📜 Diagram for Lesson 10: Signals
Visualizing Interactive Workflow Patterns
Signal handling patterns and how external systems can interact with long-running workflows through signals and queries
Signal-Based Workflow Interaction
sequenceDiagram
participant ES as External System
participant TC as Temporal Client
participant TS as Temporal Server
participant W as ApprovalWorkflow
participant A as Activity
Note over ES,A: Signal-Based Workflow Interaction
TC->>TS: Start ApprovalWorkflow
TS->>W: Initialize Workflow
W->>W: Set status = PENDING
W->>W: Workflow.await(approvalReceived || rejected)
Note over W: Workflow waits for signal...
ES->>TC: Query workflow status
TC->>TS: Query getCurrentStatus()
TS->>W: Execute query method
W->>TS: Return "PENDING"
TS->>TC: Status response
TC->>ES: Status: PENDING
Signal Delivery and Processing
sequenceDiagram
participant ES as External System
participant TC as Temporal Client
participant TS as Temporal Server
participant W as ApprovalWorkflow
participant A as Activity
ES->>TC: Send approval signal
TC->>TS: Signal: approve(decision, approver)
TS->>W: Deliver signal to workflow
W->>W: Set approvalReceived = true
W->>W: Set status = APPROVED
W->>W: Workflow.await() condition met
W->>A: Execute post-approval activity
A->>W: Activity completed
W->>W: Complete workflow
Interaction Pattern Categories
graph TB
subgraph "Signal Methods - External Events"
A[Signal Delivery]
B[State Modification]
C[Workflow Continuation]
A --> B --> C
end
subgraph "Query Methods - State Inspection"
D[Query Request]
E[Current State Read]
F[Immediate Response]
D --> E --> F
end
subgraph "Workflow.await() - Event-Driven Logic"
G[Condition Check]
H[Block Until Met]
I[Continue Execution]
G --> H --> I
end
style A fill:#e8f5e8
style D fill:#ffebee
style G fill:#e3f2fd
💡 Key Insights from Signal Flow
Signal Characteristics:
- ✅ Asynchronous delivery - External systems don't wait
- ✅ Persistent in history - Signals are replayed during workflow recovery
- ✅ State modification - Can trigger workflow logic changes
- ✅ Event-driven patterns - Enable reactive workflow behavior
Query Characteristics:
- ✅ Synchronous response - Immediate state visibility
- ✅ No side effects - Read-only operations
- ✅ Not persisted - Don't affect workflow history
- ✅ Real-time monitoring - Current state inspection
Workflow.await() Pattern
Event-Driven Blocking:
flowchart TD
A[Workflow.await() Called] --> B{Condition Met?}
B --Yes--> C[Continue Execution]
B --No--> D[Block and Wait]
D --> E[Signal Received]
E --> F[Update State]
F --> B
style A fill:#e3f2fd
style C fill:#e8f5e8
style D fill:#fff3e0
style E fill:#f3e5f5
Enables workflows to wait for external events without consuming resources
🚀 Production Benefits
This signal pattern provides:
- ✅ Interactive workflows that respond to human decisions
- ✅ Real-time observability through query methods
- ✅ Event-driven architecture for reactive systems
- ✅ Long-running processes that wait for external events
- ✅ Efficient resource usage through conditional blocking
Building responsive, interactive distributed systems! 🎉