SpinLock Struct
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Provides a mutual exclusion lock primitive where a thread trying to acquire the lock waits in a loop repeatedly checking until the lock becomes available.
public value class SpinLockpublic struct SpinLock[System.Runtime.InteropServices.ComVisible(false)]
public struct SpinLocktype SpinLock = struct[<System.Runtime.InteropServices.ComVisible(false)>]
type SpinLock = structPublic Structure SpinLock- Inheritance
- Attributes
Examples
The following example shows how to use a SpinLock:
using System;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
class SpinLockDemo
{
// Demonstrates:
// Default SpinLock construction ()
// SpinLock.Enter(ref bool)
// SpinLock.Exit()
static void SpinLockSample1()
{
SpinLock sl = new SpinLock();
StringBuilder sb = new StringBuilder();
// Action taken by each parallel job.
// Append to the StringBuilder 10000 times, protecting
// access to sb with a SpinLock.
Action action = () =>
{
bool gotLock = false;
for (int i = 0; i < 10000; i++)
{
gotLock = false;
try
{
sl.Enter(ref gotLock);
sb.Append((i % 10).ToString());
}
finally
{
// Only give up the lock if you actually acquired it
if (gotLock) sl.Exit();
}
}
};
// Invoke 3 concurrent instances of the action above
Parallel.Invoke(action, action, action);
// Check/Show the results
Console.WriteLine("sb.Length = {0} (should be 30000)", sb.Length);
Console.WriteLine("number of occurrences of '5' in sb: {0} (should be 3000)",
sb.ToString().Where(c => (c == '5')).Count());
}
// Demonstrates:
// Default SpinLock constructor (tracking thread owner)
// SpinLock.Enter(ref bool)
// SpinLock.Exit() throwing exception
// SpinLock.IsHeld
// SpinLock.IsHeldByCurrentThread
// SpinLock.IsThreadOwnerTrackingEnabled
static void SpinLockSample2()
{
// Instantiate a SpinLock
SpinLock sl = new SpinLock();
// These MRESs help to sequence the two jobs below
ManualResetEventSlim mre1 = new ManualResetEventSlim(false);
ManualResetEventSlim mre2 = new ManualResetEventSlim(false);
bool lockTaken = false;
Task taskA = Task.Factory.StartNew(() =>
{
try
{
sl.Enter(ref lockTaken);
Console.WriteLine("Task A: entered SpinLock");
mre1.Set(); // Signal Task B to commence with its logic
// Wait for Task B to complete its logic
// (Normally, you would not want to perform such a potentially
// heavyweight operation while holding a SpinLock, but we do it
// here to more effectively show off SpinLock properties in
// taskB.)
mre2.Wait();
}
finally
{
if (lockTaken) sl.Exit();
}
});
Task taskB = Task.Factory.StartNew(() =>
{
mre1.Wait(); // wait for Task A to signal me
Console.WriteLine("Task B: sl.IsHeld = {0} (should be true)", sl.IsHeld);
Console.WriteLine("Task B: sl.IsHeldByCurrentThread = {0} (should be false)", sl.IsHeldByCurrentThread);
Console.WriteLine("Task B: sl.IsThreadOwnerTrackingEnabled = {0} (should be true)", sl.IsThreadOwnerTrackingEnabled);
try
{
sl.Exit();
Console.WriteLine("Task B: Released sl, should not have been able to!");
}
catch (Exception e)
{
Console.WriteLine("Task B: sl.Exit resulted in exception, as expected: {0}", e.Message);
}
mre2.Set(); // Signal Task A to exit the SpinLock
});
// Wait for task completion and clean up
Task.WaitAll(taskA, taskB);
mre1.Dispose();
mre2.Dispose();
}
// Demonstrates:
// SpinLock constructor(false) -- thread ownership not tracked
static void SpinLockSample3()
{
// Create SpinLock that does not track ownership/threadIDs
SpinLock sl = new SpinLock(false);
// Used to synchronize with the Task below
ManualResetEventSlim mres = new ManualResetEventSlim(false);
// We will verify that the Task below runs on a separate thread
Console.WriteLine("main thread id = {0}", Thread.CurrentThread.ManagedThreadId);
// Now enter the SpinLock. Ordinarily, you would not want to spend so
// much time holding a SpinLock, but we do it here for the purpose of
// demonstrating that a non-ownership-tracking SpinLock can be exited
// by a different thread than that which was used to enter it.
