进程的fileHandleForReading可读性Handler闭包在Linux上未被调用

在macOS中编译以下代码时,它会运行并给出输出。

import Foundation

let runloop = RunLoop.current

let process = Process()
process.launchPath = "/bin/echo"
process.arguments = ["hello world"]

let output = Pipe()
process.standardOutput = output

output.fileHandleForReading.readabilityHandler = { fileHandle in
    let data = fileHandle.availableData
    print("received data: \(data.count)")
    print(String(data: data, encoding: .utf8) ?? "")
}

print("starting")
process.launch()

while runloop.run(mode: .default, before: Date(timeIntervalSinceNow: 2)) { }

输出:

received data: 12
hello world\n

但是,当我在Ubuntu Swift docker镜像(Swift 5.0.1版)中编译并运行它时 readabilityHandler 根本就没有人要求结束。