RUMM-1278 Screen Refresh Rate vitals

Datadog/Datadog.xcodeproj/project.pbxproj

@@ -461,7 +461,9 @@
 		9E58E8E324615EDA008E5063 /* JSONEncoderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9E58E8E224615EDA008E5063 /* JSONEncoderTests.swift */; };
 		9E68FB55244707FD0013A8AA /* ObjcExceptionHandler.m in Sources */ = {isa = PBXBuildFile; fileRef = 9E68FB53244707FD0013A8AA /* ObjcExceptionHandler.m */; };
 		9E68FB56244707FD0013A8AA /* ObjcExceptionHandler.h in Headers */ = {isa = PBXBuildFile; fileRef = 9E68FB54244707FD0013A8AA /* ObjcExceptionHandler.h */; settings = {ATTRIBUTES = (Public, ); }; };
+		9E986C302677B91400D62490 /* VitalRefreshRateReaderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9E986C2F2677B91400D62490 /* VitalRefreshRateReaderTests.swift */; };
 		9E989A4225F640D100235FC3 /* AppStateListenerTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9E989A4125F640D100235FC3 /* AppStateListenerTests.swift */; };
+		9EA3CA6926775A3500B16871 /* VitalRefreshRateReader.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9EA3CA6826775A3500B16871 /* VitalRefreshRateReader.swift */; };
 		9EC8B5DA2668197B000F7529 /* VitalCPUReader.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9EC8B5D92668197B000F7529 /* VitalCPUReader.swift */; };
 		9EC8B5EE2668E4DB000F7529 /* VitalCPUReaderTest.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9EC8B5ED2668E4DB000F7529 /* VitalCPUReaderTest.swift */; };
 		9ED6A6B425F2901800CB2E29 /* AppStateListener.swift in Sources */ = {isa = PBXBuildFile; fileRef = 9ED6A6B325F2901800CB2E29 /* AppStateListener.swift */; };
@@ -1074,8 +1076,10 @@
 		9E58E8E224615EDA008E5063 /* JSONEncoderTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = JSONEncoderTests.swift; sourceTree = "<group>"; };
 		9E68FB53244707FD0013A8AA /* ObjcExceptionHandler.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = ObjcExceptionHandler.m; sourceTree = "<group>"; };
 		9E68FB54244707FD0013A8AA /* ObjcExceptionHandler.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = ObjcExceptionHandler.h; sourceTree = "<group>"; };
+		9E986C2F2677B91400D62490 /* VitalRefreshRateReaderTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VitalRefreshRateReaderTests.swift; sourceTree = "<group>"; };
 		9E989A4125F640D100235FC3 /* AppStateListenerTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppStateListenerTests.swift; sourceTree = "<group>"; };
 		9E9EB37624468CE90002C80B /* Datadog.modulemap */ = {isa = PBXFileReference; lastKnownFileType = "sourcecode.module-map"; path = Datadog.modulemap; sourceTree = "<group>"; };
+		9EA3CA6826775A3500B16871 /* VitalRefreshRateReader.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VitalRefreshRateReader.swift; sourceTree = "<group>"; };
 		9EC8B5D92668197B000F7529 /* VitalCPUReader.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VitalCPUReader.swift; sourceTree = "<group>"; };
 		9EC8B5ED2668E4DB000F7529 /* VitalCPUReaderTest.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VitalCPUReaderTest.swift; sourceTree = "<group>"; };
 		9ED6A6B325F2901800CB2E29 /* AppStateListener.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppStateListener.swift; sourceTree = "<group>"; };
@@ -3070,6 +3074,7 @@
 		B3FC3C0426526EE900DEED9E /* RUMVitals */ = {
 			isa = PBXGroup;
 			children = (
+				9EA3CA6826775A3500B16871 /* VitalRefreshRateReader.swift */,
 				9EC8B5D92668197B000F7529 /* VitalCPUReader.swift */,
 				B3BBBCB0265E71C600943419 /* VitalMemoryReader.swift */,
 				B3BBBCB1265E71C600943419 /* VitalReader.swift */,
@@ -3086,6 +3091,7 @@
 				9EC8B5ED2668E4DB000F7529 /* VitalCPUReaderTest.swift */,
 				B3BBBCBB265E71D100943419 /* VitalMemoryReaderTest.swift */,
 				B3FC3C3B2653A97700DEED9E /* VitalObserverTest.swift */,
+				9E986C2F2677B91400D62490 /* VitalRefreshRateReaderTests.swift */,
 			);
 			path = RUMVitals;
 			sourceTree = "<group>";
@@ -3783,6 +3789,7 @@
 				614E9EB3244719FA007EE3E1 /* BundleType.swift in Sources */,
 				61F3CDA72512144600C816E5 /* UIKitRUMViewsPredicate.swift in Sources */,
 				61133BCE2423979B00786299 /* BatteryStatusProvider.swift in Sources */,
+				9EA3CA6926775A3500B16871 /* VitalRefreshRateReader.swift in Sources */,
 				E13A880C257922EC004FB174 /* EnvironmentSpanIntegration.swift in Sources */,
 				61B038602527247200518F3C /* URLSessionTracingHandler.swift in Sources */,
 				61122ED425B1B84D00F9C7F5 /* RUMEventSanitizer.swift in Sources */,
@@ -3834,6 +3841,7 @@
 				61411B1024EC15AC0012EAB2 /* Casting+RUM.swift in Sources */,
 				61133C622423990D00786299 /* InternalLoggersTests.swift in Sources */,
 				61FF283024BC5E2D000B3D9B /* RUMEventFileOutputTests.swift in Sources */,
+				9E986C302677B91400D62490 /* VitalRefreshRateReaderTests.swift in Sources */,
 				61133C582423990D00786299 /* FileWriterTests.swift in Sources */,
 				61E917D3246546BF00E6C631 /* TracerConfigurationTests.swift in Sources */,
 				61C5A89D24509C1100DA608C /* DDSpanTests.swift in Sources */,

