/// <summary>
/// Atomically set the next ISubscription on this arbiter.
/// </summary>
/// <param name="s">The new ISubscription instance.</param>
public void Set(ISubscription s)
{
if (Volatile.Read(ref wip) == 0 && Interlocked.CompareExchange(ref wip, 1, 0) == 0)
{
var c = current;
long r = requested;
if (SubscriptionHelper.IsCancelled(c))
{
s?.Cancel();
if (Interlocked.Decrement(ref wip) == 0)
{
return;
}
}
else
{
c?.Cancel();
current = s;
if (Interlocked.Decrement(ref wip) != 0)
{
Drain();
}
if (r != 0L)
{
s?.Request(r);
}
}
}
else
{
ISubscription c = Interlocked.Exchange(ref missedSubscription, s);
c?.Cancel();
if (Interlocked.Increment(ref wip) != 1)
{
return;
}
Drain();
}
}
void Drain()
{
long requestAmount = 0L;
ISubscription requestTarget = null;
int missed = 1;
for (;;)
{
long mRequested = Volatile.Read(ref missedRequested);
if (mRequested != 0L)
{
mRequested = Interlocked.Exchange(ref missedRequested, 0L);
}
long mProduced = Volatile.Read(ref missedProduced);
if (mProduced != 0L)
{
mProduced = Interlocked.Exchange(ref missedProduced, 0L);
}
long r = requested;
if (r != long.MaxValue)
{
long u = BackpressureHelper.AddCap(r, mRequested);
if (u != long.MaxValue)
{
long v = u - mProduced;
if (v < 0L)
{
ExceptionHelper.OnErrorDropped(new InvalidOperationException("More produced than requested: " + v));
v = 0L;
}
requested = v;
r = v;
}
else
{
requested = u;
r = u;
}
}
ISubscription mSubscription = Volatile.Read(ref missedSubscription);
if (mSubscription != null)
{
mSubscription = Interlocked.Exchange(ref missedSubscription, null);
}
var c = current;
if (SubscriptionHelper.IsCancelled(c))
{
mSubscription?.Cancel();
}
else
{
if (mSubscription != null)
{
current?.Cancel();
current = mSubscription;
if (r != 0L)
{
requestAmount = BackpressureHelper.AddCap(requestAmount, r);
requestTarget = mSubscription;
}
}
else
if (mRequested != 0)
{
requestAmount = BackpressureHelper.AddCap(requestAmount, mRequested);
requestTarget = current;
}
}
missed = QueueDrainHelper.Leave(ref wip, missed);
if (missed == 0)
{
if (requestAmount != 0L)
{
requestTarget?.Request(requestAmount);
}
break;
}
}
}