Why is Console.Readline not executing as expected

问题:

I have the following code below to work with. The problem I have here is that the code runs through the while loop without waiting for input on the line String temp = Console.ReadLine() . Need help understanding why and how to fix please. Thanks in advance!

   /*Banker's algorithm Implementation*/
  class Program
  {

        static void Main(string[] args)
        {
              int n = 0;//number of resources we will  be dealing with
              int proc_num = 0;//Total number of processes to share available resources

              IDictionary<String, SysProcess> processes = new Dictionary<String, SysProcess>();
              IDictionary<String, int> MaxR = new Dictionary<String, int>();// maximum available resources
              IDictionary<String, int> avail = new Dictionary<String, int>();// Available resources after first allocation
              Dictionary<String, int> availsum = new Dictionary<string, int>();

              //Start  
              while (true)
              {
                    Console.WriteLine(" What is number of resources to be shared? : ");
                          if (!int.TryParse(Console.ReadLine(), out n))
                          {
                                Console.WriteLine(" Error Please provide valid number --- {0}!", n);
                          }
                          else
                          {
                                break;
                          }
              }

              //get the maximum number of each Resources Ie Total Resources Available
              while (true && n>0)
              {
                    Console.WriteLine("Using a comma delimited list(e.g. 0, 0, 0, 0) list maximum of each of the {0} resources : ", n);
                    String temp;
                      temp = Console.ReadLine();

                    if (!String.IsNullOrEmpty(temp))
                    {
                          String[] maxR = temp.Split(',');
                          for (int a = 1; a <= n; a++)
                          {
                                MaxR.Add("Resource#" + a.ToString(), Convert.ToInt32(maxR[a]));
                          }
                          break;
                    }
              }


              while (true && n>0)
              {
                    Console.Write("Enter total number of processes to share the available resources :");
                    if (!int.TryParse(Console.Read().ToString(), out proc_num))
                    {
                          Console.WriteLine(" Error Please provide valid number --- {0}!", proc_num);
                    }
                    else
                    { break; }
              }

              if(proc_num > 0)
              {
                    //Request Process Max and allocated resources data
                    for (int i = 1; i <= proc_num; i++)
                    {
                          Console.Write("Using a comma delimited list, Enter total number of Resources 1 through {0} are needed by PROCESS#{1} ?", n, i);
                          String[] temps = Console.ReadLine().Split(',');
                          SysProcess tempproc = new SysProcess("Process#" + i.ToString());

                          for (int a = 0; a < temps.Length; a++)
                          {
                                tempproc.Add_max_resource("Resource#" + (a + 1).ToString(), Convert.ToInt32(temps[a]));
                          }

                          //How many resources have already been allocated to each resource
                          temps = null;
                          Console.Write("Using a comma delimited list,Enter number of resources 1 through {0} already  allocated to PROCESS#{1} ? ", n, i);
                          temps = Console.ReadLine().Split(',');
                          for (int a = 0; a < temps.Length; a++)
                          {
                                tempproc.add_alloc_resource("Resource#" + (a + 1).ToString(), Convert.ToInt32(temps[a]));
                          }
                          processes.Add("Process#" + i.ToString(), tempproc);
                    }


                    Console.WriteLine("Processing . . . ");
                    Console.WriteLine();
                    Console.WriteLine("Available resources ");

                    //Compute Available Resources 
                    for (int i = 0; i < n; i++)
                    {
                          if (!availsum.ContainsKey("Resource#" + (i + 1).ToString()))
                                availsum.Add("Resource#" + (i + 1).ToString(), 0);
                          foreach (SysProcess sp in processes.Values)
                          {     //add sum up the available
                                availsum["Resource#" + (i + 1).ToString()] += sp.alloc_resources["Resource#" + (i + 1).ToString()];
                          }
                    }

                    //print out the availables we computed 

                    Console.Write(" avail< ");
                    for (int j = 0; j < n; j++)
                    {

                          Console.Write(availsum["Resource#" + (j + 1).ToString()] + ",");

                          if (j + 1 == n)//if this is the last one, go ahead and output the rest
                                Console.Write("{0} > ", availsum["Resource#" + (j + 1).ToString()]);
                    }


                    // Printing resources still needed 
                    Console.WriteLine();
                    foreach (SysProcess p in processes.Values)
                    {
                          p.print_needed();
                    }


                    //a) Find a row in the Need matrix which is less than the Available vector. 
                    //If such a row exists, then the process represented by that row may complete
                    //with those additional resources. If no such row exists, eventual deadlock is possible.
                    Dictionary<String, int> _currentavailsum;

                    foreach (SysProcess p in processes.Values)
                    {
                          int TotalSproccounter = 0;
                          String safelead;
                          if (isprocessSafe(n, p, availsum))
                          {
                                TotalSproccounter++;
                                safelead = p.id;
                                _currentavailsum = new Dictionary<String, int>();
                                _currentavailsum = availsum;//get a copy of the original data to begin with
                                foreach (SysProcess q in processes.Values)
                                {
                                      if (q != p)//we only want to compare with the others from here
                                      {
                                            if (isprocessSafe(n, p, _currentavailsum))
                                            {
                                                  update_availsum(n, q, ref  _currentavailsum);//update the currentavail count
                                                  TotalSproccounter++;
                                                  //update print 
                                                  safelead += ", " + q.id;
                                            }
                                      }
                                }