Sources/Datadog/Core/Utils/ValuePublisher.swift

@@ -7,7 +7,7 @@
 import Foundation
 
 /// An observer subscribing to a `ValuePublisher`.
-internal protocol ValueObserver {
+internal protocol ValueObserver: AnyObject {
     associatedtype ObservedValue
 
     /// Notifies this observer on the value change. Called on the publisher's queue.
@@ -23,8 +23,10 @@ internal class ValuePublisher<Value> {
     /// Type erasure for `ValueObserver` type.
     private struct AnyObserver<ObservedValue> {
         let notifyValueChanged: (ObservedValue, ObservedValue) -> Void
+        let object: AnyObject
 
         init<Observer: ValueObserver>(wrapped: Observer) where Observer.ObservedValue == ObservedValue {
+            self.object = wrapped
             self.notifyValueChanged = wrapped.onValueChanged
         }
     }
@@ -82,12 +84,21 @@ internal class ValuePublisher<Value> {
             self.unsafeObservers.append(AnyObserver(wrapped: distinctObserver))
         }
     }
+
+    /// Removes an observer so that it will not be notified on all value changes anymore.
+    func unsubscribe<Observer: ValueObserver>(_ observer: Observer) where Observer.ObservedValue == Value {
+        concurrentQueue.async(flags: .barrier) {
+            self.unsafeObservers.removeAll { existingObserver in
+                return existingObserver.object === observer
+            }
+        }
+    }
 }
 
 // MARK: - Helpers
 
 /// `ValueObserver` wrapper which notifies the wrapped observer only on distinct changes of the `Equatable` value.
-private struct DistinctValueObserver<EquatableValue: Equatable>: ValueObserver {
+private class DistinctValueObserver<EquatableValue: Equatable>: ValueObserver {
     private let wrappedOnValueChanged: (EquatableValue, EquatableValue) -> Void
 
     init<WrappedObserver: ValueObserver>(wrapped: WrappedObserver) where WrappedObserver.ObservedValue == EquatableValue {

