Unable to determine possible causes of EXC_BAD_ACCESS (which occurs during app startup)

I'm seeing a lot of crashes in an app in the app store which I'm totally unable to reproduce or speculate from code review what the cause could be. What is particularly confusing is that this is occurring at app launch while there is low memory - confusing because if there was insufficient memory for the app to launch I might expect to see other types of crash reports as opposed to an EXC_BAD_ACCESS - i.e. if the EXC_BAD_ACCESS is being caused by accessing deleted memory, there's nowhere in the code where anything gets the chance to be deleted, as the crash is occurring as objects are in the process of being created.

I've tried many thing to recreate this - running in the simulator and sending low memory warning messages, deliberately failing the initialization of various objects in the app creation process, calling calloc during app launch to consume vast amounts of memory, running the app numerous times on a handset whose RAM is totally maxed out. I can't recreate, or see from code inspection what might be going wrong.

Here is a crash report:

Exception Type: EXC_BAD_ACCESS (SIGSEGV) Exception Subtype: KERN_INVALID_ADDRESS at 0x0000000000000000 many also at 0x0000000000000008) hread 0 name: Dispatch queue: com.apple.main-thread Thread 0 Crashed: 0 The_Name_Of_MyApp
0x000000010268ca94 SearchViewController.init(coder:) + 838292 (SearchViewController.swift:67) 1 The_Name_Of_MyApp
0x000000010268ca88 SearchViewController.init(coder:) + 838280 (SearchViewController.swift:67) 2 The_Name_Of_MyApp
0x000000010268cd4c @objc SearchViewController.init(coder:) + 838988 (SearchViewController.swift:0) 3 UIKitCore
0x00000001bca63d64 -[UIClassSwapper initWithCoder:] + 248 4
UIFoundation 0x000000019a77fe88 UINibDecoderDecodeObjectForValue + 744 5 UIFoundation
0x000000019a7800cc UINibDecoderDecodeObjectForValue + 1324 6
UIFoundation 0x000000019a71eb3c -[UINibDecoder decodeObjectForKey:] + 320 7 UIKitCore
0x00000001bd0a1288 -[UIViewController initWithCoder:] + 1420 8
UIKitCore 0x00000001bceb5dcc -[UITabBarController initWithCoder:] + 80 9 The_Name_Of_MyApp
0x000000010283f658 TabBarViewController.init(coder:) + 2618968 (TabBarViewController.swift:0) 10 The_Name_Of_MyApp
0x000000010283f70c @objc TabBarViewController.init(coder:) + 2619148 (TabBarViewController.swift:0) 11 UIKitCore
0x00000001bca63d64 -[UIClassSwapper initWithCoder:] + 248 12 UIFoundation 0x000000019a77fe88 UINibDecoderDecodeObjectForValue + 744 13 UIFoundation
0x000000019a71eb3c -[UINibDecoder decodeObjectForKey:] + 320 14 UIKitCore 0x00000001bcd9dcbc -[UIRuntimeConnection initWithCoder:] + 188 15 UIFoundation 0x000000019a77fe88 UINibDecoderDecodeObjectForValue + 744 16 UIFoundation 0x000000019a7800cc UINibDecoderDecodeObjectForValue + 1324 17 UIFoundation
0x000000019a71eb3c -[UINibDecoder decodeObjectForKey:] + 320 18 UIKitCore 0x00000001bccc4a1c -[UINib instantiateWithOwner:options:] + 1124 19 UIKitCore
0x00000001bce92f18 -[UIStoryboard instantiateViewControllerWithIdentifier:] + 196 20 The_Name_Of_MyApp 0x000000010266b4dc InitialViewController.start() + 701660 (InitialViewController.swift:118) 21 The_Name_Of_MyApp
0x000000010266bba4 @objc InitialViewController.start() + 703396 (InitialViewController.swift:0) 22 Foundation
0x0000000190bff6d0 NSFireDelayedPerform + 404 23 CoreFoundation
0x00000001900f2bf0 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION + 28 24 CoreFoundation 0x00000001900f2920 __CFRunLoopDoTimer + 864 25 CoreFoundation 0x00000001900f2154 __CFRunLoopDoTimers + 248 26 CoreFoundation 0x00000001900ed030 __CFRunLoopRun + 1880 27 CoreFoundation
0x00000001900ec5b8 CFRunLoopRunSpecific + 436 28 GraphicsServices
0x0000000192360584 GSEventRunModal + 100 29 UIKitCore
0x00000001bc9e3558 UIApplicationMain + 212 30 The_Name_Of_MyApp
0x00000001026ea6b0 main + 1222320 (AppDelegate.swift:20) 31 libdyld.dylib 0x000000018fbacb94 start + 4

