refactor: introduce dedicated refresh queue

.github/workflows/pull-request.yml

@@ -23,4 +23,4 @@ jobs:
     - name: Build
       run: swift build -v
     - name: Run unit tests
-      run: swift test -v
+      run: swift test -v

Sources/FeaturevisorSDK/Instance+Refresh.swift

@@ -52,53 +52,47 @@ extension FeaturevisorInstance {
     }
 
     public func startRefreshing() {
+        refreshQueue.async { [weak self] in
+            guard let self else { return }
 
-        guard datafileUrl != nil else {
-            logger.error("cannot start refreshing since `datafileUrl` is not provided")
-            return
-        }
+            guard self.datafileUrl != nil else {
+                self.logger.error("cannot start refreshing since `datafileUrl` is not provided")
+                return
+            }
 
-        guard timer == nil else {
-            logger.warn("refreshing has already started")
-            return
-        }
+            guard self.refreshTimer == nil else {
+                self.logger.warn("refreshing has already started")
+                return
+            }
 
-        guard let refreshInterval else {
-            logger.warn("no `refreshInterval` option provided")
-            return
-        }
+            guard let refreshInterval = self.refreshInterval else {
+                self.logger.warn("no `refreshInterval` option provided")
+                return
+            }
 
-        DispatchQueue.global()
-            .async { [weak self] in
-                self?.timer = Timer.scheduledTimer(
-                    withTimeInterval: TimeInterval(refreshInterval),
-                    repeats: true
-                ) { _ in
-                    self?.refresh()
-                }
-
-                if let timer = self?.timer {
-                    RunLoop.current.add(timer, forMode: .common)
-                    RunLoop.current.run()
-                }
+            let timer = DispatchSource.makeTimerSource(queue: self.refreshQueue)
+            timer.schedule(deadline: .now() + refreshInterval, repeating: refreshInterval)
+            timer.setEventHandler { [weak self] in
+                self?.refresh()
             }
+            timer.resume()
+
+            self.refreshTimer = timer
+        }
     }
 
     public func stopRefreshing() {
+        refreshQueue.async { [weak self] in
+            guard let self else { return }
 
-        DispatchQueue.global()
-            .async { [weak self] in
-
-                guard let intervalId = self?.timer else {
-                    self?.logger.warn("refreshing has not started yet")
-                    return
-                }
-
-                intervalId.invalidate()
-                self?.timer = nil
+            guard let timer = self.refreshTimer else {
+                self.logger.warn("refreshing has not started yet")
+                return
             }
 
-        logger.warn("refreshing has stopped")
+            timer.cancel()
+            self.refreshTimer = nil
+            self.logger.warn("refreshing has stopped")
+        }
     }
-
 }

Sources/FeaturevisorSDK/Instance.swift

@@ -185,7 +185,8 @@ public class FeaturevisorInstance {
     internal var stickyFeatures: StickyFeatures?
 
     // internally created
-    internal var timer: Timer?
+    internal let refreshQueue = DispatchQueue(label: "com.featurevisor.datafile.refresh")
+    internal var refreshTimer: DispatchSourceTimer?
     internal var datafileReader: DatafileReader
     internal var emitter: Emitter
     internal var statuses: Statuses

Tests/FeaturevisorSDKTests/InstanceTests.swift

@@ -986,10 +986,12 @@ class FeaturevisorInstanceTests: XCTestCase {
     func testShouldStopRefreshing() {
 
         // GIVEN
-        var isRefreshingStopped = false
         var revision = 1
         let refreshInterval = 1.0
 
+        let readyExpectation = expectation(description: "sdk_ready")
+        let stoppedExpectation = expectation(description: "refreshing_stopped")
+
         MockURLProtocol.requestHandler = { request in
             let jsonString =
                 "{\"schemaVersion\":\"1\",\"revision\":\"\(revision)\",\"attributes\":[],\"segments\":[],\"features\":[]}"
@@ -1007,25 +1009,27 @@ class FeaturevisorInstanceTests: XCTestCase {
         options.sessionConfiguration.protocolClasses = [MockURLProtocol.self]
         options.refreshInterval = refreshInterval
         options.datafileUrl = "https://featurevisor-awesome-url.com/tags.json"
+        options.onReady = { _ in
+            readyExpectation.fulfill()
+        }
         options.logger = createLogger { level, message, details in
             guard case .warn = level else {
                 return
             }
 
             if message.contains("refreshing has stopped") {
-                isRefreshingStopped = true
+                stoppedExpectation.fulfill()
             }
         }
 
         // WHEN
         let sdk = try! createInstance(options: options)
-
-        XCTAssertEqual(isRefreshingStopped, false)
+        wait(for: [readyExpectation], timeout: 1.0)
 
         sdk.stopRefreshing()
 
         // THEN
-        XCTAssertEqual(isRefreshingStopped, true)
+        wait(for: [stoppedExpectation], timeout: 1.0)
     }
 
     func testSetDatafileByValidJSON() {