[SR-15175] withTaskGroup(of:) leaks huge amounts of memory on linux

[kelvin13]

Previous ID	SR-15175
Radar	rdar://problem/82915223
Original Reporter	@kelvin13
Type	Bug
Status	Resolved
Resolution	Done

Environment

$ swiftc --version
Swift version 5.6-dev (LLVM ca88d53176e346a, Swift a382f58)
Target: x86_64-unknown-linux-gnu

Additional Detail from JIRA

Votes	0
Component/s	Standard Library
Labels	Bug, Concurrency
Assignee	@ktoso
Priority	Medium

md5: f1817e9d7d79ccaf4ae2040ad5ed80ce

relates to:

• SR-14973 withTaskGroup leaks memory for every task added to the group

Issue Description:

on my machine, the following test program leaks over 3.5 GB of memory per second:

// taskgroup.swift 

@main 
enum Main 
{
    static 
    func main() async
    {
        while true 
        {
            await withTaskGroup(of: Void.self) 
            { 
                _ in
            } 
        }
    }
}

$ swiftenv local DEVELOPMENT-SNAPSHOT-2021-09-07-a
$ swiftc -parse-as-library -O taskgroup.swift 
$ ./taskgroup

this issue only occurs with linux builds. macos builds do not leak memory as far as i have observed.

please note: unlike SR-14973, this memory leak occurs even when no tasks are added to the task group.

[ktoso]

@swift-ci create

[ktoso]

Thanks, it’s definitely unexpected… will dig into it.

[ktoso]

Thanks a lot for reporting!

Fixed by #39295