Async TaskGroup not releasing memory

Using Swift
#1

When I run this sample app as a command line tool in macOS, after a few seconds it is consuming 1GB of memory and it keeps ramping up from there, until it crashes. I'm not sure what I'm doing wrong. I am waiting for the result of each call to test so it should not be queueing up anything, as far as I can tell, no memory should be retained after each call to `test.

@main
struct TaskGroupTest {
    static func test() async {
        await withTaskGroup(of: Void.self) { group in
            (0..<10).forEach { _ in
                group.addTask {}
            }

            for await _ in group {}
        }
    }

    static func main() async {
        for _ in (0..<1000000) {
            await Self.test()
        }
    }
}
#2

Are you running in release mode, with optimizations enabled? That should help optimize away some of the memory use.

#3

Thanks, unfortunately I'm seeing the same behavior in release mode though - runaway memory consumption

#4

There was a bug about this which is now fixed. I'm not sure about when the fix landed, exactly. @ktoso?

#5

There was a few of those but it was a long time ago:

This specifically would have been the first one.

It seems this was already in 5.6 and 5.6.1

1 Like
#6

Hmmm, looks like I already have 5.6, maybe something else?. Interesting thing - if I put this code in iOS app, no problem. It runs forever without increasing memory.... The problem only happens to me on macOS.

xcrun --find swift
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift

xcrun swift -version
swift-driver version: 1.45.2 Apple Swift version 5.6 (swiftlang-5.6.0.323.62 clang-1316.0.20.8)

#7

This is a runtime fix, and the runtime is in the OS. So you’d have to update your macOS I suppose.

#9

OK, thanks

1 Like
#10

We're looking at whether we can back-deploy this fix among others, but as usual, we can't make any promises.

1 Like