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monix.execution

cancelables

package cancelables

Cancelables represent asynchronous units of work or other things scheduled for execution and whose execution can be canceled.

One use-case is the scheduling done by monix.execution.Scheduler, in which the scheduling methods return a Cancelable, allowing the canceling of the scheduling.

Example:

val s = ConcurrentScheduler()
val task = s.scheduleRepeated(10.seconds, 50.seconds, {
  doSomething()
})

// later, cancels the scheduling ...
task.cancel()
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package.scala
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Type Members

  1. trait AssignableCancelable extends Cancelable

    Represents a class of cancelables that can hold an internal reference to another cancelable (and thus has to support the assignment operator).

    Represents a class of cancelables that can hold an internal reference to another cancelable (and thus has to support the assignment operator).

    Examples are the OrderedCancelable and the SingleAssignCancelable.

    On assignment, if this cancelable is already canceled, then no assignment should happen and the update reference should be canceled as well.

  2. trait BooleanCancelable extends Cancelable

    Represents a Cancelable that can be queried for the canceled status.

  3. final class ChainedCancelable extends AssignableCancelable

    Represents a monix.execution.Cancelable whose underlying cancelable reference can be swapped for another.

    Represents a monix.execution.Cancelable whose underlying cancelable reference can be swapped for another. It can be "chained" to another ChainedCancelable, forwarding all operations to it.

    For most purposes it works like a OrderedCancelable:

    val s = ChainedCancelable()
    s := c1 // sets the underlying cancelable to c1
    s := c2 // swaps the underlying cancelable to c2
    
    s.cancel() // also cancels c2
    
    s := c3 // also cancels c3, because s is already canceled

    However it can also be linked to another ChainedCancelable reference, forwarding all requests to it:

    val source = ChainedCancelable()
    val child1 = ChainedCancelable()
    val child2 = ChainedCancelable()
    
    // Hence forth forwards all operations on `child1` to `source`
    child1.chainTo(source)
    
    // Also forwarding all `child2` operations to `source`.
    // This happens because `child1` was linked to `source` first
    // but order matters, as `child2` will be linked directly
    // to `source` and not to `child1`, in order for `child1` to
    // be garbage collected if it goes out of scope ;-)
    child2.chainTo(child1)
    
    // Source will be updated with a new Cancelable ref
    child1 := Cancelable(() => println("Cancelling (1)"))
    
    // Source will be updated with another Cancelable ref
    child2 := Cancelable(() => println("Cancelling (2)"))
    
    source.cancel()
    //=> Cancelling (2)

    This implementation is a special purpose AssignableCancelable, much like StackedCancelable, to be used in flatMap implementations that need it.

    The problem that it solves in Monix's codebase is that various flatMap implementations need to be memory safe. By "chaining" cancelable references, we allow the garbage collector to get rid of references created in a flatMap loop, the goal being to consume a constant amount of memory. Thus this implementation is used for CancelableFuture.

    The implementation is also relaxed about the thread-safety of the forwardTo operation, treating it like a semi-final state and using Java 8 getAndSet platform intrinsics for performance reasons.

    If unsure about what to use, then you probably don't need ChainedCancelable. Use OrderedCancelable or SingleAssignCancelable for most purposes.

  4. final class CompositeCancelable extends BooleanCancelable

    Represents a composite of multiple cancelables.

    Represents a composite of multiple cancelables. In case it is canceled, all contained cancelables will be canceled too, e.g...

    val s = CompositeCancelable()
    
    s += c1
    s += c2
    s += c3
    
    // c1, c2, c3 will also be canceled
    s.cancel()

    Additionally, once canceled, on appending of new cancelable references, those references will automatically get canceled too:

    val s = CompositeCancelable()
    s.cancel()
    
    // c1 gets canceled, because s is already canceled
    s += c1
    // c2 gets canceled, because s is already canceled
    s += c2

    Adding and removing references from this composite is thread-safe.

  5. final class MultiAssignCancelable extends Multi

    Represents a Cancelable whose underlying cancelable reference can be swapped for another.

    Represents a Cancelable whose underlying cancelable reference can be swapped for another.

    Example:

    val s = MultiAssignmentCancelable()
    s := c1 // sets the underlying cancelable to c1
    s := c2 // swaps the underlying cancelable to c2
    
    s.cancel() // also cancels c2
    
    s := c3 // also cancels c3, because s is already canceled

    Also see:

    • SerialCancelable, which is similar, except that it cancels the old cancelable upon assigning a new cancelable
    • SingleAssignCancelable that is effectively a forward reference that can be assigned at most once
    • OrderedCancelable that's very similar with MultiAssignCancelable, but with the capability of forcing ordering on concurrent updates
  6. final class OrderedCancelable extends Multi

    Represents a Cancelable whose underlying cancelable reference can be swapped for another and that has the capability to force ordering of updates.

