InterlockedIncrement Method
 

Increments a specified variable and stores the result, as an atomic operation.

Namespace:   System.Threading
Assembly:  mscorlib (in mscorlib.dll)

public static int Increment(
	ref int location
)
public:
static int Increment(
	int% location
)
static member Increment : 
        location:int byref -> int
Public Shared Function Increment (
	ByRef location As Integer
) As Integer

Parameters

location
Type:

The variable whose value is to be incremented.

Return Value

Type:

The incremented value.

Exception Condition
NullReferenceException

The address of location is a null pointer.

This method handles an overflow condition by wrapping: if location = Int32MaxValue, location + 1 = Int32MinValue. No exception is thrown.

The following example determines how many random numbers that range from 0 to 1,000 are required to generate 1,000 random numbers with a midpoint value. To keep track of the number of midpoint values, a variable, midpointCount, is set equal to 0 and incremented each time the random number generator returns a midpoint value until it reaches 10,000. Because three threads generate the random numbers, the Increment method is called to ensure that multiple threads don't update midpointCount concurrently. Note that a lock is also used to protect the random number generator, and that a CountdownEvent object is used to ensure that the Main method doesn't finish execution before the three threads.

using System;
using System.Threading;

public class Example
{
   const int LOWERBOUND = 0;
   const int UPPERBOUND = 1001;

   static Object lockObj = new Object();
   static Random rnd = new Random();
   static CountdownEvent cte;

   static int totalCount = 0;
   static int totalMidpoint = 0;
   static int midpointCount = 0;

   public static void Main()
   {
      cte = new CountdownEvent(1);
      // Start three threads. 
      for (int ctr = 0; ctr <= 2; ctr++) {
         cte.AddCount();
         Thread th = new Thread(GenerateNumbers);
         th.Name = "Thread" + ctr.ToString();
         th.Start();
      }
      cte.Signal();
      cte.Wait();
      Console.WriteLine();
      Console.WriteLine("Total midpoint values:  {0,10:N0} ({1:P3})",
                        totalMidpoint, totalMidpoint/((double)totalCount));
      Console.WriteLine("Total number of values: {0,10:N0}", 
                        totalCount);                  
   }

   private static void GenerateNumbers()
   {
      int midpoint = (UPPERBOUND - LOWERBOUND) / 2;
      int value = 0;
      int total = 0;
      int midpt = 0;

      do {
         lock (lockObj) {
            value = rnd.Next(LOWERBOUND, UPPERBOUND);
         }
         if (value == midpoint) { 
            Interlocked.Increment(ref midpointCount);
            midpt++;
         }
         total++;    
      } while (midpointCount < 10000);

      Interlocked.Add(ref totalCount, total);
      Interlocked.Add(ref totalMidpoint, midpt);

      string s = String.Format("Thread {0}:\n", Thread.CurrentThread.Name) +
                 String.Format("   Random Numbers: {0:N0}\n", total) + 
                 String.Format("   Midpoint values: {0:N0} ({1:P3})", midpt, 
                               ((double) midpt)/total);
      Console.WriteLine(s);
      cte.Signal();
   }
}
// The example displays output like the following:
//       Thread Thread2:
//          Random Numbers: 2,776,674
//          Midpoint values: 2,773 (0.100 %)
//       Thread Thread1:
//          Random Numbers: 4,876,100
//          Midpoint values: 4,873 (0.100 %)
//       Thread Thread0:
//          Random Numbers: 2,312,310
//          Midpoint values: 2,354 (0.102 %)
//       
//       Total midpoint values:      10,000 (0.100 %)
//       Total number of values:  9,965,084
Imports System.Threading

Module Example
   Const LOWERBOUND As Integer = 0
   Const UPPERBOUND As Integer = 1001

   Dim lockObj As New Object()
   Dim rnd As New Random()
   Dim cte As CountdownEvent

   Dim totalCount As Integer = 0
   Dim totalMidpoint As Integer = 0
   Dim midpointCount As Integer = 0

   Public Sub Main()
      cte = New CountdownEvent(1)
      ' Start three threads. 
      For ctr As Integer = 0 To 2
         cte.AddCount()
         Dim th As New Thread(AddressOf GenerateNumbers)
         th.Name = "Thread" + ctr.ToString()
         th.Start()
      Next
      cte.Signal()
      cte.Wait()
      Console.WriteLine()
      Console.WriteLine("Total midpoint values:  {0,10:N0} ({1:P3})",
                        totalMidpoint, totalMidpoint/totalCount)
      Console.WriteLine("Total number of values: {0,10:N0}", 
                        totalCount)                  
   End Sub

   Private Sub GenerateNumbers()
      Dim midpoint As Integer = (upperBound - lowerBound) \ 2
      Dim value As Integer = 0
      Dim total As Integer = 0
      Dim midpt As Integer = 0
      Do
         SyncLock lockObj
            value = rnd.Next(lowerBound, upperBound)
         End SyncLock
         If value = midpoint Then 
            Interlocked.Increment(midpointCount)
            midpt += 1
         End If
         total += 1    
      Loop While midpointCount < 10000

      Interlocked.Add(totalCount, total)
      Interlocked.Add(totalMidpoint, midpt)

