public async Task <IEnumerator <Tuple> > GetEnumeratorAsync(EnumerationContext context, CancellationToken token)
{
const string enumerationMarker = "Enumerated";
var enumerated = context.GetValue <bool>(this, enumerationMarker);
bool onEnumerationExecuted = false;
if (!enumerated)
{
OnBeforeEnumerate(context);
}
try {
context.SetValue(this, enumerationMarker, true);
var enumerator = (await OnEnumerateAsync(context, token).ConfigureAwait(false))
.ToEnumerator(
() => {
if (!enumerated)
{
OnAfterEnumerate(context);
}
});
onEnumerationExecuted = true;
return(enumerator);
}
finally {
if (!enumerated && !onEnumerationExecuted)
{
OnAfterEnumerate(context);
}
}
}
private async ValueTask Prepare(bool executeAsync)
{
enumerationScope = context.BeginEnumeration();
enumerated = context.GetValue <bool>(provider, enumerationMarker);
if (!enumerated)
{
provider.OnBeforeEnumerate(context);
context.SetValue(provider, enumerationMarker, true);
}
try {
dataReader = executeAsync
? await provider.OnEnumerateAsync(context, token).ConfigureAwait(false)
: provider.OnEnumerate(context);
if (isGreedy && !dataReader.IsInMemory)
{
var tuples = new List <Tuple>();
if (executeAsync)
{
await using (dataReader.ConfigureAwait(false)) {
while (await dataReader.MoveNextAsync().ConfigureAwait(false))
{
tuples.Add(dataReader.Current);
}
}
}
else
{
using (dataReader) {
while (dataReader.MoveNext())
{
tuples.Add(dataReader.Current);
}
}
}
dataReader = new DataReader(tuples);
}
}
catch {
FinishEnumeration(true);
throw;
}
state = State.Prepared;
}
protected T GetValue <T>(EnumerationContext context, string name)
where T : class
{
context.EnsureIsActive();
return(context.GetValue <T>(this, name));
}
/// <summary>
/// Gets value of type <typeparamref name="T"/> previously cached in
/// <see cref="EnumerationContext"/> by its <paramref name="name"/>.
/// </summary>
/// <param name="context"><see cref="EnumerationContext"/> instance where value cache resides.</param>
/// <param name="name">The name of the required cached value.</param>
/// <typeparam name="T">The type of the value in cache.</typeparam>
/// <returns> Cached value with the specified key;
/// or <see langword="null"/>, if no cached value is found, or it has already expired.
/// </returns>
protected T GetValue <T>(EnumerationContext context, string name)
where T : class =>
context.GetValue <T>(this, name);