Sources/Datadog/CrashReporting/CrashContext/CrashContextProvider.swift

@@ -24,12 +24,17 @@ internal class CrashContextProvider: CrashContextProviderType {
     }
 
     /// Observes changes to a particular `Value` in the `CrashContext` and manages its updates.
-    private struct ContextValueUpdater<Value>: ValueObserver {
+    private class ContextValueUpdater<Value>: ValueObserver {
         let queue: DispatchQueue
         let update: (Value) -> Void
 
+        init(queue: DispatchQueue, update: @escaping (Value) -> Void) {
+            self.queue = queue
+            self.update = update
+        }
+
         func onValueChanged(oldValue: Value, newValue: Value) {
-            queue.async { update(newValue) }
+            queue.async { self.update(newValue) }
         }
     }
 

Sources/Datadog/RUM/RUMVitals/VitalObserver.swift

@@ -10,7 +10,7 @@ import Foundation
 internal class VitalObserver: ValueObserver {
     let listener: VitalListener
 
-    private var vitalInfo = VitalInfo(
+    private(set) var vitalInfo = VitalInfo(
         sampleCount: 0,
         minValue: Double.greatestFiniteMagnitude,
         maxValue: -Double.greatestFiniteMagnitude,

Sources/Datadog/RUM/RUMVitals/VitalRefreshRateReader.swift

@@ -0,0 +1,86 @@
+/*
+ * Unless explicitly stated otherwise all files in this repository are licensed under the Apache License Version 2.0.
+ * This product includes software developed at Datadog (https://www.datadoghq.com/).
+ * Copyright 2019-2020 Datadog, Inc.
+ */
+
+import Foundation
+import UIKit
+
+/// A class reading the refresh rate (frames per second) of the main screen
+internal class VitalRefreshRateReader {
+    private let valuePublisher = ValuePublisher(initialValue: 0.0)
+
+    private var displayLink: CADisplayLink?
+    private var lastFrameTimestamp: CFTimeInterval?
+
+    init(notificationCenter: NotificationCenter = .default) {
+        notificationCenter.addObserver(
+            self,
+            selector: #selector(appWillResignActive),
+            name: UIApplication.willResignActiveNotification,
+            object: nil
+        )
+        notificationCenter.addObserver(
+            self,
+            selector: #selector(appDidBecomeActive),
+            name: UIApplication.didBecomeActiveNotification,
+            object: nil
+        )
+
+        start()
+    }
+
+    deinit {
+        stop()
+    }
+
+    /// `VitalRefreshRateReader` keeps pushing data to its `observers` at every new frame.
+    /// - Parameter observer: receiver of refresh rate per frame.
+    func register(_ observer: VitalObserver) {
+        valuePublisher.subscribe(observer)
+    }
+
+    /// `VitalRefreshRateReader` stops pushing data to `observer` once unregistered.
+    /// - Parameter observer: already added observer; otherwise nothing happens.
+    func unregister(_ observer: VitalObserver) {
+        valuePublisher.unsubscribe(observer)
+    }
+
+    // MARK: - Private
+
+    @objc
+    private func displayTick(link: CADisplayLink) {
+        if let lastTimestamp = self.lastFrameTimestamp {
+            let frameDuration = link.timestamp - lastTimestamp
+            let currentFPS = 1.0 / frameDuration
+            valuePublisher.publishAsync(currentFPS)
+        }
+        lastFrameTimestamp = link.timestamp
+    }
+
+    private func start() {
+        if displayLink != nil {
+            return
+        }
+
+        displayLink = CADisplayLink(target: self, selector: #selector(displayTick(link:)))
+        displayLink?.add(to: .main, forMode: .default)
+    }
+
+    private func stop() {
+        displayLink?.invalidate()
+        displayLink = nil
+        lastFrameTimestamp = nil
+    }
+
+    @objc
+    private func appWillResignActive() {
+        stop()
+    }
+
+    @objc
+    private func appDidBecomeActive() {
+        start()
+    }
+}

