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hOOt - full text search engine

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24 Feb 2019CPOL17 min read 1M   22.5K   388  
Smallest full text search engine (lucene replacement) built from scratch using inverted MGRB bitmap index, highly compact storage, operating in database and document modes
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

namespace EPocalipse.IFilter
{
  [ComVisible(false)]
  [ComImport, InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("00000001-0000-0000-C000-000000000046")]
  internal interface IClassFactory
  {
    void CreateInstance([MarshalAs(UnmanagedType.Interface)] object pUnkOuter, ref Guid refiid, [MarshalAs(UnmanagedType.Interface)] out object ppunk);
    void LockServer(bool fLock);
  }

  /// <summary>
  /// Utility class to get a Class Factory for a certain Class ID 
  /// by loading the dll that implements that class
  /// </summary>
  internal static class ComHelper
  {
    //DllGetClassObject fuction pointer signature
    private delegate int DllGetClassObject(ref Guid ClassId, ref Guid InterfaceId, [Out, MarshalAs(UnmanagedType.Interface)] out object ppunk);

    //Some win32 methods to load\unload dlls and get a function pointer
    private class Win32NativeMethods
    {
      [DllImport("kernel32.dll", CharSet=CharSet.Ansi)]
      public static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);

      [DllImport("kernel32.dll")]
      public static extern bool FreeLibrary(IntPtr hModule);

      [DllImport("kernel32.dll")]
      public static extern IntPtr LoadLibrary(string lpFileName);
    }

    /// <summary>
    /// Holds a list of dll handles and unloads the dlls 
    /// in the destructor
    /// </summary>
    private class DllList
    {
      private List<IntPtr> _dllList=new List<IntPtr>();
      public void AddDllHandle(IntPtr dllHandle)
      {
        lock (_dllList)
        {
          _dllList.Add(dllHandle);
        }
      }

      ~DllList()
      {
        foreach (IntPtr dllHandle in _dllList)
        {
          try
          {
            Win32NativeMethods.FreeLibrary(dllHandle);
          }
          catch { };
        }
      }
    }

    static DllList _dllList=new DllList();

    /// <summary>
    /// Gets a class factory for a specific COM Class ID. 
    /// </summary>
    /// <param name="dllName">The dll where the COM class is implemented</param>
    /// <param name="filterPersistClass">The requested Class ID</param>
    /// <returns>IClassFactory instance used to create instances of that class</returns>
    internal static IClassFactory GetClassFactory(string dllName, string filterPersistClass)
    {
      //Load the class factory from the dll
      IClassFactory classFactory=GetClassFactoryFromDll(dllName, filterPersistClass);
      return classFactory;
    }

    private static IClassFactory GetClassFactoryFromDll(string dllName, string filterPersistClass)
    {
      //Load the dll
      IntPtr dllHandle=Win32NativeMethods.LoadLibrary(dllName);
      if (dllHandle==IntPtr.Zero)
        return null;

      //Keep a reference to the dll until the process\AppDomain dies
      _dllList.AddDllHandle(dllHandle);

      //Get a pointer to the DllGetClassObject function
      IntPtr dllGetClassObjectPtr=Win32NativeMethods.GetProcAddress(dllHandle, "DllGetClassObject");
      if (dllGetClassObjectPtr==IntPtr.Zero)
        return null;

      //Convert the function pointer to a .net delegate
      DllGetClassObject dllGetClassObject=(DllGetClassObject)Marshal.GetDelegateForFunctionPointer(dllGetClassObjectPtr, typeof(DllGetClassObject));

      //Call the DllGetClassObject to retreive a class factory for out Filter class
      Guid filterPersistGUID=new Guid(filterPersistClass);
      Guid IClassFactoryGUID=new Guid("00000001-0000-0000-C000-000000000046"); //IClassFactory class id
      Object unk;
      if (dllGetClassObject(ref filterPersistGUID, ref IClassFactoryGUID, out unk)!=0)
        return null;

      //Yippie! cast the returned object to IClassFactory
      return (unk as IClassFactory);
    }
  }
}

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License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Architect -
United Kingdom United Kingdom
Mehdi first started programming when he was 8 on BBC+128k machine in 6512 processor language, after various hardware and software changes he eventually came across .net and c# which he has been using since v1.0.
He is formally educated as a system analyst Industrial engineer, but his programming passion continues.

* Mehdi is the 5th person to get 6 out of 7 Platinum's on Code-Project (13th Jan'12)
* Mehdi is the 3rd person to get 7 out of 7 Platinum's on Code-Project (26th Aug'16)

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