Potential memory leak in code

Question

In an app I'm working on, there is a requirement to periodically poll for device's data like acceleration, gyro and motion. I wrote the following class to handle all the related tasks (I also use the third-party library SOMotionDetector to detect whether the device is moving. if only then, I call the didReceiveAcceleration delegate method).

import CoreMotion
import Foundation
import SOMotionDetector

protocol MotionManagerDelegate: class {
    func didReceiveAcceleration(_ acceleration: (x: Double, y: Double, z: Double))
    func didReceiveGyro(_ gyro: (x: Double, y: Double, z: Double))
    func didReceiveMotion(_ motion: (x: Double, y: Double, z: Double, w: Double))
}

class MotionManager: NSObject {

    weak var delegate: MotionManagerDelegate?

    fileprivate let motionDetector = SOMotionDetector.sharedInstance()
    fileprivate let accelerationCaptureInterval: TimeInterval = 0.02
    fileprivate let gyroCaptureInterval: TimeInterval = 1
    fileprivate var lastAcceleration: (x: Double, y: Double, z: Double) = (x: 0.0, y: 0.0, z: 0.0)
    fileprivate var isMoving: Bool = false
    fileprivate var motionManager: CMMotionManager!

    override init() {
        super.init()

        motionManager = CMMotionManager()
        motionManager.gyroUpdateInterval = gyroCaptureInterval
        motionManager.accelerometerUpdateInterval = accelerationCaptureInterval
        motionManager.deviceMotionUpdateInterval = gyroCaptureInterval
        motionDetector?.useM7IfAvailable = true
    }

    func startCapturing() throws {
        motionManager.startGyroUpdates(to: OperationQueue()) { gyroData, error in
            if let rotation = gyroData?.rotationRate {
                let gyro = (x: rotation.x, y: rotation.y, z: rotation.z)
                self.delegate?.didReceiveGyro(gyro)
            } else {
                let gyro = (x: 0.0, y: 0.0, z: 0.0)
                self.delegate?.didReceiveGyro(gyro)
            }
        }

        motionDetector?.motionTypeChangedBlock = { motionType in
            if motionType == MotionTypeNotMoving {
                self.isMoving = false
            } else {
                self.isMoving = true
            }
        }
        motionDetector?.startDetection()

        motionManager.startAccelerometerUpdates(to: OperationQueue()) { accelerometerData, error in
            var x = 0.0
            var y = 0.0
            var z = 0.0
            if let acceleration = accelerometerData?.acceleration {
                x = acceleration.x
                y = acceleration.y
                z = acceleration.z
            }

            if self.isMoving {
                if let delegate = self.delegate {
                    delegate.didReceiveAcceleration((x: x, y: y, z: z))
                }
            }
        }

        motionManager.startDeviceMotionUpdates(to: OperationQueue()) { motionData, error in
            if let quaternion = motionData?.attitude.quaternion {
                let motion = (x: quaternion.x, y: quaternion.y, z: quaternion.z, w: quaternion.w)
                self.delegate?.didReceiveMotion(motion)
            }
        }
    }

    func stopCapturing() {
        motionManager.stopGyroUpdates()
        motionManager.stopAccelerometerUpdates()
        motionManager.stopDeviceMotionUpdates()
        motionDetector?.stopDetection()
    }
}

This works fine. But I get random crash reports saying there is a memory leak/heap corruption in the code. Since I can't attach the debugger and move about with the app running on the phone, I can't pinpoint where this is occurring.

I'd greatly appreciate any help figuring out what the problematic code might be. Is any of my code above prone to issues like retain cycles?

