Setup

To setup the example, you must have:

• docker and docker-compose / local Postgres DB
• Java 8 or higher JDK
• IDE with Lombok support
• Maven 3

State machine diagram

                    +--------------+
                    |              |
                    |  NOT_STARTED |
                    |              |
                    +------+-------+
                           |  RUN
                           v
                    +------+-------+
                    |              |
                    |  TASKS_FORK  |
                    |              |
                    +------+-------+
                           |
+--------------------------v----------------------------------+
|                                                  TOOL_TASKS |
| +----------------+                 +-------------------+    |
| |                |                 |                   |    |
| |                |                 |                   |    |
| |    TASK_1      |                 |      TASK_2       |    |
| |                |                 |                   |    |
| +-------+--------+                 +----------+--------+    |
|         |                                     |             |
| +-------v--------+                 +----------v--------+    |
| |                |                 |                   |    |
| |  TASK_1_WORK   |                 |    TASK_2_WORK    |    |
| |                |                 |                   |    |
| |                |                 |                   |    |
| +-------+--------+                 +----------+--------+    |
|         |                                     |             |
| +-------v--------+                 +----------v--------+    |
| |                |                 |                   |    |
| |TASK_1_WORK_MORE|                 | TASK_2_WORK_MORE  |    |
| |                |                 |                   |    |
| |                |                 |                   |    |
| +-------+--------+                 +----------+--------+    |
|         |                                     |             |
| +-------v--------+                 +----------v--------+    |
| |                |                 |                   |    |
| |   TASK_1_END   |                 |    TASK_2_DONE    |    |
| |                |                 |                   |    |
| +----------------+                 +-------------------+    |
+---------------------------+---------------------------------+
                            |                                                                                       <---------+
                            |                                                                                                 |
                    +-------v-------+                                                                                         |
                    |               |                                                                                         +
                    |  TASKS_JOIN   |
                    +-------+-------+
                            |
                    +-------v-------+
                    |               |
                    |      END      |
                    +---------------+

Problem statement

Overview

It appears that the current state of each sub-region is persisted using the parent context (except in the case of initial state). This in turn overwrites the last sub-statemachine state, instead of being additive. This works on explicit persistence of entire SM, so it may be that there might be an issue with context building.

Issues

• Using default configuration (with persistence provided by JpaRepositoryStateMachinePersist), all sub-regions seem to be reset upon restarting the SM. It continues from the fork parent task and re-runs all children.
• It seems that if one of the sub-regions is in end-state and one is not (and persisted as such), the finalization (reaching end-state) of the latter will not trigger transition to join state and SM is stuck.

Expectations

• The expectation is that all sub-regions current states are persisted by default. Once a SM is acquired from persistence source, it should initialize all sub-state current states correctly and begin transitioning
• If one or more forked regions are saved with end-state, restarting parent SM should not inhibit transitioning to join-state, if remaining regions reach end-state.

Steps to reproduce

Running with default configuration

• Run application once with clean DB (set spring.jpa.hibernate.ddl-auto=create). This will kill the SM before transitioning to each sub-region end-state. The current state of both sub-regions should be TASK_<N>_WORK or TASK_<N>_WORK_MORE
• Run the application again, with the modified DB (set spring.jpa.hibernate.ddl-auto=none).
• The sub-regions will rest and log will display Transitioning from TASK_<N> -> TASK_<N>_WORK

Running with explicit persist

• Change statemachine.persist.force flag to true
• Run application once with clean DB (set spring.jpa.hibernate.ddl-auto=create). This will kill the SM before transitioning to each sub-region end-state. The current state of both sub-regions should be TASK_<N>_WORK or TASK_<N>_WORK_MORE
• Run the application again, with the modified DB (set spring.jpa.hibernate.ddl-auto=none).
• The sub-regions will have correct state but do no start [getIds()=[TOOLS_TASKS, TASK_1_WORK, TASK_2_WORK], getClass()=class org.springframework.statemachine.state.RegionState, hashCode()=1171097095, toString()=AbstractState [id=TOOLS_TASKS, pseudoState=org.springframework.statemachine.state.DefaultPseudoState@9e33a6a, deferred=[], entryActions=[], exitActions=[], stateActions=[], regions=[TASK_1_WORK TASK_1_DONE TASK_1_WORK_MORE TASK_1 / TASK_1_WORK / uuid=d5a3d9bf-1a00-4c4a-bd25-06ffb2d85634 / id=test, TASK_2_DONE TASK_2 TASK_2_WORK TASK_2_WORK_MORE / TASK_2_WORK / uuid=c4aea4c1-0571-4cc6-ad64-c990e31ca06e / id=test], submachine=null]],