Crash when calling completion handler for `UNUserNotificationCenter` - ios

Question

I'm working on an app that, when receiving a silent push notification; will make two networking calls to get some data, and then use that data to create a local push notification.
This mostly works great in the foreground and the background; with the exception of some occasional crashes that I'm having a difficult time diagnosing.
This is my full implementation for the delegate method that gets called when the silent push notification arrives:
func application(_ application: UIApplication,
didReceiveRemoteNotification userInfo: [AnyHashable : Any],
fetchCompletionHandler completionHandler: #escaping (UIBackgroundFetchResult) -> Void) {
print("Notification received!")
UNUserNotificationCenter.current().delegate = self
let id = updateNotificationID()
let payload = userInfo
guard let ship: String = payload["ship"] as? String else {
return
}
guard let node: String = payload["node"] as? String else {
return
}
guard let graph: String = payload["graph"] as? String else {
return
}
var groupName: String = ""
networkStore.scryForGroupInfo(ship: ship, graph: graph) { groupTitle in
if groupTitle == "" {
//one on one
} else {
//groupchat
groupName = groupTitle
}
networkStore.scryOnNotificationReceipt(ship: ship, node: node, graph: graph) { [self] messageString, author in
let content = UNMutableNotificationContent()
if groupName == "" {
//group chat
content.title = "New Message from \(author)"
let chatShipDict:[String: String] = ["ChatShip": author]
content.userInfo = chatShipDict
} else {
content.title = "\(author) posted in \(groupName)"
let chatShipDict:[String: String] = ["ChatShip": groupName]
content.userInfo = chatShipDict
}
//Don't show a notification for a chat that we're currently in
if airlockStore.selectedChannel != nil {
let author = "~"+author
if airlockStore.selectedChannel.channelShip == author || airlockStore.selectedChannel.channelName == groupName {
completionHandler(.noData)
return
}
} else {
//One on one chat
if groupName == "" {
let author = "~"+author
for channel in airlockStore.unPinnedChannelDataObjects {
if channel.channelShip == author {
notificationChannel = channel
}
}
} else {
//Group chat
for channel in airlockStore.unPinnedChannelDataObjects {
if channel.channelName == groupName {
notificationChannel = channel
}
}
}
}
content.body = messageString
let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 2, repeats: false)
let request = UNNotificationRequest(identifier: "notification.id.\(id)", content: content, trigger: trigger)
UNUserNotificationCenter.current().add(request) { Error in
print("Showing Notification")
completionHandler(.newData)
}
}
}
}
The crashes seem to occur at the completionHandler(.newData) line.
Here's my stack trace:
Thread 10 name:
Thread 10 Crashed:
0 libdispatch.dylib 0x00000001a0b147b8 dispatch_group_leave.cold.1 + 36 (semaphore.c:303)
1 libdispatch.dylib 0x00000001a0ae0668 dispatch_group_leave + 140 (semaphore.c:0)
2 Pocket 0x000000010464333c partial apply for closure #1 in closure #1 in closure #1 in AppDelegate.application(_:didReceiveRemoteNotification:fetchCompletionHandler:) + 136 (AppDelegate.swift:137)
3 Pocket 0x00000001046419ac thunk for #escaping #callee_guaranteed (#guaranteed Error?) -> () + 44 (<compiler-generated>:0)
4 libdispatch.dylib 0x00000001a0adda84 _dispatch_call_block_and_release + 32 (init.c:1466)
5 libdispatch.dylib 0x00000001a0adf81c _dispatch_client_callout + 20 (object.m:559)
6 libdispatch.dylib 0x00000001a0ae7004 _dispatch_lane_serial_drain + 620 (inline_internal.h:2557)
7 libdispatch.dylib 0x00000001a0ae7c34 _dispatch_lane_invoke + 456 (queue.c:3862)
8 libdispatch.dylib 0x00000001a0af24bc _dispatch_workloop_worker_thread + 764 (queue.c:6589)
9 libsystem_pthread.dylib 0x00000001ecc7e7a4 _pthread_wqthread + 276 (pthread.c:2437)
10 libsystem_pthread.dylib 0x00000001ecc8574c start_wqthread + 8

Answer 1

You say you are making two different network calls.
Are you sure you are not calling the completion handler twice sometimes? Make sure it is only called once.