compiler-generated crash in Swift in my react-native app - ios

Question

My healthkit swift code keeps crashing in the background in production, and I can't figure it out for the life of me. I am fairly new to Swift, so maybe I am making a fundamental error in my implementation.
Features of the crash:
It seems to happen only in production. (our internal test program contains 10 devices only (so maybe it is co-incidence that it doesn't get picked up there).
Occurs in iOS versions - 10,11,12,13
Occurs for a very small set of users (1.5% of active audience), but very frequently for these same users.
Please find the crash log from my Crashlytics account below.
Crashed: com.facebook.react.HKManagerQueue
0 stepapp 0x100f4f324 specialized HKManager.getTotal(_:typeStr:unit:options:completion:) + 4372984612 (<compiler-generated>:4372984612)
1 stepapp 0x100f52e04 HKManager._getTotals(_:completion:) + 397 (HKManager.swift:397)
2 stepapp 0x100f532ac #objc HKManager.getTotals(_:resolver:rejecter:) + 4373000876 (<compiler-generated>:4373000876)
3 CoreFoundation 0x1af698c20 __invoking___ + 144
4 CoreFoundation 0x1af568d30 -[NSInvocation invoke] + 300
5 CoreFoundation 0x1af569908 -[NSInvocation invokeWithTarget:] + 76
6 stepapp 0x101184e6c -[RCTModuleMethod invokeWithBridge:module:arguments:] + 241556
7 stepapp 0x101187248 facebook::react::invokeInner(RCTBridge*, RCTModuleData*, unsigned int, folly::dynamic const&) + 250736
8 stepapp 0x101186fac invocation function for block in facebook::react::RCTNativeModule::invoke(unsigned int, folly::dynamic&&, int) + 250068
9 libdispatch.dylib 0x1af35e610 _dispatch_call_block_and_release + 24
10 libdispatch.dylib 0x1af35f184 _dispatch_client_callout + 16
11 libdispatch.dylib 0x1af30b404 _dispatch_lane_serial_drain$VARIANT$mp + 608
12 libdispatch.dylib 0x1af30bdf8 _dispatch_lane_invoke$VARIANT$mp + 420
13 libdispatch.dylib 0x1af315314 _dispatch_workloop_worker_thread + 588
14 libsystem_pthread.dylib 0x1af3aeb88 _pthread_wqthread + 276
15 libsystem_pthread.dylib 0x1af3b1760 start_wqthread + 8
com.apple.main-thread
0 libsystem_kernel.dylib 0x19c960634 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x19c95faa0 mach_msg + 72
2 CoreFoundation 0x19cb08288 __CFRunLoopServiceMachPort + 216
3 CoreFoundation 0x19cb033a8 __CFRunLoopRun + 1444
4 CoreFoundation 0x19cb02adc CFRunLoopRunSpecific + 464
5 GraphicsServices 0x1a6aa3328 GSEventRunModal + 104
6 UIKitCore 0x1a0c1063c UIApplicationMain + 1936
7 stepapp 0x100edf330 main + 14 (main.m:14)
8 libdyld.dylib 0x19c98c360 start + 4
com.apple.uikit.eventfetch-thread
0 libsystem_kernel.dylib 0x19c960634 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x19c95faa0 mach_msg + 72
2 CoreFoundation 0x19cb08288 __CFRunLoopServiceMachPort + 216
3 CoreFoundation 0x19cb033a8 __CFRunLoopRun + 1444
4 CoreFoundation 0x19cb02adc CFRunLoopRunSpecific + 464
5 Foundation 0x19ce42784 -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 228
6 Foundation 0x19ce42664 -[NSRunLoop(NSRunLoop) runUntilDate:] + 88
7 UIKitCore 0x1a0ca8e80 -[UIEventFetcher threadMain] + 152
8 Foundation 0x19cf7309c __NSThread__start__ + 848
9 libsystem_pthread.dylib 0x19c8a5d8c _pthread_start + 156
10 libsystem_pthread.dylib 0x19c8a976c thread_start + 8
I have attached my implementation below, which contains the line mentioned in the crash logs
func _getTotals(_ options: Dictionary<String, Any>, completion: #escaping (Dictionary<String, Double>?) -> Void) {
var stepsDone = false;
var distanceDone = false;
var caloriesDone = false;
let steps = HKQuantityType.quantityType(forIdentifier: .stepCount);
let distance = HKQuantityType.quantityType(forIdentifier: .distanceWalkingRunning);
let calories = HKQuantityType.quantityType(forIdentifier: .activeEnergyBurned);
var results = Dictionary<String, Double>();
// 👇 THIS IS LINE 397 which is indicated in the crash report above
self.getTotal(steps!, typeStr: HKManager.STEP_TYPE_STR, unit: HKUnit.count(), options: options) { (totalSteps, error) in
stepsDone = true;
if (totalSteps != nil) {
results["steps"] = totalSteps;
}
if (stepsDone == true && distanceDone == true && caloriesDone == true) {
return completion(results);
}
}
self.getTotal(distance!, typeStr: HKManager.DISTANCE_TYPE_STR, unit: HKUnit.meter(), options: options) { (totalDistance, error) in
distanceDone = true;
if (totalDistance != nil) {
