Re: For review: pidfd_send_signal(2) manual page

On Mon, Sep 23, 2019 at 2:12 AM Michael Kerrisk (man-pages)
[off-list ref] wrote:

       The  pidfd_send_signal()  system call allows the avoidance of race
       conditions that occur when using traditional interfaces  (such  as
       kill(2)) to signal a process.  The problem is that the traditional
       interfaces specify the target process via a process ID (PID), with
       the  result  that the sender may accidentally send a signal to the
       wrong process if the originally intended target process has termi‐
       nated  and its PID has been recycled for another process.  By con‐
       trast, a PID file descriptor is a stable reference to  a  specific
       process;  if  that  process  terminates,  then the file descriptor
       ceases to be  valid

The file *descriptor* remains valid even after the process to which it
refers exits. You can close(2) the file descriptor without getting
EBADF. I'd say, instead, that "a PID file descriptor is a stable
reference to a specific process; process-related operations on a PID
file descriptor fail after that process exits".