using System;
using System.Runtime.ConstrainedExecution;
+using System.Runtime.InteropServices;
-#if NET_4_0
+#if NET_4_0 || BOOTSTRAP_NET_4_0
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
+ // TODO: some 32 bits platform apparently doesn't support CAS with 64 bits value
public struct SpinLock
{
- const int isFree = 0;
- const int isOwned = 1;
- int lockState;
- readonly SpinWait sw;
+ TicketType ticket;
+
int threadWhoTookLock;
readonly bool isThreadOwnerTrackingEnabled;
-
+
public bool IsThreadOwnerTrackingEnabled {
get {
return isThreadOwnerTrackingEnabled;
}
}
-
+
public bool IsHeld {
get {
- return lockState == isOwned;
+ // No need for barrier here
+ long totalValue = ticket.TotalValue;
+ return (totalValue >> 32) != (totalValue & 0xFFFFFFFF);
}
}
-
+
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();
+ this.ticket = new TicketType ();
}
-
- void CheckAndSetThreadId ()
- {
- if (threadWhoTookLock == Thread.CurrentThread.ManagedThreadId)
- throw new LockRecursionException("The current thread has already acquired this lock.");
- threadWhoTookLock = Thread.CurrentThread.ManagedThreadId;
- }
-
+
+ [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 ();
+
+ int slot = Interlocked.Increment (ref ticket.Users) - 1;
+
+ SpinWait wait = new SpinWait ();
+ while (slot != ticket.Value)
+ wait.SpinOnce ();
- 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;
- }
- }
+ lockTaken = true;
- 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 {
+ long u = ticket.Users;
+ long totalValue = (u << 32) | u;
+ long newTotalValue
+ = BitConverter.IsLittleEndian ? (u << 32) | (u + 1) : ((u + 1) << 32) | u;
+
+ lockTaken = Interlocked.CompareExchange (ref ticket.TotalValue, newTotalValue, totalValue) == totalValue;
+
+ if (lockTaken) {
+ 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);
- }
+ if (flushReleaseWrites)
+ Interlocked.Increment (ref ticket.Value);
+ else
+ ticket.Value++;
}
}
-
+
// 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
projects / mono.git / blobdiff