I have
var idleScanTimer = DispatchSource.makeTimerSource()
as a class ivar. When the object is started, I have
self.idleScanTimer.schedule(deadline: .now(), repeating: Double(5.0*60))
(and it sets an event handler, that checks some times.)
When the object is stopped, it calls self.idleScanTimer.cancel().
At some point, the object containing it is deallocated, and ... sometimes, I think, not always, it crashes:
Crashed Thread: 61 Dispatch queue: NEFlow queue
[...]
Application Specific Information:
BUG IN CLIENT OF LIBDISPATCH: Release of an inactive object
[...]
Thread 61 Crashed:: Dispatch queue: NEFlow queue
0 libdispatch.dylib 0x7ff81c1232cd _dispatch_queue_xref_dispose.cold.2 + 24
1 libdispatch.dylib 0x7ff81c0f84f6 _dispatch_queue_xref_dispose + 55
2 libdispatch.dylib 0x7ff81c0f2dec -[OS_dispatch_source _xref_dispose] + 17
3 com.kithrup.simpleprovider 0x101df5fa7 MyClass.deinit + 87
4 com.kithrup.simpleprovider 0x101dfbdbb MyClass.__deallocating_deinit + 11
5 libswiftCore.dylib 0x7ff829a63460 _swift_release_dealloc + 16
6 com.kithrup.simpleprovider 0x101e122f4 0x101de7000 + 176884
7 libswiftCore.dylib 0x7ff829a63460 _swift_release_dealloc + 16
8 libsystem_blocks.dylib 0x7ff81bfdc654 _Block_release + 130
9 libsystem_blocks.dylib 0x7ff81bfdc654 _Block_release + 130
10 libdispatch.dylib 0x7ff81c0f3317 _dispatch_client_callout + 8
11 libdispatch.dylib 0x7ff81c0f9317 _dispatch_lane_serial_drain + 672
12 libdispatch.dylib 0x7ff81c0f9dfd _dispatch_lane_invoke + 366
13 libdispatch.dylib 0x7ff81c103eee _dispatch_workloop_worker_thread + 753
14 libsystem_pthread.dylib 0x7ff81c2a7fd0 _pthread_wqthread + 326
15 libsystem_pthread.dylib 0x7ff81c2a6f57 start_wqthread + 15
I tried changing it to an optional and having the deinit call .cancel() and set it to nil, but it still crashes.
I can't figure out how to get it deallocated in a small, standalone test program.
This crash means that you’ve released a suspended source. Most folks never suspend and resume sources, so the most common cause is releasing a source without ever resuming it. For example, this code will crash as you’ve described:
import Dispatch
func main() {
autoreleasepool {
let source = DispatchSource.makeTimerSource()
print(source)
}
}
main()
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