using System;
using System.Runtime.ConstrainedExecution;
+using System.Runtime.InteropServices;
#if NET_4_0
namespace System.Threading
{
+ // Implement the ticket SpinLock algorithm described on http://locklessinc.com/articles/locks/
+ // This lock is usable on both endianness
+ // TODO: some 32 bits platform apparently doesn't support CAS with 64 bits value
+ internal static class SpinLockHelpers
+ {
+ [StructLayout(LayoutKind.Explicit)]
+ internal struct TicketType {
+ [FieldOffset(0)]
+ public long TotalValue;
+ [FieldOffset(0)]
+ public int Value;
+ [FieldOffset(4)]
+ public int Users;
+ }
+
+ internal static void EnterLock (ref TicketType ticket)
+ {
+ int slot = Interlocked.Increment (ref ticket.Users) - 1;
+
+ SpinWait wait;
+ while (slot != ticket.Value)
+ wait.SpinOnce ();
+ }
+
+ internal static void ReleaseLock (ref TicketType ticket, bool flush)
+ {
+ if (flush)
+ Interlocked.Increment (ref ticket.Value);
+ else
+ ticket.Value++;
+ }
+
+ internal static bool TryEnterLock (ref TicketType ticket)
+ {
+ long u = ticket.Users;
+ long totalValue = (u << 32) | u;
+ long newTotalValue
+ = BitConverter.IsLittleEndian ? (u << 32) | (u + 1) : ((u + 1) << 32) | u;
+
+ return Interlocked.CompareExchange (ref ticket.TotalValue, newTotalValue, totalValue) == totalValue;
+ }
+
+ internal static bool IsLockHeld (ref TicketType ticket)
+ {
+ // No need for barrier here
+ long totalValue = ticket.TotalValue;
+ return (totalValue >> 32) != (totalValue & 0xFFFFFFFF);
+ }
+ }
+
public struct SpinLock
{
- const int isFree = 0;
- const int isOwned = 1;
- int lockState;
- readonly SpinWait sw;
+ SpinLockHelpers.TicketType tickets;
+
int threadWhoTookLock;
readonly bool isThreadOwnerTrackingEnabled;
-
+
public bool IsThreadOwnerTrackingEnabled {
get {
return isThreadOwnerTrackingEnabled;
}
}
-
+
public bool IsHeld {
get {
- return lockState == isOwned;
+ return SpinLockHelpers.IsLockHeld (ref tickets);
}
}
-
+
public bool IsHeldByCurrentThread {
get {
if (isThreadOwnerTrackingEnabled)
- return lockState == isOwned && Thread.CurrentThread.ManagedThreadId == threadWhoTookLock;
+ return IsHeld && Thread.CurrentThread.ManagedThreadId == threadWhoTookLock;
else
- return lockState == isOwned;
+ return IsHeld;
}
}
{
this.isThreadOwnerTrackingEnabled = trackId;
this.threadWhoTookLock = 0;
- this.lockState = isFree;
- this.sw = new SpinWait();
- }
-
- void CheckAndSetThreadId ()
- {
- if (threadWhoTookLock == Thread.CurrentThread.ManagedThreadId)
- throw new LockRecursionException("The current thread has already acquired this lock.");
- threadWhoTookLock = Thread.CurrentThread.ManagedThreadId;
+ this.tickets = new SpinLockHelpers.TicketType ();
}
-
+
+ [MonoTODO("This method is not rigorously correct. Need CER treatment")]
public void Enter (ref bool lockTaken)
{
if (lockTaken)
throw new ArgumentException ("lockTaken", "lockTaken must be initialized to false");
if (isThreadOwnerTrackingEnabled && IsHeldByCurrentThread)
throw new LockRecursionException ();
+
+ SpinLockHelpers.EnterLock (ref tickets);
+ lockTaken = true;
- try {
- Enter ();
- lockTaken = lockState == isOwned && Thread.CurrentThread.ManagedThreadId == threadWhoTookLock;
- } catch {
- lockTaken = false;
- }
- }
-
- internal void Enter ()
- {
- int result = Interlocked.Exchange (ref lockState, isOwned);
-
- while (result == isOwned) {
- sw.SpinOnce ();
-
- // Efficiently spin, until the resource looks like it might
- // be free. NOTE: Just reading here (as compared to repeatedly
- // calling Exchange) improves performance because writing
- // forces all CPUs to update this value
- result = Thread.VolatileRead (ref lockState);
-
- if (result == isFree) {
- result = Interlocked.Exchange (ref lockState, isOwned);
- if (result == isFree)
- break;
- }
- }
-
- CheckAndSetThreadId ();
- }
-
- bool TryEnter ()
- {
- // If resource available, set it to in-use and return
- if (Interlocked.Exchange (ref lockState, isOwned) == isFree) {
- CheckAndSetThreadId ();
- return true;
- }
