If I'm changing the time on an existing alarm, and keeping the same id, do I need to stop and set it, or just set it?

[ApplySci]

As per the title - If I'm changing the time on an existing alarm, and keeping the same id, do I need to stop and set it, or just set it?

It's just that I keep getting a crash on iPhone (works fine on android) when I try to set an alarm with same id and same time as currently exists

[gdelataillade]

Hi @ApplySci

If you set an alarm keeping the same id, it will first stop the existing alarm and schedule the new one, even if they are exactly the same.

Can you tell me more about your crash on iOS ? How to reproduce, what version ? Make sure you use await when you call Alarm.set

[ApplySci]

I've found a workaround now, which is to call stopAllAlarms before setting any.

I've got quite a convoluted setup for Mac, which might create a situation that is (1) not a real world case and (2) hard to reproduce: I've got a windows pc running Mac Monterey ios on VMWare, and then I'm simulating an iPhone 14 on that.

I've got a few alarms that get set, and sometimes one or two of the times get updated. To keep it simple, I re-set all the alarms when I get a notification that a time has been updated. If a time has changed, then Alarm.set behaves fine. But if the alarm hasn't changed, then it crashes.

But now I'm awaiting stopAllAlarms before setting any, there's no crash.

I may have an actual iPhone to test on in a couple of weeks, and I'll let you know if I can reproduce this on that.

[ApplySci]

thread dump:

hread 47 Crashed::  Dispatch queue: com.gdelataillade.alarm.resourceAccessQueue
0   libobjc.A.dylib               	    0x7ff80002d6cb objc_msgSend + 11
1   libswiftCore.dylib            	    0x7ff80d6a474e Dictionary._Variant.removeValue(forKey:) + 190
2   alarm                         	       0x10529fa3f closure #1 in SwiftAlarmPlugin.stopAlarm(id:cancelNotif:result:) + 783 (SwiftAlarmPlugin.swift:293)
3   alarm                         	       0x105299442 closure #1 in SwiftAlarmPlugin.safeModifyResources(_:) + 50 (SwiftAlarmPlugin.swift:67)
4   alarm                         	       0x105298f88 thunk for @escaping @callee_guaranteed () -> () + 40
5   libdispatch.dylib             	    0x7ff80013b7fb _dispatch_call_block_and_release + 12
6   libdispatch.dylib             	    0x7ff80013ca3a _dispatch_client_callout + 8
7   libdispatch.dylib             	    0x7ff800144346 _dispatch_lane_serial_drain + 949
8   libdispatch.dylib             	    0x7ff800144fe3 _dispatch_lane_invoke + 400
9   libdispatch.dylib             	    0x7ff800151b46 _dispatch_workloop_worker_thread + 870
10  libsystem_pthread.dylib       	    0x7ff833e39fd0 _pthread_wqthread + 326
11  libsystem_pthread.dylib       	    0x7ff833e38f57 start_wqthread + 15

[gdelataillade]

What happened is that when you run Alarm.set without waiting for stopAllAlarms to finish, my iOS native code will try to access and modify the same resources at the same time and that causes the crash.

[ApplySci]

Sorry, I wasn't clear.

stopAllAlarms was the fix. stopAllAlarms wasn't in the code when the crash was happening.