OoasTools

// C5 example: locking 2005-11-07

// Compile with 

//   csc /r:C5.dll Locking.cs 

using System;

using System.Threading;

using C5;

using SCG = System.Collections.Generic;

namespace Locking {

  class Locking {

    static ArrayList<int> coll = new ArrayList<int>();

    // static SCG.List<int> coll = new SCG.List<int>();

    static readonly int count = 1000;

    public static void Main(String[] args) {

      Console.WriteLine("Adding and removing without locking:");

      RunTwoThreads(delegate { AddAndRemove(15000); });

      Console.WriteLine("coll has {0} items, should be 0", coll.Count);

      coll = new ArrayList<int>();

      Console.WriteLine("Adding and removing with locking:");

      RunTwoThreads(delegate { SafeAddAndRemove(15000); });

      Console.WriteLine("coll has {0} items, should be 0", coll.Count);

      Console.WriteLine("Moving items without locking:");

      ArrayList<int> from, to;

      from = new ArrayList<int>();

      to = new ArrayList<int>();

      for (int i=0; i<count; i++) 

        from.Add(i);

      RunTwoThreads(delegate { while (!from.IsEmpty) Move(from, to); });

      Console.WriteLine("coll has {0} items, should be {1}", to.Count, count);

      Console.WriteLine("Moving items with locking:");

      from = new ArrayList<int>();

      to = new ArrayList<int>();

      for (int i=0; i<count; i++) 

        from.Add(i);

      RunTwoThreads(delegate { while (!from.IsEmpty) SafeMove(from, to); });

      Console.WriteLine("coll has {0} items, should be {1}", to.Count, count);

    }

    public static void RunTwoThreads(Act run) {

      Thread t1 = new Thread(new ThreadStart(run)),

             t2 = new Thread(new ThreadStart(run));

      t1.Start(); t2.Start();

      t1.Join(); t2.Join();

    }

    // Concurrently adding to and removing from an arraylist

    public static void AddAndRemove(int count) {

      for (int i=0; i<count; i++) 

        coll.Add(i);

      for (int i=0; i<count; i++)

        coll.Remove(i);

    }

    private static readonly Object sync = new Object();

    public static void SafeAddAndRemove(int count) {

      for (int i=0; i<count; i++) 

        lock (sync)

          coll.Add(i);

      for (int i=0; i<count; i++)

        lock (sync)

          coll.Remove(i);

    }

    public static void SafeAdd<T>(IExtensible<T> coll, T x) { 

      lock (sync) {

        coll.Add(x);

      }

    }

    public static void Move<T>(ICollection<T> from, ICollection<T> to) { 

      if (!from.IsEmpty) {  

        T x = from.Choose();

        Thread.Sleep(0);        // yield processor to other threads

        from.Remove(x);

        to.Add(x);

      }

    }

    public static void SafeMove<T>(ICollection<T> from, ICollection<T> to) { 

      lock (sync) 

        if (!from.IsEmpty) {  

          T x = from.Choose();

          Thread.Sleep(0);      // yield processor to other threads

          from.Remove(x);

          to.Add(x);

        }

    }

  }

}