class_docstr: A context that helps collecting runtime parameters during compilation.
  
  This context object should be only used by PipelineBuilder during compilation,
  to collect all the RuntimeParameter encountered. For example:
  ```
  tasks = []
  with ParameterContext() as pc:
    for component in components:
      tasks.append(step_builder.StepBuilder(...).build())
      ...
  ```
  Then later on, `pc.parameters` stores the list of all RuntimeParameters
  occurred when building each steps, which can be used to populate
  pipeline_spec.runtime_parameters field.
code: def __init__(self):
      self.parameters = []
  
imports: import threading
  from tfx.orchestration import data_types
label_desc: Use image node_id 1 to create a new ParameterContext object  with example: obj = ParameterContext()