Channel statistics improvements

submodules/GraphCore/Sources/Helpers/DisplayLinkService.swift

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+//
+//  DisplayLinkService.swift
+//  GraphTest
+//
+//  Created by Andrei Salavei on 4/7/19.
+//  Copyright © 2019 Andrei Salavei. All rights reserved.
+//
+
+import Foundation
+#if os(macOS)
+import Cocoa
+#else
+import UIKit
+#endif
+import CoreGraphics
+
+public protocol DisplayLinkListner: class {
+    func update(delta: TimeInterval)
+}
+
+// DispatchSource mares refreshes more accurate
+class DisplayLinkService {
+    let listners = NSHashTable<AnyObject>.weakObjects()
+    static let shared = DisplayLinkService()
+
+    public func add(listner: DisplayLinkListner) {
+        listners.add(listner)
+        startDisplayLink()
+    }
+
+    public func remove(listner: DisplayLinkListner) {
+        listners.remove(listner)
+
+        if listners.count == 0 {
+            stopDisplayLink()
+        }
+    }
+
+//    private init() {
+//        displayLink.add(to: .main, forMode: .common)
+//        displayLink.preferredFramesPerSecond = 60
+//        displayLink.isPaused = true
+//    }
+//
+//    // MARK: - Display Link
+//    private lazy var displayLink: CADisplayLink! = { CADisplayLink(target: self, selector: #selector(displayLinkDidFire)) } ()
+//    private var previousTickTime = 0.0
+//
+//    private func startDisplayLink() {
+//        guard displayLink.isPaused else {
+//            return
+//        }
+//        previousTickTime = CACurrentMediaTime()
+//        displayLink.isPaused = false
+//    }
+//
+//    @objc private func displayLinkDidFire(_ displayLink: CADisplayLink) {
+//        let currentTime = CACurrentMediaTime()
+//        let delta = currentTime - previousTickTime
+//        previousTickTime = currentTime
+//        let allListners = listners.allObjects
+//        var hasListners = false
+//        for listner in allListners {
+//            (listner as! DisplayLinkListner).update(delta: delta)
+//            hasListners = true
+//        }
+//
+//        if !hasListners {
+//            stopDisplayLink()
+//        }
+//    }
+//
+//    private func stopDisplayLink() {
+//        displayLink.isPaused = true
+//    }
+
+    private init() {
+        dispatchSourceTimer.schedule(deadline: .now() + 1.0 / 60, repeating: 1.0 / 60)
+        dispatchSourceTimer.setEventHandler {
+            DispatchQueue.main.sync {
+                self.fire()
+            }
+        }
+    }
+
+    private var dispatchSourceTimer = DispatchSource.makeTimerSource(flags: [], queue: .global(qos: .userInteractive))
+    private var dispatchSourceTimerStarted: Bool = false
+    private var previousTickTime = 0.0
+
+    private func startDisplayLink() {
+        guard !dispatchSourceTimerStarted else { return }
+        dispatchSourceTimerStarted = true
+        previousTickTime = CACurrentMediaTime()
+        dispatchSourceTimer.resume()
+    }
+
+    private func stopDisplayLink() {
+        guard dispatchSourceTimerStarted else { return }
+        dispatchSourceTimerStarted = false
+        dispatchSourceTimer.suspend()
+    }
+
+    public func fire() {
+        let currentTime = CACurrentMediaTime()
+
+        let delta = currentTime - previousTickTime
+        previousTickTime = currentTime
+        let allListners = listners.allObjects
+        var hasListners = false
+        for listner in allListners {
+            (listner as! DisplayLinkListner).update(delta: delta)
+            hasListners = true
+        }
+
+        if !hasListners {
+            stopDisplayLink()
+        }
+    }
+}