Timer behaviour is incorrect on Linux when using init(timeInterval: TimeInterval, repeats: Bool, block: (Timer) -> Void)

[Diggory]

Hello,

https://forums.swift.org/t/timer-behaviour-different-on-linux-and-macos-timer-block-executed-upon-timer-creation-too-early/63509

The Timer initialiser init(timeInterval: TimeInterval, repeats: Bool, block: (Timer) -> Void) behaves wrongly on Linux.

if the user creates a non-scheduled timer and adds it to a runloop, the closure/block that is executed when the timer fires, also fires at creation time.

Demonstration Code

---

import Foundation

@main
public struct TimerRunloop {
    public private(set) var text = "Hello, World!"

    public static func main() {
//        print(TimerRunloop().text)
		
		let runLoop = RunLoop.current
		let distantFuture = Date.distantFuture
		///	Set this to false when we want to exit the app...
		let shouldKeepRunning = true
		
		// Set a scheduled timer going
		print("\(Date()) Program starts.")
		let timer = Timer.scheduledTimer(withTimeInterval: 5.0, repeats: true) { timer in
			print("\(Date()) Timer fired.")
		}
		
		//	Set a timer and add it tp the runloop manually
		let timer2 = Timer(timeInterval: 5.0, repeats: true) { timer in
			print("\(Date()) Timer2 fired")
		}

		//	Make sure that it is scheduled onto the main thread.
		DispatchQueue.main.async {
			RunLoop.current.add(timer2, forMode: .default)
		}
		
		//	Run forever
		while shouldKeepRunning == true &&
				runLoop.run(mode:.default, before: distantFuture) {}

    }
}

Results:

---

macOS

swift-driver version: 1.62.15 Apple Swift version 5.7.2 (swiftlang-5.7.2.135.5 clang-1400.0.29.51)
Target: x86_64-apple-macosx13.0

2023-03-03 5:32:03 pm +0000 Program starts.
2023-03-03 5:32:08 pm +0000 Timer fired.
2023-03-03 5:32:08 pm +0000 Timer2 fired
2023-03-03 5:32:13 pm +0000 Timer fired.
2023-03-03 5:32:13 pm +0000 Timer2 fired

Linux

Swift version 5.7.2 (swift-5.7.2-RELEASE)
Target: aarch64-unknown-linux-gnu

pi@piPrincedaleSpare:~/swift/TimerRunloop $ swift run
Building for debugging...
[5/5] Linking TimerRunloop
Build complete! (3.24s)
2023-03-03 17:32:52 +0000 Program starts.
2023-03-03 17:32:52 +0000 Timer2 fired
2023-03-03 17:32:57 +0000 Timer fired.
2023-03-03 17:32:57 +0000 Timer2 fired
2023-03-03 17:33:02 +0000 Timer fired.
2023-03-03 17:33:02 +0000 Timer2 fired