- return false;
+ threadWhoTookLock = Thread.CurrentThread.ManagedThreadId;
}
-
+
+ [MonoTODO("This method is not rigorously correct. Need CER treatment")]
public void TryEnter (ref bool lockTaken)
{
- TryEnter (-1, ref lockTaken);
+ TryEnter (0, ref lockTaken);
}
-
+
+ [MonoTODO("This method is not rigorously correct. Need CER treatment")]
public void TryEnter (TimeSpan timeout, ref bool lockTaken)
{
TryEnter ((int)timeout.TotalMilliseconds, ref lockTaken);
}
-
+
+ [MonoTODO("This method is not rigorously correct. Need CER treatment")]
public void TryEnter (int milliSeconds, ref bool lockTaken)
{
if (milliSeconds < -1)
throw new ArgumentException ("lockTaken", "lockTaken must be initialized to false");
if (isThreadOwnerTrackingEnabled && IsHeldByCurrentThread)
throw new LockRecursionException ();
-
+
Watch sw = Watch.StartNew ();
-
- while (milliSeconds == -1 || sw.ElapsedMilliseconds < milliSeconds) {
- lockTaken = TryEnter ();
- }
-
- sw.Stop ();
+
+ do {
+ if (lockTaken = SpinLockHelpers.TryEnterLock (ref tickets)) {
+ threadWhoTookLock = Thread.CurrentThread.ManagedThreadId;
+ break;
+ }
+ } while (milliSeconds == -1 || (milliSeconds > 0 && sw.ElapsedMilliseconds < milliSeconds));
}
- public void Exit ()
- {
+ public void Exit ()
+ {
Exit (false);
}
- public void Exit (bool flushReleaseWrites)
+ public void Exit (bool flushReleaseWrites)
{
if (isThreadOwnerTrackingEnabled && !IsHeldByCurrentThread)
throw new SynchronizationLockException ("Current thread is not the owner of this lock");
-
+
threadWhoTookLock = int.MinValue;
-
- // Mark the resource as available
- if (!flushReleaseWrites) {
- lockState = isFree;
- } else {
- Interlocked.Exchange (ref lockState, isFree);
- }
+ SpinLockHelpers.ReleaseLock (ref tickets, flushReleaseWrites);
}
}
-
+
// Wraps a SpinLock in a reference when we need to pass
// around the lock
internal class SpinLockWrapper
{
- public readonly SpinLock Lock = new SpinLock (false);
+ public SpinLock Lock = new SpinLock (false);
}
}
#endif
--- /dev/null
+#if NET_4_0
+//
+// SpinLockTests.cs
+//
+// Author:
+// Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
+//
+// Copyright (c) 2010 Jérémie "Garuma" Laval
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+using System;
+using System.Threading;
+
+using NUnit.Framework;
+
+namespace MonoTests.System.Threading
+{
+ [TestFixture]
+ public class SpinLockTests
+ {
+ SpinLock sl;
+
+ [SetUp]
+ public void Setup ()
+ {
+ sl = new SpinLock (false);
+ }
+
+ [Test, ExpectedException (typeof (LockRecursionException))]
+ public void RecursionExceptionTest ()
+ {
+ sl = new SpinLock (true);
+ bool taken = false, taken2 = false;
+
+ sl.Enter (ref taken);
+ Assert.IsTrue (taken, "#1");
+ sl.Enter (ref taken2);
+ }
+
+ [Test]
+ public void SimpleEnterExitSchemeTest ()
+ {
+ bool taken = false;
+
+ for (int i = 0; i < 50000; i++) {
+ sl.Enter (ref taken);
+ Assert.IsTrue (taken, "#" + i.ToString ());
+ sl.Exit ();
+ taken = false;
+ }
+ }
+
+ [Test]
+ public void SemanticCorrectnessTest ()
+ {
+ bool taken = false;
+ bool taken2 = false;
+
+ sl.Enter (ref taken);
+ Assert.IsTrue (taken, "#1");
+ sl.TryEnter (ref taken2);
+ Assert.IsFalse (taken2, "#2");
+ sl.Exit ();
+
+ sl.TryEnter (ref taken2);
+ Assert.IsTrue (taken2, "#3");
+ }
+
+ [Test, ExpectedException (typeof (ArgumentException))]
+ public void FirstTakenParameterTest ()
+ {
+ bool taken = true;
+
+ sl.Enter (ref taken);
+ }
+
+ [Test, ExpectedException (typeof (ArgumentException))]
+ public void SecondTakenParameterTest ()
+ {
+ bool taken = true;
+
+ sl.TryEnter (ref taken);
+ }
+
+ [Test]
+ public void IsHeldByCurrentThreadTest ()
+ {
+ bool lockTaken = false;
+
+ sl.Enter (ref lockTaken);
+ Assert.IsTrue (lockTaken, "#1");
+ Assert.IsTrue (sl.IsHeldByCurrentThread, "#2");
+
+ lockTaken = false;
+ sl = new SpinLock (true);
+
+ sl.Enter (ref lockTaken);
+ Assert.IsTrue (lockTaken, "#3");
+ Assert.IsTrue (sl.IsHeldByCurrentThread, "#4");
+ }
+ }
+}
+#endif
projects / mono.git / commitdiff