Parallel states and examples - CloudFlow - Alibaba Cloud Documentation Center

This topic describes Parallel states and provides related examples.

Overview

Parallel states are used to execute multiple child states in parallel. A Parallel state defines multiple branches, each of which contains a series of child states.

When a Parallel state is executed, the child states contained in all branches are concurrently executed. After all branches are executed, a map[string]any output that contains the results of all branches is returned by default. Then, the system uses the output constructor to further process the results.

Note

You can configure up to 50 branches for a Parallel state.

The following table describes the attributes that a Parallel state contains.

Attribute	Data type	Required	Description	Example
Name	string	Yes	The name of the state.	my-state-name
Description	string	No	The description of the state.	describe it here
Type	string	Yes	The type of the state.	Parallel
InputConstructor	map[string]any	No	The input constructor.	See Inputs and outputs.
Branches	ParallelBranch	Yes	The branches to be executed in parallel.	See ParallelBranch.
OutputConstructor	map[string]any	No	The output constructor.	See the State OutputConstructor section of the "Inputs and outputs" topic.
Next	string	No	The next state that is executed after the current state is complete. If the End attribute is true, you do not need to specify this attribute.	my-next-state
End	bool	No	Specifies whether to end the current scope.	true
Retry	Retry	No	The information about the retry policy.	See Error handling.
Catch	Catch	No	The information about the catch policy.	See Error handling.

ParallelBranch

Attribute	Data type	Required	Description	Example
States	array	Yes	The array of states that are contained in the workflow.	See the Use case section of this topic.
StartAt	string	Yes	The state from which the execution of the workflow starts.	my start task

Use case

The following sample workflow defines a Parallel state. The Parallel state contains two branches, and each branch contains a Pass child state.

Type: StateMachine
Name: my-wkfl
SpecVersion: v1
StartAt: Parallel1
States:
  - Type: Parallel
    Name: Parallel1
    End: true
    Branches:
      - StartAt: Pass1
        States:
          - Type: Pass
            Name: Pass1
            End: true
            OutputConstructor:
              FieldA: 123
      - StartAt: Pass2
        States:
          - Type: Pass
            InputConstructor:
              FieldA: 321
            Name: Pass2
            End: true

The following code shows the output of the Pass1 child state.
```
{
    "FieldA": 123
}
```
The following code shows the output of the Pass2 child state.
```
{
    "FieldA": 321
}
```
The following code shows the output of the Parallel1 state. Default names are assigned to the branches. The output is constructed in the format of Branch<Index>.
```
{
    "Branch0": {
        "FieldA": 123
    },
    "Branch1": {
        "FieldA": 321
    }
}
```