Return the latest value of the topic set using this update stream.
The returned 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.
This method will throw an Error if called before the first
call to set
the cached value of the topic
Sets the topic to a specified value.
null or undefined can only be passed to the
value parameter when updating string,
int64 or double topics.
When a topic of type string, int64 or double is set to `null` or `undefined` , the topic will be updated to have no value. If a previous value was present subscribers will receive a notification that the new value is `undefined` . New subscribers will not receive a value notification.
the value. Update streams for string, int64, and double
topics accept null or undefined, as described above.
Using null with other topic types is an error and will
result in an Error .
a Result that completes when a response is received from the server.
The first set operation will return a TopicCreationResult indicating whether a new topic was created or it already exists.
If the task fails, the Result will resolve with an
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. If validation fails, the Result
will resolve with an Error.
If this method fails all subsequent calls to set or
validate will resolve with an Error.
a Result that completes when a response is received from the server.
An update stream provides a method 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 constraint. 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 session locks as constraints.
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:
6.2