Directory lock error with Lucene.Net usage in an ASP.NET MVC site

Question

I'm building an ASP.NET MVC site where I want to use Lucene.Net for search. I've already built a SearchController and all of its methods, but I'm getting an error at runtime that occurs when the SearchController is first initialized.

In SearchController, here's how I'm creating an IndexWriter:

public static string IndexLocation = HostingEnvironment.MapPath("~/lucene");
public static Lucene.Net.Analysis.Standard.StandardAnalyzer analyzer = new Lucene.Net.Analysis.Standard.StandardAnalyzer();
public static IndexWriter writer = new IndexWriter(IndexLocation,analyzer);

The error occurs on the last line. Here's the message that I'm getting:

Lucene.Net.Store.LockObtainFailedException: Lock obtain timed out: SimpleFSLock@C:\Users\Username\Desktop\SiteSolution\Site\lucene\write.lock

Furthermore, here's the stack trace:

[LockObtainFailedException: Lock obtain timed out: SimpleFSLock@C:\Users\Username\Desktop\SiteSolution\Site\lucene\write.lock]
   Lucene.Net.Store.Lock.Obtain(Int64 lockWaitTimeout) in C:\Users\Username\Desktop\Lucene.Net_2_9_2\src\Lucene.Net\Store\Lock.cs:107
   Lucene.Net.Index.IndexWriter.Init(Directory d, Analyzer a, Boolean create, Boolean closeDir, IndexDeletionPolicy deletionPolicy, Boolean autoCommit, Int32 maxFieldLength, IndexingChain indexingChain, IndexCommit commit) in C:\Users\Username\Desktop\Lucene.Net_2_9_2\src\Lucene.Net\Index\IndexWriter.cs:1827
   Lucene.Net.Index.IndexWriter.Init(Directory d, Analyzer a, Boolean closeDir, IndexDeletionPolicy deletionPolicy, Boolean autoCommit, Int32 maxFieldLength, IndexingChain indexingChain, IndexCommit commit) in C:\Users\Username\Desktop\Lucene.Net_2_9_2\src\Lucene.Net\Index\IndexWriter.cs:1801
   Lucene.Net.Index.IndexWriter..ctor(String path, Analyzer a) in C:\Users\Username\Desktop\Lucene.Net_2_9_2\src\Lucene.Net\Index\IndexWriter.cs:1350
   Site.Controllers.SearchController..cctor() in C:\Users\Username\Desktop\SiteSolution\Site\Controllers\SearchController.cs:95

[TypeInitializationException: The type initializer for 'Site.Controllers.SearchController' threw an exception.]

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
   System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandle& ctor, Boolean& bNeedSecurityCheck) +0
   System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean fillCache) +86
   System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) +230
   System.Activator.CreateInstance(Type type, Boolean nonPublic) +67
   System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +80

[InvalidOperationException: An error occurred when trying to create a controller of type 'Site.Controllers.SearchController'. Make sure that the controller has a parameterless public constructor.]
   System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +190
   System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +68
   System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +118
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +46
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +63
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +13
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8682818
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

How can I resolve this issue?

UPDATE: I've started working on this particular project again, and it seems that I haven't fully resolved this issue yet.

The real issue is that the write.lock file isn't being removed after index usage ends. Based on the answer I have accepted, I understand the basic implementation logic, but I'm not sure if I have implemented it correctly. Here are some other methods in my class that are probably invalid:

    public ActionResult Search(string query)
    {

        var reader = writer.GetReader(); // Get reader from writer
        var searcher = new IndexSearcher(reader); // Build IndexSearch

        //Execute search...

        // Dispose of objects
        searcher = null;
        reader = null;

        return View();
    }

    public void AddToIndex(Document doc)
    {
        writer.AddDocument(doc);
        writer.Flush();
        writer.Optimize();
        writer.Flush();
    }

    private bool disposed = false;

    protected override void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
            {
                // Release managed resources.
            }
            try
            {
                writer.Close();
                writer = null;
            }
            catch
            {

            }
            // Release unmanaged resources.
            // Set large fields to null.
            // Call Dispose on your base class.
            disposed = true;
        }
        base.Dispose(disposing);
    }

Any thoughts?

Answer 1

The reason why this happens is that the writer creates an empty file called write.lock as a cross-process lock. When that file exists, Lucene assumes that someone has a write lock on that directory.

When you terminate your process incorrectly, the file will not get deleted. So Lucene thinks that someone is still holding on to the lock. That's why you should always have a finally statement which closes the index.

If you are sure that the file is there in error (i.e. no Lucene processes are running) it is fine to just delete the file. Your index may, however, be in a corrupted state, since the writing was obviously terminated midstream.