.NET Framework Class Library
Thread..::.SpinWait Method

Causes a thread to wait the number of times defined by the iterations parameter.

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)
Syntax
Visual Basic (Declaration) 
<HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization := True,  _
    ExternalThreading := True)> _
Public Shared Sub SpinWait ( _
    iterations As Integer _
)
Visual Basic (Usage) 
Dim iterations As Integer

Thread.SpinWait(iterations)
C# 
[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, 
    ExternalThreading = true)]
public static void SpinWait(
    int iterations
)
Visual C++ 
[HostProtectionAttribute(SecurityAction::LinkDemand, Synchronization = true, 
    ExternalThreading = true)]
public:
static void SpinWait(
    int iterations
)
JScript 
public static function SpinWait(
    iterations : int
)

Parameters

iterations
Type: System..::.Int32
A 32-bit signed integer that defines how long a thread is to wait.
Remarks
NoteNote:

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: Synchronization | ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The SpinWait method is useful for implementing locks. Classes in the .NET Framework, such as Monitor and ReaderWriterLock, use this method internally. SpinWait essentially puts the processor into a very tight loop, with the loop count specified by the iterations parameter. The duration of the wait therefore depends on the speed of the processor.

Contrast this with the Sleep method. A thread that calls Sleep yields the rest of its current slice of processor time, even if the specified interval is zero. Specifying a non-zero interval for Sleep removes the thread from consideration by the thread scheduler until the time interval has elapsed.

SpinWait is not generally useful for ordinary applications. In most cases, you should use the synchronization classes provided by the .NET Framework; for example, call Monitor..::.Enter or a statement that wraps Monitor..::.Enter (lock in C# or SyncLock in Visual Basic).

Caution noteCaution:

In the rare case where it is advantageous to avoid a context switch, such as when you know that a state change is imminent, make a call to the SpinWait method in your loop. The code SpinWait executes is designed to prevent problems that can occur on computers with multiple processors. For example, on computers with multiple Intel™ processors employing Hyper-Threading™ technology, SpinWait prevents processor starvation in certain situations.
Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
See Also

Reference

Thread Class
Thread Members
System.Threading Namespace


Community Content

LukeSkywalker
Intel recommends avoiding SpinWait on Hyper-Threaded CPUs but...

Jeffrey Richter implies that the .NET implementation calls a version which will compile correctly for your architecture (HTT must use PAUSE which is in YieldProcessor macro which is in the Thread.SpinWait implementation):

"When executing spin loops on hyper-threaded CPUs, you need to force the current thread to pause so that the other thread has access to the chip's resources. The x86 architecture supports the PAUSE assembly language instruction. The PAUSE instruction ensures that a memory order violation is avoided, improving performance. In addition, the instruction reduces power consumption by placing a hiccup into what would be a very hot, tight loop. On x86, the PAUSE instruction is equivalent to a REP NOP instruction, which makes it compatible on earlier IA-32 CPUs that do not support hyper-threading. PAUSE causes a finite delay (0 on some CPUs). In the Win32 API, the x86 PAUSE instruction is executed by calling the YieldProcessor macro defined in WinNT.h. This macro exists so that you can write unmanaged code in a CPU architecture-independent way. Use of the macro expands the code inline, thus avoiding the overhead of a function call. In the .NET Framework, the Thread class's SpinWait method internally calls the Win32 YieldProcessor macro. In fact, SpinWait is effectively implemented like this on x86 platforms "

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