Extension Points

Paramixel does not currently expose a large separate SPI package.

The main supported extension points are the public core APIs:

Custom actions

Implement Action directly or extend AbstractAction.

For most custom actions, extending AbstractAction is the simplest option because it provides:

• ID generation (4-character unique string) and name handling
• parent tracking (atomic, one-time-only assignment with self-parent and re-assignment checks)
• default skip(Context) behavior
• shared child validation for composite actions

Action hierarchy

Action (interface)
  └─ AbstractAction (abstract)
       ├─ LeafAction (abstract) — no children
       │    ├─ Direct — takes Executable callback
       │    └─ Noop — always passes
       └─ BranchAction (abstract) — has children
           ├─ Sequential
           ├─ DependentSequential
           ├─ RandomSequential
           ├─ DependentRandomSequential
           ├─ Parallel
           └─ Lifecycle

• LeafAction provides skip() that returns a single skipped result
• BranchAction provides skip() that recursively skips all children and computeStatus(List<Result>) for computing parent status from children

If you implement Action directly, your implementation must:

• maintain its own parent reference
• implement setParent(Action parent) using atomic compare-and-set or equivalent synchronization
• reject null parents
• reject setting itself as its own parent
• reject assigning a second parent (must be thread-safe)

In both cases, custom actions implement execute(Context). Use direct Action implementations only when you need full control over the action model.

Pre-execution validation

When implementing custom composite actions, be aware that DefaultRunner validates the action tree before execution:

• CycleDetector rejects parent-child cycles — throws CycleDetectedException
• DeadlockDetector rejects nested Parallel configurations that would cause thread starvation — throws DeadlockDetected

Custom actions that introduce cycles or deeply nested parallel structures will be caught by these validators.

Custom listeners

Implement Listener and pass it to Runner.builder().listener(...).

All callbacks receive Result (not Context + Action):

Listener listener = new Listener() {
    @Override
    public void beforeAction(Result result) {
        System.out.println("starting " + result.getAction().getName());
    }
};

Custom runner configuration

Use Runner.builder() to provide:

• configuration
• listener
• executor service

Discovery selection

Use Resolver and Selector to control which factories are discovered.

Selector.builder() supports:

• packageMatch(String regex) / packageOf(Class<?>)
• classMatch(String regex) / classOf(Class<?>)
• tagMatch(String regex) — matches @Paramixel.Tag values

If you need deeper framework integration, treat the current public types in org.paramixel.core as the supported boundary.