Check whether a process PID exists or not
pid_exists(pid, debug = getOption("future.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 Windows, various alternatives of system2("tasklist", ...) are used.
1. The Open Group Base Specifications Issue 7, 2018 edition, IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008) http://pubs.opengroup.org/onlinepubs/9699919799/functions/kill.html
2. Microsoft, tasklist, 2018-08-30, https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/tasklist
3. 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