Disposables

IDisposable helper types.

Main Types

• Disposable/AsyncDisposable - When disposed, invokes an Action/Func<ValueTask>.
• CollectionDisposable/AsyncCollectionDisposable - When disposed, disposes a collection of other disposables.
• IReferenceCountedDisposable<T> - Maintains a reference count for a disposable and disposes it when the reference count reaches zero.
• NoopDisposable - When disposed, does nothing.

Disposable and AsyncDisposable

The Disposable type wraps an Action, and invokes that Action exactly once when it is disposed. The first thread to call Dispose is the one that invokes the Action; all other threads that call Dispose are blocked until the Action is completed. Once the Action is completed, it is never invoked again; future calls to Disposable.Dispose are no-ops.

You can create a Disposable by calling Disposable.Create(Action) or new Disposable(Action).

AsyncDisposable is exactly the same as Disposable except it wraps a Func<ValueTask>.

You can call Abandon to have the Disposable/AsyncDisposable abandon its disposal work and do nothing when it is disposed. Abandon returns the Action (or Func<ValueTask>) that it would have taken on disposal; this can be passed to Create to transfer ownership of the disposal actions.

If the Action (or Func<Task>) throws an exception, only the first caller of Dispose (or DisposeAsync) will observe the exception. All other calls to Dispose / DisposeAsync will wait for the delegate to complete, but they will not observe the exception.

Advanced

You can append an Action to a Disposable by calling its Add method with the Action to add. When the Disposable is disposed, it will call its actions in reverse order. When Add is called, if the Disposable is already disposed (or is in the process of being disposed by another thread), then the additional Action is invoked immediately by the current thread after the disposal completes, and the other thread is not blocked waiting for the Action to complete.

AsyncDisposable may also have multiple delegates. By default, they are all invoked serially in reverse order, but you can change this to concurrent by creating the instance with the AsyncDisposeFlags.ExecuteConcurrently flag.

CollectionDisposable

CollectionDisposable contains a collection of IDisposable instances, and disposes them all exactly once when it is disposed. The first thread to call Dispose is the one that disposes all instances; all other threads that call Dispose are blocked until all instances have been disposed. Once disposed, future calls to CollectionDisposable.Dispose are no-ops.

You can create a CollectionDisposable by calling CollectionDisposable.Create(...) or new CollectionDisposable(...), passing the collection of disposables.

You can also append a disposable to the CollectionDisposable by calling its Add method and passing it the disposable. If the CollectionDisposable is already disposed (or is in the process of being disposed by another thread), then the additional disposable is disposed immediately by the current thread after the disposal completes, and the other thread is not blocked waiting for the additional disposable to dispose.

AsyncCollectionDisposable is exactly the same as CollectionDisposable except it is a collection of IAsyncDisposable instances. You can also create a mixed collection (containing both IDisposable and IAsyncDisposable instances) by calling ToAsyncDisposable on your IDisposable instances.

You can call Abandon to have the CollectionDisposable/AsyncCollectionDisposable abandon its disposal work and do nothing when it is disposed. Abandon returns the IEnumerable<IDisposable> (or IEnumerable<IAsyncDisposable>) that it would have disposed; this can be passed to Create to transfer ownership of the disposal actions.

By default, all IAsyncDisposable instances are disposed serially in reverse order, but you can change this to concurrent by creating the AsyncCollectionDisposable instance with the AsyncDisposeFlags.ExecuteConcurrently flag.

Fixing Other Disposables

CollectionDisposable can be used as a wrapper to enforce only-dispose-once semantics on another disposable. If a type IncorrectDisposable has a Dispose method that breaks if it is called more than once, then CollectionDisposable.Create(incorrectDisposable) returns an IDisposable that will only invoke IncorrectDisposable.Dispose a single time, regardless of how many times you call CollectionDisposable.Dispose.

Reference Counted Disposables

You can create a reference-counted disposable wrapping a target disposable by passing the target disposable to ReferenceCountedDisposable.Create. The reference-counted disposable represents an increment of the reference count, and decrements that reference count when disposed. When the reference count reaches zero, the target disposable is disposed.

You can increment the reference count by calling IReferenceCountedDisposable<T>.AddReference, which returns an independent reference-counted disposable representing its own increment of the reference count.

A reference-counted disposable can access its underlying target disposable via IReferenceCountedDisposable<T>.Target.

Advanced: Weak Reference Counted Disposables

You can create a weak-reference-counted disposable by calling IReferenceCountedDisposable<T>.AddWeakReference. Weak-reference-counted disposables weakly reference the target disposable and the reference count. They do not represent an increment of the reference count.

You can attempt to increment the reference count for a weak-reference-counted disposable by calling IWeakReferenceCountedDisposable<T>.TryAddReference. If successful, this method returns a (strong) reference-counted disposable.

You can also attempt to access the underlying target disposable via IWeakReferenceCountedDisposable<T>.TryGetTarget.

Advanced: Custom Reference Counting

Reference-counted disposables by default use an ephemeron for the reference count, so calling ReferenceCountedDisposable.Create multiple times on the same target disposable instance will share the underlying reference count. If the reference count is already be zero, this method will throw ObjectDisposedException; to avoid this exception, you can call ReferenceCountedDisposable.TryCreate.

If you want to use a new reference count and not use the ephemeron, you can call ReferenceCountedDisposable.CreateWithNewReferenceCounter. This usage avoids ephemerons, which put pressure on the garbage collector.

NoopDisposable

A type implementing both IDisposable and IAsyncDisposable that does nothing when disposed.

You can retrieve the singleton instance via NoopDisposable.Instance.

Advanced Types

SingleDisposable<T>

The SingleDisposable<T> type is a base type for disposables that desire exactly-once semantics, blocking other threads calling Dispose until the initial Dispose is complete. Both Disposable and CollectionDisposable inherit from this type.

The type T is an immutable type that represents the contextual state of the instance. It is initialized in the constructor, optionally updated by calling TryUpdateContext, and finally retrieved and passed to Dispose(T) exactly once when Dispose() is called.

When the base type invokes Dispose(T), your derived type should perform whatever disposing logic it needs to.

AsyncSingleDisposable<T> is exactly the same as SingleDisposable<T> except that it implements IAsyncDisposable instead of IDisposable.

If Dispose(T) (or DisposeAsync(T)) throws an exception, only the first caller of Dispose (or DisposeAsync) will observe the exception. All other calls to Dispose / DisposeAsync will wait for the delegate to complete, but they will not observe the exception.

SingleNonblockingDisposable<T>

The SingleNonblockingDisposable<T> type is a base type for disposables that desire exactly-once semantics without blocking other threads calling Dispose. It works exactly like SingleDisposable<T>, except that once disposal has started, other threads calling Dispose will return immediately, treating the additional Dispose calls as a no-op.

AsyncSingleNonblockingDisposable<T> is exactly the same as SingleNonblockingDisposable<T> except that it implements IAsyncDisposable instead of IDisposable.