os: manually instantiated os.Process methods return EBADF

[prattmic]

package main

import (
        "fmt"
        "os"
        "syscall"
)

func main() {
        p := &os.Process{Pid: os.Getpid()}
        err := p.Signal(syscall.SIGWINCH)
        fmt.Println("error:", err)
}

With 1.22 this works without issue. As of https://go.dev/cl/570036, this prints error: bad file descriptor.

The problem is that 0 is a valid value of os.Process.handle, so the Signal method tries to use it as a pidfd.

This is easy to fix with an additional field to report whether handle is initialized (N.B. that handle could really be FD 0, so we can't just look for 0). I will send a CL.

(As far as I know, this form of using os.Process has never worked on Windows, as it always uses the handle field.)

cc @kolyshkin

[gopherbot]

Change https://go.dev/cl/588675 mentions this issue: os: overhaul handling of PID vs pidfd within Process