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• The Fork Instruction is offered to fork and to join orders to enable parallel processing in a workflow.
• The Fork Instruction allows to create a number of parallel branches that process any further instructions and jobs.
  
  • Branches can include any number of instructions and jobs.
  • The max. number of parallel branches is limited to 15.
• When an order enters a Fork Instruction then a child order is created for each branch. Each child order will pass the nodes in its branch independently of parallel child orders.
• Child orders can return results to parent orders by passing variables.
• While child orders are running, the parent order waits for its child orders to be completed, i.e. to arrive at the Join Instruction. The parent order therefore is assigned the WAITING state, see JS7 - Order State Transitions.
  • The following options apply to error handling with child orders:
    
    • Default: If a job in a child order's branch fails then the child order is assigned the FAILED state. Such child orders require user intervention to resume execution. When resuming a child order then it can restart from the same or from any previous or later node in the child order's branch. This includes the option to move a child order to the branch end.
      • Note that resuming a child order from its branch end will not modify its FAILED state that is adopted by the parent order.
      • Users who want to force successful execution of a failed child order should resume the child order from a job node that is executed successfully.
    • If a job in a child order's branch fails then the child order terminates immediately and the parent order is put to the FAILED state. This behavior can be activated by use of the Join if Failed flag of the Fork Instruction.
  • Child orders cannot be cancelled as they are required to pass the Join Instruction. Should child orders not be intended to pass the remaining instructions in a branch then a user can resume failed child orders from the Join Instruction.
  • Consider that child orders can take the role of parent orders in nested Fork Instructions.

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• The Workflows View shows three levels of orders: the parent order sitting with the initial Fork Instruction and two levels of child orders passing their respective branches.
• As soon as the inner child orders are completed then the outer level of parent orders continues and completes respectively.

Passing Variables from Fork Branches

Jobs in branches of a Fork Instruction can pass results to the parent order by use of variables, see JS7 - Order Variables:

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By default such variables are available to subsequent nodes in the same branch only as they are confined to child order scope.

In addition, the Fork Instruction allows to specify which child order variables should be passed to the parent order.

Download Workflow Example: pdwForkReturnValues.json

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Explanation:

• Each branch of a Fork Instruction allows to specify a pair of names and values for variables that are passed to the parent order:
  • For the parent order a variable with the given name and value is created.
  • Variable names have to be unique across branches, i.e. no two branches can return the same variable names.
  • Users are free to choose variable names for the parent order and to assign variable values of the child order or constant values.
• The Join Instruction adds any variables declared with branches to the parent order.