results["distance"] = totalDistance;
}
if (stepsDone == true && distanceDone == true && caloriesDone == true) {
return completion(results);
}
}
self.getTotal(calories!, typeStr: HKManager.CALORIES_TYPE_STR, unit: HKUnit.kilocalorie(), options: options) { (totalCalories, error) in
caloriesDone = true;
if (totalCalories != nil) {
results["calories"] = totalCalories;
}
if (stepsDone == true && distanceDone == true && caloriesDone == true) {
return completion(results);
}
}
}
I have also attached my implementation of the self.getTotal(...) function which is used in the above code. Point to note in this function, I switch to performing my HealthKit query in the background qos to ensure that these queries don't run on the main thread. I think it might be the cause for the crash.
func getTotal(_ type: HKQuantityType, typeStr: String, unit: HKUnit, options: Dictionary<String, Any>, completion: #escaping (Double?, Error?) -> Void) {
guard (self.healthStore != nil) else {
let error = NSError(domain: "Healthkit not initialized", code: 50, userInfo: [:]);
return completion(nil, error);
}
var start: Date;
if (options["startDate"] != nil) {
start = self.strToDate(dateStr: options["startDate"] as! String);
} else {
let date = Date()
let cal = Calendar(identifier: .gregorian)
let midnight = cal.startOfDay(for: date);
start = midnight;
}
var ignoreMin = false;
if (options["ignoreMin"] != nil) {
ignoreMin = options["ignoreMin"] as! Bool;
}
if (ignoreMin != true && start < self.minStartDate && self.minStartDate != nil) {
start = self.minStartDate;
}
var end: Date = Date();
if (options["endDate"] != nil) {
end = self.strToDate(dateStr: options["endDate"] as! String);
}
var sources = options["sources"] as? [String];
if (sources == nil || (sources?.capacity)! < 1) {
sources = ["com.apple.health."];
}
DispatchQueue.global(qos: .background).async { [weak self] in
// fetch sources
self?.getSources(sampleTypeStr: typeStr, sampleType: type, sources: sources!) { (s, error) in
if (s == nil || ((s?.capacity) ?? 0) < 1) {
return completion(0.0, nil);
}
let sourcePredicate = HKQuery.predicateForObjects(from: s!);
// todo: enter date patterns
let datePredicate = HKQuery.predicateForSamples(withStart: start, end: end, options: []);
// predicate = [NSPredicate predicateWithFormat:#"metadata.%K != YES", HKMetadataKeyWasUserEntered];
let manualPredicate = HKQuery.predicateForObjects(withMetadataKey: HKMetadataKeyWasUserEntered, operatorType: .notEqualTo, value: "YES");
let compound = NSCompoundPredicate(andPredicateWithSubpredicates: [
sourcePredicate,
datePredicate,
manualPredicate
]);
let statOptions = HKStatisticsOptions.cumulativeSum;
let query = HKStatisticsQuery.init(quantityType:type , quantitySamplePredicate: compound, options: statOptions, completionHandler: { (query, results, error) in
if (error != nil) {
return completion(nil, error);
}
var total = 0.0;
// handle if results came back as nil, or sum came back as nil
guard (results != nil && results?.sumQuantity() != nil) else {
return completion(total, nil);
}
total = results?.sumQuantity()?.doubleValue(for: unit) ?? 0.0;
return completion(total, nil);
});
// execute stats query for step counts by source
self?.healthStore?.execute(query);
}
}
}
I would really appreciate any form of help, or pointers. Thanks in advance.

Answer 1

The obvious issue is parallel write from several threads to dictionary object. In pseudo code:
results = [:]
getTotal() // start thread 1
getTotal() // start thread 2
getTotal() // start thread 3
thread 1: write results
thread 2: write results
thread 3: write results
Swift Dictionary is not thread-safe, parallel writes have to be synchronized.
In your code, simple change would be to move DispatchQueue async up, into _getTotals, and removing DispatchQueue from getTotal:
func _getTotals(_ options: Dictionary<String, Any>, completion: #escaping (Dictionary<String, Double>?) -> Void) {
DispatchQueue.global(qos: .background).async {
var results = Dictionary<String, Double>()
self.getTotal(...)
self.getTotal(...)
self.getTotal(...)
}
}
In this way everything runs inside single background thread; getTotal calls are invoked serially one after another.
But if you need to run getTotal in parallel, you have to synchronize access to results variable. This is commonly done with another call to DispatchQueue async with a predefined shared serial queue.