Parallel Nodes

Parallel nodes execute all their children concurrently, but not in separate threads. All children are ticked in sequence within a single tick of the tree, and multiple children may be in the RUNNING state at the same time.

caution

"Parallel" refers to the fact that multiple children can be RUNNING concurrently. The children are still ticked sequentially within the same thread. For actual multi-threaded execution, children must be asynchronous nodes internally.

Currently the framework provides two kinds of nodes:

• Parallel
• ParallelAll

The Parallel Nodes are the only ones that can have multiple children RUNNING at the same time.

Parallel

It is completed when either the SUCCESS or FAILURE threshold is reached. Any remaining running children are halted.

Port	Type	Default	Description
success_count	InputPort<int>	-1	Number of children that must succeed to return SUCCESS.
failure_count	InputPort<int>	1	Number of children that must fail to return FAILURE.

Threshold values support Python-style negative indexing: -1 is equivalent to the total number of children. For example, with 4 children, success_count="-1" means all 4 must succeed.

Default behavior (success_count=-1, failure_count=1): all children must succeed; if any single child fails, the node returns FAILURE.

<Parallel success_count="2" failure_count="2">
    <ActionA/>
    <ActionB/>
    <ActionC/>
</Parallel>

In this example with 3 children:

• If 2 children return SUCCESS (before 2 fail), the node returns SUCCESS.
• If 2 children return FAILURE (before 2 succeed), the node returns FAILURE.
• Remaining RUNNING children are halted when either threshold is reached.

ParallelAll

Unlike Parallel, the ParallelAll node always executes ALL children to completion. It never halts children early. This is useful when you need all side effects to complete.

Port	Type	Default	Description
max_failures	InputPort<int>	1	Maximum number of child failures allowed before returning FAILURE.

• Returns SUCCESS if the number of FAILUREs is less than max_failures.
• Returns FAILURE if the number of FAILUREs equals or exceeds max_failures.
• Use max_failures="-1" (number of children) to always return SUCCESS regardless of child results.

<ParallelAll max_failures="2">
    <ActionA/>
    <ActionB/>
    <ActionC/>
</ParallelAll>

Parallel vs ParallelAll

Feature	Parallel	ParallelAll
Early termination	Yes (halts children when threshold reached)	No (always runs all children)
Success threshold	Configurable (success_count)	All non-failed children
Failure threshold	Configurable (failure_count)	Configurable (max_failures)
Use case	Race conditions, N-of-M success	All tasks must attempt completion