bool lockTaken = false;
sl.Enter(ref lockTaken);
// Create a separate Task from which to Exit() the SpinLock
Task worker = Task.Factory.StartNew(() =>
{
Console.WriteLine("worker task thread id = {0} (should be different than main thread id)",
Thread.CurrentThread.ManagedThreadId);
// Now exit the SpinLock
try
{
sl.Exit();
Console.WriteLine("worker task: successfully exited SpinLock, as expected");
}
catch (Exception e)
{
Console.WriteLine("worker task: unexpected failure in exiting SpinLock: {0}", e.Message);
}
// Notify main thread to continue
mres.Set();
});
// Do this instead of worker.Wait(), because worker.Wait() could inline the worker Task,
// causing it to be run on the same thread. The purpose of this example is to show that
// a different thread can exit the SpinLock created (without thread tracking) on your thread.
mres.Wait();
// now Wait() on worker and clean up
worker.Wait();
mres.Dispose();
}
}
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Module SpinLockDemo
' Demonstrates:
' Default SpinLock construction ()
' SpinLock.Enter(ref bool)
' SpinLock.Exit()
Private Sub SpinLockSample1()
Dim sl As New SpinLock()
Dim sb As New StringBuilder()
' Action taken by each parallel job.
' Append to the StringBuilder 10000 times, protecting
' access to sb with a SpinLock.
Dim action As Action =
Sub()
Dim gotLock As Boolean = False
For i As Integer = 0 To 9999
gotLock = False
Try
sl.Enter(gotLock)
sb.Append((i Mod 10).ToString())
Finally
' Only give up the lock if you actually acquired it
If gotLock Then
sl.[Exit]()
End If
End Try
Next
End Sub
' Invoke 3 concurrent instances of the action above
Parallel.Invoke(action, action, action)
' Check/Show the results
Console.WriteLine("sb.Length = {0} (should be 30000)", sb.Length)
Console.WriteLine("number of occurrences of '5' in sb: {0} (should be 3000)", sb.ToString().Where(Function(c) (c = "5"c)).Count())
End Sub
' Demonstrates:
' Default SpinLock constructor (tracking thread owner)
' SpinLock.Enter(ref bool)
' SpinLock.Exit() throwing exception
' SpinLock.IsHeld
' SpinLock.IsHeldByCurrentThread
' SpinLock.IsThreadOwnerTrackingEnabled
Private Sub SpinLockSample2()
' Instantiate a SpinLock
Dim sl As New SpinLock()
' These MRESs help to sequence the two jobs below
Dim mre1 As New ManualResetEventSlim(False)
Dim mre2 As New ManualResetEventSlim(False)
Dim lockTaken As Boolean = False
Dim taskA As Task = Task.Factory.StartNew(
Sub()
Try
sl.Enter(lockTaken)
Console.WriteLine("Task A: entered SpinLock")
mre1.[Set]()
' Signal Task B to commence with its logic
' Wait for Task B to complete its logic
' (Normally, you would not want to perform such a potentially
' heavyweight operation while holding a SpinLock, but we do it
' here to more effectively show off SpinLock properties in
' taskB.)
mre2.Wait()
Finally
If lockTaken Then
sl.[Exit]()
End If
End Try
End Sub)
Dim taskB As Task = Task.Factory.StartNew(
Sub()
mre1.Wait()
' wait for Task A to signal me
Console.WriteLine("Task B: sl.IsHeld = {0} (should be true)", sl.IsHeld)
Console.WriteLine("Task B: sl.IsHeldByCurrentThread = {0} (should be false)", sl.IsHeldByCurrentThread)
Console.WriteLine("Task B: sl.IsThreadOwnerTrackingEnabled = {0} (should be true)", sl.IsThreadOwnerTrackingEnabled)
Try
sl.[Exit]()
Console.WriteLine("Task B: Released sl, should not have been able to!")
