Open
Description
| Previous ID | SR-11647 |
| Radar | None |
| Original Reporter | freak4pc (JIRA User) |
| Type | Bug |
Environment
Swift 5.1.1 latest Docker image
Additional Detail from JIRA
| Votes | 0 |
| Component/s | Foundation, libdispatch |
| Labels | Bug, 5.1Regression |
| Assignee | None |
| Priority | Medium |
md5: 4aa6a76a0b5ee28f3059851ef77c1f74
relates to:
- SR-11864 Availability warnings in dead code paths
Issue Description:
We've bumped into an interesting regression in RxSwift's OperationQueueScheduler that wraps OperationQueue, specifically under Linux. It seems concurrency is broken or hangs.
The full issue is here:
ReactiveX/RxSwift#2077 (comment)
I was able to reduce the issue using only OperationQueue, without Rx:
import Foundation
let condition = NSCondition()
let sema = DispatchSemaphore(value: 0)
var writtenStarted = 0
var writtenEnded = 0
var events = [String]()
var lock = NSLock()
func performLocked(_ action: () -> Void) {
lock.lock()
action()
lock.unlock()
}
let concurrent = {
performLocked {
print("Started")
events.append("Started")
}
condition.lock()
writtenStarted += 1
condition.signal()
while writtenStarted < 2 {
condition.wait()
}
condition.unlock()
performLocked {
print("Ended")
events.append("Ended")
}
condition.lock()
writtenEnded += 1
condition.signal()
while writtenEnded < 2 {
condition.wait()
}
condition.unlock()
sema.signal()
}
let op1 = BlockOperation(block: concurrent)
let op2 = BlockOperation(block: concurrent)
let operationQueue = OperationQueue()
operationQueue.maxConcurrentOperationCount = 8
operationQueue.addOperation(op1)
operationQueue.addOperation(op2)
sema.wait()Running the following code on macOS (in Swift 5.1 as well) or Linux with Swift 5.0 yields:
$ swift regression.swift
Started
Started
Ended
EndedRunning it under Linux with Swift 5.1:
$ swift -v
Swift version 5.1.1 (swift-5.1.1-RELEASE)
$ swift regression.swift
Started
-> At this point the process hangs and never completesThis seems to be an open regression in Swift 5.1 under Linux, but happy for any feedback or to provide any additional information.