private Func <WeakReference <ConcurrentAsyncEnumerator <T> >, Task> BuildProducerWrapperFactory(
Func <ConcurrentAsyncProducer <T>, Task> producerFunc
)
{
return(async weakEnumerator =>
{
ConcurrentAsyncEnumerator <T> enumerator;
weakEnumerator.TryGetTarget(out enumerator);
Trace2("Producer container started");
var producer = new ConcurrentAsyncProducer <T>(item => enumerator.Yield(item), _cancellationToken);
try
{
// Wait for the consumer to call MoveNext() the first time.
// This is only necessary to synchronize the enumerator when the
// producer is started.
await enumerator._emitNextValue;
Trace2("Invoker user produder factory");
await producerFunc(producer);
enumerator.EndOfStream();
}
catch (OperationCanceledException)
{
// The consumer decided to stop the enumeration (by calling Dispose or DisposeAsync).
// The idea here is to make sure that any code after the call to Yield that caused
// this exception is not executed.
// Throwing an exception is the only way to ensure that resources are cleaned up
// correctly (try/catch/finally).
//
// In the the case where
// * The consumer cancel the enumeration by calling Dispose (or DisposeAsync)
// * The consumer invoke Yield again
// * Yield will then throw an ObjectDisposedException to signal
// that something is not working as intended.
//
// But there are cases that are not easily handled.
// If the producer code has a "catch all" clause (catch {} or catch(Exception){})
// then the producer need to explicitely handle cooperatively to stop the execution
// correctly.
enumerator.EndOfStream();
}
catch (Exception e)
{
// There was an exception (other than EnumerationAbandonedException)
// in the producer code.
enumerator.EndOfStream(e);
// Ensure that this is propagated in Dispose too
throw;
}
});
}
internal ConcurrentAsyncEnumerator(Func <ConcurrentAsyncProducer <T>, Task> producerFunc)
{
var producer = new ConcurrentAsyncProducer <T>(async item =>
{
await valueBufferBlock.SendAsync(item).ConfigureAwait(false);
});
producerFunc(producer).ContinueWith(t =>
{
if (t.Exception != null)
{
exception = t.Exception;
}
valueBufferBlock.Complete();
}, TaskContinuationOptions.ExecuteSynchronously);
}
internal ConcurrentAsyncEnumerator(Func <ConcurrentAsyncProducer <T>, Task> producerFunc)
{
_producer = async enumerator =>
{
var producer = new ConcurrentAsyncProducer <T>(item => enumerator.Yield(item));
try
{
// Wait for the consumer to call MoveNext() the first time.
// Note that after the first time, this will be always signalled.
// This is only necessary to synchronize the enumerator when the
// producer is started.
await _moveNextSignal.Wait().ConfigureAwait(false);
await producerFunc(producer);
}
finally
{
enumerator.EndOfStream();
}
};
}
internal ConversionObserver(ConcurrentAsyncProducer <T> producer)
{
this.producer = producer;
}
public static Task ForEach <T>(this IAsyncEnumerable <T> enumerable, ConcurrentAsyncProducer <T> producer)
{
return(ForEach(enumerable, loopState => producer.Yield(loopState.Item)));
}