Check whether a process PID exists or not
pid_exists(pid, debug = getOption2("parallelly.debug", FALSE))A positive integer.
Returns TRUE if a process with the given PID exists,
FALSE if a process with the given PID does not exists, and
NA if it is not possible to check PIDs on the current system.
There is no single go-to function in R for testing whether a PID exists
or not. Instead, this function tries to identify a working one among
multiple possible alternatives. A method is considered working if the
PID of the current process is successfully identified as being existing
such that pid_exists(Sys.getpid()) is TRUE. If no working
approach is found, pid_exists() will always return NA
regardless of PID tested.
On Unix, including macOS, alternatives tools::pskill(pid, signal = 0L)
and system2("ps", args = pid) are used.
On MS Windows, various alternatives of system2("tasklist", ...) are used.
Note, some MS Windows machines are configures to not allow using
tasklist on other process IDs than the current one.
The Open Group Base Specifications Issue 7, 2018 edition, IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008) https://pubs.opengroup.org/onlinepubs/9699919799/functions/kill.html
Microsoft, tasklist, 2021-03-03, https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/tasklist
R-devel thread 'Detecting whether a process exists or not by its PID?', 2018-08-30. https://stat.ethz.ch/pipermail/r-devel/2018-August/076702.html