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Hello,

I need to display realtime chart with 20 series of data. My data is arriving at 500Hz. When I’m displaying this data, I find that after a while SciChart hangs with what appears to be a deadlock.

I’ve read as much as I can find about realtime graphing with SciChart and I started with tutorial 4 – Adding Realtime Updates. This article (https://www.scichart.com/questions/wpf/is-xydataseries-safe-to-being-changed-in-a-separate-thread) suggests that SciChart is thread safe so I tried using a second thread to feed data into a graph. My only change was to move from the main thread timer in the example to a GCD timer running at 500Hz. With this, I’m easily able to reproduce the deadlock in around 1.5 seconds.

Here is the main thread which is attempting to render:

Thread 1 Queue : com.apple.main-thread (serial)
#0  0x0000000192bc8c20 in __psynch_rw_rdlock ()
#1  0x0000000192ae4864 in _pthread_rwlock_lock_wait ()
#2  0x0000000192ae47fc in _pthread_rwlock_lock_slow$VARIANT$mp ()
#3  0x0000000104a93828 in -[SCIRenderableSeriesLock initWithRenderableSeries:] ()
#4  0x0000000104ab742c in -[SCIRenderSurfaceRenderer p_SCI_updateCoreData:renderPassState:viewportSize:] ()
#5  0x0000000104ab6f4c in -[SCIRenderSurfaceRenderer p_SCI_renderLoop:assetManager:renderPassState:] ()
#6  0x0000000104ab6dc4 in -[SCIRenderSurfaceRenderer onDrawWithContext:andAssetManager:] ()
#7  0x00000001049c50c0 in -[SCIRenderSurfaceDrawable2D drawFrameIn:withDrawableSize:] ()
#8  0x0000000104ad4db8 in -[SCITwisterRendererBase drawFrameIn:withDrawableSize:] ()
#9  0x00000001049e56c8 in -[SCIMetalRenderer drawFrameIn:withDrawableSize:] ()
#10 0x0000000104a25b70 in -[SCIMetalRenderSurfaceBase draw] ()
#11 0x00000001999861ec in -[CALayer display] ()
#12 0x00000001999984d4 in CA::Layer::layout_and_display_if_needed(CA::Transaction*) ()
#13 0x00000001998e11d8 in CA::Context::commit_transaction(CA::Transaction*, double) ()
#14 0x000000019990ab78 in CA::Transaction::commit() ()
#15 0x000000019990b58c in CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) ()
#16 0x0000000192d50fbc in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ ()
#17 0x0000000192d4beb0 in __CFRunLoopDoObservers ()
#18 0x0000000192d4c32c in __CFRunLoopRun ()
#19 0x0000000192d4bc38 in CFRunLoopRunSpecific ()
#20 0x000000019d39a38c in GSEventRunModal ()
#21 0x0000000196e7c444 in UIApplicationMain ()
#22 0x00000001042cc478 in main at /Users/mall/Downloads/SciChart.iOS.Examples-SciChart_v3_Release/tutorials/tutorials-2d/Tutorial 04 - Adding Realtime Updates/Tutorial 04 - Adding Realtime Updates/AppDelegate.swift:5
#23 0x0000000192bd38f0 in start ()

and here is my worker thread adding data to a series:

Thread 11 Queue : com.apple.root.default-qos.overcommit (concurrent)
#0  0x0000000192bc8c20 in __psynch_rw_rdlock ()
#1  0x0000000192ae4864 in _pthread_rwlock_lock_wait ()
#2  0x0000000192ae47fc in _pthread_rwlock_lock_slow$VARIANT$mp ()
#3  0x0000000104ac1518 in -[SCIXDataSeries p_SCI_searchDataIndexOn:xMinAsDouble:xMaxAsDouble:downSearchMode:upSearchMode:] ()
#4  0x0000000104ac1368 in -[SCIXDataSeries getIndicesXRange:xMinAsDouble:xMaxAsDouble:isCategoryAxis:] ()
#5  0x0000000104ac1b34 in -[SCIXDataSeries getWindowYRangeWithXCoordCalc:getPositiveRange:] ()
#6  0x0000000104aceddc in -[SCIRenderableSeriesBase getYRange:positive:] ()
#7  0x00000001049b25ac in -[SCIRangeCalculationHelper2DBase getWindowedYRangeWithXCalculators:] ()
#8  0x0000000104a05f84 in -[SCIAxisBase getWindowedYRangeWithXRanges:] ()
#9  0x00000001049f4184 in -[SCIChartSurface p_SCI_zoomExtentsYWithCalculators:andDuration:] ()
#10 0x00000001049f3d14 in -[SCIChartSurface p_SCI_zoomExtentsWithDuration:] ()
#11 0x00000001042c79e8 in closure #1 in ViewController.handleTimer() at /Users/mall/Downloads/SciChart.iOS.Examples-SciChart_v3_Release/tutorials/tutorials-2d/Tutorial 04 - Adding Realtime Updates/Tutorial 04 - Adding Realtime Updates/ViewController.swift:84
#12 0x00000001042c7500 in thunk for @escaping @callee_guaranteed () -> () ()
#13 0x0000000104abdae0 in +[SCIUpdateSuspender usingWithSuspendable:withBlock:] ()
#14 0x00000001042c7824 in ViewController.handleTimer() at /Users/mall/Downloads/SciChart.iOS.Examples-SciChart_v3_Release/tutorials/tutorials-2d/Tutorial 04 - Adding Realtime Updates/Tutorial 04 - Adding Realtime Updates/ViewController.swift:79
#15 0x00000001042c9250 in partial apply ()
#16 0x00000001042cb1e4 in closure #1 in closure #1 in RepeatingTimer.timer.getter at /Users/mall/Downloads/SciChart.iOS.Examples-SciChart_v3_Release/tutorials/tutorials-2d/Tutorial 04 - Adding Realtime Updates/Tutorial 04 - Adding Realtime Updates/RepeatingTimer.swift:26
#17 0x00000001042c7500 in thunk for @escaping @callee_guaranteed () -> () ()
#18 0x0000000107093730 in _dispatch_client_callout ()
#19 0x0000000107096390 in _dispatch_continuation_pop ()
#20 0x00000001070a9614 in _dispatch_source_invoke ()
#21 0x00000001070a4d74 in _dispatch_root_queue_drain ()
#22 0x00000001070a5698 in _dispatch_worker_thread2 ()
#23 0x0000000192aeab38 in _pthread_wqthread ()

