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// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
#if !NO_PERF
using System;
using System.Collections.Generic;
using System.Reactive.Threading;
using System.Threading;
namespace System.Reactive.Linq.ObservableImpl
{
class Next<TSource> : PushToPullAdapter<TSource, TSource>
{
public Next(IObservable<TSource> source)
: base(source)
{
}
protected override PushToPullSink<TSource, TSource> Run(IDisposable subscription)
{
return new _(subscription);
}
class _ : PushToPullSink<TSource, TSource>
{
private readonly object _gate;
#if !NO_CDS
private readonly SemaphoreSlim _semaphore;
#else
private readonly Semaphore _semaphore;
#endif
public _(IDisposable subscription)
: base(subscription)
{
_gate = new object();
#if !NO_CDS
_semaphore = new SemaphoreSlim(0, 1);
#else
_semaphore = new Semaphore(0, 1);
#endif
}
private bool _waiting;
private NotificationKind _kind;
private TSource _value;
private Exception _error;
public override void OnNext(TSource value)
{
lock (_gate)
{
if (_waiting)
{
_value = value;
_kind = NotificationKind.OnNext;
_semaphore.Release();
}
_waiting = false;
}
}
public override void OnError(Exception error)
{
base.Dispose();
lock (_gate)
{
//
// BREAKING CHANGE v2 > v1.x - Next doesn't block indefinitely when it reaches the end.
//
_error = error;
_kind = NotificationKind.OnError;
if (_waiting)
_semaphore.Release();
_waiting = false;
}
}
public override void OnCompleted()
{
base.Dispose();
lock (_gate)
{
//
// BREAKING CHANGE v2 > v1.x - Next doesn't block indefinitely when it reaches the end.
//
_kind = NotificationKind.OnCompleted;
if (_waiting)
_semaphore.Release();
_waiting = false;
}
}
public override bool TryMoveNext(out TSource current)
{
var done = false;
lock (_gate)
{
_waiting = true;
//
// BREAKING CHANGE v2 > v1.x - Next doesn't block indefinitely when it reaches the end.
//
done = _kind != NotificationKind.OnNext;
}
if (!done)
{
#if !NO_CDS
_semaphore.Wait();
#else
_semaphore.WaitOne();
#endif
}
//
// When we reach this point, we released the lock and got the next notification
// from the observer. We assume no concurrent calls to the TryMoveNext method
// are made (per general guidance on usage of IEnumerable<T>). If the observer
// enters the lock again, it should have quit it first, causing _waiting to be
// set to false, hence future accesses of the lock won't set the _kind, _value,
// and _error fields, until TryMoveNext is entered again and _waiting is reset
// to true. In conclusion, the fields are stable for read below.
//
// Notice we rely on memory barrier acquire/release behavior due to the use of
// the semaphore, not the lock (we're still under the lock when we release the
// semaphore in the On* methods!).
//
switch (_kind)
{
case NotificationKind.OnNext:
current = _value;
return true;
case NotificationKind.OnError:
_error.Throw();
break;
case NotificationKind.OnCompleted:
break;
}
current = default(TSource);
return false;
}
}
}
}
#endif
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