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// ReaderWriterLockSlimmer.cs
//
// 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;
namespace Mono.Threading
{
public struct ReaderWriterLockSlimmer
{
const int RwWait = 1;
const int RwWrite = 2;
const int RwRead = 4;
int rwlock;
public void EnterReadLock (ref bool taken)
{
if (taken)
throw new ArgumentException ("taken", "taken needs to be set to false");
SpinWait sw = new SpinWait ();
bool cont = true;
do {
while ((rwlock & (RwWrite | RwWait)) > 0)
sw.SpinOnce ();
try {}
finally {
if ((Interlocked.Add (ref rwlock, RwRead) & (RwWait | RwWait)) == 0) {
taken = true;
cont = false;
} else {
Interlocked.Add (ref rwlock, -RwRead);
}
}
} while (cont);
}
public void TryEnterReadLock (ref bool taken)
{
if (taken)
throw new ArgumentException ("taken", "taken needs to be set to false");
try {}
finally {
if ((Interlocked.Add (ref rwlock, RwRead) & (RwWait | RwWrite)) == 0)
taken = true;
else
Interlocked.Add (ref rwlock, -RwRead);
}
}
public void ExitReadLock ()
{
Interlocked.Add (ref rwlock, -RwRead);
}
public void EnterWriteLock (ref bool taken)
{
if (taken)
throw new ArgumentException ("taken", "taken needs to be set to false");
SpinWait sw = new SpinWait ();
int state = rwlock;
try {
do {
state = rwlock;
if (state < RwWrite) {
try {}
finally {
if (Interlocked.CompareExchange (ref rwlock, RwWrite, state) == state)
taken = true;
}
if (taken)
return;
state = rwlock;
}
while ((state & RwWait) == 0 && Interlocked.CompareExchange (ref rwlock, state | RwWait, state) != state)
state = rwlock;
while (rwlock > RwWait)
sw.SpinOnce ();
} while (true);
} finally {
state = rwlock;
if (!taken && (state & RwWait) != 0)
Interlocked.CompareExchange (ref rwlock, state - RwWait, state);
}
}
public void TryEnterWriteLock (ref bool taken)
{
if (taken)
throw new ArgumentException ("taken", "taken needs to be set to false");
int state = rwlock;
if (state >= RwWrite)
return;
try {}
finally {
if (Interlocked.CompareExchange (ref rwlock, RwWrite, state) == state)
taken = true;
}
}
public void ExitWriteLock ()
{
Interlocked.Add (ref rwlock, -RwWrite);
}
}
}
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