ParallelLoopState.Stop Method
Definition
Important
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Communicates that the Parallel loop should cease execution at the system's earliest convenience.
public:
void Stop();public void Stop ();member this.Stop : unit -> unitPublic Sub Stop ()Exceptions
The Break() method was called previously. Break() and Stop() may not be used in combination by iterations of the same loop.
Examples
The following example executes up to 10,000 iterations of a loop in parallel. Each iteration pauses for a random interval from 1 to 1,000 milliseconds. A randomly generated value determines on which iteration of the loop the Stop method is called. As the output from the example shows, no iterations execute after the call to the Stop method.
using System;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
var rnd = new Random();
long stopIndex = rnd.Next(1, 11);
Console.WriteLine("Will call Stop in iteration {0}\n", stopIndex);
var result = Parallel.For(1, 10000, (i, state) => {
Console.WriteLine("Beginning iteration {0}", i);
int delay;
Monitor.Enter(rnd);
delay = rnd.Next(1, 1001);
Monitor.Exit(rnd);
Thread.Sleep(delay);
if (i == stopIndex) {
Console.WriteLine("Stop in iteration {0}", i);
state.Stop();
return;
}
if (state.IsStopped) {
return;
}
Console.WriteLine("Completed iteration {0}", i);
});
}
}
// The example displays output like the following:
// Will call Stop in iteration 5
//
// Beginning iteration 1
// Beginning iteration 9993
// Beginning iteration 8744
// Beginning iteration 6246
// Beginning iteration 7495
// Beginning iteration 3748
// Beginning iteration 4997
// Beginning iteration 2499
// Beginning iteration 1250
// Completed iteration 6246
// Beginning iteration 6247
// Completed iteration 3748
// Beginning iteration 3749
// Completed iteration 8744
// Beginning iteration 8745
// Completed iteration 7495
// Beginning iteration 7496
// Completed iteration 1250
// Beginning iteration 1251
// Completed iteration 2499
// Beginning iteration 2500
// Completed iteration 1
// Beginning iteration 2
// Completed iteration 2500
// Beginning iteration 2501
// Completed iteration 3749
// Beginning iteration 3750
// Completed iteration 6247
// Beginning iteration 6248
// Completed iteration 7496
// Beginning iteration 7497
// Completed iteration 3750
// Beginning iteration 3751
// Completed iteration 2
// Beginning iteration 3
// Completed iteration 9993
// Beginning iteration 9994
// Completed iteration 8745
// Beginning iteration 8746
// Completed iteration 4997
// Completed iteration 9994
// Beginning iteration 9995
// Beginning iteration 4998
// Completed iteration 6248
// Beginning iteration 6249
// Completed iteration 7497
// Beginning iteration 7498
// Completed iteration 1251
// Beginning iteration 1252
// Completed iteration 2501
// Beginning iteration 2502
// Completed iteration 9995
// Beginning iteration 9996
// Completed iteration 4998
// Beginning iteration 4999
// Completed iteration 2502
// Beginning iteration 2503
// Completed iteration 1252
// Beginning iteration 1253
// Completed iteration 7498
// Beginning iteration 7499
// Completed iteration 3751
// Beginning iteration 3752
// Completed iteration 9996
// Beginning iteration 9997
// Completed iteration 1253
// Beginning iteration 1254
// Completed iteration 9997
// Beginning iteration 9998
// Completed iteration 1254
// Beginning iteration 1255
// Completed iteration 6249
// Beginning iteration 6250
// Completed iteration 3
// Beginning iteration 4
// Completed iteration 4
// Beginning iteration 5
// Completed iteration 4999
// Beginning iteration 5000
// Completed iteration 8746
// Beginning iteration 8747
// Stop in iteration 5
Imports System.Threading
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim rnd As New Random()
Dim stopIndex As Long = rnd.Next(1, 11)
Console.WriteLine("Will call Stop in iteration {0}", stopIndex)
Console.WriteLine()
Dim result = Parallel.For(1, 10000, Sub(i, state)
Console.WriteLine("Beginning iteration {0}", i)
Dim delay As Integer
Monitor.Enter(rnd)
delay = rnd.Next(1, 1001)
Monitor.Exit(rnd)
Thread.Sleep(delay)
If i = stopIndex Then
Console.WriteLine("Stop in iteration {0}", i)
state.Stop()
Return
End If
If state.IsStopped Then
Return
End If
Console.WriteLine("Completed iteration {0}", i)
End Sub)
End Sub
End Module
' The example displays output like the following:
' Will call Stop in iteration 5
'
' Beginning iteration 1
' Beginning iteration 9993
' Beginning iteration 8744
' Beginning iteration 6246
' Beginning iteration 7495
' Beginning iteration 3748
' Beginning iteration 4997
' Beginning iteration 2499
' Beginning iteration 1250
' Completed iteration 6246
' Beginning iteration 6247
' Completed iteration 3748
' Beginning iteration 3749
' Completed iteration 8744
' Beginning iteration 8745
' Completed iteration 7495
' Beginning iteration 7496
' Completed iteration 1250
' Beginning iteration 1251
' Completed iteration 2499
' Beginning iteration 2500
' Completed iteration 1
' Beginning iteration 2
' Completed iteration 2500
' Beginning iteration 2501
' Completed iteration 3749
' Beginning iteration 3750
' Completed iteration 6247
' Beginning iteration 6248
' Completed iteration 7496
' Beginning iteration 7497
' Completed iteration 3750
' Beginning iteration 3751
' Completed iteration 2
' Beginning iteration 3
' Completed iteration 9993
' Beginning iteration 9994
' Completed iteration 8745
' Beginning iteration 8746
' Completed iteration 4997
' Completed iteration 9994
' Beginning iteration 9995
' Beginning iteration 4998
' Completed iteration 6248
' Beginning iteration 6249
' Completed iteration 7497
' Beginning iteration 7498
' Completed iteration 1251
' Beginning iteration 1252
' Completed iteration 2501
' Beginning iteration 2502
' Completed iteration 9995
' Beginning iteration 9996
' Completed iteration 4998
' Beginning iteration 4999
' Completed iteration 2502
' Beginning iteration 2503
' Completed iteration 1252
' Beginning iteration 1253
' Completed iteration 7498
' Beginning iteration 7499
' Completed iteration 3751
' Beginning iteration 3752
' Completed iteration 9996
' Beginning iteration 9997
' Completed iteration 1253
' Beginning iteration 1254
' Completed iteration 9997
' Beginning iteration 9998
' Completed iteration 1254
' Beginning iteration 1255
' Completed iteration 6249
' Beginning iteration 6250
' Completed iteration 3
' Beginning iteration 4
' Completed iteration 4
' Beginning iteration 5
' Completed iteration 4999
' Beginning iteration 5000
' Completed iteration 8746
' Beginning iteration 8747
' Stop in iteration 5
Because iterations of the loop are still likely to be executing when the Stop method is called, each iteration calls the IsStopped method to check whether another iteration has called the Stop method. If it returns true, the iteration returns immediately.
Remarks
Calling the Stop method indicates that any iterations of the loop that have not yet started need not be run. It effectively cancels any additional iterations of the loop. However, it does not stop any iterations that have already begun execution.
Calling the Stop method causes the IsStopped property to return true for any iteration of the loop that is still executing. This is particularly useful for long-running iterations, which can check the IsStopped property and exit early if its value is true.
Stop is typically employed in search-based algorithms, where once a result is found, no other iterations need be executed.