Tests/DatadogTests/Datadog/RUM/RUMVitals/VitalRefreshRateReaderTests.swift

@@ -0,0 +1,78 @@
+/*
+ * Unless explicitly stated otherwise all files in this repository are licensed under the Apache License Version 2.0.
+ * This product includes software developed at Datadog (https://www.datadoghq.com/).
+ * Copyright 2019-2020 Datadog, Inc.
+ */
+
+import XCTest
+import UIKit
+@testable import Datadog
+
+class VitalRefreshRateReaderTests: XCTestCase {
+    private let mockNotificationCenter = NotificationCenter()
+
+    func testHighAndLowRefreshRates() {
+        let reader = VitalRefreshRateReader(notificationCenter: mockNotificationCenter)
+        let observer_view1 = VitalObserver(listener: VitalListenerMock())
+        let observer_view2 = VitalObserver(listener: VitalListenerMock())
+
+        // View1 has simple UI, high FPS expected
+        reader.register(observer_view1)
+
+        // Wait without blocking UI thread
+        let expectation1 = expectation(description: "async expectation for first observer")
+        DispatchQueue.global().asyncAfter(deadline: .now() + 0.5) {
+            expectation1.fulfill()
+        }
+
+        waitForExpectations(timeout: 1.0) { _ in
+            XCTAssertGreaterThan(observer_view1.vitalInfo.sampleCount, 0)
+            XCTAssertGreaterThan(UIScreen.main.maximumFramesPerSecond, Int(observer_view1.vitalInfo.maxValue))
+            XCTAssertGreaterThan(observer_view1.vitalInfo.minValue, 0.0)
+        }
+
+        reader.unregister(observer_view1)
+        // View2 has complex UI, lower FPS expected
+        reader.register(observer_view2)
+
+        // Wait without blocking UI thread
+        let expectation2 = expectation(description: "async expectation for second observer")
+        DispatchQueue.global().asyncAfter(deadline: .now() + 0.5) {
+            expectation2.fulfill()
+        }
+        waitForExpectations(timeout: 1.0) { _ in }
+
+        // Block UI thread
+        Thread.sleep(forTimeInterval: 1.5)
+
+        XCTAssertGreaterThan(observer_view2.vitalInfo.sampleCount, 0)
+        XCTAssertGreaterThan(observer_view1.vitalInfo.meanValue, observer_view2.vitalInfo.meanValue)
+    }
+
+    func testAppStateHandling() {
+        let reader = VitalRefreshRateReader(notificationCenter: mockNotificationCenter)
+        let observer = VitalObserver(listener: VitalListenerMock())
+
+        mockNotificationCenter.post(name: UIApplication.didBecomeActiveNotification, object: nil)
+        mockNotificationCenter.post(name: UIApplication.willResignActiveNotification, object: nil)
+        reader.register(observer)
+
+        let expectation1 = expectation(description: "async expectation for first observer")
+        DispatchQueue.global().asyncAfter(deadline: .now() + 0.5) {
+            expectation1.fulfill()
+        }
+
+        waitForExpectations(timeout: 1.0) { _ in }
+        XCTAssertEqual(observer.vitalInfo.sampleCount, 0)
+
+        mockNotificationCenter.post(name: UIApplication.didBecomeActiveNotification, object: nil)
+
+        let expectation2 = expectation(description: "async expectation for second observer")
+        DispatchQueue.global().asyncAfter(deadline: .now() + 0.5) {
+            expectation2.fulfill()
+        }
+
+        waitForExpectations(timeout: 1.0) { _ in }
+        XCTAssertGreaterThan(observer.vitalInfo.sampleCount, 0)
+    }
+}