I don't see anything obvious. You may want to replace your "if let delegate = self.delegate {...}" with the syntax you've used elsewhere self.delegate?.didReci... Otherwise the only thing I can suggest is to use the Xcode Instruments, in particular the one titled Leaks. — ekscrypto, Sep 24 '17 at 13:19

score 3 · Answer 1 · answered Sep 24 '17 at 13:19

You directly access self in blocks, that may cause retain cycle. Try to use weak self like:

motionDetector?.motionTypeChangedBlock = { [weak self] motionType in
    if motionType == MotionTypeNotMoving {
        self?.isMoving = false
    } else {
        self?.isMoving = true
    }
}

So does others blocks.

score 3 · Accepted Answer · answered Sep 24 '17 at 13:19

You have retain cycles on self. You are capturing self strongly inside your blocks but self is retaining those blocks and variables..

Example:

class MotionManager: NSObject {
   override init() {
        super.init()

        motionManager = CMMotionManager() //retains motionManager..
    }

    func usage() {
        motionManager.execute({ foo in
            self.blah(foo);  //capturing self strongly in motionManager block.. motionManager is retained by self.. retain cycle..
        })
    }
}

You need to use weak self or unowned self in the block's capture frame.

class MotionManager: NSObject {
   override init() {
        super.init()

        motionManager = CMMotionManager() //retains motionManager..
    }

    func usage() {
        motionManager.execute({ [weak self] (foo) in
            self?.blah(foo);  //Doesn't retain self. Fixed :D
        })
    }
}

Do something like:

class MotionManager: NSObject {

    weak var delegate: MotionManagerDelegate?

    fileprivate let motionDetector = SOMotionDetector.sharedInstance()
    fileprivate let accelerationCaptureInterval: TimeInterval = 0.02
    fileprivate let gyroCaptureInterval: TimeInterval = 1
    fileprivate var lastAcceleration: (x: Double, y: Double, z: Double) = (x: 0.0, y: 0.0, z: 0.0)
    fileprivate var isMoving: Bool = false

    fileprivate var motionManager: CMMotionManager!


    override init() {
        super.init()

        motionManager = CMMotionManager()
        motionManager.gyroUpdateInterval = gyroCaptureInterval
        motionManager.accelerometerUpdateInterval = accelerationCaptureInterval
        motionManager.deviceMotionUpdateInterval = gyroCaptureInterval

        motionDetector?.useM7IfAvailable = true
    }

    func startCapturing() throws {
        motionManager.startGyroUpdates(to: OperationQueue()) { [weak self] (gyroData, error) in
            if let rotation = gyroData?.rotationRate {
                let gyro = (x: rotation.x, y: rotation.y, z: rotation.z)
                self?.delegate?.didReceiveGyro(gyro)
            } else {
                let gyro = (x: 0.0, y: 0.0, z: 0.0)
                self?.delegate?.didReceiveGyro(gyro)
            }
        }

        motionDetector?.motionTypeChangedBlock = { [weak self] (motionType) in
            if motionType == MotionTypeNotMoving {
                self?.isMoving = false
            } else {
                self?.isMoving = true
            }
        }

        motionDetector?.startDetection()

        motionManager.startAccelerometerUpdates(to: OperationQueue()) { [weak self] (accelerometerData, error) in
            var x = 0.0
            var y = 0.0
            var z = 0.0
            if let acceleration = accelerometerData?.acceleration {
                x = acceleration.x
                y = acceleration.y
                z = acceleration.z
            }

            if (self?.isMoving)! {
                if let delegate = self?.delegate {
                    delegate.didReceiveAcceleration((x: x, y: y, z: z))
                }
            }
        }

        motionManager.startDeviceMotionUpdates(to: OperationQueue()) { [weak self] (motionData, error) in
            if let quaternion = motionData?.attitude.quaternion {
                let motion = (x: quaternion.x, y: quaternion.y, z: quaternion.z, w: quaternion.w)
                self?.delegate?.didReceiveMotion(motion)
            }
        }
    }

    func stopCapturing() {
        motionManager.stopGyroUpdates()
        motionManager.stopAccelerometerUpdates()
        motionManager.stopDeviceMotionUpdates()
        motionDetector?.stopDetection()
    }
}

Potential memory leak in code

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