/// <summary>
/// Atomically tries to set the first value on the target field and returns
/// false if its not null.
/// </summary>
/// <param name="field"></param>
/// <param name="first"></param>
/// <returns></returns>
public static bool SetOnce(ref ISubscription field, ISubscription first)
{
for (;;)
{
ISubscription a = Volatile.Read(ref field);
if (a == Cancelled)
{
first?.Cancel();
return(false);
}
if (a != null)
{
first?.Cancel();
OnSubscribeHelper.ReportSubscriptionSet();
return(false);
}
if (Interlocked.CompareExchange(ref field, first, null) == null)
{
return(true);
}
}
}
public void OnSubscribe(ISubscription s)
{
if (SubscriptionHelper.SetOnce(ref this.other, s))
{
s.Request(long.MaxValue);
}
else
{
s.Cancel();
OnSubscribeHelper.ReportSubscriptionSet();
}
}
public void Set(ISubscription s)
{
ISubscription a = Interlocked.CompareExchange(ref secondSubscription, s, null);
if (a == null)
{
long r = Interlocked.Exchange(ref requested, 0);
if (r != 0)
{
s.Request(r);
}
}
else
{
s?.Cancel();
if (a != SubscriptionHelper.Cancelled)
{
OnSubscribeHelper.ReportSubscriptionSet();
}
}
}
