Add os_signpost logs for render() and Workflow and Worker lifecycle

swift/Workflow/Sources/SubtreeManager.swift

@@ -204,7 +204,11 @@ extension WorkflowNode.SubtreeManager {
         func makeSink<Action>(of actionType: Action.Type) -> Sink<Action> where Action: WorkflowAction, WorkflowType == Action.WorkflowType {
             let reusableSink = sinkStore.findOrCreate(actionType: Action.self)
 
+            let signpostRef = NSObject()
+
             let sink = Sink<Action> { action in
+                WorkflowLogger.logSinkEvent(ref: signpostRef, action: action)
+
                 reusableSink.handle(action: action)
             }
 
@@ -407,11 +411,25 @@ extension WorkflowNode.SubtreeManager {
             self.outputMap = outputMap
             super.init(eventPipe: eventPipe)
 
+            let signpostRef = NSObject()
+            WorkflowLogger.logWorkerStartedRunning(ref: signpostRef, workerType: W.self)
+
             signalProducer
                 .take(during: lifetime)
                 .observe(on: QueueScheduler.workflowExecution)
-                .startWithValues { [weak self] output in
-                    self?.handle(output: output)
+                .start { [weak self] event in
+                    switch event {
+                    case .value(let output):
+                        WorkflowLogger.logWorkerOutput(ref: signpostRef, output: output)
+
+                        self?.handle(output: output)
+                    case .completed:
+                        WorkflowLogger.logWorkerFinishedRunning(ref: signpostRef)
+                    case .interrupted:
+                        WorkflowLogger.logWorkerFinishedRunning(ref: signpostRef, status: "Interrupted")
+                    case .failed:
+                        WorkflowLogger.logWorkerFinishedRunning(ref: signpostRef, status: "Failed")
+                    }
                 }
         }
 

swift/Workflow/Sources/WorkflowLogger.swift

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2020 Square Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import os.signpost
+
+fileprivate extension OSLog {
+    static let workflow = OSLog(subsystem: "com.squareup.Workflow", category: "Workflow")
+    static let worker = OSLog(subsystem: "com.squareup.Workflow", category: "Worker")
+}
+
+// MARK: -
+
+final class WorkflowLogger {
+    // MARK: Workflows
+
+    static func logWorkflowStarted<WorkflowType>(ref: WorkflowNode<WorkflowType>) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .workflow, object: ref)
+            os_signpost(.begin, log: .workflow, name: "Alive", signpostID: signpostID,
+                        "Workflow: %{public}@", String(describing: WorkflowType.self))
+        }
+    }
+
+    static func logWorkflowFinished<WorkflowType>(ref: WorkflowNode<WorkflowType>) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .workflow, object: ref)
+            os_signpost(.end, log: .workflow, name: "Alive", signpostID: signpostID)
+        }
+    }
+
+    static func logSinkEvent<Action>(ref: AnyObject, action: Action) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .workflow, object: ref)
+            os_signpost(.event, log: .workflow, name: "Sink Event", signpostID: signpostID,
+                        "Event: %@", String(describing: action))
+        }
+    }
+
+    // MARK: Rendering
+
+    static func logWorkflowStartedRendering<WorkflowType>(ref: WorkflowNode<WorkflowType>) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .workflow, object: ref)
+            os_signpost(.begin, log: .workflow, name: "Render", signpostID: signpostID,
+                        "Render Workflow: %{public}@", String(describing: WorkflowType.self))
+        }
+    }
+
+    static func logWorkflowFinishedRendering<WorkflowType>(ref: WorkflowNode<WorkflowType>) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .workflow, object: ref)
+            os_signpost(.end, log: .workflow, name: "Render", signpostID: signpostID)
+        }
+    }
+
+    // MARK: - Workers
+
+    static func logWorkerStartedRunning<WorkerType>(ref: AnyObject, workerType: WorkerType.Type) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .worker, object: ref)
+            os_signpost(.begin, log: .worker, name: "Running", signpostID: signpostID,
+                        "Worker: %{public}@", String(describing: WorkerType.self))
+        }
+    }
+
+    static func logWorkerFinishedRunning(ref: AnyObject, status: StaticString? = nil) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .worker, object: ref)
+            if let status = status {
+                os_signpost(.end, log: .worker, name: "Running", signpostID: signpostID, status)
+            } else {
+                os_signpost(.end, log: .worker, name: "Running", signpostID: signpostID)
+            }
+        }
+    }
+
+    static func logWorkerOutput<Output>(ref: AnyObject, output: Output) {
+        if #available(iOS 12.0, macOS 10.14, *) {
+            let signpostID = OSSignpostID(log: .worker, object: ref)
+            os_signpost(.event, log: .worker, name: "Worker Event", signpostID: signpostID,
+                        "Event: %@", String(describing: output))
+        }
+    }
+}

swift/Workflow/Sources/WorkflowNode.swift

@@ -34,11 +34,17 @@ final class WorkflowNode<WorkflowType: Workflow> {
         self.workflow = workflow
         self.state = workflow.makeInitialState()
 
+        WorkflowLogger.logWorkflowStarted(ref: self)
+
         subtreeManager.onUpdate = { [weak self] output in
             self?.handle(subtreeOutput: output)
         }
     }
 
+    deinit {
+        WorkflowLogger.logWorkflowFinished(ref: self)
+    }
+
     /// Handles an event produced by the subtree manager
     private func handle(subtreeOutput: SubtreeManager.Output) {
         let output: Output
@@ -71,6 +77,12 @@ final class WorkflowNode<WorkflowType: Workflow> {
     }
 
     func render() -> WorkflowType.Rendering {
+        WorkflowLogger.logWorkflowStartedRendering(ref: self)
+
+        defer {
+            WorkflowLogger.logWorkflowFinishedRendering(ref: self)
+        }
+
         return subtreeManager.render { context in
             workflow
                 .render(