This optional callback is called during a single-threaded phase where memory is usually allocated in preparation
for the multi-threaded evaluation phase. For example, we can use this callback to attach some pre-thread data to
a node. The BeginEvaluate callback uses the ICENodeContext
object to store the user data allocated.
| Warning |
The input and output ports cannot be accessed through the ICENodeContext
object in this callback, except when the node is set as an element generator and then only input ports are available.
The Evaluate callback can access both input and output port information.
|
| Note |
The user data stored in BeginEvaluate or Init is always accessible from
the Evaluate callback. However, unless the custom node threading mode
is single-threading, the Context::PutUserData property
cannot be used from the Evaluate callback.
|