Introduction

An update stream that provides a base functionality for updating a specific topic.

An update stream is associated with a specific topic. The type of the topic must match the type of values passed to the update stream. It can be created with an optional PTDiffusionUpdateConstraint. The existence of the topic, its type and the constraint are validated lazily by the first 'set' or 'validate' operation. Subsequent operations issued before the first operation completes will be deferred until the completion of the first operation.

An update stream can be used to send any number of updates. It sends a sequence of updates for a specific topic to the server. If supported by the data type, updates will be sent to the server as a stream of binary deltas. An update stream does not prevent other sessions from updating the topic. If exclusive access is required update streams should be used with a PTDiffusionSessionLock as a constraint.

Once validated an update stream can be invalidated. An invalidated update stream rejects the operations applied to it. The update stream will be invalidated if:

the topic is removed
another update stream is created for the same topic
the topic is updated to a new value by anything other than the stream
the session does not have the UPDATE_TOPIC update permission
an operation fails because of cluster repartitioning

Update streams are thread-safe.

See Also: PTDiffusionTopicUpdateFeature

Since: 6.3

Inheritance diagram for PTDiffusionUpdateStream:

Properties
ObjectType	value

Instance Methods
(BOOL)	- validateWithCompletionHandler:error:

(BOOL)	- setValue:completionHandler:error:

Protected Attributes
	__pad0__: NSObject+(instancetype)new

Method Documentation

- (BOOL) setValue:	(ObjectType)	value
completionHandler:	(PTDiffusionUpdateStreamHandlerBlock)	completionHandler
error:	(NSError **)	error

Sets the topic to a specified value.

The first call to this method may fail with a "no such topic" or "incompatible topic" error. Subsequent calls may fail with "invalid update stream". Any call can fail with a "cluster repartition", "session security" or "session closed" error.

If a PTDiffusionUpdateConstraint was provided when creating the update stream, the first call to this method may also fail with an "unsatisified constraint" error.

If the update stream was created with one of the "create update stream" methods, the first call to this method may also fail with an "incompatible existing topic" error and it will not fail with a "no such topic" error.

If this method fails all subsequent calls to 'set' or 'validate' will fail with an "invalid update stream" error.

If the task fails, the completionHandler will be called with an error. Common reasons for failure include:

no such topic if there is no topic bound to path.
incompatible topic if updates cannot be applied to the topic, for example if a topic view has bound a reference topic to the path.
incompatible topic state if the topic is managed by a component (such as fan-out) that prohibits updates from the caller.
unsatisfied constraint if the constraint is not satisfied by the topic path.
invalid update stream if the update stream has been invalidated.
invalid topic path if path is not a valid topic path.
invalid topic specification if the specification is invalid, possibly because mandatory properties were not supplied.
topic license limit if the topic could not be added as it would breach a licensing limit.
cluster repartition if the cluster was repartitioning.
session security if the calling session does not have the MODIFY_TOPIC or UPDATE_TOPIC permission for path.
session closed if the session is closed.

Parameters

value	The value to set the topic to.
completionHandler	Block to be called asynchronously on success or failure. If the operation was successful, the `error` argument passed to the block will be `nil` and `result` will be non-`nil`. The completion handler will be called asynchronously on the main dispatch queue.
error	If this method returns `NO` to indicate that an error occurred then this will be populated with the reason for that failure.

Returns: YES on success; or NO if an error occurred, in which case *error will be populated with the failure reason.

Exceptions

NSInvalidArgumentException If either value or completionHandler is nil.

Since: 6.10

- (BOOL) validateWithCompletionHandler:	(PTDiffusionUpdateStreamHandlerBlock)	completionHandler
error:	(NSError **)	error

Validates the update stream.

Update streams are validated lazily when setting the value. This method allows the stream to be validated before a value needs to be set.

If the update stream has not been validated yet, calling this method checks the topic exists, the topic type is correct, the constraint is satisfied and the session has permission to update the topic. Once it has been validated calling this method checks the topic has not been removed, no other stream has been created for the topic, the value of the topic has not been changed by anything else and the session still has permission to update the topic.

This method may fail with an "incompatible existing topic" error if it is the first call to validate, set has not been called and a PTDiffusionTopicSpecification was provided when creating the update stream, otherwise it will never fail with this error.

The first call to this method may fail with a "no such topic" or "incompatible topic" error. Subsequent calls may fail with "invalid update stream". Any call can fail with a "cluster repartition", "session security" or "session closed" error.

If a PTDiffusionUpdateConstraint was provided when creating the update stream, the first call to this method may also fail with an "unsatisified constraint" error.

If the update stream was created with one of the "create update stream" methods, the first call to this method may also fail with an "incompatible existing topic" error and it will not fail with a "no such topic" error.

If this method fails all subsequent calls to 'set' or 'validate' will fail with an "invalid update stream" error.

If the task fails, the completionHandler will be called with an error. Common reasons for failure include:

no such topic if there is no topic bound to path.
incompatible topic if updates cannot be applied to the topic, for example if a topic view has bound a reference topic to the path.
incompatible topic state if the topic is managed by a component (such as fan-out) that prohibits updates from the caller.
unsatisfied constraint if the constraint is not satisfied by the topic path.
invalid update stream if the update stream has been invalidated.
cluster repartition if the cluster was repartitioning.
session security if the calling session does not have the MODIFY_TOPIC or UPDATE_TOPIC permission for path.
session closed if the session is closed.

Parameters

completionHandler	Block to be called asynchronously on success or failure. If the operation was successful, the `error` argument passed to the block will be `nil` and `result` will be non-`nil`. The completion handler will be called asynchronously on the main dispatch queue.
error	If this method returns `NO` to indicate that an error occurred then this will be populated with the reason for that failure.

Returns: YES on success; or NO if an error occurred, in which case *error will be populated with the failure reason.

Exceptions

NSInvalidArgumentException If completionHandler is nil.

Since: 6.3

Property Documentation

- (ObjectType) value

readnonatomicassign

The latest value of the topic set using this update stream, from local cache.

This value reflects the last value that has been set, before it is sent to the server.

If the server rejects a set operation, the topic value will not change and this update stream will be invalidated.

Since: 6.10

Introduction

Properties

Instance Methods

Protected Attributes

Method Documentation

Property Documentation