Thread 1: 0 libsystem_pthread.dylib 0x000000018fd80cfc start_wqthread + 0

Thread 2 name: Dispatch queue: com.myQueue.backgroundSerialQueue Thread 2: 0 libsystem_c.dylib 0x000000018fc60ae4 __v2printf + 616 1 libsystem_c.dylib 0x000000018fc60a00 __v2printf + 388 2 libsystem_c.dylib 0x000000018fc46ac0 _vsnprintf + 264 3 libsystem_c.dylib 0x000000018fc3b9c0 snprintf_l + 28 4 CoreFoundation 0x000000019010fa88 __CFStringAppendFormatCore + 8548 5 CoreFoundation 0x00000001901111b8 _CFStringCreateWithFormatAndArgumentsAux2 + 136 6 Foundation 0x0000000190afd3ec -[NSString initWithFormat:locale:] + 36 7 Foundation
0x0000000190afd364 -[NSNumber descriptionWithLocale:] + 1044 8
CoreFoundation 0x000000019004d9a8 -[__NSCFNumber descriptionWithLocale:] + 72 9 CoreFoundation
0x0000000190053268 -[__NSCFNumber stringValue] + 64 10 The_Name_Of_MyApp 0x00000001025f6494 -[RobocallerManager readCityAndStateData] + 222356 (RobocallerManager.m:596) 11 The_Name_Of_MyApp 0x00000001025f343c __25-[RobocallerManager init]_block_invoke + 209980 (RobocallerManager.m:148) 12 libdispatch.dylib
0x000000018fb9b6c8 _dispatch_call_block_and_release + 24 13 libdispatch.dylib 0x000000018fb9c484 _dispatch_client_callout + 16 14 libdispatch.dylib 0x000000018fb43c18 _dispatch_lane_serial_drain$VARIANT$mp + 592 15 libdispatch.dylib 0x000000018fb44760 _dispatch_lane_invoke$VARIANT$mp + 432 16 libdispatch.dylib 0x000000018fb4cf00 _dispatch_workloop_worker_thread + 600 17 libsystem_pthread.dylib 0x000000018fd7e0f0 _pthread_wqthread + 312 18 libsystem_pthread.dylib 0x000000018fd80d00 start_wqthread + 4

Thread 3: 0 libsystem_pthread.dylib 0x000000018fd80cfc start_wqthread + 0

Thread 4 name: com.apple.uikit.eventfetch-thread Thread 4: 0
libsystem_kernel.dylib 0x000000018fceded0 mach_msg_trap + 8 1 libsystem_kernel.dylib 0x000000018fced3a8 mach_msg + 72 2
CoreFoundation 0x00000001900f1fb0 CFRunLoopServiceMachPort + 236 3 CoreFoundation 0x00000001900ece4c __CFRunLoopRun + 1396 4 CoreFoundation
0x00000001900ec5b8 CFRunLoopRunSpecific + 436 5 Foundation
0x0000000190ae06a4 -[NSRunLoop+ 34468 (NSRunLoop) runMode:beforeDate:] + 300 6 Foundation
0x0000000190ae0514 -[NSRunLoop+ 34068 (NSRunLoop) runUntilDate:] + 88 7 UIKitCore 0x00000001bc940ac0 -[UIEventFetcher threadMain] + 136 8 Foundation
0x0000000190c133b0 __NSThread__start + 1040 9
libsystem_pthread.dylib 0x000000018fd7d2fc _pthread_body + 128 10 libsystem_pthread.dylib 0x000000018fd7d25c _pthread_start + 48 11 libsystem_pthread.dylib 0x000000018fd80d08 thread_start + 4

Thread 5 name: com.twitter.crashlytics.ios.MachExceptionServer Thread 5: 0 libsystem_kernel.dylib 0x000000018fceded0 mach_msg_trap + 8 1 libsystem_kernel.dylib 0x000000018fced3a8 mach_msg + 72 2 The_Name_Of_MyApp 0x000000010288d08c CLSMachExceptionServer + 1180 3 libsystem_pthread.dylib
0x000000018fd7d2fc _pthread_body + 128 4 libsystem_pthread.dylib
0x000000018fd7d25c _pthread_start + 48 5 libsystem_pthread.dylib
0x000000018fd80d08 thread_start + 4

Thread 6: 0 libsystem_pthread.dylib 0x000000018fd80cfc start_wqthread + 0

Thread 7: 0 libsystem_pthread.dylib 0x000000018fd80cfc start_wqthread + 0

Thread 8: 0 libsystem_pthread.dylib 0x000000018fd80cfc start_wqthread + 0

Thread 9: 0 libsystem_pthread.dylib 0x000000018fd80cfc start_wqthread + 0

Thread 10 name: com.apple.NSURLConnectionLoader Thread 10: 0
libsystem_kernel.dylib 0x000000018fceded0 mach_msg_trap + 8 1 libsystem_kernel.dylib 0x000000018fced3a8 mach_msg + 72 2
CoreFoundation 0x00000001900f1fb0 CFRunLoopServiceMachPort + 236 3 CoreFoundation 0x00000001900ece4c __CFRunLoopRun + 1396 4 CoreFoundation
0x00000001900ec5b8 CFRunLoopRunSpecific + 436 5 CFNetwork
0x000000019070ce18 -[__CoreSchedulingSetRunnable runForever] + 212 6 Foundation 0x0000000190c133b0 __NSThread__start + 1040 7 libsystem_pthread.dylib 0x000000018fd7d2fc _pthread_body + 128 8 libsystem_pthread.dylib 0x000000018fd7d25c _pthread_start + 48 9 libsystem_pthread.dylib
0x000000018fd80d08 thread_start + 4

