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// SpinLock.cs
//
// Copyright (c) 2008 Jérémie "Garuma" Laval
// Copyright 2011 Xamarin Inc (http://www.xamarin.com).
//
// 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.
//
//
#if NET_4_0
using System;
using System.Collections.Concurrent;
using System.Runtime.ConstrainedExecution;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
namespace System.Threading
{
[StructLayout(LayoutKind.Explicit)]
internal struct TicketType {
[FieldOffset(0)]
public long TotalValue;
[FieldOffset(0)]
public int Value;
[FieldOffset(4)]
public int Users;
}
/* Implement the ticket SpinLock algorithm described on http://locklessinc.com/articles/locks/
* This lock is usable on both endianness.
* All the try/finally patterns in this class and various extra gimmicks compared to the original
* algorithm are here to avoid problems caused by asynchronous exceptions.
*/
[System.Diagnostics.DebuggerDisplay ("IsHeld = {IsHeld}")]
[System.Diagnostics.DebuggerTypeProxy ("System.Threading.SpinLock+SystemThreading_SpinLockDebugView")]
public struct SpinLock
{
TicketType ticket;
int threadWhoTookLock;
readonly bool isThreadOwnerTrackingEnabled;
static readonly Watch sw = Watch.StartNew ();
ConcurrentOrderedList<int> stallTickets;
public bool IsThreadOwnerTrackingEnabled {
get {
return isThreadOwnerTrackingEnabled;
}
}
public bool IsHeld {
get {
// No need for barrier here
long totalValue = ticket.TotalValue;
return (totalValue >> 32) != (totalValue & 0xFFFFFFFF);
}
}
public bool IsHeldByCurrentThread {
get {
if (isThreadOwnerTrackingEnabled)
return IsHeld && Thread.CurrentThread.ManagedThreadId == threadWhoTookLock;
else
return IsHeld;
}
}
public SpinLock (bool enableThreadOwnerTracking)
{
this.isThreadOwnerTrackingEnabled = enableThreadOwnerTracking;
this.threadWhoTookLock = 0;
this.ticket = new TicketType ();
this.stallTickets = null;
}
[MonoTODO ("Not safe against async exceptions")]
public void Enter (ref bool lockTaken)
{
if (lockTaken)
throw new ArgumentException ("lockTaken", "lockTaken must be initialized to false");
if (isThreadOwnerTrackingEnabled && IsHeldByCurrentThread)
throw new LockRecursionException ();
int slot = -1;
RuntimeHelpers.PrepareConstrainedRegions ();
try {
slot = Interlocked.Increment (ref ticket.Users) - 1;
SpinWait wait = new SpinWait ();
while (slot != ticket.Value) {
wait.SpinOnce ();
while (stallTickets != null && stallTickets.TryRemove (ticket.Value))
++ticket.Value;
}
} finally {
if (slot == ticket.Value) {
lockTaken = true;
threadWhoTookLock = Thread.CurrentThread.ManagedThreadId;
} else if (slot != -1) {
// We have been interrupted, initialize stallTickets
if (stallTickets == null)
Interlocked.CompareExchange (ref stallTickets, new ConcurrentOrderedList<int> (), null);
stallTickets.TryAdd (slot);
}
}
}
public void TryEnter (ref bool lockTaken)
{
TryEnter (0, ref lockTaken);
}
public void TryEnter (TimeSpan timeout, ref bool lockTaken)
{
TryEnter ((int)timeout.TotalMilliseconds, ref lockTaken);
}
public void TryEnter (int millisecondsTimeout, ref bool lockTaken)
{
if (millisecondsTimeout < -1)
throw new ArgumentOutOfRangeException ("milliSeconds", "millisecondsTimeout is a negative number other than -1");
if (lockTaken)
throw new ArgumentException ("lockTaken", "lockTaken must be initialized to false");
if (isThreadOwnerTrackingEnabled && IsHeldByCurrentThread)
throw new LockRecursionException ();
long start = millisecondsTimeout == -1 ? 0 : sw.ElapsedMilliseconds;
bool stop = false;
do {
while (stallTickets != null && stallTickets.TryRemove (ticket.Value))
++ticket.Value;
long u = ticket.Users;
long totalValue = (u << 32) | u;
long newTotalValue
= BitConverter.IsLittleEndian ? (u << 32) | (u + 1) : ((u + 1) << 32) | u;
RuntimeHelpers.PrepareConstrainedRegions ();
try {}
finally {
lockTaken = Interlocked.CompareExchange (ref ticket.TotalValue, newTotalValue, totalValue) == totalValue;
if (lockTaken) {
threadWhoTookLock = Thread.CurrentThread.ManagedThreadId;
stop = true;
}
}
} while (!stop && (millisecondsTimeout == -1 || (sw.ElapsedMilliseconds - start) < millisecondsTimeout));
}
[ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
public void Exit ()
{
Exit (false);
}
[ReliabilityContract (Consistency.WillNotCorruptState, Cer.Success)]
public void Exit (bool useMemoryBarrier)
{
RuntimeHelpers.PrepareConstrainedRegions ();
try {}
finally {
if (isThreadOwnerTrackingEnabled && !IsHeldByCurrentThread)
throw new SynchronizationLockException ("Current thread is not the owner of this lock");
threadWhoTookLock = int.MinValue;
do {
if (useMemoryBarrier)
Interlocked.Increment (ref ticket.Value);
else
ticket.Value++;
} while (stallTickets != null && stallTickets.TryRemove (ticket.Value));
}
}
}
}
#endif
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