[SR-5759] DispatchSources should be independently cancellable

[weissi]

Previous ID	SR-5759
Radar	None
Original Reporter	@weissi
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	libdispatch
Labels	Bug, Linux
Assignee	phabouzit (JIRA)
Priority	Medium

md5: ce6f2127d12f4b5b86ad03472c82a552

Issue Description:

DispatchSources should be independently cancellable.

In other words, when compiling this program

import Dispatch

func makeSource(fd: Int32, queue: DispatchQueue, handler: DispatchWorkItem) -> DispatchSourceRead {
    let s = DispatchSource.makeReadSource(fileDescriptor: Int32(fd), queue: queue)
    s.setEventHandler(handler: handler)
    s.resume()
    return s
}

let q = DispatchQueue(label: "some q", attributes: .concurrent)
let numFakeSources = 32
var fakeSources: [DispatchSourceRead] = []
let fd: Int32 = 0
let sem = DispatchSemaphore(value: 0)

for f in 0..<numFakeSources {
    fakeSources.append(makeSource(fd: fd, queue: q, handler: DispatchWorkItem(block: {
        print("fake source A \(f) fired")
    })))
}

let realSource = makeSource(fd: fd, queue: q, handler: DispatchWorkItem(block: {
    print("real source fired")
    sem.signal()
}))

for f in 0..<numFakeSources {
    fakeSources.append(makeSource(fd: fd, queue: q, handler: DispatchWorkItem(block: {
        print("fake source B \(f) fired")
    })))
}

_ = fakeSources.map { $0.cancel() }

sem.wait()

and running it as

for f in $(seq 100); do cat /dev/null | ./test; done

it should not hang. That's true on Darwin but not on Linux. I showed this to phabouzit (JIRA User) and he found the bug and is working on a patch. Filing because I'll be on holiday from tomorrow and want to finish the work after I'm back.

The bug described in SR-4567 is pretty certainly this bug too.

[swift-ci]

Comment by Pierre Habouzit (JIRA)

#295 merged in master & swift-4