Thread 0 crashed with ARM Thread State (64-bit): x0: 0x0000000000000000 x1: 0x0000000000000000 x2: 0x0000000282718580 x3: 0x0000000000000000 x4: 0x0000000104870680 x5: 0x0000000000000000 x6: 0x0000000000000072 x7: 0x00000000000000a0 x8: 0x0000000103f03650 x9: 0x0000000000000000 x10: 0x000000000000001f x11: 0x0000000000000005 x12: 0x0000000000000005 x13: 0x0000000000000000 x14: 0x0000000000000068 x15: 0x00000001ae696425 x16: 0x000000018f34b858 x17: 0x0000000102601328 x18: 0x0000000000000000 x19: 0x0000000104853200 x20: 0x00000001048709c8 x21: 0x0000000280b73880 x22: 0x00000001c92684c0 x23: 0x0000000104870600 x24: 0x0000000281e51ec0 x25: 0x00000001c73e2000 x26: 0x0000000000000002 x27: 0x00000001c73e2000
x28: 0x0000000000000171 fp: 0x000000016d83c0b0 lr: 0x000000010268ca88 sp: 0x000000016d83bcc0 pc: 0x000000010268ca94 cpsr: 0x60000000

Here's a diagram outlining the relationship between the objects shown in the crash report. Basically at app launch the AppDelegate causes a LicenceManger object to be instantiated, which in turn causes a DatabaseManager and Database objects to be created, all of which are model type classes. Meanwhile the GUI is launching with InitialVC being a root VC which instantiates a TabBar VC which causes the instantiation of the SearchVC. The SearchVC accesses the DatabaseModel object and that is where the crash occurs.

And here is the code (reduced to just relevant portions, note the code is Swift except the DataBaseManager is Ojb-C)

////////////////// InitialViewController ////////////////////////////
class InitialViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        self.perform(#selector(InitialViewController.start), with: nil, afterDelay: 1.5)
    }
}

@objc func start() {
    let tbvc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "TabBarViewControllerID") as! TabBarViewController
navigationController.pushViewController(tbvc, animated: true)
}



SearchViewController gets created as a consequence of there being a relationship segue between it and TabBarViewControllerSp


///////////////////////// SearchViewController ///////////////////////////////
class SearchViewController: UITableViewController, UISearchBarDelegate {
    var searchResultsList   = DatabaseManager.instance().database.emptyList()  line 67




////////////////////// App Delegate ///////////////////////////
AppDelegate:didFinishLaunchingWithOptions() {
    let _ = LicenseManager.instance
}



//////////////////////// LicenseManager ////////////////////////
@objc class LicenseManager : NSObject {
    @objc open static let instance = LicenseManager()
    private let databaseManager = DatabaseManager.instance()
}

override private init() {
    super.init()
}



///////////////////// DatabaseManager ////////////////////////
+ (DatabaseManager*) instance {
    static DatabaseManager *theInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^ {
        theInstance = [[DatabaseManager alloc] init];
    });
    return theInstance;
}

@interface DatabaseManager()
@property (strong, nonatomic)   Database*  _Nonnull database;
@end


@implementation DatabaseManager
- (id) init {
    self = [super init];
    if (self)
    {
        _database   = Database.instance;
        [_database openOrCreateDatabase];


        dispatch_async(robocallerQueue(), ^{
            [self readCityAndStateData];
        });
    }
}

- (void) readCityAndStateData {
     Populates a very large dictionary > 100K entries
}



////////////////////// Database //////////////////////
@objcMembers class Database : NSObject {
    open static let instance = Database()
    fileprivate var configuration:Realm.Configuration?    = nil

    override init()
    {
    }
}


@objc func openOrCreateDatabase() {
       configuration = Realm.Configuration(encryptionKey: Database.getKey() as Data)
}

class func getKey() -> NSData {
    let string = "AED16D8B-7762-4CBF-A313-48FDCAD51B9C23456754635498123450ka&9dB6t"
    let data = string.data(using: String.Encoding.utf8)
    return data! as NSData
}

func emptyList() -> Results<Caller> {        
    let realm = try! Realm(configuration: configuration!)
    let mdn = "DoesNotExist"
    let searchTerm = "number ==  " + "\"" + mdn + "\""
    let results = realm.objects(Caller.self).filter(searchTerm)
    return results
 }





//////////////// Caller ///////////
@objc public class Caller : Object {
    @objc dynamic var name:String? = nil
    // More simple types, strings, dates, ints etc.
}

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