corrade-vassal – Rev 1
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//
// System.Threading.ReaderWriterLockSlim.cs
//
// Authors:
// Miguel de Icaza (miguel@novell.com)
// Dick Porter (dick@ximian.com)
// Jackson Harper (jackson@ximian.com)
// Lluis Sanchez Gual (lluis@ximian.com)
// Marek Safar (marek.safar@gmail.com)
//
// Copyright 2004-2008 Novell, Inc (http://www.novell.com)
// Copyright 2003, Ximian, Inc.
//
// NoRecursion code based on the blog post from Vance Morrison:
// http://blogs.msdn.com/vancem/archive/2006/03/28/563180.aspx
//
// Recursion code based on Mono's implementation of ReaderWriterLock.
//
// 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.Collections;
using System.Collections.Generic;
using System.Security.Permissions;
using System.Diagnostics;
using System.Runtime.Serialization;
using System.Threading;
namespace OpenMetaverse
{
[Serializable]
public class LockRecursionException : Exception
{
public LockRecursionException()
: base()
{
}
public LockRecursionException(string message)
: base(message)
{
}
public LockRecursionException(string message, Exception e)
: base(message, e)
{
}
protected LockRecursionException(SerializationInfo info, StreamingContext sc)
: base(info, sc)
{
}
}
//
// This implementation is based on the light-weight
// Reader/Writer lock sample from Vance Morrison's blog:
//
// http://blogs.msdn.com/vancem/archive/2006/03/28/563180.aspx
//
// And in Mono's ReaderWriterLock
//
[HostProtectionAttribute(SecurityAction.LinkDemand, MayLeakOnAbort = true)]
[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true, ExternalThreading = true)]
public class ReaderWriterLockSlim : IDisposable
{
sealed class LockDetails
{
public int ThreadId;
public int ReadLocks;
}
// Are we on a multiprocessor?
static readonly bool smp;
// Lock specifiation for myLock: This lock protects exactly the local fields associted
// instance of MyReaderWriterLock. It does NOT protect the memory associted with the
// the events that hang off this lock (eg writeEvent, readEvent upgradeEvent).
int myLock;
// Who owns the lock owners > 0 => readers
// owners = -1 means there is one writer, Owners must be >= -1.
int owners;
Thread upgradable_thread;
Thread write_thread;
// These variables allow use to avoid Setting events (which is expensive) if we don't have to.
uint numWriteWaiters; // maximum number of threads that can be doing a WaitOne on the writeEvent
uint numReadWaiters; // maximum number of threads that can be doing a WaitOne on the readEvent
uint numUpgradeWaiters; // maximum number of threads that can be doing a WaitOne on the upgradeEvent (at most 1).
// conditions we wait on.
EventWaitHandle writeEvent; // threads waiting to aquire a write lock go here.
EventWaitHandle readEvent; // threads waiting to aquire a read lock go here (will be released in bulk)
EventWaitHandle upgradeEvent; // thread waiting to upgrade a read lock to a write lock go here (at most one)
//int lock_owner;
// Only set if we are a recursive lock
//Dictionary<int,int> reader_locks;
LockDetails[] read_locks = new LockDetails[8];
static ReaderWriterLockSlim()
{
smp = Environment.ProcessorCount > 1;
}
public ReaderWriterLockSlim()
{
// NoRecursion (0) is the default value
}
public void EnterReadLock()
{
TryEnterReadLock(-1);
}
public bool TryEnterReadLock(int millisecondsTimeout)
{
if (millisecondsTimeout < Timeout.Infinite)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if (read_locks == null)
throw new ObjectDisposedException(null);
if (Thread.CurrentThread == write_thread)
throw new LockRecursionException("Read lock cannot be acquired while write lock is held");
EnterMyLock();
LockDetails ld = GetReadLockDetails(Thread.CurrentThread.ManagedThreadId, true);
if (ld.ReadLocks != 0)
{
ExitMyLock();
throw new LockRecursionException("Recursive read lock can only be aquired in SupportsRecursion mode");
}
++ld.ReadLocks;
while (true)
{
// Easy case, no contention
// owners >= 0 means there might be readers (but no writer)
if (owners >= 0 && numWriteWaiters == 0)
{
owners++;
break;
}
// If the request is to probe.
if (millisecondsTimeout == 0)
{
ExitMyLock();
return false;
}
// We need to wait. Mark that we have waiters and wait.
if (readEvent == null)
{
LazyCreateEvent(ref readEvent, false);
// since we left the lock, start over.
continue;
}
if (!WaitOnEvent(readEvent, ref numReadWaiters, millisecondsTimeout))
return false;
}
ExitMyLock();
return true;
}
public bool TryEnterReadLock(TimeSpan timeout)
{
return TryEnterReadLock(CheckTimeout(timeout));
}
//
// TODO: What to do if we are releasing a ReadLock and we do not own it?
