public UncheckedReaderWriterLock()
{
this.sentinelToken = new WaitingToken();
this.innerLock = new LightweightSpinLock();
this.id = Interlocked.Increment(ref counter);
this.readerCount = 0;
this.writerPending = 0;
}
public UncheckedReaderWriterLock()
{
this.sentinelToken = new WaitingToken();
this.innerLock = new LightweightSpinLock();
this.id = Interlocked.Increment(ref counter);
this.readerCount = 0;
this.writerPending = 0;
}
public void EnterWrite()
{
// Indicate that a writer operation entered
Interlocked.CompareExchange(ref this.writerPending, 1, 0);
// Allocate wait token
WaitingToken wait = this.AllocateWaitingToken();
this.WaitForWrite(wait);
}
private void WaitForWrite(WaitingToken wait)
{
int retry = 0;
while (true)
{
// Check if out token is the next and all readers has left
if (Interlocked.CompareExchange(ref this.sentinelToken.Next, wait, wait) == wait &&
Interlocked.CompareExchange(ref this.readerCount, 0, 0) == 0)
{
return;
}
LightweightSpinLock.SpinWait(ref retry);
}
}
private void DropWaitingToken()
{
this.innerLock.Enter();
// sentinelToken.next = current token (it should not be null)
WaitingToken next = this.sentinelToken.Next.Next;
this.sentinelToken.Next = next;
if (next == null)
{
// Indicat that no operation wants to write anymore
Interlocked.CompareExchange(ref this.writerPending, 0, 1);
}
this.innerLock.Exit();
}
private WaitingToken AllocateWaitingToken()
{
WaitingToken wait = new WaitingToken();
this.innerLock.Enter();
// Find the last token
WaitingToken last = this.sentinelToken;
while (last.Next != null)
{
last = last.Next;
}
// Concat to the end
last.Next = wait;
this.innerLock.Exit();
return(wait);
}
private WaitingToken AllocateWaitingToken()
{
WaitingToken wait = new WaitingToken();
this.innerLock.Enter();
// Find the last token
WaitingToken last = this.sentinelToken;
while (last.Next != null)
{
last = last.Next;
}
// Concat to the end
last.Next = wait;
this.innerLock.Exit();
return wait;
}
private void WaitForWrite(WaitingToken wait)
{
int retry = 0;
while (true)
{
// Check if out token is the next and all readers has left
if (Interlocked.CompareExchange(ref this.sentinelToken.Next, wait, wait) == wait &&
Interlocked.CompareExchange(ref this.readerCount, 0, 0) == 0)
{
return;
}
LightweightSpinLock.SpinWait(ref retry);
}
}
