public void UnlockCompetition(CancellationToken cancellationToken)
{
CancellationTokenRegistration registration = cancellationToken
.Register
(
state =>
{
ExclusiveCompletionSourceGroup <T> group = state as ExclusiveCompletionSourceGroup <T>;
/// There are 2 cases here.
///
/// #1: The token is canceled before <see cref="UnlockCompetition(CancellationToken)"/> is called, but after the token is validated higher up the stack.
/// Is this is the case, the cancellation callbak will be called synchronously while <see cref="_completedSource"/> is still set to <see cref="State.Locked"/>.
/// So the competition will never progress to <see cref="State.Unlocked"/> and we have to check for this explicitly.
///
/// #2: We're canceled after the competition has been unlocked.
/// If this is the case, we have a simple race against the awaiters to progress from <see cref="State.Unlocked"/> to <see cref="State.Canceled"/>.
if (group.TryTransitionToCanceledIfStateIs(State.Locked) || group.TryTransitionToCanceledIfStateIs(State.Unlocked))
{
group._realCompetionSource.SetCanceled();
}
},
this,
useSynchronizationContext: false
);
// We can't do volatile reads/writes on a custom value type field, so we have to wrap the registration into a holder instance.
// But there's no point in allocating the wrapper if the token can never be canceled.
if (cancellationToken.CanBeCanceled)
{
Volatile.Write(ref _cancellationRegistrationHolder, new CancellationRegistrationHolder(registration));
}
// If the cancellation was processed synchronously, the state will already be set to Canceled and we must *NOT* unlock the competition.
Interlocked.CompareExchange(ref _completedSource, State.Unlocked, State.Locked);
}
public Factory(ExclusiveCompletionSourceGroup <T> group, int index)
{
_group = group;
_index = index;
}
public ExclusiveCompletionSource(ExclusiveCompletionSourceGroup <T> group, int id)
{
_group = group;
_id = id;
}