//
public void ExitReadLock()
{
EnterMyLock();
if (owners < 1)
{
ExitMyLock();
throw new SynchronizationLockException("Releasing lock and no read lock taken");
}
--owners;
--GetReadLockDetails(Thread.CurrentThread.ManagedThreadId, false).ReadLocks;
ExitAndWakeUpAppropriateWaiters();
}
public void EnterWriteLock()
{
TryEnterWriteLock(-1);
}
public bool TryEnterWriteLock(int millisecondsTimeout)
{
if (millisecondsTimeout < Timeout.Infinite)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if (read_locks == null)
throw new ObjectDisposedException(null);
if (IsWriteLockHeld)
throw new LockRecursionException();
EnterMyLock();
LockDetails ld = GetReadLockDetails(Thread.CurrentThread.ManagedThreadId, false);
if (ld != null && ld.ReadLocks > 0)
{
ExitMyLock();
throw new LockRecursionException("Write lock cannot be acquired while read lock is held");
}
while (true)
{
// There is no contention, we are done
if (owners == 0)
{
// Indicate that we have a writer
owners = -1;
write_thread = Thread.CurrentThread;
break;
}
// If we are the thread that took the Upgradable read lock
if (owners == 1 && upgradable_thread == Thread.CurrentThread)
{
owners = -1;
write_thread = Thread.CurrentThread;
break;
}
// If the request is to probe.
if (millisecondsTimeout == 0)
{
ExitMyLock();
return false;
}
// We need to wait, figure out what kind of waiting.
if (upgradable_thread == Thread.CurrentThread)
{
// We are the upgradable thread, register our interest.
if (upgradeEvent == null)
{
LazyCreateEvent(ref upgradeEvent, false);
// since we left the lock, start over.
continue;
}
if (numUpgradeWaiters > 0)
{
ExitMyLock();
throw new ApplicationException("Upgrading lock to writer lock already in process, deadlock");
}
if (!WaitOnEvent(upgradeEvent, ref numUpgradeWaiters, millisecondsTimeout))
return false;
}
else
{
if (writeEvent == null)
{
LazyCreateEvent(ref writeEvent, true);
// since we left the lock, retry
continue;
}
if (!WaitOnEvent(writeEvent, ref numWriteWaiters, millisecondsTimeout))
return false;
}
}
Debug.Assert(owners == -1, "Owners is not -1");
ExitMyLock();
return true;
}
public bool TryEnterWriteLock(TimeSpan timeout)
{
return TryEnterWriteLock(CheckTimeout(timeout));
}
public void ExitWriteLock()
{
EnterMyLock();
if (owners != -1)
{
ExitMyLock();
throw new SynchronizationLockException("Calling ExitWriterLock when no write lock is held");
}
//Debug.Assert (numUpgradeWaiters > 0);
write_thread = upgradable_thread = null;
owners = 0;
ExitAndWakeUpAppropriateWaiters();
}
public void EnterUpgradeableReadLock()
{
TryEnterUpgradeableReadLock(-1);
}
//
// Taking the Upgradable read lock is like taking a read lock
// but we limit it to a single upgradable at a time.
//
public bool TryEnterUpgradeableReadLock(int millisecondsTimeout)
{
if (millisecondsTimeout < Timeout.Infinite)
throw new ArgumentOutOfRangeException("millisecondsTimeout");
if (read_locks == null)
throw new ObjectDisposedException(null);
if (IsUpgradeableReadLockHeld)
throw new LockRecursionException();
if (IsWriteLockHeld)
throw new LockRecursionException();
EnterMyLock();
while (true)
{
if (owners == 0 && numWriteWaiters == 0 && upgradable_thread == null)
{
owners++;
upgradable_thread = Thread.CurrentThread;
break;
}
// If the request is to probe
if (millisecondsTimeout == 0)
{
ExitMyLock();
return false;
}
if (readEvent == null)
{
LazyCreateEvent(ref readEvent, false);
// since we left the lock, start over.
