[SR-3199] Cancel handler is never called on DispatchSource after invoking `.cancel()`

[swift-ci]

Previous ID	SR-3199
Radar	None
Original Reporter	tylercloutier (JIRA User)
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Foundation, libdispatch
Labels	Bug
Assignee	mww (JIRA)
Priority	Medium

md5: 1641e42bfc66b37d5426aff6370cf49c

Issue Description:

It appears that the cancel handler is never invoked after calling cancel on a DispatchSource in Swift 3 on macOS.

This issue can be replicated by following steps with Swift 3.0.1.

1. Clone https://github.com/SwiftOnEdge/Edge.git
2. Check out the commit 1bc2552c3f7cb0d33080d65b1290008ac5342cdf
3. Comment out line 125 of /Sources/TCP/Server.swift and insert print statement there.
4. Insert a print statement in the cancelHandler on line 47 of the same file
5. Run the test RouterTests.testMiddleware

You should see that although the cancel in invoked, the test completes without ever invoking the cancel handler configured on line 47.

Shouldn't the listeningSource maintain a strong reference to the handler and submit it to the main queue (in this case) to be run when cancel is invoked or am I misunderstanding something about the contract of cancel?

Note: This is on macOS. I have not tested this for Linux.

[swift-ci]

Comment by Pierre Habouzit (JIRA)

This definitely works in C, which would make it a swift issue?

[swift-ci]

Comment by Tyler Cloutier (JIRA)

I would also assume it's a Swift issue. Maybe something to do with object lifetimes.

[swift-ci]

Comment by Tyler Cloutier (JIRA)

As a note, I am only ever using the main queue for all dispatch tasks.

[swift-ci]

Comment by Pierre Habouzit (JIRA)

are you calling dispatch_main() ? if not, you need to run the main runloop else sources won't be drained.

[swift-ci]

Comment by Tyler Cloutier (JIRA)

I'm unable to call dispatch_main directly inside an XCTest. I am, however, calling waitForExpectations which should have the same effect. waitForExpectations certainly works fine to schedule my other blocks to run on the main queue.