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// SpinWait construction
// SpinWait.SpinOnce()
// SpinWait.NextSpinWillYield
// SpinWait.Count
static void Main()
bool someBoolean = false;
int numYields = 0;
// First task: SpinWait until someBoolean is set to true
Task t1 = Task.Factory.StartNew(() =>
SpinWait sw = new SpinWait();
while (!someBoolean)
// The NextSpinWillYield property returns true if
// calling sw.SpinOnce() will result in yielding the
// processor instead of simply spinning.
if (sw.NextSpinWillYield) numYields++;
sw.SpinOnce();
// As of .NET Framework 4: After some initial spinning, SpinWait.SpinOnce() will yield every time.
Console.WriteLine("SpinWait called {0} times, yielded {1} times", sw.Count, numYields);
// Second task: Wait 100ms, then set someBoolean to true
Task t2 = Task.Factory.StartNew(() =>
Thread.Sleep(100);
someBoolean = true;
// Wait for tasks to complete
Task.WaitAll(t1, t2);
Imports System.Threading
Imports System.Threading.Tasks
Module SpinWaitDemo
' Demonstrates:
' SpinWait construction
' SpinWait.SpinOnce()
' SpinWait.NextSpinWillYield
' SpinWait.Count
Private Sub SpinWaitSample()
Dim someBoolean As Boolean = False
Dim numYields As Integer = 0
' First task: SpinWait until someBoolean is set to true
Dim t1 As Task = Task.Factory.StartNew(
Sub()
Dim sw As New SpinWait()
While Not someBoolean
' The NextSpinWillYield property returns true if
' calling sw.SpinOnce() will result in yielding the
' processor instead of simply spinning.
If sw.NextSpinWillYield Then
numYields += 1
End If
sw.SpinOnce()
End While
' As of .NET Framework 4: After some initial spinning, SpinWait.SpinOnce() will yield every time.
Console.WriteLine("SpinWait called {0} times, yielded {1} times", sw.Count, numYields)
End Sub)
' Second task: Wait 100ms, then set someBoolean to true
Dim t2 As Task = Task.Factory.StartNew(
Sub()
Thread.Sleep(100)
someBoolean = True
End Sub)
' Wait for tasks to complete
Task.WaitAll(t1, t2)
End Sub
End Module
SpinWait
encapsulates common spinning logic. On single-processor machines, yields are always used instead of busy waits, and on computers with Intel processors employing Hyper-Threading technology, it helps to prevent hardware thread starvation. SpinWait encapsulates a good mixture of spinning and true yielding.
SpinWait
is a value type, which means that low-level code can utilize SpinWait without fear of unnecessary allocation overheads. SpinWait is not generally useful for ordinary applications. In most cases, you should use the synchronization classes provided by the .NET Framework, such as
Monitor
. For most purposes where spin waiting is required, however, the
SpinWait
type should be preferred over the
Thread.SpinWait
method.
Thread Safety
While
SpinWait
is designed to be used in concurrent applications, it is not designed to be used from multiple threads concurrently.
SpinWait
members are not thread-safe. If multiple threads must spin, each should use its own instance of
SpinWait
.
See also
SpinWait
How to: Use SpinWait to Implement a Two-Phase Wait Operation
