Bug: `Delay` ignores `delay_msec` when created from XML / `NodeConfig`

[jvanzuijlen]

Bug Description

When using the built-in Delay decorator from XML, the input port delay_msec is ignored.

• Expected behavior: <Delay delay_msec="1500">…</Delay> returns RUNNING for ~1500 ms, then ticks its child and returns the child status.
• Actual behavior: Delay completes immediately (effectively 0 ms) and the child is executed immediately, regardless of the delay_msec value.

This makes the Delay decorator unusable in XML trees (and any NodeConfig-based construction path).

How to reproduce

Option A (recommended): failing unit test (easy to verify)

Create a gtest that builds a tree from XML containing a Delay with delay_msec, then assert it stays RUNNING before the delay and only completes after the delay.

• Reference file to add to: https://github.com/BehaviorTree/BehaviorTree.CPP/tree/46fe51606c00f71e646b7b3575426de39ab1fb9f/tests
• Reference test CMake list: https://github.com/BehaviorTree/BehaviorTree.CPP/blob/46fe51606c00f71e646b7b3575426de39ab1fb9f/tests/CMakeLists.txt

Build and run tests:

cmake -S . -B build
cmake --build build -j
ctest --test-dir build --output-on-failure

Option B: minimal XML (demonstrates end-user impact)

Use any application that loads BehaviorTree.CPP v4 XML and ticks it. A minimal tree is:

<root BTCPP_format="4">
  <BehaviorTree ID="MainTree">
    <Delay delay_msec="1500">
      <AlwaysSuccess/>
    </Delay>
  </BehaviorTree>
</root>

Observed behavior: the tree finishes immediately instead of taking ~1.5 seconds.

Root cause analysis

In DelayNode::tick(), delay_msec is only read if read_parameter_from_ports_ is true:

• BehaviorTree.CPP/src/decorators/delay_node.cpp

  Lines 25 to 33 in 46fe516

  	NodeStatus DelayNode::tick()
  	{
  	if(read_parameter_from_ports_)
  	{
  	if(!getInput("delay_msec", msec_))
  	{
  	throw RuntimeError("Missing parameter [delay_msec] in DelayNode");
  	}
  	}

However, in the DelayNode(const std::string& name, const NodeConfig& config) constructor, read_parameter_from_ports_ is never enabled, and msec_ is initialized to 0:

• BehaviorTree.CPP/src/decorators/delay_node.cpp

  Lines 14 to 16 in 46fe516

  	DelayNode::DelayNode(const std::string& name, const NodeConfig& config)
  	: DecoratorNode(name, config), timer_id_(0), msec_(0)
  	{}

Therefore, when created from XML / NodeConfig, msec_ stays at 0 and the timer is started with 0 ms.

For comparison, TimeoutNode uses the same read_parameter_from_ports_ gating logic:

• BehaviorTree.CPP/src/decorators/timeout_node.cpp

  Lines 18 to 27 in 46fe516

  	NodeStatus TimeoutNode::tick()
  	{
  	if(read_parameter_from_ports_)
  	{
  	if(!getInput("msec", msec_))
  	{
  	throw RuntimeError("Missing parameter [msec] in TimeoutNode");
  	}
  	}

…but it correctly enables the port-reading behavior in its NodeConfig-based construction path (pattern that DelayNode should mirror).

Suggested fix

Enable port-reading in the NodeConfig-based constructor for DelayNode (i.e., ensure read_parameter_from_ports_ is set to true when constructed with a NodeConfig).

This makes <Delay delay_msec="…"> honor the configured delay.

Environment

• OS: Ubuntu 22.04
• Use case: XML trees (BTCPP format 4)
• Commit tested: 46fe516

[facontidavide]

thanks for reporting

[jvanzuijlen]

@facontidavide, when is the next patch release planned?

[facontidavide]

end of the week, 4.9