[SR-15133] Crash when deallocating a never-resumed DispatchSourceTimer

[mickeyl]

Previous ID	SR-15133
Radar	rdar://problem/82535083
Original Reporter	@mickeyl
Type	Bug

Environment

macOS 12 beta, Xcode 13 (13A233).

Additional Detail from JIRA

Votes	0
Component/s	libdispatch
Labels	Bug, DispatchSourceTimer
Assignee	None
Priority	Medium

md5: 61e077b082169a945b058843ee5c3245

Issue Description:

Please consider the following example program which I have uploaded to

https://github.com/mickeyl/swift-bugs/tree/main/SR15133

Running it from within Xcode crashes with the following backtrace:

(lldb) bt

• thread #3, queue = 'com.apple.root.default-qos.cooperative', stop reason = EXC_BREAKPOINT (code=1, subcode=0x100624d9c)
  frame #0: 0x0000000100624d9c libdispatch.dylib`_dispatch_queue_xref_dispose.cold.2 + 36
  frame #1: 0x00000001005ea2ec libdispatch.dylib`_dispatch_queue_xref_dispose + 64
  frame #2: 0x00000001005e17f8 libdispatch.dylib`-[OS_dispatch_source _xref_dispose] + 28
  frame #3: 0x00000001000060f8 SR15133`StreamCommand.deinit(self=0x0000000105105820) at StreamCommandQueue.swift:0
  frame #4: 0x0000000100006120 SR15133`StreamCommand.__deallocating_deinit(self=0x0000000105105820) at StreamCommandQueue.swift:0
  frame #5: 0x00000001a2f6b774 libswiftCore.dylib`_swift_release_dealloc + 56

• frame #6: 0x00000001000081bc SR15133`StreamCommandQueue.handleErrorCondition(stream=0x0000000100712b90, event=.errorOccurred, self=0x0000000100712e90) at StreamCommandQueue.swift:182:9
  frame #7: 0x0000000100009040 SR15133`closure #3 in StreamCommandQueue.stream(self=0x0000000100712e90, aStream=0x0000000100712b90, eventCode=.errorOccurred) at StreamCommandQueue.swift:202:44
  frame #8: 0x000000010000ac48 SR15133`partial apply for closure #3 in StreamCommandQueue.stream(_:handle🙂 at <compiler-generated>:0
  frame #9: 0x0000000100005d5c SR15133`thunk for @escaping @callee_guaranteed @sendable @async () -> () at <compiler-generated>:0
  frame #10: 0x000000010000ad9c SR15133`thunk for @escaping @callee_guaranteed @sendable @async () -> ()partial apply at <compiler-generated>:0
  frame #11: 0x000000010000bfac SR15133`thunk for @escaping @callee_guaranteed @sendable @async () -> (@out A) at <compiler-generated>:0
  frame #12: 0x000000010000cc5c SR15133`partial apply for thunk for @escaping @callee_guaranteed @sendable @async () -> (@out A) at <compiler-generated>:0
  (lldb)

I suspect there is a memory management problem when the stored continuation in the `StreamCommand` gets deallocated due to `self.activeCommand = nil` while the continuation may continue to run in another task.

[mickeyl]

It also crashes when running on the command line with `swift run`, btw.

[typesanitizer]

@swift-ci create

[mickeyl]

Same in Xcode 13 release version.

[mickeyl]

On Linux w/ Swift version 5.6-dev (LLVM ca88d53176e346a, Swift a382f589a5ec230), this seems to work.

It still fails on macOS 12 with Swift development toolchain 2021-09-18.

[mickeyl]

After digging deeper, it seems that the actual crash happens when deallocating the `DispatchTimerSource`. Obviously `libdispatch` is to blame here and it has nothing to do with the continuation. I will adjust the metadata accordingly.