continue;
}
if (!WaitOnEvent(readEvent, ref numReadWaiters, millisecondsTimeout))
return false;
}
ExitMyLock();
return true;
}
public bool TryEnterUpgradeableReadLock(TimeSpan timeout)
{
return TryEnterUpgradeableReadLock(CheckTimeout(timeout));
}
public void ExitUpgradeableReadLock()
{
EnterMyLock();
Debug.Assert(owners > 0, "Releasing an upgradable lock, but there was no reader!");
--owners;
upgradable_thread = null;
ExitAndWakeUpAppropriateWaiters();
}
public void Dispose()
{
read_locks = null;
}
public bool IsReadLockHeld
{
get { return RecursiveReadCount != 0; }
}
public bool IsWriteLockHeld
{
get { return RecursiveWriteCount != 0; }
}
public bool IsUpgradeableReadLockHeld
{
get { return RecursiveUpgradeCount != 0; }
}
public int CurrentReadCount
{
get { return owners & 0xFFFFFFF; }
}
public int RecursiveReadCount
{
get
{
EnterMyLock();
LockDetails ld = GetReadLockDetails(Thread.CurrentThread.ManagedThreadId, false);
int count = ld == null ? 0 : ld.ReadLocks;
ExitMyLock();
return count;
}
}
public int RecursiveUpgradeCount
{
get { return upgradable_thread == Thread.CurrentThread ? 1 : 0; }
}
public int RecursiveWriteCount
{
get { return write_thread == Thread.CurrentThread ? 1 : 0; }
}
public int WaitingReadCount
{
get { return (int)numReadWaiters; }
}
public int WaitingUpgradeCount
{
get { return (int)numUpgradeWaiters; }
}
public int WaitingWriteCount
{
get { return (int)numWriteWaiters; }
}
#region Private methods
void EnterMyLock()
{
if (Interlocked.CompareExchange(ref myLock, 1, 0) != 0)
EnterMyLockSpin();
}
void EnterMyLockSpin()
{
for (int i = 0; ; i++)
{
if (i < 3 && smp)
Thread.SpinWait(20); // Wait a few dozen instructions to let another processor release lock.
else
Thread.Sleep(0); // Give up my quantum.
if (Interlocked.CompareExchange(ref myLock, 1, 0) == 0)
return;
}
}
void ExitMyLock()
{
Debug.Assert(myLock != 0, "Exiting spin lock that is not held");
myLock = 0;
}
bool MyLockHeld { get { return myLock != 0; } }
/// <summary>
/// Determines the appropriate events to set, leaves the locks, and sets the events.
/// </summary>
private void ExitAndWakeUpAppropriateWaiters()
{
Debug.Assert(MyLockHeld);
// First a writing thread waiting on being upgraded
if (owners == 1 && numUpgradeWaiters != 0)
{
// Exit before signaling to improve efficiency (wakee will need the lock)
ExitMyLock();
// release all upgraders (however there can be at most one).
upgradeEvent.Set();
//
// TODO: What does the following comment mean?
// two threads upgrading is a guarenteed deadlock, so we throw in that case.
}
else if (owners == 0 && numWriteWaiters > 0)
{
// Exit before signaling to improve efficiency (wakee will need the lock)
ExitMyLock();
// release one writer.
writeEvent.Set();
}
else if (owners >= 0 && numReadWaiters != 0)
{
// Exit before signaling to improve efficiency (wakee will need the lock)
ExitMyLock();
// release all readers.
readEvent.Set();
}
else
ExitMyLock();
}
/// <summary>
/// A routine for lazily creating a event outside the lock (so if errors
/// happen they are outside the lock and that we don't do much work
/// while holding a spin lock). If all goes well, reenter the lock and
/// set 'waitEvent'
/// </summary>
void LazyCreateEvent(ref EventWaitHandle waitEvent, bool makeAutoResetEvent)
{
Debug.Assert(MyLockHeld);
Debug.Assert(waitEvent == null);
ExitMyLock();
EventWaitHandle newEvent;
if (makeAutoResetEvent)
newEvent = new AutoResetEvent(false);
else
newEvent = new ManualResetEvent(false);
EnterMyLock();
// maybe someone snuck in.
if (waitEvent == null)
waitEvent = newEvent;
}
/// <summary>
/// Waits on 'waitEvent' with a timeout of 'millisceondsTimeout.
/// Before the wait 'numWaiters' is incremented and is restored before leaving this routine.
/// </summary>
bool WaitOnEvent(EventWaitHandle waitEvent, ref uint numWaiters, int millisecondsTimeout)
{
Debug.Assert(MyLockHeld);
waitEvent.Reset();
numWaiters++;
bool waitSuccessful = false;
// Do the wait outside of any lock
ExitMyLock();
try
{
waitSuccessful = waitEvent.WaitOne(millisecondsTimeout, false);
}
finally
{
EnterMyLock();
--numWaiters;
if (!waitSuccessful)
ExitMyLock();
}
return waitSuccessful;
}
static int CheckTimeout(TimeSpan timeout)
{
try
{
return checked((int)timeout.TotalMilliseconds);
}
catch (System.OverflowException)
{
throw new ArgumentOutOfRangeException("timeout");
}
}
LockDetails GetReadLockDetails(int threadId, bool create)
{
int i;
LockDetails ld;
for (i = 0; i < read_locks.Length; ++i)
{
ld = read_locks[i];
if (ld == null)
break;
if (ld.ThreadId == threadId)
return ld;
}
if (!create)
return null;
if (i == read_locks.Length)
Array.Resize(ref read_locks, read_locks.Length * 2);
ld = read_locks[i] = new LockDetails();
ld.ThreadId = threadId;
return ld;
}
#endregion
}
}