      Dim s As String = String.Format("Thread {0}:", Thread.CurrentThread.Name) + vbCrLf +
                        String.Format("   Random Numbers: {0:N0}", total) + vbCrLf +
                        String.Format("   Midpoint values: {0:N0} ({1:P3})", midpt, midpt/total)
      Console.WriteLine(s)
      cte.Signal()
   End Sub
End Module
' The example displays output like the following:
'       Thread Thread2:
'          Random Numbers: 2,776,674
'          Midpoint values: 2,773 (0.100 %)
'       Thread Thread1:
'          Random Numbers: 4,876,100
'          Midpoint values: 4,873 (0.100 %)
'       Thread Thread0:
'          Random Numbers: 2,312,310
'          Midpoint values: 2,354 (0.102 %)
'       
'       Total midpoint values:      10,000 (0.100 %)
'       Total number of values:  9,965,084

The following example is similar to the previous one, except that it uses the instead of a thread procedure to generate 50,000 random midpoint integers. In this example, a lambda expression replaces the GenerateNumbers thread procedure, and the call to the TaskWaitAll method eliminates the need for the CountdownEvent object.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
   const int LOWERBOUND = 0;
   const int UPPERBOUND = 1001;

   static Object lockObj = new Object();
   static Random rnd = new Random();

   static int totalCount = 0;
   static int totalMidpoint = 0;
   static int midpointCount = 0;

   public static void Main()
   {
      List<Task> tasks = new List<Task>();
      // Start three tasks. 
      for (int ctr = 0; ctr <= 2; ctr++) 
         tasks.Add(Task.Run( () => { int midpoint = (UPPERBOUND - LOWERBOUND) / 2;
                                     int value = 0;
                                     int total = 0;
                                     int midpt = 0;

                                     do {
                                        lock (lockObj) {
                                           value = rnd.Next(LOWERBOUND, UPPERBOUND);
                                        }
                                        if (value == midpoint) { 
                                           Interlocked.Increment(ref midpointCount);
                                           midpt++;
                                        }
                                        total++;    
                                     } while (midpointCount < 50000);

                                     Interlocked.Add(ref totalCount, total);
                                     Interlocked.Add(ref totalMidpoint, midpt);

                                     string s = String.Format("Task {0}:\n", Task.CurrentId) +
                                                String.Format("   Random Numbers: {0:N0}\n", total) + 
                                                String.Format("   Midpoint values: {0:N0} ({1:P3})", midpt, 
                                                              ((double) midpt)/total);
                                     Console.WriteLine(s); } ));

      Task.WaitAll(tasks.ToArray());
      Console.WriteLine();
      Console.WriteLine("Total midpoint values:  {0,10:N0} ({1:P3})",
                        totalMidpoint, totalMidpoint/((double)totalCount));
      Console.WriteLine("Total number of values: {0,10:N0}", 
                        totalCount);                  
   }
}
// The example displays output like the following:
//       Task 3:
//          Random Numbers: 10,855,250
//          Midpoint values: 10,823 (0.100 %)
//       Task 1:
//          Random Numbers: 15,243,703
//          Midpoint values: 15,110 (0.099 %)
//       Task 2:
//          Random Numbers: 24,107,425
//          Midpoint values: 24,067 (0.100 %)
//       
//       Total midpoint values:      50,000 (0.100 %)
//       Total number of values: 50,206,378
Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Const LOWERBOUND As Integer = 0
   Const UPPERBOUND As Integer = 1001

   Dim lockObj As New Object()
   Dim rnd As New Random()

   Dim totalCount As Integer = 0
   Dim totalMidpoint As Integer = 0
   Dim midpointCount As Integer = 0

   Public Sub Main()
      Dim tasks As New List(Of Task)()
      ' Start three tasks. 
      For ctr As Integer = 0 To 2
         tasks.Add(Task.Run( Sub()
                                Dim midpoint As Integer = (upperBound - lowerBound) \ 2
                                Dim value As Integer = 0
                                Dim total As Integer = 0
                                Dim midpt As Integer = 0
                                Do
                                   SyncLock lockObj
                                      value = rnd.Next(lowerBound, upperBound)
                                   End SyncLock
                                   If value = midpoint Then 
                                      Interlocked.Increment(midpointCount)
                                      midpt += 1
                                   End If
                                   total += 1    
                                Loop While midpointCount < 50000

                                Interlocked.Add(totalCount, total)
                                Interlocked.Add(totalMidpoint, midpt)

                                Dim s As String = String.Format("Task {0}:", Task.CurrentId) + vbCrLf +
                                                  String.Format("   Random Numbers: {0:N0}", total) + vbCrLf +
                                                  String.Format("   Midpoint values: {0:N0} ({1:P3})", midpt, midpt/total)
                                Console.WriteLine(s)
                             End Sub ))
      Next

      Task.WaitAll(tasks.ToArray())
      Console.WriteLine()
      Console.WriteLine("Total midpoint values:  {0,10:N0} ({1:P3})",
                        totalMidpoint, totalMidpoint/totalCount)
      Console.WriteLine("Total number of values: {0,10:N0}", 
                        totalCount)                  
   End Sub
End Module
' The example displays output like the following:
'       Task 3:
'          Random Numbers: 10,855,250
'          Midpoint values: 10,823 (0.100 %)
'       Task 1:
'          Random Numbers: 15,243,703
'          Midpoint values: 15,110 (0.099 %)
'       Task 2:
'          Random Numbers: 24,107,425
'          Midpoint values: 24,067 (0.100 %)
'       
'       Total midpoint values:      50,000 (0.100 %)
'       Total number of values: 50,206,378
Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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