Here is my version of the ViewController class from Tutorial 4 with the GCD timer (note that it uses RepeatingTimer class found here: https://gist.github.com/danielgalasko/1da90276f23ea24cb3467c33d2c05768) – my changes are marked with the //MALL comment:

import UIKit
import SciChart

class ViewController: UIViewController {

    //MALL
    private var timer = RepeatingTimer(timeInterval: 1.0/500.0)

    private let pointsCount = 200
    private var count: Int = 0

    private let lineData = SCIDoubleValues()
    private lazy var lineDataSeries: SCIXyDataSeries = {
        let lineDataSeries = SCIXyDataSeries(xType: .int, yType: .double)
        lineDataSeries.seriesName = "Line Series"
        lineDataSeries.fifoCapacity = 300
        return lineDataSeries
    }()
    private let scatterData = SCIDoubleValues()
    private lazy var scatterDataSeries: SCIXyDataSeries = {
        let scatterDataSeries = SCIXyDataSeries(xType: .int, yType: .double)
        scatterDataSeries.seriesName = "Scatter Series"
        scatterDataSeries.fifoCapacity = 300
        return scatterDataSeries
    }()

    private var surface: SCIChartSurface {
        return view as! SCIChartSurface
    }

    override func loadView() {
        viewRespectsSystemMinimumLayoutMargins = false
        view = SCIChartSurface()
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        let xValues = SCIIntegerValues()
        for i in 0 ..< pointsCount {
            xValues.add(Int32(i))
            lineData.add(sin(Double(i) * 0.1))
            scatterData.add(cos(Double(i) * 0.1))
            count += 1
        }
        lineDataSeries.append(x: xValues, y: lineData)
        scatterDataSeries.append(x: xValues, y: scatterData)

        let lineSeries = SCIFastLineRenderableSeries()
        lineSeries.dataSeries = lineDataSeries

        let pointMarker = SCIEllipsePointMarker()
        pointMarker.fillStyle = SCISolidBrushStyle(colorCode: 0xFF32CD32)
        pointMarker.size = CGSize(width: 10, height: 10)

        let scatterSeries = SCIXyScatterRenderableSeries()
        scatterSeries.dataSeries = scatterDataSeries
        scatterSeries.pointMarker = pointMarker

        let legendModifier = SCILegendModifier()
        legendModifier.orientation = .horizontal
        legendModifier.position = [.bottom, .centerHorizontal]
        legendModifier.margins = UIEdgeInsets(top: 0, left: 0, bottom: 10, right: 0)

        SCIUpdateSuspender.usingWith(self.surface) {
            self.surface.xAxes.add(items: SCINumericAxis())
            self.surface.yAxes.add(items: SCINumericAxis())
            self.surface.renderableSeries.add(items: lineSeries, scatterSeries)
            self.surface.chartModifiers.add(items: SCIPinchZoomModifier(), SCIZoomExtentsModifier())
            self.surface.chartModifiers.add(items: SCIRolloverModifier(), legendModifier)
        }

        //  MALL
        timer.eventHandler = handleTimer
        timer.resume()
    }

    //  MALL
    private func handleTimer() {
        let x = count
        SCIUpdateSuspender.usingWith(surface) {
            self.lineDataSeries.append(x: x, y: sin(Double(x) * 0.1))
            self.scatterDataSeries.append(x: x, y: cos(Double(x) * 0.1))

            // zoom series to fit viewport size into X-Axis direction
            self.surface.zoomExtents()
            self.count += 1
        }
    }
}

Thanks in advance for any help you can offer.

Version
3.1.0.5178
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1
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Hi, Mark.

Thanks for pointing out this bug and provide a reproducible example. We think we’ve found a possible issue and fixed it in ‘3.1.0-nightly.5268’ build. Please, try it and let us know if the issue has gone.

Also, from your code, I see that you update the surface from the background thread. Since SCIChartSurface is UIView under the hood, you will get XCode warning ‘must be used from the main thread only’. While you can update lineDataSeries and scatterDataSeries in the background thread, you must do surface.zoomExtents() in the main thread.

Thanks in advance for letting us know the result of our fix.

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0
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I’ve added an example project illustrating the problem.

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0
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Thank you for the fix. Two questions:

  • how do I get to the 3.1.0-nightly.5268 build from CocoaPods?
  • is there a SciChart pre-render callback that I can use to make the surface.zoomExtents() call rather than using a timer. I’m thinking that it is going to be difficult to know how frequently to call surface.zoomExtents() depending on the device’s screen refresh rate.
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I’m sorry to take so long to respond. I’ve finally been able to test with 18 channels of simulated data and there are no more deadlocks – thank you. Do you have an ETA for when this fix will be released in production SciChart builds?

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