    Represents a Cancelable whose underlying cancelable reference can be swapped for another and that has the capability to force ordering of updates.

    For the most part it's very similar with MultiAssignCancelable:

    val s = OrderedCancelable()
    s := c1 // sets the underlying cancelable to c1
    s := c2 // swaps the underlying cancelable to c2
    
    s.cancel() // also cancels c2
    
    s := c3 // also cancels c3, because s is already canceled

    However it also has the capability of doing orderedUpdate:

    val s = OrderedCancelable()
    
    ec.execute(new Runnable {
      def run() =
        s.orderedUpdate(ref2, 2)
    })
    
    // The ordered updates are guarding against reversed ordering
    // due to the created thread being able to execute before the
    // following update
    s.orderedUpdate(ref1, 1)

    Also see:

    • SerialCancelable, which is similar, except that it cancels the old cancelable upon assigning a new cancelable
    • SingleAssignCancelable that is effectively a forward reference that can be assigned at most once
    • MultiAssignCancelable that's very similar with OrderedCancelable, but simpler, without the capability of doing ordered updates and possibly more efficient
  7. final class RefCountCancelable extends BooleanCancelable

    Represents a Cancelable that only executes the canceling logic when all dependent cancelable objects have been canceled.

    Represents a Cancelable that only executes the canceling logic when all dependent cancelable objects have been canceled.

    The given callback gets called after our RefCountCancelable is canceled and after all dependent cancelables have been canceled along with the main cancelable.

    In other words, lets say for example that we have acquired 2 children. In order for the cancelable to get canceled, we need to:

    • cancel both children
    • cancel the main RefCountCancelable

    The implementation is thread-safe and cancellation order doesn't matter.

  8. final class SerialCancelable extends Multi

    Represents a monix.execution.Cancelable whose underlying cancelable can be swapped for another cancelable which causes the previous underlying cancelable to be canceled.

    Represents a monix.execution.Cancelable whose underlying cancelable can be swapped for another cancelable which causes the previous underlying cancelable to be canceled.

    Example:

    val s = SerialCancelable()
    s := c1 // sets the underlying cancelable to c1
    s := c2 // cancels c1 and swaps the underlying cancelable to c2
    
    s.cancel() // also cancels c2
    
    s := c3 // also cancels c3, because s is already canceled

    Also see OrderedCancelable, which is similar, but doesn't cancel the old cancelable upon assignment.

  9. final class SingleAssignCancelable extends Bool

    Represents a monix.execution.Cancelable that can be assigned only once to another cancelable reference.

    Represents a monix.execution.Cancelable that can be assigned only once to another cancelable reference.

    Similar to monix.execution.cancelables.OrderedCancelable, except that in case of multi-assignment, it throws a java.lang.IllegalStateException.

    If the assignment happens after this cancelable has been canceled, then on assignment the reference will get canceled too.

    Useful in case you need a forward reference.

  10. sealed abstract class StackedCancelable extends BooleanCancelable

    Represents a composite of cancelables that are stacked, so you can push a new reference, or pop an existing one and when it gets canceled, then the whole stack gets canceled.

    Represents a composite of cancelables that are stacked, so you can push a new reference, or pop an existing one and when it gets canceled, then the whole stack gets canceled.

    Similar in spirit with CompositeCancelable, except that you can only pull out references in a FIFO fashion.

    Used in the implementation of monix.eval.Task.

  11. type MultiAssignmentCancelable = OrderedCancelable

    DEPRECATED — renamed to OrderedCancelable.

    DEPRECATED — renamed to OrderedCancelable.

    Annotations
    @deprecated
    Deprecated

    (Since version 3.0.0) Renamed to OrderedCancelable

  12. type SingleAssignmentCancelable = SingleAssignCancelable

    DEPRECATED — renamed to SingleAssignCancelable.

    DEPRECATED — renamed to SingleAssignCancelable.

    Annotations
    @deprecated
    Deprecated

    (Since version 3.0.0) Renamed to SingleAssignCancelable

Deprecated Value Members

  1. val MultiAssignmentCancelable: OrderedCancelable.type

    DEPRECATED — renamed to OrderedCancelable.

    DEPRECATED — renamed to OrderedCancelable.

    Annotations
    @deprecated
    Deprecated

    (Since version 3.0.0) Renamed to OrderedCancelable

  2. val SingleAssignmentCancelable: SingleAssignCancelable.type

    DEPRECATED — renamed to SingleAssignCancelable.

    DEPRECATED — renamed to SingleAssignCancelable.

    Annotations
    @deprecated
    Deprecated

    (Since version 3.0.0) Renamed to SingleAssignCancelable

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