[SR-15963] swift::TaskGroup::offer crash

[antonvmironov]

Previous ID	SR-15963
Radar	None
Original Reporter	@antonvmironov
Type	Bug

Attachment: Download

Environment

iOS app on various versions of iOS 14 and 15. Apps built on CI with

Swift version 5.5.2 (swiftlang-1300.0.47.5 clang-1300.0.29.30)

Xcode Version 13.2.1 (13C100)

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Bug
Assignee	None
Priority	Medium

md5: 249dbc8206812cc7fccfeaff65944b0e

Issue Description:

A crash observed only in production. Roughly 0.7 crashes per thousand of users daily.

call stack on iOS 14 (65% of logged crashes):

swift::TaskGroup::offer(swift::AsyncTask*, swift::AsyncContext*) + 504
swift::TaskGroup::offer(swift::AsyncTask*, swift::AsyncContext*) + 504
swift::AsyncTask::completeFuture(swift::AsyncContext*) + 132
completeTaskAndRelease(swift::AsyncContext*, swift::SwiftError*) + 128
swift::runJobInEstablishedExecutorContext(swift::Job*) + 144
swift_job_run + 84
_dispatch_client_callout + 20
_dispatch_continuation_pop + 448
_dispatch_async_redirect_invoke + 592
_dispatch_root_queue_drain + 388
_dispatch_worker_thread2 + 112
_pthread_wqthread + 216
start_wqthread + 8

call stack on iOS 15 (35% of logged crashes):

swift::TaskGroup::offer(swift::AsyncTask*, swift::AsyncContext*) + 504
swift::AsyncTask::completeFuture(swift::AsyncContext*) + 132
completeTaskAndRelease(swift::AsyncContext*, swift::SwiftError*) + 128
swift::runJobInEstablishedExecutorContext(swift::Job*) + 196
processDefaultActor((anonymous namespace)::DefaultActorImpl*, (anonymous namespace)::RunningJobInfo) + 976
swift::runJobInEstablishedExecutorContext(swift::Job*) + 60
swift_job_run + 152
_dispatch_root_queue_drain + 328
_dispatch_worker_thread2 + 160
_pthread_wqthread + 224
start_wqthread + 8

Attaching a sample code that closely resembles the one running in production.