C# Using threads and semaphores and need help to see if code is blocking

C# ASP .NET 2.0 Ajax Web Application

I have a web application that is responsible for queuing a set of tasks to be performed based on a task id. The way the system is setup is there is another web application (java) that will connect to our mainframe and get necessary information based on a task id. The web page simply loads with a phrase that says whether the task completed or did not complete.

So, in essence, my web application just submits a series of calls to another web application and uses the WebClient class to download the string of the page's results.

Here's where things get tricky. The web application I am calling via the WebClient class can only have 3 active task requests to the mainframe at any given time and it does not handle that implementation itself.

The code below takes a series of task ids. I then create a thread array and limit the max # of concurrent requests to the web application via the use of a semaphore. My worry is that something is blocking all other threads somewhere. I believe if any line of code is blocking it is this one (as denoted by the comment):

               String result = client.DownloadString(uri);

where client is my WebClient object.

I tried using the Asynchronous version of this, but my issue is the web page loads all the way and I have no way of getting results back to the page that I know of. Currently the main page that calls this code is in a while loop that checks the ThreadsAlive property and as long as one of the created threads is alive, the main thread sleeps.

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Net;
using System.IO;
 
 
public class DoTask {
 
     //Used for object locking for log file
     static Object writeLogLock = new Object();
 
     //Used for object locking for task/thread status
     static Object statusLogLock = new Object();
 
     //Don't think this is used...
     static Object threadCountLock = new Object();
 
     //Maximum # of concurrent threads
     static int maxThreads = 3;
     
     //Controls max # of concurrent threads
     private static Semaphore semaphore ;
 
     private DoTask() {
     }
 
     public DoTask(List<String> pIds) {
 
          if (DoTask.status != null)
               DoTask.status.Clear();
 
          this.ids = pIds;
 
     }
 
     //List that contains the results of each task processed.
     public static List<String> status = new List<string>();
 
     //Called _rope b/c when dealing w/ threads you get plenty to hang yourself with.
     private Thread[] _rope;
 
     //Property so that calling code can know if threads are still being processed
     public Boolean ThreadsAlive {
          get {
               if (_rope != null) {
                    int cnt = _rope.Length;
                    for (int i = 0; i < cnt; i++) {
                         if (_rope[i].IsAlive) {
                              return true;
                         }
                    }
               }
               return false;
          }
     }
 
     private List<String> _ids;
 
 
     public void RunRev() {
          /* hold all available semaphore slots till threads are created */
          semaphore = new Semaphore(0, maxThreads);
          int c = ids.Count;
          this._rope = new Thread[c];
          writeLog("   /*************************BEGIN ENTRY************* ");
          for (int i = 0; i < c; i++) {
               String s = ids[i];
               _rope[i] = new Thread(new ParameterizedThreadStart(doTask));
               _rope[i].Start(s);
          }
          /* make maxThreads (3) number of threads available */
          semaphore.Release(maxThreads);
     }
 
     //Keep track of results so calling code can know what ids failed and what ids succeeded
     public static void writeStatus(String logMessage) {
          lock (statusLogLock) {
               status.Add(logMessage);
          }
     }
 
     //Writes message to a log file
     public static void writeLog(String logMessage) {
          lock (writeLogLock) {
               String logFile = "C:\\log.txt";
               using (StreamWriter logEntry = new StreamWriter(logFile, true)) {
                    logEntry.WriteLine(DateTime.Now.ToString() + " " + logMessage);
                    logEntry.Close();
               }
          }
     }
 
     /*
      * Note that semaphore.WaitOne(); will force the thread to wait until there is a freed thread
      *  semaphore.Release(1); releases a spot in the allocated threads from the semaphore
      */
     public void doTask(Object pId) {
          WebClient client = null;
          String id = (String)pId;
          String err = "";
          String uri = null;
          try {
 
		//Force waiting for free/open thread slot in semaphore
               semaphore.WaitOne();
               uri = "http://retrieveDataPage?" + "id=" + id ;
              
 
               client = new WebClient();
               //client.Headers.Add("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
               client.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
 
		//Is this blocking?????
               String result = client.DownloadString(uri);
               
               if (result != null && result.Contains("completed"))
               {
                    writeStatus(String.Format("SUCCESS: {0} ", result));
                    writeLog(String.Format("SUCCESS: {0} ", result));
               }
               else
               {
                    writeStatus(String.Format("FAILED: {0} ", result));
                    writeLog(String.Format("FAILED: {0} ", result));
               }      
               
               //Asynchronous testing
               //client.DownloadStringAsync(siteUri);
               //Uri siteUri = new Uri(uri);               
               //client.DownloadStringCompleted += Test;
           
          } catch (Exception e) {
               err = e.Message;
               writeStatus(String.Format("ERROR: {0} ", id));
               writeLog(String.Format("ERROR: {0} ", id));
               writeLog("ERROR: " + e.Message + " FOR ID: " + id + "\n" + "STACK TRACE: " + e.StackTrace);
          } finally {
               semaphore.Release(1);
          }
     }
 
     private void Test(Object sender, DownloadStringCompletedEventArgs args) 
     {
          String result = args.Result;
 
          if (result != null && result.Contains("completed"))
          {
               writeStatus(String.Format("SUCCESS: {0} ", result));
               writeLog(String.Format("SUCCESS: {0} ", result));
          }
          else
          {
               writeStatus(String.Format("FAILED: {0} ", result));
               writeLog(String.Format("FAILED: {0} ", result));
          }          
     }
 
}

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