Remove data race caused by doing sample on rum thread

Sources/Datadog/RUM/RUMVitals/VitalCPUReader.swift

@@ -11,8 +11,8 @@ import UIKit.UIApplication
 internal class VitalCPUReader: SamplingBasedVitalReader {
     /// host_cpu_load_info_count is 4 (tested in iOS 14.4)
     private static let host_cpu_load_info_count = MemoryLayout<host_cpu_load_info>.stride / MemoryLayout<integer_t>.stride
-    private var totalInactiveTicks: natural_t = 0
-    private var utilizedTicksWhenResigningActive: natural_t? = nil
+    private var totalInactiveTicks: UInt64 = 0
+    private var utilizedTicksWhenResigningActive: UInt64? = nil
 
     init(notificationCenter: NotificationCenter = .default) {
         notificationCenter.addObserver(self, selector: #selector(appWillResignActive), name: UIApplication.willResignActiveNotification, object: nil)
@@ -44,7 +44,7 @@ internal class VitalCPUReader: SamplingBasedVitalReader {
         }
     }
 
-    private func readUtilizedTicks() -> natural_t? {
+    private func readUtilizedTicks() -> UInt64? {
         // it must be set to host_cpu_load_info_count_size >= host_cpu_load_info_count
         // implementation: https://github.com/opensource-apple/xnu/blob/master/osfmk/kern/host.c#L425
         var host_cpu_load_info_count_size = mach_msg_type_number_t(Self.host_cpu_load_info_count)
@@ -82,6 +82,6 @@ internal class VitalCPUReader: SamplingBasedVitalReader {
          therefore even at the worst-case, precision isn't lost during this conversion below.
          */
         let userTicks = cpuLoadInfo.cpu_ticks.0
-        return userTicks
+        return UInt64(userTicks)
     }
 }

Sources/Datadog/RUM/RUMVitals/VitalInfoSampler.swift

@@ -63,13 +63,17 @@ internal final class VitalInfoSampler {
         self.refreshRateReader.register(self.refreshRatePublisher)
         self.maximumRefreshRate = maximumRefreshRate
 
-        takeSample()
+        // Schedule reoccuring samples
         let timer = Timer(
             timeInterval: frequency,
             repeats: true
         ) { [weak self] _ in
             self?.takeSample()
         }
+        // Take initial sample
+        RunLoop.main.perform {
+            timer.fire()
+        }
         // NOTE: RUMM-1280 based on my running Example app
         // non-main run loops don't fire the timer.
         // Although i can't catch this in unit tests

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

@@ -42,7 +42,7 @@ class VitalInfoSamplerTests: XCTestCase {
         }
     }
 
-    func testItDoesSamplePeriodicallyWithLowFrequency() {
+    func testItDoesInitialSample() {
         let mockCPUReader = SamplingBasedVitalReaderMock()
         let mockMemoryReader = SamplingBasedVitalReaderMock()
 
@@ -57,7 +57,7 @@ class VitalInfoSamplerTests: XCTestCase {
         mockMemoryReader.vitalData = 321.0
 
         let samplingExpectation = expectation(description: "sampling expectation")
-        DispatchQueue.global().asyncAfter(deadline: .now() + 0.6) {
+        DispatchQueue.global().asyncAfter(deadline: .now() + 0.1) {
             samplingExpectation.fulfill()
         }
 
@@ -67,6 +67,32 @@ class VitalInfoSamplerTests: XCTestCase {
         }
     }
 
+    func testItDoesSamplePeriodicallyWithLowFrequency() {
+        let mockCPUReader = SamplingBasedVitalReaderMock()
+        let mockMemoryReader = SamplingBasedVitalReaderMock()
+
+        let sampler = VitalInfoSampler(
+            cpuReader: mockCPUReader,
+            memoryReader: mockMemoryReader,
+            refreshRateReader: ContinuousVitalReaderMock(),
+            frequency: 0.5
+        )
+
+        mockCPUReader.vitalData = 123.0
+        mockMemoryReader.vitalData = 321.0
+
+        let samplingExpectation = expectation(description: "sampling expectation")
+        DispatchQueue.global().asyncAfter(deadline: .now() + 0.6) {
+            samplingExpectation.fulfill()
+        }
+
+        waitForExpectations(timeout: 1.0) { _ in
+            // 2 samples, initial sample and one periodic sample
+            XCTAssertEqual(sampler.cpu.sampleCount, 2)
+            XCTAssertEqual(sampler.memory.sampleCount, 2)
+        }
+    }
+
     func testItSamplesDataFromBackgroundThreads() {
         // swiftlint:disable implicitly_unwrapped_optional
         var sampler: VitalInfoSampler!