Catch e As Exception
Console.WriteLine("Task B: sl.Exit resulted in exception, as expected: {0}", e.Message)
End Try
' Signal Task A to exit the SpinLock
mre2.[Set]()
End Sub)
' Wait for task completion and clean up
Task.WaitAll(taskA, taskB)
mre1.Dispose()
mre2.Dispose()
End Sub
' Demonstrates:
' SpinLock constructor(false) -- thread ownership not tracked
Private Sub SpinLockSample3()
' Create SpinLock that does not track ownership/threadIDs
Dim sl As New SpinLock(False)
' Used to synchronize with the Task below
Dim mres As New ManualResetEventSlim(False)
' We will verify that the Task below runs on a separate thread
Console.WriteLine("main thread id = {0}", Thread.CurrentThread.ManagedThreadId)
' Now enter the SpinLock. Ordinarily, you would not want to spend so
' much time holding a SpinLock, but we do it here for the purpose of
' demonstrating that a non-ownership-tracking SpinLock can be exited
' by a different thread than that which was used to enter it.
Dim lockTaken As Boolean = False
sl.Enter(lockTaken)
' Create a separate Task
Dim worker As Task = Task.Factory.StartNew(
Sub()
Console.WriteLine("worker task thread id = {0} (should be different than main thread id)", Thread.CurrentThread.ManagedThreadId)
' Now exit the SpinLock
Try
sl.[Exit]()
Console.WriteLine("worker task: successfully exited SpinLock, as expected")
Catch e As Exception
Console.WriteLine("worker task: unexpected failure in exiting SpinLock: {0}", e.Message)
End Try
' Notify main thread to continue
mres.[Set]()
End Sub)
' Do this instead of worker.Wait(), because worker.Wait() could inline the worker Task,
' causing it to be run on the same thread. The purpose of this example is to show that
' a different thread can exit the SpinLock created (without thread tracking) on your thread.
mres.Wait()
' now Wait() on worker and clean up
worker.Wait()
mres.Dispose()
End Sub
End Module
Remarks
For an example of how to use a Spin Lock, see How to: Use SpinLock for Low-Level Synchronization.
Spin locks can be used for leaf-level locks where the object allocation implied by using a Monitor, in size or due to garbage collection pressure, is overly expensive. A spin lock can be useful to avoid blocking; however, if you expect a significant amount of blocking, you should probably not use spin locks due to excessive spinning. Spinning can be beneficial when locks are fine-grained and large in number (for example, a lock per node in a linked list) and also when lock hold-times are always extremely short. In general, while holding a spin lock, one should avoid any of these actions:
blocking,
calling anything that itself may block,
holding more than one spin lock at once,
making dynamically dispatched calls (interface and virtuals),
making statically dispatched calls into any code one doesn't own, or
allocating memory.
SpinLock should only be used after you have been determined that doing so will improve an application's performance. It is also important to note that SpinLock is a value type, for performance reasons. For this reason, you must be very careful not to accidentally copy a SpinLock instance, as the two instances (the original and the copy) would then be completely independent of one another, which would likely lead to erroneous behavior of the application. If a SpinLock instance must be passed around, it should be passed by reference rather than by value.
Do not store SpinLock instances in readonly fields.
Constructors
| SpinLock(Boolean) |
Initializes a new instance of the SpinLock structure with the option to track thread IDs to improve debugging. |
Properties
| IsHeld |
Gets whether the lock is currently held by any thread. |
| IsHeldByCurrentThread |
Gets whether the lock is held by the current thread. |
| IsThreadOwnerTrackingEnabled |
Gets whether thread ownership tracking is enabled for this instance. |
Methods
| Enter(Boolean) |
Acquires the lock in a reliable manner, such that even if an exception occurs within the method call, |
| Exit() |
Releases the lock. |
| Exit(Boolean) |
Releases the lock. |
| TryEnter(Boolean) |
Attempts to acquire the lock in a reliable manner, such that even if an exception occurs within the method call, |
| TryEnter(Int32, Boolean) |
Attempts to acquire the lock in a reliable manner, such that even if an exception occurs within the method call, |
| TryEnter(TimeSpan, Boolean) |
Attempts to acquire the lock in a reliable manner, such that even if an exception occurs within the method call, |
Applies to
Thread Safety
All members of SpinLock are thread-safe and may be used from multiple threads concurrently.
