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// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
using System.Reactive.Disposables;
namespace System.Reactive.Subjects
{
/// <summary>
/// Represents a value that changes over time.
/// Observers can subscribe to the subject to receive the last (or initial) value and all subsequent notifications.
/// </summary>
/// <typeparam name="T">The type of the elements processed by the subject.</typeparam>
public sealed class BehaviorSubject<T> : ISubject<T>, IDisposable
{
private readonly object _gate = new object();
private ImmutableList<IObserver<T>> _observers;
private bool _isStopped;
private T _value;
private Exception _exception;
private bool _isDisposed;
/// <summary>
/// Initializes a new instance of the <see cref="System.Reactive.Subjects.BehaviorSubject<T>"/> class which creates a subject that caches its last value and starts with the specified value.
/// </summary>
/// <param name="value">Initial value sent to observers when no other value has been received by the subject yet.</param>
public BehaviorSubject(T value)
{
_value = value;
_observers = new ImmutableList<IObserver<T>>();
}
/// <summary>
/// Indicates whether the subject has observers subscribed to it.
/// </summary>
public bool HasObservers
{
get
{
var observers = _observers;
return observers != null && observers.Data.Length > 0;
}
}
/// <summary>
/// Notifies all subscribed observers about the end of the sequence.
/// </summary>
public void OnCompleted()
{
var os = default(IObserver<T>[]);
lock (_gate)
{
CheckDisposed();
if (!_isStopped)
{
os = _observers.Data;
_observers = new ImmutableList<IObserver<T>>();
_isStopped = true;
}
}
if (os != null)
{
foreach (var o in os)
o.OnCompleted();
}
}
/// <summary>
/// Notifies all subscribed observers about the exception.
/// </summary>
/// <param name="error">The exception to send to all observers.</param>
/// <exception cref="ArgumentNullException"><paramref name="error"/> is null.</exception>
public void OnError(Exception error)
{
if (error == null)
throw new ArgumentNullException("error");
var os = default(IObserver<T>[]);
lock (_gate)
{
CheckDisposed();
if (!_isStopped)
{
os = _observers.Data;
_observers = new ImmutableList<IObserver<T>>();
_isStopped = true;
_exception = error;
}
}
if (os != null)
foreach (var o in os)
o.OnError(error);
}
/// <summary>
/// Notifies all subscribed observers about the arrival of the specified element in the sequence.
/// </summary>
/// <param name="value">The value to send to all observers.</param>
public void OnNext(T value)
{
var os = default(IObserver<T>[]);
lock (_gate)
{
CheckDisposed();
if (!_isStopped)
{
_value = value;
os = _observers.Data;
}
}
if (os != null)
{
foreach (var o in os)
o.OnNext(value);
}
}
/// <summary>
/// Subscribes an observer to the subject.
/// </summary>
/// <param name="observer">Observer to subscribe to the subject.</param>
/// <returns>Disposable object that can be used to unsubscribe the observer from the subject.</returns>
/// <exception cref="ArgumentNullException"><paramref name="observer"/> is null.</exception>
public IDisposable Subscribe(IObserver<T> observer)
{
if (observer == null)
throw new ArgumentNullException("observer");
var ex = default(Exception);
lock (_gate)
{
CheckDisposed();
if (!_isStopped)
{
_observers = _observers.Add(observer);
observer.OnNext(_value);
return new Subscription(this, observer);
}
ex = _exception;
}
if (ex != null)
observer.OnError(ex);
else
observer.OnCompleted();
return Disposable.Empty;
}
class Subscription : IDisposable
{
private readonly BehaviorSubject<T> _subject;
private IObserver<T> _observer;
public Subscription(BehaviorSubject<T> subject, IObserver<T> observer)
{
_subject = subject;
_observer = observer;
}
public void Dispose()
{
if (_observer != null)
{
lock (_subject._gate)
{
if (!_subject._isDisposed && _observer != null)
{
_subject._observers = _subject._observers.Remove(_observer);
_observer = null;
}
}
}
}
}
void CheckDisposed()
{
if (_isDisposed)
throw new ObjectDisposedException(string.Empty);
}
/// <summary>
/// Unsubscribe all observers and release resources.
/// </summary>
public void Dispose()
{
lock (_gate)
{
_isDisposed = true;
_observers = null;
_value = default(T);
_exception = null;
}
}
}
}
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