                                if (TotalSproccounter == proc_num)
                                {
                                      Console.WriteLine("Safe allocation < {0} >", safelead);
                                }
                                else
                                {
                                      Console.WriteLine("Deadlock reached/unsafe allocation :  < {0} >", safelead);
                                }
                          }
                    }
               }
              Console.ReadLine();
        }

        //compares the number of resources needed against the number of resources available
        public static Boolean isprocessSafe(int n, SysProcess p, IDictionary<String, int> avail)
        {
              int safecount = 0;
              foreach (String resourcekey in avail.Keys)
              {
                    if (p.need_resources.ContainsKey(resourcekey) && p.need_resources[resourcekey] <= avail[resourcekey])
                    {
                          safecount++;
                    }

              }
              if (safecount == n)
              {

                    return true;
              }
              return false;
        }

        //compares the number of resources needed against the number of resources available
        public static void update_availsum(int n, SysProcess p, ref Dictionary<String, int> _currentavailsum)
        {
              foreach (String resourcekey in _currentavailsum.Keys)
              {
                    if (p.need_resources.ContainsKey(resourcekey))
                    {
                          _currentavailsum[resourcekey] += p.need_resources[resourcekey];
                    }

              }
        }

  }

  //container class for processes 
  public class SysProcess
  {
        public String id { get; set; }
        Dictionary<String, int> _max_resources = null; // will hold the Resource name and the  the number of resources 
        Dictionary<String, int> _alloc_resources = null;//allocated resources
        Dictionary<String, int> _need_resources = null;//allocated resources

        public Dictionary<String, int> max_resources
        {
              get
              { return _max_resources; }

        }

        public Dictionary<String, int> alloc_resources
        {
              get
              {
                    return _alloc_resources;

              }
        }

        public Dictionary<String, int> need_resources
        {
              get
              {
                    return _need_resources;

              }
        }

        public SysProcess(String procID)
        {
              _max_resources = new Dictionary<String, int>();
              _alloc_resources = new Dictionary<String, int>();
              id = procID;
        }

        public void Add_max_resource(String resource, int count)
        {
              _max_resources.Add(resource, count);
        }

        public void add_alloc_resource(String resource, int count)
        {
              _alloc_resources.Add(resource, count);
              _need_resources.Add(resource, _max_resources[resource] - alloc_resources[resource]);
        }

        public void print_needed()
        {
              Console.Write(id);
              foreach (int s in _need_resources.Values)
              {
                    Console.Write(" {0}", s);
              }

        }
  }

Probably a good idea to add the whole code here since I am still unable to figure this one out. Please help

回答1:

The problem is the use of the problematic method Console.Read(). This method will block until a full line of text is entered, but it only returns the first character, leaving the remaining text in the input buffer. The carriage return that was used to enter the first value and unblock the read operation is still sitting in the input buffer when the Console.ReadLine() operation is performed. Consequently, a blank line is returned.

I recommend that you replace Console.Read().ToString() with Console.ReadLine() to fix this problem.

The problem can be demonstrated with this code:

    static void Main(string[] args)
    {
        string value = Console.Read().ToString();
        Console.WriteLine("You entered: {0}", value);
        Console.WriteLine("Press ENTER to continue...");
        Console.ReadLine();   // Returns immediately.
        Console.WriteLine("Continuing....");
    }

And fixed like this:

        string value = Console.ReadLine();

回答2:

Is your project configured as a console application? It needs to be built with different switches in order to set the flags in the exe file so that the OS loader will know that it needs to create a console window for the process. GUI apps don't set that flag, and don't get a console window.

In VS2010, right click on your project's Properties link, click on the Application tab, and change Output Type from Windows Application to Console Application. Rebuild and run.

回答3:

You probably have duplicate / extra newlines in your input. This code looks perfectly fine for parsing a comma-delimited file...

回答4:

The issue could be stuff already in the input stream you're trying to read from the console. If you don't want to worry about what's already in the buffer, you can try to flush it so that you start with a fresh, empty input state. Offhand, all the Console.Read* functions appear to be blocking functions. However, there's also the KeyAvailable property which indicates if there is content available.

This provides for the following code:

private void clearInputBuffer()
{
   while(Console.KeyAvailable)
   {
       Console.Read(); // read next key, but discard
   }
}

Alternatively, the buffer for input is, at the basic level, a stream. A TextReader, to be specific. And that is available from

Console.In

So you can use the functions there, such as .ReadToEnd(), to clear out the buffer right before you enter in your While(true) loop.

回答5:

The problem is that you're misinterpreting what Console.Read does. It reads the next character from the input stream and returns it as an integer. But ... and here's the good part, nothing comes in until you hit Enter. So if you enter "abc" at the first prompt and press Enter, you're going to get the first character from the buffer, as an integer (97). But the input buffer will contain "bc" and the newline, which will then be consumed by the Readline.

If you want a string from the Console, call ReadLine, not Read.