SeleniumServer()
        {
            this.Dispose(false);
        }
        #endregion

        #region Properties
        /// <summary>
        /// Gets a thread safe instance of the Selenium Server class.
        /// </summary>
        public static SeleniumServer Instance
        {
            get
            {
                // This approach ensures that only one instance is created and 
                // only when the instance is needed. Also, the variable is 
                // declared to be volatile to ensure that assignment to the 
                // instance variable completes before the instance variable can 
                // be accessed. Lastly, this approach uses a syncRoot instance 
                // to lock on, rather than locking on the type itself, to avoid 
                // deadlocks.
                // This double-check locking approach solves the thread 
                // concurrency problems while avoiding an exclusive lock in 
                // every call to the Instance property method. It also allows 
                // you to delay instantiation until the object is first 
                // accessed. In practice, an application rarely requires this 
                // type of implementation. In most cases, the static 
                // initialization approach is sufficient.
                if (instance == null)
                {
                    lock (syncRoot)
                    {
                        if (instance == null)
                        {
                            instance = new SeleniumServer();
                        }
                    }
                }

                return instance;
            }
        }
        #endregion

        #region Methods
        /// <summary>
        /// Dispose of the class and stop the Selenium server process.
        /// </summary>
        public void Dispose()
        {
            this.Dispose(true);
            GC.SuppressFinalize(this);
        }

        /// <summary>
        /// Stops the process.
        /// </summary>
        /// <param name="disposing">
        /// True if managed resources need to be disposed
        /// </param>
        private void Dispose(bool disposing)
        {
            if (!this.isDisposed)
            {
                if (disposing)
                {         
                    // If this class is expanded:
                    // Code to dispose the managed resources of the class
                }

                // Kill the server
                if (this.seleniumServer != null)
                {
                    try
                    {
                        this.seleniumServer.Kill();
                        this.seleniumServer = null;
                    }
                    catch (Exception)
                    {
                        MessageBox.Show(
                            "The Selenium Java Server could not be stopped, please start Task Manager and killed \"java.exe\"",
                            "Failed to Stop Jave Server",
                            MessageBoxButtons.OK,
                            MessageBoxIcon.Error);
                    }
                }
            }

            // All done!
            this.isDisposed = true;
        }

        /// <summary>
        /// Attempts to get the Java installation folder from the registry.  If 
        /// it cannot be found the default installation folder is checked before 
        /// failing.
        /// </summary>
        /// <returns>The Java executable file path.</returns>
        /// <exception cref="System.Exception">
        /// Thrown when the user does not have permission to access the 
        /// registry.
        /// </exception>
        /// <exception cref="System.ObjectDisposedException">
        /// Thrown if the registry key object is disposed of.
        /// </exception>
        /// <exception cref="System.IOException">
        /// Thrown if the registry key object is marked for deletion.
        /// </exception>
        private string GetJavaFileLocation()
        {
            string javaFileLocation = string.Empty;
            RegistryKey regKey = Registry.LocalMachine;
            RegistryKey subKey = null;
            try
            {
                // Check for Java in the native bitness
                string javaRegistryLocation = @"SOFTWARE\JavaSoft\Java Runtime Environment\";
                subKey = regKey.OpenSubKey(javaRegistryLocation);

                // Check if we are running in WOW64 and only 32 bit Java is installed.
                if (subKey == null)
                {
                    javaRegistryLocation = @"SOFTWARE\Wow6432Node\JavaSoft\Java Runtime Environment\";
                    subKey = regKey.OpenSubKey(javaRegistryLocation);
                }

                // If Java was not found in either of these location the user 
                // needs to install it.  Note that Java 32 bit is a prerequisite 
                // for the installer so should always be installed.
                if (subKey == null)
                {
                    MessageBox.Show(
                        "You must have Java installed to run the commands server. This allows browser commands to be routed to the browser window.\n\nPlease visit: http://www.java.com/ to download.",
                        "Please Install Java",
                        MessageBoxButtons.OK,
                        MessageBoxIcon.Information);

                    throw new Exception("No installation of Java was detected to run the selenium server.");
                }

                // Get all the sub keys (could be multiple versions of Java 
                // installed) and get the most recent (last one)
                string[] subKeyNames = subKey.GetSubKeyNames();
                subKey = regKey.OpenSubKey(javaRegistryLocation + subKeyNames[subKeyNames.Length - 1]);

                // Specify the java executable location
                javaFileLocation = subKey.GetValue("JavaHome").ToString() + @"\bin\java.exe";
            }
            catch (SecurityException e)
            {
                // Attempt to find the java executable at the default location.
                javaFileLocation = @"C:\Program Files\Java\jre6\bin\java.exe";
                if (!File.Exists(javaFileLocation))
                {
                    MessageBox.Show(
                        "The program did not have permission to access the registry to obtain the installation folder of Java.\n\nThe default location (" + javaFileLocation + ") of Java was used and the Java executable was not found.\n\nPlease install Java in this folder or see the help under the RegistryKey.OpenSubKey method on MSDN.",
                        "Java Executable Not Found",
                        MessageBoxButtons.OK,
                        MessageBoxIcon.Error);

                    throw new Exception("The program did not have permission to access the registry to obtain the installation folder of Java.", e);
                }
            }
            catch (UnauthorizedAccessException e)
            {
                // Attempt to find the java executable at the default location.
                javaFileLocation = @"C:\Program Files\Java\jre6\bin\java.exe";
                if (!File.Exists(javaFileLocation))
                {
                    MessageBox.Show(
                        "The user does not have the necessary registry rights to obtain the installation folder of Java.\n\nThe default location (" + javaFileLocation + ") of Java was used and the Java executable was not found.\n\nPlease install Java in this folder or see the help under the RegistryKey.OpenSubKey method on MSDN.",
                        "Java Executable Not Found",
                        MessageBoxButtons.OK,
                        MessageBoxIcon.Error);

                    throw new Exception("The user does not have the necessary registry rights to obtain the installation folder of Java.", e);
                }
            }
            catch (ObjectDisposedException e)
            {
                // This hopefully shouldn't happen so ask the user to report it.
                MessageBox.Show(
                    "The Java registry object was closed, resulting in the Java server not being started.  Please report this error.",
                    "Error",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                throw new ObjectDisposedException("The Java registry object was closed.  Please report this error.", e);
            }
            catch (IOException e)
            {
                // This hopefully shouldn't happen so ask the user to report it.
                MessageBox.Show(
                    "The Java registry object was marked for deletion, resulting in the Java server not being started.  Please report this error.",
                    "Error",
                    MessageBoxButtons.OK,
                    MessageBoxIcon.Error);
                throw new ObjectDisposedException("The Java registry object was marked for deletion.  Please report this error.", e);
            }

            return javaFileLocation;
        }
        #endregion
    }
}

:

SeleniumServer seleniumServer = SeleniumServer.Instance;

SetUp .

, , - .