import threading

class TaskJournal:
    """State machine for tracking tasks through their asynchronous lifecycle."""
    def __init__(self):
        self.lock = threading.Lock()
        self.tasks = {} # task_id -> { "event": Event, "result": None, "node_id": str }

    def register(self, task_id, node_id=None):
        """Initializes state for a new task and returns its notification event."""
        event = threading.Event()
        with self.lock:
            self.tasks[task_id] = {"event": event, "result": None, "node_id": node_id}
        return event

    def fulfill(self, task_id, result):
        """Processes a result from a node and triggers the waiting thread."""
        with self.lock:
            if task_id in self.tasks:
                self.tasks[task_id]["result"] = result
                self.tasks[task_id]["event"].set()
                return True
        return False

    def get_result(self, task_id):
        """Returns the result associated with the given task ID."""
        with self.lock:
            data = self.tasks.get(task_id)
            return data["result"] if data else None

    def pop(self, task_id):
        """Removes the task's state from the journal."""
        with self.lock:
            return self.tasks.pop(task_id, None)